5. smallanglescattering (sas)

This module allows smearing/desmearing of SAXS/SANS data.

Smearing is for line collimation as in Kratky SAXS cameras and for point collimation for SANS. For SANS the resolution smearing a la Pedersen is realised (resFunct).

For desmearing the Lake algorithm is an iterative procedure to desmear smeared data. We follow here the improvements according to Vad using a convergence criterion and smoothing.

2D SAXS dat can be read into sasImage, background subtracted , transmission corrected….

As references the waterXray scattering and a AgBe reference spectrum are available.

For form factors and structure factors see the respective modules.

5.1. Smear/desmear 1D

smear(data, beamProfile, **kwargs) Smearing data for line-collimated SAXS (Kratky camera) or as point collimation SANS/SAXS.
desmear(Ios, beamProfile[, NIterations, …]) Desmearing according to Lake algorithm with possibility to stop recursion at best desmearing.
resFunct(S[, collDist, collAperture, …]) Resolution smearing of small angle scattering for SANS or SAXS according to Pedersen for radial averaged data.
prepareBeamProfile([data]) Prepare beam profile from Beam Profile measurement or according to given parameters.
getBeamWidth(empty[, minmax, show]) Extract primary beam of empty cell or buffer measurement for semitransparent beam stops.
plotBeamProfile(beam[, p]) Plots beam profile and weight function according to parameters in beam.
transmissionCorrection(data, dark[, …]) Subtract dark current, find primary beam, get transmission and normalize by transmission and exposure time.
waterXrayScattering([composition, T, units]) Absolute scattering of water with components (salt, buffer) at Q=0 as reference for X-ray.
AgBeReference(q, wavelength[, n, ampn, …]) The scattering intensity expected from AgBe as a reference for wavelength calibration.

5.2. 2D sasImage

Read 2D image files (TIFF) from SAXS cameras and extract the corresponding data.

The sasImage is a 2D array that allows direct subtraction and multiplication (e.g. transmission) respecting given masks in operations. E.g.

sample=js.sas.sasImage('sample.tiff')
solvent=js.sas.sasImage('solvent.tiff')
corrected = sample/sampletransmission - solvent/solventtransmission

Calibration of detector distance, radial average, size reduction and more. .showPolar allows sensitive detection of the beamcenter.

An example is shown in sasImage .


sasImage Creates sasImage as maskedArray from a detector image for evaluation.
sasImage.maskRegion(xmin, xmax, ymin, ymax) Mask rectangular region.
sasImage.maskFromImage(image) Use/copy mask from image.
sasImage.maskRegion(xmin, xmax, ymin, ymax) Mask rectangular region.
sasImage.maskRegions(regions) Mask several regions.
sasImage.maskbelowLine(p1, p2) Mask points at one side of line.
sasImage.maskTriangle(p1, p2, p3[, invert]) Mask inside triangle.
sasImage.mask4Polygon(p1, p2, p3, p4[, invert]) Mask inside polygon of 4 points.
sasImage.maskCircle(center, radius[, invert]) Mask points inside circle.
sasImage.save(file[, format]) Saves image under the given filename.
sasImage.setDetectorDistance(detector_distance) Set detector distance.
sasImage.findCenterOfIntensity([beamcenter, …]) Find beam center as center of intensity around beamcenter.
sasImage.radialAverage([beamcenter, number]) Radial average of image and conversion to wavevector q.
sasImage.lineAverage([beamcenter, number, …]) Line average of image and conversion to wavevector q for line collimation cameras.
sasImage.recalibrateDetDistance([…]) Recalibration of detectorDistance by AgBe reference for point collimation.
sasImage.gaussianFilter([sigma]) Gaussian filter in place.
sasImage.showPolar([beamcenter, scaleR]) Show image transformed to polar coordinates around beamcenter.
sasImage.reduceSize([size]) Reduce size of image using uniform average in box.
sasImage.show([scale, levels, axis]) Show image.
sasImage.getfromcomment(name[, replace, newname]) Extract name from .artist or .imageDescription with attribute name in front.
sasImage.array Strip of all attributes and return a simple array without mask.

5.3. 2D sasImage convenience

createLogPNG(filenames[, center, size, …]) Create .png files from grayscale images with log scale conversion to values between [1,255].
createImageDescriptions(images) Create text file with image descriptions as list of content.
readImages(filenames) Read a list of images returning sasImage`s.

5.4. Housekeeping

readpdh(pdhFileName) Opens and reads a SAXS data file in the .pdh (Primary Data Handling) format.
autoscaleYinoverlapX(dataa[, key, keep]) Scales elements of data to have same mean .Y value in the overlap region of .X .
removeSpikesMinmaxMethod(dataa[, order, …]) Takes a dataset and removes single spikes from data by substitution with spline.
removeSpikes(dataa[, xmin, xmax, medwindow, …]) Takes a dataset and removes single spikes.
locateFiles(pattern[, root]) Locate all files matching supplied filename pattern in and below supplied root directory.
copyFiles(pattern[, root, destination, link]) Copies all files matching pattern in tree below root to destination directory
addXMLParameter(data) Adds the parameters stored in xml part of a .pdh file as eg.
moveSAXSPACE(pattern[, root, destination, …]) Read SAXSPACE .pdh files and removes spikes by removeSpikes.

This module allows smearing/desmearing of SAXS/SANS data.

Smearing is for line collimation as in Kratky SAXS cameras and for point collimation for SANS. For SANS the resolution smearing a la Pedersen is realised (resFunct).

For desmearing the Lake algorithm is an iterative procedure to desmear smeared data. We follow here the improvements according to Vad using a convergence criterion and smoothing.

2D SAXS dat can be read into sasImage, background subtracted , transmission corrected….

As references the waterXray scattering and a AgBe reference spectrum are available.

For form factors and structure factors see the respective modules.

jscatter.smallanglescattering.AgBeReference(q, wavelength, n=array([1, 2, 3, 4, 5, 6, 7, 8, 9]), ampn=[1, 1, 1, 1, 1, 1, 1, 1, 1, 1], domainsize=100, udw=0.1, asym=0, lg=1)[source]

The scattering intensity expected from AgBe as a reference for wavelength calibration.

The intensities assume a d-spacing of 5.8378 nm and a reduction of the intensity as q**-2. The domain size determines the width according to Scherrer equation [2]. The first peak is at 1.076 1/nm. The result needs to be convoluted with the instrument resolution by resFunct or smear.

Parameters:
q : array

Wavevector

wavelength : float

Wavelength

n : array of int

Order of the peaks.

ampn : list of float

Amplitudes of the peaks

domainsize : float

Domainsize of AgBe crystals in nm. default 100 nm as is given in [1].

udw : float

Displacement u in Debye Waller factor exp(-u**2*q**2/3)

asym : float

Factor asymmetry in Voigt function describing the peaks.

lg : float

Lorenzian/gaussian fraction of both FWHM, describes the contributions of gaussian and lorenzian shape. See Voigt for details.

Returns:
dataArray

References

[1](1, 2) T. C. Huang, H. Toraya, T. N. Blanton and Y. Wu X-ray Powder Diffraction Analysis of Silver Behenate, a Possible Low-Angle Diffraction Standard J. Appl.Cryst.(1993).26,180-184
[2](1, 2) Patterson, A. The Scherrer Formula for X-Ray Particle Size Determination Phys. Rev. 56 (10): 978–982 (1939) doi:10.1103/PhysRev.56.978.
jscatter.smallanglescattering.addXMLParameter(data)[source]

Adds the parameters stored in xml part of a .pdh file as eg. in SAXSPACE .pdh files.

