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| == Help on immath task: ==
| | {{immath}} |
| <pre>
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| Perform math operations on images
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| This task evaluates mathematical expressions involving existing
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| image files. The results of the calculations are stored in the
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| designated output file. Options are available to specify mathematical
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| expression directly or pre-defined expression for calculation of
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| spectral index image, and polarization intensity and position angle
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| images are available. The image file names imbedded in the expression or
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| specified in the imagename parameter for the pre-defined calculations may
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| be CASA images or FITS images.
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| NOTE: Index values start at 0 Use the imhead task to see the range of
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| index values for each axes.
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| Keyword arguments:
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| imagename -- input image name(s)
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| Default: none;
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| Examples: mode='evalexpr'; imagename=['image1.im', 'image2.im' ]
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| The text 'IM0' is replaced by 'image1.im' in the
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| expression and 'IM1' is repalced with 'image2.im'
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| mode='spix'; imagename=['image1.im','image2.im'] will calculate
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| an image of log(S1/S2)/log(f1/f2), where S1 and S2 are fluxes and
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| f1 and f2 are frequencies
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| mode='pola'; imagename=['imageQ.im','imageU.im'] will calculate
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| an image of polarization angle distribution, where imageQ.im and
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| imageU.im are Stokes Q and U images, respectively. Calculate 0.5*arctan(U/Q).
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| mode='poli'; imagename=['imageQ.im','imageU.im','imageV.im'] will calculate
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| total polarization intensity image, where imageQ.im, imageU.im, imageV.im
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| are Stokes Q, U, and V images, respectively.
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| mode -- mode for mathematical operation
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| Default: evalexpr
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| Options: 'evalexpr' : evalulate a mathematical expression defined in 'expr'
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| 'spix' : spectalindex image
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| 'pola' : polarization position angle image
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| 'poli' : polarization intesity image
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| >>> mode expandable parameters
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| sigma - (for mode='poli') standard deviation of noise of Stokes images with unit such as
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| Jy/beam to correct for bias
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| Default: '0.0Jy/beam' (= no debiasing)
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| expr -- (for mode='evalexpr') A mathematical expression with images.
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| Image file names are specified in the imagenames paramter, and
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| the variables IM0, IM1, ... are used to represent these files
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| in the expression. Explicit notations of file names in the
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| expression are also supported, in which cases the file names must
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| be enclosed in double quotes (") and imagename is ignored.
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| Default: none
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| Examples:
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| Make an image that is image1.im - image2.im
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| expr=' (IM0 - IM1 )'
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| or with an explicit notation,
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| expr='("image1.im" - "image2.im")'
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| Clip an image below a value (0.5 in this case)
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| expr = ' iif( IM0 >=0.5, IM0, 0.0) '
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| Note: iif (a, b, c) a is the boolian expression
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| b is the value if true
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| c is the value if false
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| Take the rms value of two images
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| expr = ' sqrt(IM0 * IM0 + IM1 * IM1) '
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| Note: No exponentiaion available?
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| Build an image pixel by pixel from the minimum of (image2.im, 2*image1.im)
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| expr='min(IM1,2*max(IM0))'
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| outfile -- The file where the results of the image calculations
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| are stored. Overwriting an existing outfile is not permitted.
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| Default: immath_results.im; Example: outfile='results.im'
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| mask -- Name of mask applied to each image in the calculation
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| Default '' means no mask; Example: mask='orion.mask'.
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| region -- File path to an ImageRegion file.
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| An ImageRegion file can be created with the CASA
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| viewer's region manager. Typically ImageRegion files
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| will have the suffix '.rgn'. If a region file is given
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| then the box, chans, and stokes selections whill be
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| ignored.
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| Default: none
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| Example: region='myimage.im.rgn'
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| box -- A box region on the directional plane
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| Only pixel values acceptable at this time.
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| Default: none (whole 2-D plane); Example: box='10,10,50,50'
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| chans -- channel numbers, velocity, and/or frequency
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| Only channel numbers acceptable at this time.
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| Default: none (all); Example: chans='3~20'
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| stokes -- Stokes parameters to image, may or may not be separated
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| by commas but best if you use commas.
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| Default: none (all); Example: stokes='IQUV';
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| Options: 'I','Q','U','V','RR','RL','LR','LL','XX','YX','XY','YY', ...
