Examples

mode='evalexpr'; imagename=['image1.im', 'image2.im' ]
# in the parameter expr, the value 'IM0' is replaced by 'image1.im'
# and 'IM1' is replaced with 'image2.im'

mode='spix'; imagename=['image1.im','image2.im']
# will calculate an image of log(S1/S2)/log(f1/f2), where S1 and S2 are fluxes and
# f1 and f2 are frequencies

mode='pola'; imagename='multistokes.im' (where that image contains both Q and U stokes planes) or imagename=['imageQ.im','imageU.im']
# will calculate an image of the polarization angle distribution 0.5*arctan(U/Q),
# where imageQ.im and imageU.im are Stokes Q and U images, respectively.

mode='poli'; imagename=['imageQ.im','imageU.im','imageV.im']
# will calculate the total polarization intensity image, where imageQ.im, imageU.im,
# imageV.im are Stokes Q, U, and V images, respectively. Alternatively,
mode='poli'; imagename = ['imageQ.im','imageU.im']
# will calculate the linear polarization intensity image.
# In the case where imagename is a single multi-stokes image, the total polarization
# image will be calculated if all of the Q, U, and V stokes planes are present, and
# the linear polarization intensity image will be calculated if the Q and U (but not V) planes
# are present.

#Make an image that is image1.im - image2.im
expr=’ (IM0 - IM1 )’
#or with an explicit notation,
expr=’("image1.im" - "image2.im")’

#Double all values in an image.
immath( imagename='myimage.im', expr='IM0*2', outfile='double.im' )
# or with an explicit notation,
immath( expr='"myimage.im"*2', outfile='double.im' )

# Taking the sin of an image and adding it to another
# Note that the images need to be the same size
immath(imagename=['image1.im', 'image2.im'], expr='sin(IM1)+IM0;',outfile='newImage.im')

# Adding only the plane associated with the 'V' stokes value and
# the 1st channel together in two images
immath(imagename=[image1', 'image2'], expr='IM0+IM1',chans='1',stokes='V')

# Selecting a single plane (5th channel), of the 3-D cube and
# adding it to the original image. In this example the 2-D plane
# gets expanded out and the values are applied to each plane in the
# 3-D cube.
default('immath')
imagename='ngc7538.image'
outfile='chanFive.im'
expr='IM0'
chans='5'
go
default('immath')
imagename=['ngc7538.image', chanFive.im']
outfile='ngc7538_chanFive.im'
expr='IM0+IM1'
go

# Selecting and saving the inner 3/4 of an image for channels 40,42,44
# as well as channels less than 10
default('immath')
imagename='my_image.im'
expr='IM0'
box='25,25,123,123'
chans='<10;40,42,44'
outfile='my_image_inner.im' )
go

# Dividing an image by another, making sure we aren't dividing by zero
default('immath')
imagename=['orion.image', 'my.image']
expr='IM0/iif(IM1==0,1.0,IM1)' #note: iif (a, b, c) a is the boolean expression
#                                                   b is the value if true
#                                                   c is the value if false  
outfile='my_orion.image'
go

# Applying a mask to all of the images in the expression
default('immath')
imagename=['ngc7538.image','ngc7538_clean.image']
expr='(IM0*10)+IM1'
mask='"ngc7538.mask"'
outfile='really_noisy_ngc7538.image'
go

# Applying a pixel mask contained in the image information
default('immath')
imagename='ngc5921.image'
expr='IM0*10'
mask='mask("ngc5921.mask")'
outfile='ngc5921.masked.image'
go

# Creating a total polarization intensity image from an multi-stokes image
# containing IQUV.
default('immath')
outfile='pol_intensity'
stokes=''
# in imagename, you can also specify a list containing single stokes images
# of Q and U (for linear polarization intensity) and V (for total
# polarization intensity)
imagename='3C138_pcal'
mode='poli'
go

# Creating a polarization position angle image
default('immath')
outfile='pol_angle.im'
mode='pola'
# you can also do imagename=['Q.im','U.im'] for single stokes images, order of
# the two Stokes images does not matter
imagename='3C138_pcal' # multi-stokes image containing at least Q and U stokes
go

# same as before but write a mask with values of False for pixels for which the
# corresponding linear polarization ( sqrt(Q*Q+U*U)) is less than 30 microJy/beam
polithresh='30uJy/beam'
go

# Creating a spectral index image from the images at two different observing frequencies
default('immath')
outfile='mySource_sp.im'
mode='spix'
imagename=['mySource_5GHz.im','mySource_8GHz.im']
go