Parameters:
data : dataArray

Already read pdh file. XML content is found in comments of the read files and starts with ‘<’.

jscatter.smallanglescattering.autoscaleYinoverlapX(dataa, key=None, keep='lowest')[source]

Scales elements of data to have same mean .Y value in the overlap region of .X .

Parameters:
dataa : dataList

data to scale

key : string

Data are grouped into unique values of attribute key before scaling. E.g. to do it for a series of concentrations for each concentration individually.

keep : default ‘l’

If ‘l’ the lowest X are kept and higher X are scaled successively to next lower X. Anything else highest X are kept and other are scaled to next higher.

Returns:
dataList

new scaled dataList

Notes

First data are sorted along .X.mean() scaling value is stored in .autoscalefactor

jscatter.smallanglescattering.copyFiles(pattern, root='.', destination='copy', link=False)[source]

Copies all files matching pattern in tree below root to destination directory

Parameters:
pattern : file pattern

Pattern used in fnmatch.filter

root : directory, default is os.curdir

Directory where to start

destination : dirname

Destination

link : bool

If True links are created.

jscatter.smallanglescattering.desmear(Ios, beamProfile, NIterations=-15, windowsize=4, qmax=4, **kwargs)[source]

Desmearing according to Lake algorithm with possibility to stop recursion at best desmearing.

For negative NIterations the iterations are stopped if a convergence criterion reaches a minimum as described by Vad [2]. In each step a smoothing based on the ratio desmeared/observed as described in [2] is used (point average with windowsize).

Parameters:
Ios : dataArray

Original smeared data

beamProfile : dataArray

Beam profile as prepared with prepareBeamProfile

NIterations : int, default=-15

Number of iterations to stop. Negative values indicate to use the convergence criterion described by Vad [2] and abs(NIterations) gives the maximum iterations to stop.

qmax : float, default=4

Maximum in scattering vector q up to where the convergence criterion is evaluated. This reduces the influence of the noise at larger a.

windowsize : odd int , default=4

Window size for smoothing in each step of desmearing (running average).

Returns:
dataArray

References

[1]Lake, J. A. (1967). Acta Cryst. 23, 191–194.
[2](1, 2, 3, 4) Comparison of iterative desmearing procedures for one-dimensional small-angle scattering data Vad and Sager, J. Appl. Cryst. (2011) 44,32-42
jscatter.smallanglescattering.fitDarkCurrent(darkfile)[source]

Fits dark current with 5th order polynom + cosine.

This is dangerous as the darkcurrent has a noise that is not random but depends on used detector and count time.

jscatter.smallanglescattering.getBeamWidth(empty, minmax='auto', show=False)[source]

Extract primary beam of empty cell or buffer measurement for semitransparent beam stops.

The primary beam is searched and cut between the next minima found, then normalized. Additionally a Gaussian fit is done and hwhm is included in result profile.

Parameters:
empty : dataArray

Empty cell measurement with the transmitted beam included.

minmax : ‘auto’,[float,float]

Automatic or interval for search of primary beam. E.g. [-0.03,0.03] allow for explicitly setting the interval.

show : bool

Show the fit result

Returns:
dataArray with beam width profile

.sigma sigma of fit with Gaussian .hwhm half width half maximum

jscatter.smallanglescattering.locateFiles(pattern, root='.')[source]

Locate all files matching supplied filename pattern in and below supplied root directory.

Parameters:
pattern : file pattern

Pattern used in fnmatch.filter

root : directory, default is os.curdir

Directory where to start

Returns:
file list
jscatter.smallanglescattering.moveSAXSPACE(pattern, root='./', destination='./despiked', medwindow=5, SGwindow=5, sigma=0.2, order=2)[source]

Read SAXSPACE .pdh files and removes spikes by removeSpikes.

This is mainly for use at JCNS SAXSPACE with CCD camera as detector :-))))

Parameters:
pattern : string

Search pattern for filenames

root : string

Root path

destination : string

Where to save the files

medwindow : odd integer

Window size of scipy.signal.medfilt

SGwindow : odd int, None

Savitzky-Golay filter see scipy.signal.savgol_filter

order : int

Polynominal order of scipy.signal.savgol_filter

sigma : float

Deviation factor of eY If datapoint-median> sigma*std its a spike

Notes

Default values are adjusted to typical SAXSPACE measurement.

jscatter.smallanglescattering.plotBeamProfile(beam, p=None)[source]

Plots beam profile and weight function according to parameters in beam.

Parameters:
beam

beam with parameters

p : GracePlot instance

Reuse the given plot

jscatter.smallanglescattering.prepareBeamProfile(data=None, **kwargs)[source]

Prepare beam profile from Beam Profile measurement or according to given parameters.

Parameters:
data : dataArray,’trapez’,’SANS’
Contains measured beam profile, explicit Gaussian width list or type ‘SANS’, ‘trapz’.
  • dataArray Line collimation as measured can be given and will be smoothed and made symmetric.
  • dataArray with explicit given Gaussian width for each Q values, missing values will be interpolated.
  • ‘trapez’ : Line collimation with trapezoidal parameters a, b, bxw, dIW.
  • ‘SANS’ : Smearing a la Pedersen; see resFunct for parameters
collDist,collAperture,detDist,sampleAperture : float

Parameters as described in resFunct for SANS These are determined from the experimental setup.

wavelength,wavespread,dpixelWidth,dringwidth,extrapolfunc : float

Parameters as described in resFunct for SANS These are determined from the experimental setup.

a : float

Larger full length of trapezoidal profile in detector q units. Ignored for measured profile.

b : float

Shorter full length of trapezoidal profile in detector q units If a=b ==> a=a*(1+1e-7), b=b*(1-1e-7) Ignored for measured profile.

bxw : float,dataArray

Beam width profile. Use getBeamWidth to cut the primary beam and fit a Gaussian. A float describes the beam half-width at half maximum (hwhm of Gaussian). If bxw is the profile prepared by getBeamWidth the experimental profile is used.

dIW : float

Detector slit width in detector q units. Length on detector to integrate parallel to beam length for line collimation. On my SAXSpace this is 1.332 as given in the header of the file (20 mm in real coordinates).

wavelength : float,

Wavelength in nm default 0.155418 nm for SAXS 0.5 nm for SANS

detDist : float, default 305.3558

Detector distance in units mm Default is detector distance of SAXSpace

explicit : int

For explicit given Gaussian width the index of the column with the width. For merged dataFiles of KWS2@MLZ this is the forth column with index 3.

Returns:
beam profile as dataArray

Notes

  • For measured beam profiles parameters a,b are determined from the flanks for trapezoidal profile.
  • Detector q units are equivalent to the pixel distance as expressed in a corrected measurement.
  • For ‘explicit’ Gaussian width a SANS measurement as on KWS2 can be used which has sigma as 4th column. Missing values are interpolated.