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| Available functions in the expr and mask paramters:
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| pi(), e(), sin(), sinh(), asinh(), cos(), cosh(), tan(), tanh(),
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| atan(), exp(), log(), log10(), pow(), sqrt(), complex(), conj()
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| real(), imag(), abs(), arg(), phase(), aplitude(), min(), max()
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| round(), isgn(), floor(), ceil(), rebin(), spectralindex(), pa(),
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| iif(), indexin(), replace(), ...
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| For a full description of the allowed syntax see the
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| Lattice Expression Language (LEL) documentation on the at:
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| http://aips2.nrao.edu/docs/notes/223/223.html
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| NOTE: where indexing and axis numbering are used in the above
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| functions they are 1-based, ie. numbering starts at 1.
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| Examples:
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| # Double all values in an image.
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| immath( imagesname='myimage.im', expr='IM0*2', outfile='double.im' )
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| # or with an explicit notation,
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| immath( expr='"myimage.im"*2', outfile='double.im' )
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| # Taking the sin of an image and adding it to another
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| # Note that the images need to be the same size
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| immath(images=['image1.im', 'image2.im'], expr='sin(IM1)+IM0;',outfile='newImage.im')
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| # Adding only the plane associated with the 'V' stokes value and
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| # the 1st channel together in two images
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| immath(imagename=[image1', 'image2'], expr='IM0+IM1',chans='1',stokes='V')
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| # Selecting a single plane (5th channel), of the 3-D cube and
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| # adding it to the original image. In this example the 2-D plane
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| # gets expanded out and the values are applied to each plane in the
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| # 3-D cube.
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| default('immath')
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| imagename='ngc7538.image'
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| outfile='chanFive.im'
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| expr='IM0'
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| chans='5'
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| go
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| default('immath')
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| imagename=['ngc7538.image', chanFive.im']
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| outfile='ngc7538_chanFive.im'
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| expr='IM0+IM1'
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| go
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| # Selecting and saving the inner 3/4 of an image for channels 40,42,44
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| # as well as channels less than 10
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| default('immath')
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| imagename='my_image.im'
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| expr='IM0'
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| box='25,25,123,123'
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| chans='<10;40,42,44'
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| outfile='my_image_inner.im' )
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| go
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| # Dividing an image by another, making sure we aren't dividing by zero
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| default('immath')
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| imagename=['orion.image', 'my.image']
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| expr='IM0/iif(IM1==0,1.0,IM1)'
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| outfile='my_orion.image'
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| go
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| # Applying a mask to all of the images in the expression
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| default('immath')
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| imagename=['ngc7538.image','ngc7538_clean.image']
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| expr='(IM0*10)+IM1'
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| mask='"ngc7538.mask"'
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| outfile='really_noisy_ngc7538.image'
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| go
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| # Applying a pixel mask contained in the image information
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| default('immath')
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| imagename='ngc5921.image'
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| expr='IM0*10'
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| mask='mask("ngc5921.mask")'
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| outfile='ngc5921.masked.image'
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| go
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| # Creating a Polarization Itensity image from an [Q, U, V] image.
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| default('immath')
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| outfile='Q.im'; imagename='3C138_pcal'; expr='IM0'; stokes='Q'; go();
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| outfile='U.im'; imagename='3C138_pcal'; expr='IM0'; stokes='U'; go();
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| outfile='V.im'; imagename='3C138_pcal'; expr='IM0'; stokes='V'; go();
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| #
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| outfile='pol_intensity'
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| stokes=''
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| imagename=['Q.im', 'U.im', 'V.im']
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| expr='sqrt(IM0*IM0 + IM1*IM1 + IM2*IM2)'
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| go
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| # or using pre-defined expression
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| default('immath')
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| outfile='pol_intensity'
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| mode='poli'
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| imagename=['Q.im','U.im','V.im']
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| go
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| # Creating a polarization position angle image
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| default('immath')
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| outfile='pol_angle.im'
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| mode='pola'
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| imagename=['Q.im','U.im'] # order of the two Stokes images does not matter
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| go
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| # Creating a spectral index image from the images at two different observing frequencies
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| default('immath')
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| outfile='mySource_sp.im'
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| mode='spix'
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| imagename=['mySource_5GHz.im','mySource_8GHz.im']
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| go
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| </pre>
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