Examples

# use as
# prepare measured beamprofile
mbeam = js.sas.prepareBeamProfile(beam, bxw=0.01, dIW=1.)
# prepare profile with trapezoidal shape (a,b are fitted above)
tbeam = js.sas.prepareBeamProfile('trapz', a=mbeam.a, b=mbeam.b, bxw=0.01, dIW=1)
# prepare profile SANS (missing parameters get defaults)
Sbeam = js.sas.prepareBeamProfile('SANS', detDist=2000,wavelength=0.4,wavespread=0.15)
# prepare profile with explicit given Gaussian width in column 3 as e.g. KWS2@MLZ
Gbeam = js.sas.prepareBeamProfile(measurement,explicit=3)
jscatter.smallanglescattering.readpdh(pdhFileName)[source]

Opens and reads a SAXS data file in the .pdh (Primary Data Handling) format.

If data contain X values <0 it is assumed that the primary beam is included as for SAXSpace instruments. Use js.sas.transmissionCorrection to subtract dark counts and do transmission correction.

Parameters:
pdhFileName : string

file name

Returns:
dataArray

Notes

Alternatively the files can be read ignoring the information in the header (it is stored in the comments)

data=dA(pdhFileName,lines2parameter=[2,3,4])

PDH format used in the PCG SAXS software suite developed by the Glatter group at the University of Graz, Austria. This format is described in the appendix of the PCG manual (below from version 4.05.12 page 159).

In the PDH format, lines 1-5 contain header information, followed by the SAXS data.

line 1:  format A80             -> description
line 2:  format 16(A4,1X)       -> description in 16x4 character groups (1X = space separated)
line 3:  format 8(I9,1X)        -> 8 integers (1X = space separated)
line 4:  format 5(E14.6,1X)     -> 5 float (1X = space separated)
line 5:  format 5(E14.6,1X      -> 5 float(1X = space separated)
line 6+  format 3(E14.6,1X)     - SAXS data x,y,error (1X = space separated)
with:
  • line 3 field 0 : number of points
  • line 4 field 4 : normalization constant (default 1, never zero!!)

Anything else can have different meanings.

The SAXSpace and SAXSess (AntonPaar) format add:
  • line 4 field 2 : detector distance in mm
  • line 4 field 5 : wavelength
  • line 5 field 2 : detector slit length (equivalent to width of integration area) in q units

Additional xml parameter as in the SAXSPACE format appended can be extracted to attributes by addXMLParameter. Mainly this is “Exposure” time.

Example data for SAXSpace

<emptyline>
SAXS BOX
      2057         0         0         0         0         0         0         0
  0.000000E+00   3.052516E+02   0.000000E+00   1.000000E+00   1.541800E-01
  0.000000E+00   1.332843E+00   0.000000E+00   0.000000E+00   0.000000E+00
-1.033335E-01   2.241656E+03   1.024389E+00
-1.001430E-01   2.199972E+03   1.052537E+00
...
jscatter.smallanglescattering.removeSpikes(dataa, xmin=None, xmax=None, medwindow=5, SGwindow=None, sigma=0.2, SGorder=2)[source]

Takes a dataset and removes single spikes.

A median filter is used to find single spikes. If abs(data.Y-medianY)/data.eY>sigma then the medianY value is used. If SGwindow!=None Savitzky-Golay filtered values are used. If sigma is 0 then new values (median or Savitzky-Golay filtered) are used everywhere.

Parameters:
xmin,xmax : float

Minimum and maximum X values

dataa : dataArray

dataset with eY data

medwindow : odd integer

window size of scipy.signal.medfilt

SGwindow : odd int, None

Savitzky-Golay filter see scipy.signal.savgol_filter without the spikes; window should be smaller than instrument resolution

SGorder : int

Polynomial order of scipy.signal.savgol_filter needs to be smaller than SGwindow

sigma : float

relative deviation from eY if datapoint-median> sigma*eY its a spike

Returns:
Filtered and smoothed dataArray
jscatter.smallanglescattering.removeSpikesMinmaxMethod(dataa, order=7, sigma=2, nrepeat=1, removePoints=None)[source]

Takes a dataset and removes single spikes from data by substitution with spline.

Find minima and maxima of data including double point spikes; no 3 point spikes scipy.signal.argrelextrema with np.greater and np.less are used to find extrema

Parameters:
dataa : dataArray

Dataset with eY data.

order : int

Number of points see scipy.signal.argrelextrema. Distance between extrema.

sigma : float

Deviation factor from std dev; from eY. If datapoint -spline> sigma*std its a spike.

nrepeat : int

Repeat the procedure nrepeat times.

removePoints : list of integer

Instrument related points to remove because of dead pixels. ‘JCNS’ results in a list for SAXSPACE at JCNS Jülich.

Returns:
data with spikes removed
jscatter.smallanglescattering.resFunct(S, collDist=8000.0, collAperture=10, detDist=8000.0, sampleAperture=10, wavelength=0.5, wavespread=0.2, dpixelWidth=10, dringwidth=1, extrapolfunc=None)[source]

Resolution smearing of small angle scattering for SANS or SAXS according to Pedersen for radial averaged data.

I(q0)= Integral{(R(q,q0)*S(q)}dq with Kernel R(q,q0) of equ. 33 in [1] including wavelength spread, finite collimation and detector resolution. Default parameters are typical for a SANS machine like KWS2@JCNS with rectangular apertures. Low Q can be extrapolated as power law or Guinier like or constant.

Parameters:
S : array like

dataArray with X. and .Y theoretical Scattering function q in nm^-1 .Y can be arbitrary unit

collDist : float, default 8000

collimation distance in mm

collAperture : float, default 10

collimation rectangular aperture size in mm

detDist : float, default 8000

detector distance in mm

sampleAperture : float, default 10

sample rectangular aperture size in mm

wavelength : float, default 0.5

wavelength in nm

wavespread : float, default 0.1

FWHM wavelengthspread dlambda/lambda

dpixelWidth : float, default 10

Detector pixel width in mm

dringwidth : integer, default 1

number of pixel for averaging

extrapolfunc : list , default None

Type of extrapolation at low and high X edges as list for [low edge,high edge]. If a singe value is given this is used for both.

  • Low edge towards zero
  • float : Power law extrapolation
  • None : A constant value as Y(X.min()).
  • anything else : Low X data are log scaled, then X**2 extrapolated as Guinier like extrapolation.
  • High edge towards infinity
  • float : Power law extrapolation of low X e.g. a=-4 for q**a for Porod scaling.
  • None : A constant value as Y(X.max()).
Returns:
dataArray

columns [‘wavevector; smeared scattering; unsmeared scattering; half width smearing function’]

Notes

  • HalfWidthSmearingFunction is the FWHM the Gaussian used for smearing including all effects.
  • The resolution is assumed to be equal in direction parallel and perpendicular to q on a 2D detector as described in chap. 2.5 in [1].
  • We neglect additional smearing due to radial averaging (last paragraph in chap 2.5 of [1]).
  • Defaults correspond to a typical medium resolution measurement.
  • extrapolfunc allows extrapolation at both edges to reduce edge effects. The best values depends on the measured signal shape at the edge. The optimal way is to calculate the used model for the whole Q range, smear it and prune to the needed range. This is demonstrated in example 2. If at low q only a power law is observed use the corresponding extrapolation. Same for high q.
  • An example for SANS fitting with resFunc is given in example_SANSsmearing.py.

References

[1](1, 2, 3, 4, 5) Analytical Treatment of the Resolution Function for Small-Angle Scattering JAN SKOV PEDERSEN, DORTHE POSSELTAND KELL MORTENSEN J. Appl. Cryst. (1990). 23, 321-333

Examples

Reproducing Table 1 of [1]

import jscatter as js
q=js.loglist(0.1,10,500)
S=js.ff.sphere(q,6)
# this is the direct call of resFunc, use smear instead as shown in next example
Sr=js.sas.resFunct(S, collDist=2000.0, collAperture=20, detDist=2000.0, sampleAperture=10, wavelength=0.5, wavespread=0.2,dpixelWidth=0,dringwidth=0)
# plot it
p=js.grace()
p.plot( S,sy=[1,0.3],li=1,legend='sphere')
p.plot( Sr,sy=[2,0.3,2],li=2,legend='smeared sphere')
p.plot(Sr.X,Sr[-1],li=4,sy=0,legend='FWHM in nm\S-1 ')
p.yaxis(min=1e-3,scale='l',charsize=1.5,label='I(q) / a.u.',tick=[10,9])
p.yaxis(min=1e-1,tick=[10,9])
p.xaxis(scale='l',charsize=1.5,label='q / nm\S-1',tick=[10,9])
p.legend(x=0.8,y=5e5)

Example 2:

# smear model over full range and interpolate to needed data
# this is the best way to smear a model for fitting, but is not possible for desmearing
meas=js.dA('measureddata.dat')     # load data
# define profile
resol2m = js.sas.prepareBeamProfile('SANS', detDist=2000,collDist=2000.,wavelength=0.4,wavespread=0.15)
q=np.r_[0.01:5:0.01] # or np.r_[0:meas.X.min():0.01,meas.X,meas.X.max():meas.X.max()*2:0.1]
# calc model
temp=js.ff.ellipsoid(q,2,3)
# smear it
smearedmodel=js.sas.smear(temp,resol2m).interpolate(X=meas.X)
jscatter.smallanglescattering.resFunctExplicit(S, beamprofile, extrapolfunc=None)[source]

Resolution smearing of small angle scattering for SANS or SAXS according to explict given Gaussian width.

I(q0)= Integral{(R(q,q0)*S(q)}dq with Gaussian kernel R(q,q0). E.g. for merged dataFiles of KWS2@MLZ the explicit width is given in the 4th column.

Parameters:
S : array like

dataArray with X. and .Y theoretical Scattering function q in nm^-1 .Y can be arbitrary unit

beamprofile : beamProfile ‘explicit’

Beam profile as prepared from prepareBeamProfile ‘explicit’

extrapolfunc : list , default None

Type of extrapolation at low and high X edges for handling of the border as list for [low edge,high edge]. If a singe value is given this is used for both.

  • Low edge
  • float : Power law extrapolation of low X e.g. a=-4 for q**a for Porod scaling.
  • None : A constant value as Y(X.min()).
  • anything else : Low X data are log scaled, then X**2 extrapolated as Guinier like extrapolation.
  • High edge
  • float : Power law extrapolation of low X e.g. a=-4 for q**a for Porod scaling.
  • None : A constant value as Y(X.max()).
Returns:
dataArray

columns [‘wavevector; smeared scattering; unsmeared scattering; half width smearing function’]

Notes

  • HalfWidthSmearingFunction is the FWHM the Gaussian used for smearing including all effects.
jscatter.smallanglescattering.smear(data, beamProfile, **kwargs)[source]

Smearing data for line-collimated SAXS (Kratky camera) or as point collimation SANS/SAXS.

The full resolution for point collimation SAXS/SANS is described in resFunct.

Parameters:
data : dataArray

Data to be smeared.

beamProfile : beamProfile or ‘trap’, ‘SANS’, ‘explicit’, dataArray

Beam profile as prepared from prepareBeamProfile or type as ‘trapezoidal’, ‘SANS’,’explicit’ or a measured beam profile as dataArray for line collimation. Measured Profile is treated by prepareBeamProfile.

kwargs :

See prepareBeamProfile for kwargs.

Returns:
dataArray

Notes

  • If data has attributes a, b, dIW, bxw, detDist these are used, if not given in function call.
  • If wavelength is missing in data a default of 0.155418 nm for Xray K_{\alpha} line is assumed. For SANS 0.6 A.
  • During smearing for Kratky camera an integration over the beam width and beam length are performed. In this integration q_{w,l}= ((q+q_{w})^2)+q_{l}^2)^{1/2} is used with q_{w} along the beam width and q_{l} along the beam length. in regions q_{w,l} > max(q_{data}) we estimate the measured scattering intensity by the mean of the last 10 points of the measured spectra to allow for a maximum in q range. The strictly valid q range can be estimated by calculating q_{x,y} < max(q) with 2 times the used beam width and beam length. As the smearing for larger q has no real effect the estimate might be still ok.

Examples

# use as
# prepare measured line collimation beamprofile
mbeam = js.sas.prepareBeamProfile(beam, bxw=0.01, dIW=1.)
# prepare profile with trapezoidal shape (a,b can be fitted above)
tbeam = js.sas.prepareBeamProfile('trapz', a=mbeam.a, b=mbeam.b, bxw=0.01, dIW=1)
# prepare profile SANS (missing parameters get defaults, see resFunct)
Sbeam = js.sas.prepareBeamProfile('SANS', detDist=2000,wavelength=0.4,wavespread=0.15)
# prepare profile with explicit given Gaussian width in column 3 as e.g. KWS2@JCNS
Gbeam = js.sas.prepareBeamProfile(measurement,explicit=3)
# smear
datasm= js.sas.smear(data,mbeam)
datast= js.sas.smear(data,tbeam)
datasS= js.sas.smear(data,Sbeam)
datasG= js.sas.smear(data,Gbeam)
jscatter.smallanglescattering.transmissionCorrection(data, dark, emptybeam=None, edge=0.03, exposure=None)[source]

Subtract dark current, find primary beam, get transmission and normalize by transmission and exposure time. IN PLACE.

For measurements including the primary beam from a semitransparent beamstop as from SAXSpace. Transmission is the maximum of the primary beam peak after dark subtraction. Allows easier comparison of measurements with aged source (primary intensity change).

Parameters:
data : dataArray

A measurement from a SAXSpace instrument read by js.dA(‘filename.pdh’,lines2parameter=[2,3,4])

dark : dataArray

Dark current measurement.

emptybeam : dataArray,default=None

Empty beam measurement to subtract from measurement. dark will be subtracted of empty beam.

edge : float, default 0.03

Wavevector value below beam stop edge. The primary beam is searched below this value.

exposure : float, default None

Exposure time in unit ‘s’. If not given the xml description at the end of the file is examined.

Returns:
None

Notes

Files from SAXSpace instrument (.pdh) can be read by

js.dA('filename.pdh',lines2parameter=[2,3,4])

Correction

Brulet at al [1] describe the data correction for SANS, which is in principle also valid for SAXS, if incoherent contributions are neglected.

The difference is, that SAXS has typical transmission around ~0.3 for 1mm water sample in quartz cell due to absorption, while in SANS typical values are around ~0.9 for D2O. Larger volume fractions in the sample play a more important rule for SANS as hydrogenated ingredients reduce the transmission significantly, while in SAXS still the water and the cell (quartz) dominate.

One finds for a sample inside of a container with thicknesses (z) for sample, buffer (solvent), empty cell and empty beam measurement (omitting the overall q dependence):

I_s = \frac{1}{z_S}\big((\frac{I_S-I_{dark}}{T_S}-I_{b}T_S\big) -\big(\frac{I_{EC}-I_{dark}}{T_{EC}}-I_{b}T_{EC})\big) - \frac{1}{z_B}\big((\frac{I_B-I_{dark}}{T_B}-I_{b}T_B\big) -\big(\frac{I_{EC}-I_{dark}}{T_{EC}}-I_{b}T_{EC})\big)

where
  • I_s is the interesting species
  • I_S is the sample of species in solvent (buffer)
  • I_B is the pure solvent (describing a constant background)
  • I_{dark} is the dark current measurement
  • I_b is the empty beam measurement
  • I_{EC} is the empty cell measurement
  • z_x corresponding sample thickness
  • T_x corresponding transmission

The recurring pattern \big((\frac{I-I_{dark}}{T}-I_{b}T\big) shows that the the beam tail (border of primary beam not absorbed by the beam stop) is attenuated by the corresponding sample.

For equal sample thickness z the empty beam is included in subtraction of I_B:

I_s = \frac{1}{z} \big((\frac{I_S-I_{dark}}{T_S}-I_{b}T_S) - (\frac{I_B-I_{dark}}{T_B}-I_{b}T_B)\big)

The simple case

If the transmissions are nearly equal as for e.g. protein samples with low concentration (T_S \approx T_B) we only need to subtract the transmission and dark current corrected buffer measurement from the sample.

I_s = \frac{1}{z} \big((\frac{I_S-I_{dark}}{T_S}) - (\frac{I_B-I_{dark}}{T_B}\big)

Higher accuracy for large volume fractions

For larger volume fractions \Phi the transmission might be different and we have to take into account that only 1-\Phi of solvent contributes to I_S. We may incorporate this in the sense of an optical density changing the effective thickness \frac{1}{z_B}\rightarrow\frac{1-\Phi}{z_B} resulting in different thicknesses z_S \neq z_B

Transmission

The transmission is measured as the ratio T=\frac{I(q=0)_{sample}}{I(q=0)_{emptybeam}} with I(q=0) as the primary beam intensity.

If the primary beam tail is neglected in the above equation I(q=0)_{emptybeam} only gives a common scaling factor and can be omitted if arbitrary units are used. Alternatively one can scale to the EC transmission with T_{EC}=1 For absolute calibration the same needs to be done. One finds T_{sample in cell}=T_{empty cell}T_{sample without cell}.

References

[1](1, 2) Improvement of data treatment in small-angle neutron scattering Brûlet et al Journal of Applied Crystallography 40, 165-177 (2007)
jscatter.smallanglescattering.waterXrayScattering(composition='h2o1', T=293, units='mol')[source]

Absolute scattering of water with components (salt, buffer) at Q=0 as reference for X-ray.

According to [2] a buffer of water with components might be used. Ions need to be given separatly as [‘55.51h2o1’,‘0.15Na’,‘0.15Cl’] for 0.15 M NaCl solution. It is accounted for the temperature dependence of water density and compressibility.

Parameters:
composition : string

Buffer composition as in scatteringLengthDensityCalc give dissociated ions separatly as [‘1Na’,‘1Cl’] with concentration in mol prepended the additional scattering as ionic liquid of the ions in water is taken into account see [2] mass in g; 1000g water are 55.508 mol

T : float

temperature in °K

units : ‘mol’

anything except ‘mol’ prepended unit is mass fraction ‘mol’ prepended units is mol and mass fraction is calculated as mass=[mol] mass_{molecule} e.g. 1l Water with 123 mmol NaCl [‘55.508H2O1’,‘0.123Na1Cl1’]

Returns:
float absolute scattering length in Units 1/cm

Notes

I(0)=(\sigma_{water}^2f_e^2 n_{ew}^2 k_B T \chi + \sum_{ci} n_i N_A 1000 n_{ei}^2 f_e^2 )/100

with

\sigma_{water} water density \chi compressibility n_{ew} number of electrons per water molecule f_e cross section of electron in nm k_B Boltzmann constant n_i concentration component i n_{ei} number of electrons per molecule component i in Mol \sum_{ci} is done for all ions separately if given

References

[1]SAXS experiments on absolute scale with Kratky systems using water as a secondary standard Doris Orthaber et al. J. Appl. Cryst. (2000). 33, 218±225
[2](1, 2, 3) A high sensitivity pinhole camera for soft condensed matter T. Zemb, O. Tache, F. Né, and O. Spalla, J. Appl. Crystallogr. 36, 800 (2003).

Read 2D image files (TIFF) from SAXS cameras and extract the corresponding data.

The sasImage is a 2D array that allows direct subtraction and multiplication (e.g. transmission) respecting given masks in operations. E.g.

sample=js.sas.sasImage('sample.tiff')
solvent=js.sas.sasImage('solvent.tiff')
corrected = sample/sampletransmission - solvent/solventtransmission

Calibration of detector distance, radial average, size reduction and more. .showPolar allows sensitive detection of the beamcenter.

An example is shown in sasImage .


jscatter.sasimagelib.AgBepeaks = [1.0753, 2.1521, 3.2286, 4.3049, 5.3813, 6.4576, 7.5339, 8.6102, 9.6865, 10.7628]

AgBe peak positions

class jscatter.sasimagelib.SubArray[source]

Bases: numpy.ndarray

array
attr

Show specific attribute names as sorted list of attribute names.

setattr(objekt, prepend='', keyadd='_')[source]

Set (copy) attributes from objekt.

Parameters:
objekt : objekt with attr or dictionary

Can be a dictionary of names:value pairs like {‘name’:[1,2,3,7,9]} If object has property attr the returned attribut names are copied.

prepend : string, default ‘’

Prepend this string to all attribute names.

keyadd : char, default=’_’

If reserved attributes (T, mean, ..) are found the name is ‘T’+keyadd

showattr(maxlength=None, exclude=['comment'])[source]

Show specific attributes with values as overview.

Parameters:
maxlength : int

Truncate string representation after maxlength char.

exclude : list of str

List of attribute names to exclude from result.

jscatter.sasimagelib.createImageDescriptions(images)[source]

Create text file with image descriptions as list of content.

Parameters:
images : list of sasImages or glob pattern

List of images

jscatter.sasimagelib.createLogPNG(filenames, center=None, size=None, colormap='jet', equalize=False, contrast=None)[source]

Create .png files from grayscale images with log scale conversion to values between [1,255].

This generates images viewable in simple image viewers as overview. The new files are stored in the same folder as the original files.

Parameters:
filenames : string

Filename with glob pattern as ‘file*.tif’

center : [int,int]

Center of crop region.

size : int

Size of crop region as around center as 2*size. If center is None the border is cut by size.

colormap : string, None

Colormap from matplotlib or None for grayscale. For standard colormap names look in mpl.showColors().

equalize : bool

Equalize the images.

contrast : None, float

Autocontrast for the image. The value (0.1=10%) determines how much percent are cut from the intensity histogram before linear spread of intensities.

jscatter.sasimagelib.etree_to_dict(root)[source]
jscatter.sasimagelib.parseXML(text)[source]
jscatter.sasimagelib.phase(phases)[source]

Transform to [-pi,pi] range.

jscatter.sasimagelib.readImages(filenames)[source]

Read a list of images returning sasImage`s.

Parameters:
filenames : string

Glob pattern to read

Returns:
list of sasImage`s

Notes

To get a list of image descriptions:

images=js.sas.readImages(path+'/latest*.tiff')
[i.description for i in images]
class jscatter.sasimagelib.sasImage[source]

Bases: jscatter.sasimagelib.SubArray, numpy.ma.core.MaskedArray

Creates sasImage as maskedArray from a detector image for evaluation.

Reads a .tif file including the information in the EXIF tag.
  • All methods of maskedArrays including masking of invalid areas work.
  • Masked areas are automatically masked for all math operations.
  • Arithmetic operations for sasImages work as for numpy arrays e.g. to subtract background image or multiplying with transmission.
Parameters:
file : string

Filename to open.

detector_distance : float, sasImage

Detector distance from calibration measurement or calibrated image. Overwrites value in the file EXIF tag.

beamcenter : None, list 2xfloat, sasImage

Position of the beamcenter or copy from sasImage with beamcenter given. Overwrites value given in the file EXIF tag.

Returns:
image : sasImage with attributes
  • .beamcenter : beam center
  • .iX : X pixel position
  • .iY : Y pixel position
  • .filename
  • .artist : Additional attributes from EXIF Tag Artist
  • .imageDescription : Additional attributes from EXIF Tag ImageDescription

Notes

  • Unmasked data can be accessed as .data
  • The mask is .mask and initial set to all negative values.
  • Masking of a pixel is done as image[i,j]=np.ma.masked. Use mask methods as implemented.
  • TIFF tags with index above 700 are ignored.
  • Tested for reading tiff image files from Pilatus detectors as given from our metal jet SAXS machines Ganesha and Galaxi at JCNS, Jülich.
  • Additional SAXSpace TIFF files are supported which show frames per pixel on the Y axis. This allows to examine the time evolution of the measurement on these line collimation cameras (Kratky camera). Instead of the old PIL the newer fork Pillow is needed for the multi page TIFFs. Additional the pixel_size is set to 0.024 (µm) as for the JCNS CCD camera.
  • Beamcenter & orientation:
    The x,y orientation is not well defined and dependent on the implementation on the specific camera setup. The default used here corresponds to our in house Ganesha which needs to revert the EXIF beamcenter. We use the lower left image corner as zero with X as lower axis. Please check if your beamcenter corresponds to this. If not just change it.

References

[1]Everything SAXS: small-angle scattering pattern collection and correction Brian Richard Pauw J. Phys.: Condens. Matter 25, 383201 (2013) DOI https://doi.org/10.1088/0953-8984/25/38/383201

Examples

import jscatter as js
#
# Look at calibration measurement
calibration = js.sas.sasImage(js.examples.datapath+'/calibration.tiff')
# Check beamcenter
# For correct beamcenter it should show straight lines (change beamcenter to see change)
calibration.showPolar(beamcenter=[122,254],scaleR=3)
# Recalibrate with previous found beamcenter (calibration sets it already)
calibration.recalibrateDetDistance(showfits=True)
iqcal=calibration.radialAverage()
# This might be used to calibrate detector distance for following measurements as
# empty.setDetectorDistance(calibration)
#
empty = js.sas.sasImage(js.examples.datapath+'/emptycell.tiff')
# Mask beamstop (not the same as calibration, unluckily)
empty.mask4Polygon([92,185],[92,190],[0,233],[0,228])
empty.maskCircle(empty.beamcenter, 9)
empty.show()
buffer = js.sas.sasImage(js.examples.datapath+'/buffer.tiff')
buffer.maskFromImage(empty)
buffer.show()
bsa = js.sas.sasImage(js.examples.datapath+'/BSA11mg.tiff')
bsa.maskFromImage(empty)
bsa.show() # by default a log scaled image
#
# subtract buffer (transmission factor is just a guess here, sorry)
new=bsa-buffer*0.2
new.show()
#
iqempty=empty.radialAverage()
iqbuffer=buffer.radialAverage()
iqbsa=bsa.radialAverage()
#
p=js.grace(1,1)
p.plot(iqempty,le='empty cell')
p.plot(iqbuffer,le='buffer')
p.plot(iqbsa,le='bsa 11 mg/ml')
p.title('raw data, no transmission correction')
p.yaxis(min=1,max=1e3,scale='l',label='I(q) / a.u.')
p.xaxis(scale='l',label='q / nm\S-1')
p.legend()
array

Strip of all attributes and return a simple array without mask.

findCenterOfIntensity(beamcenter=None, size=None)[source]

Find beam center as center of intensity around beamcenter.

Only values above the mean value are used to calc center of intensity. Use an image with a clear symmetric and strong scattering sample as AgBe. Use .showPolar([600,699],scaleR=5) to see if peak is symmetric.

Parameters:
beamcenter : list 2x int

First estimate of beamcenter. If not given preliminary beamcenter is estimated as center of intensity of full image.

size : int

Defines size of rectangular region of interest (ROI) around the beamcenter to look at.

Returns:
Adds (replaces) .beamcenter as attribute.

Notes

If ROI is to large the result may be biased due to asymmetry of the intensity distribution inside of ROI.

gaussianFilter(sigma=2)[source]

Gaussian filter in place.

Uses ndimage.filters.gaussian_filter with default parameters except sigma.

Parameters:
sigma : float

Gaussian kernel sigma.

getPixelQ()[source]

Get scattering vector along pixel dimension around beamcenter.

Returns:
qx,qy with image x and y dimension
getfromcomment(name, replace=None, newname=None)[source]

Extract name from .artist or .imageDescription with attribute name in front.

If multiple names start with parname first one is used. Used line is deleted from .artist or .imageDescription.

Parameters:
name : string

Name of the parameter in first place.

replace : dict

Dictionary with pairs to replace in all lines.

newname : string

New attribute name

iX
iY
lineAverage(beamcenter=None, number=None, minmax='auto', show=False)[source]

Line average of image and conversion to wavevector q for line collimation cameras.

Remember to set .detector_distance to calibrated value.

Parameters:
beamcenter : float

Sets beam center in data and uses this. If not given the beam center is determined from semitransparent beam.

number : int, default None

Number of intervals on new X scale. None means all pixels.

minmax : [int,int], ‘auto’

Interval for determination of beamcenter.

show : bool

Show the fit of the primary beam.

Returns:
dataArray
  • .filename
  • .detector_distance
  • .description
  • .beamcenter

Notes

  • Detector distance in attributes is used.
  • The primary beam is automatically detected.
  • Correction for flat detector projected to Ewald sphere included.
mask4Polygon(p1, p2, p3, p4, invert=False)[source]

Mask inside polygon of 4 points.

Points need to be given in right hand order.

Parameters:
p1,p2,p3,p4 : list of 2x float

Edge points.

invert : bool

Invert region. Mask outside circle.

maskCircle(center, radius, invert=False)[source]

Mask points inside circle.

Parameters:
center : list of 2x float

Center point.

radius : float

Radius in pixel units

invert : bool

Invert region. Mask outside circle.

maskFromImage(image)[source]

Use/copy mask from image.

Parameters:
image : sasImage

sasImage to use mask for resetting mask. image needs to have same dimension.

maskRegion(xmin, xmax, ymin, ymax)[source]

Mask rectangular region.

Parameters:
xmin,xmax,ymin,ymax : int

Corners of the region to mask

maskRegions(regions)[source]

Mask several regions.

Parameters:
regions : list

List of regions as in maskRegion.

maskTriangle(p1, p2, p3, invert=False)[source]

Mask inside triangle.

Parameters:
p1,p2,p3 : list of 2x float

Edge points of triangle.

invert : bool

Invert region. Mask outside circle.

maskbelowLine(p1, p2)[source]

Mask points at one side of line.

The masked side is left looking from p1 to p2.

Parameters:
p1, p2 : list of 2x float

Points in pixel coordinates defining line.

radialAverage(beamcenter=None, number=500)[source]

Radial average of image and conversion to wavevector q.

Remember to set .detector_distance to calibrated value.

Parameters:
beamcenter : list 2x float

Sets beam center or radial center in data and uses this. If not given the attribut beamcenter in the data is used.

number : int, default 500

Number of intervals on new X scale.

Returns:
dataArray

Notes

  • Correction of pixel size for flat detector projected to Ewald sphere included.
  • The value in a q binning is the average count rate c(q)=(\sum c_i)/N with counts in pixel i c_i and number of pixels N
  • The error (standard deviation) is calculated in a q binning as e=(\sum c_i)^{1/2}/N
  • The error is valid for single photon counting detectors showing Poisson statistics
    as the today typical Pilatus detectors from DECTRIS.
recalibrateDetDistance(beamcenter=None, number=500, showfits=False)[source]

Recalibration of detectorDistance by AgBe reference for point collimation.

Use only for AgBe reference measurements to determine the correction factor. For non AgBe measurements set during reading or .detector_distance to the new value. May not work if the detector distance is totally wrong.

Parameters:
beamcenter : list 2x float

Sets beam center or radial center in data and uses this. If not given the attribut beamcenter in the data is used.

number : int, default 1000

number of intervals on new X scale.

showfits : bool

Show the AgBe peak fits.

Notes

  • .distanceCorrection will contain factor for correction. Repeating this results in a .distanceCorrection close to 1.
reduceSize(size=2)[source]

Reduce size of image using uniform average in box.

XResolution,YResolution are scaled correspondingly.

Parameters:
size : int

Pixel size of the box to average. Also factor for reduction.

Returns:
sasImage
save(file, format=None, **params)[source]

Saves image under the given filename.

If no format is specified, the format to use is determined from the filename extension. See PIL save for formats and options.

Parameters:
file : string

Filename to save to.

format :

Optional format override. If omitted, the format to use is determined from the filename extension. If a file object was used instead of a filename, this parameter should always be used.

params : -

Additional parameters.

setBeamcenter(beamcenter)[source]

Set beamcenter.

Parameters:
beamcenter : float, sasImage

New value for beamcenter. If sasImage the beamcenter is copied.

setDetectorDistance(detector_distance)[source]

Set detector distance.

Parameters:
detector_distance : float, sasImage

New value for detector distance. If sasImage the detector_distance is copied.

show(scale=None, levels=8, axis='pixel')[source]

Show image.

Parameters:
scale : ‘norm’, default ‘log’,

If log the image is first log scaled

levels : int, None

Number of countour levels.

axis : ‘pixel’, None

Force pixel as coordinates, otherwise wavevectors if possible.

Returns:
image handle
showPolar(beamcenter=None, scaleR=1)[source]

Show image transformed to polar coordinates around beamcenter.

Azimuth corresponds: center line to beamcenter upwards, upper quarter beamcenter to right upper/lower edge = beamcenter downwards, lower quarter beamcenter to left

Parameters:
beamcenter : [int,int]

Beamcenter

scaleR : float

Scaling factor for radial component to zoom the beamcenter.

Returns:
Handle to figure
jscatter.sasimagelib.shortprint(values, threshold=6, edgeitems=2)[source]

Creates a short handy representation string for array values.

Parameters:
values : object

Values to print.

threshold: int default 6

Number of elements to switch to reduced form.

edgeitems : int default 2

Items at the edge.

jscatter.sasimagelib.subarray

alias of jscatter.sasimagelib.SubArray

class jscatter.sasimagelib.sasImage[source]

Creates sasImage as maskedArray from a detector image for evaluation.

Reads a .tif file including the information in the EXIF tag.
  • All methods of maskedArrays including masking of invalid areas work.
  • Masked areas are automatically masked for all math operations.
  • Arithmetic operations for sasImages work as for numpy arrays e.g. to subtract background image or multiplying with transmission.
Parameters:
file : string

Filename to open.

detector_distance : float, sasImage

Detector distance from calibration measurement or calibrated image. Overwrites value in the file EXIF tag.

beamcenter : None, list 2xfloat, sasImage

Position of the beamcenter or copy from sasImage with beamcenter given. Overwrites value given in the file EXIF tag.

Returns:
image : sasImage with attributes
  • .beamcenter : beam center
  • .iX : X pixel position
  • .iY : Y pixel position
  • .filename
  • .artist : Additional attributes from EXIF Tag Artist
  • .imageDescription : Additional attributes from EXIF Tag ImageDescription

Notes

  • Unmasked data can be accessed as .data
  • The mask is .mask and initial set to all negative values.
  • Masking of a pixel is done as image[i,j]=np.ma.masked. Use mask methods as implemented.
  • TIFF tags with index above 700 are ignored.
  • Tested for reading tiff image files from Pilatus detectors as given from our metal jet SAXS machines Ganesha and Galaxi at JCNS, Jülich.
  • Additional SAXSpace TIFF files are supported which show frames per pixel on the Y axis. This allows to examine the time evolution of the measurement on these line collimation cameras (Kratky camera). Instead of the old PIL the newer fork Pillow is needed for the multi page TIFFs. Additional the pixel_size is set to 0.024 (µm) as for the JCNS CCD camera.
  • Beamcenter & orientation:
    The x,y orientation is not well defined and dependent on the implementation on the specific camera setup. The default used here corresponds to our in house Ganesha which needs to revert the EXIF beamcenter. We use the lower left image corner as zero with X as lower axis. Please check if your beamcenter corresponds to this. If not just change it.

References

[1]Everything SAXS: small-angle scattering pattern collection and correction Brian Richard Pauw J. Phys.: Condens. Matter 25, 383201 (2013) DOI https://doi.org/10.1088/0953-8984/25/38/383201

Examples

import jscatter as js
#
# Look at calibration measurement
calibration = js.sas.sasImage(js.examples.datapath+'/calibration.tiff')
# Check beamcenter
# For correct beamcenter it should show straight lines (change beamcenter to see change)
calibration.showPolar(beamcenter=[122,254],scaleR=3)
# Recalibrate with previous found beamcenter (calibration sets it already)
calibration.recalibrateDetDistance(showfits=True)
iqcal=calibration.radialAverage()
# This might be used to calibrate detector distance for following measurements as
# empty.setDetectorDistance(calibration)
#
empty = js.sas.sasImage(js.examples.datapath+'/emptycell.tiff')
# Mask beamstop (not the same as calibration, unluckily)
empty.mask4Polygon([92,185],[92,190],[0,233],[0,228])
empty.maskCircle(empty.beamcenter, 9)
empty.show()
buffer = js.sas.sasImage(js.examples.datapath+'/buffer.tiff')
buffer.maskFromImage(empty)
buffer.show()
bsa = js.sas.sasImage(js.examples.datapath+'/BSA11mg.tiff')
bsa.maskFromImage(empty)
bsa.show() # by default a log scaled image
#
# subtract buffer (transmission factor is just a guess here, sorry)
new=bsa-buffer*0.2
new.show()
#
iqempty=empty.radialAverage()
iqbuffer=buffer.radialAverage()
iqbsa=bsa.radialAverage()
#
p=js.grace(1,1)
p.plot(iqempty,le='empty cell')
p.plot(iqbuffer,le='buffer')
p.plot(iqbsa,le='bsa 11 mg/ml')
p.title('raw data, no transmission correction')
p.yaxis(min=1,max=1e3,scale='l',label='I(q) / a.u.')
p.xaxis(scale='l',label='q / nm\S-1')
p.legend()
array

Strip of all attributes and return a simple array without mask.

findCenterOfIntensity(beamcenter=None, size=None)[source]

Find beam center as center of intensity around beamcenter.

Only values above the mean value are used to calc center of intensity. Use an image with a clear symmetric and strong scattering sample as AgBe. Use .showPolar([600,699],scaleR=5) to see if peak is symmetric.

Parameters:
beamcenter : list 2x int

First estimate of beamcenter. If not given preliminary beamcenter is estimated as center of intensity of full image.

size : int

Defines size of rectangular region of interest (ROI) around the beamcenter to look at.

Returns:
Adds (replaces) .beamcenter as attribute.

Notes

If ROI is to large the result may be biased due to asymmetry of the intensity distribution inside of ROI.

gaussianFilter(sigma=2)[source]

Gaussian filter in place.

Uses ndimage.filters.gaussian_filter with default parameters except sigma.

Parameters:
sigma : float

Gaussian kernel sigma.

getPixelQ()[source]

Get scattering vector along pixel dimension around beamcenter.

Returns:
qx,qy with image x and y dimension
getfromcomment(name, replace=None, newname=None)[source]

Extract name from .artist or .imageDescription with attribute name in front.

If multiple names start with parname first one is used. Used line is deleted from .artist or .imageDescription.

Parameters:
name : string

Name of the parameter in first place.

replace : dict

Dictionary with pairs to replace in all lines.

newname : string

New attribute name

iX
iY
lineAverage(beamcenter=None, number=None, minmax='auto', show=False)[source]

Line average of image and conversion to wavevector q for line collimation cameras.

Remember to set .detector_distance to calibrated value.

Parameters:
beamcenter : float

Sets beam center in data and uses this. If not given the beam center is determined from semitransparent beam.

number : int, default None

Number of intervals on new X scale. None means all pixels.

minmax : [int,int], ‘auto’

Interval for determination of beamcenter.

show : bool

Show the fit of the primary beam.

Returns:
dataArray
  • .filename
  • .detector_distance
  • .description
  • .beamcenter

Notes

  • Detector distance in attributes is used.
  • The primary beam is automatically detected.
  • Correction for flat detector projected to Ewald sphere included.
mask4Polygon(p1, p2, p3, p4, invert=False)[source]

Mask inside polygon of 4 points.

Points need to be given in right hand order.

Parameters:
p1,p2,p3,p4 : list of 2x float

Edge points.

invert : bool

Invert region. Mask outside circle.

maskCircle(center, radius, invert=False)[source]

Mask points inside circle.

Parameters:
center : list of 2x float

Center point.

radius : float

Radius in pixel units

invert : bool

Invert region. Mask outside circle.

maskFromImage(image)[source]

Use/copy mask from image.

Parameters:
image : sasImage

sasImage to use mask for resetting mask. image needs to have same dimension.

maskRegion(xmin, xmax, ymin, ymax)[source]

Mask rectangular region.

Parameters:
xmin,xmax,ymin,ymax : int

Corners of the region to mask

maskRegions(regions)[source]

Mask several regions.

Parameters:
regions : list

List of regions as in maskRegion.

maskTriangle(p1, p2, p3, invert=False)[source]

Mask inside triangle.

Parameters:
p1,p2,p3 : list of 2x float

Edge points of triangle.

invert : bool

Invert region. Mask outside circle.

maskbelowLine(p1, p2)[source]

Mask points at one side of line.

The masked side is left looking from p1 to p2.

Parameters:
p1, p2 : list of 2x float

Points in pixel coordinates defining line.

radialAverage(beamcenter=None, number=500)[source]

Radial average of image and conversion to wavevector q.

Remember to set .detector_distance to calibrated value.

Parameters:
beamcenter : list 2x float

Sets beam center or radial center in data and uses this. If not given the attribut beamcenter in the data is used.

number : int, default 500

Number of intervals on new X scale.

Returns:
dataArray

Notes

  • Correction of pixel size for flat detector projected to Ewald sphere included.
  • The value in a q binning is the average count rate c(q)=(\sum c_i)/N with counts in pixel i c_i and number of pixels N
  • The error (standard deviation) is calculated in a q binning as e=(\sum c_i)^{1/2}/N
  • The error is valid for single photon counting detectors showing Poisson statistics
    as the today typical Pilatus detectors from DECTRIS.
recalibrateDetDistance(beamcenter=None, number=500, showfits=False)[source]

Recalibration of detectorDistance by AgBe reference for point collimation.

Use only for AgBe reference measurements to determine the correction factor. For non AgBe measurements set during reading or .detector_distance to the new value. May not work if the detector distance is totally wrong.

Parameters:
beamcenter : list 2x float

Sets beam center or radial center in data and uses this. If not given the attribut beamcenter in the data is used.

number : int, default 1000

number of intervals on new X scale.

showfits : bool

Show the AgBe peak fits.

Notes

  • .distanceCorrection will contain factor for correction. Repeating this results in a .distanceCorrection close to 1.
reduceSize(size=2)[source]

Reduce size of image using uniform average in box.

XResolution,YResolution are scaled correspondingly.

Parameters:
size : int

Pixel size of the box to average. Also factor for reduction.

Returns:
sasImage
save(file, format=None, **params)[source]

Saves image under the given filename.

If no format is specified, the format to use is determined from the filename extension. See PIL save for formats and options.

Parameters:
file : string

Filename to save to.

format :

Optional format override. If omitted, the format to use is determined from the filename extension. If a file object was used instead of a filename, this parameter should always be used.

params : -

Additional parameters.

setBeamcenter(beamcenter)[source]

Set beamcenter.

Parameters:
beamcenter : float, sasImage

New value for beamcenter. If sasImage the beamcenter is copied.

setDetectorDistance(detector_distance)[source]

Set detector distance.

Parameters:
detector_distance : float, sasImage

New value for detector distance. If sasImage the detector_distance is copied.

show(scale=None, levels=8, axis='pixel')[source]

Show image.

Parameters:
scale : ‘norm’, default ‘log’,

If log the image is first log scaled

levels : int, None

Number of countour levels.

axis : ‘pixel’, None

Force pixel as coordinates, otherwise wavevectors if possible.

Returns:
image handle
showPolar(beamcenter=None, scaleR=1)[source]

Show image transformed to polar coordinates around beamcenter.

Azimuth corresponds: center line to beamcenter upwards, upper quarter beamcenter to right upper/lower edge = beamcenter downwards, lower quarter beamcenter to left

Parameters:
beamcenter : [int,int]

Beamcenter

scaleR : float

Scaling factor for radial component to zoom the beamcenter.

Returns:
Handle to figure