Note that this task is suited only to small shifts, expansions and scale factors. You can use the self-explanatory task shifty for large integral pixel shifts. The keyword in2 gives the image which must be adjusted to look like the image given by keyword in1. Task imdiff can also output a residual image - see the help file for the definition of the residual, but it is basically a combination of all the residuals of all the adjustable parameters.
To hold any particular parameter fixed, you simply specify the appropriate options string (see help file). Otherwise, imdiff will solve for that parameter. Initial guesses can be entered through the keyword for each parameter.
|in2=vela.vla||Adjust this image|
|resid=vela.resid||The residual image|
|region||Unset for entire image|
|guard||Unset for default OK|
|xshift||Unset for initial guess of 0|
|yshift||Unset for initial guess of 0|
|expand||Unset for initial guess of 1|
|amp||Unset for initial guess of 1|
|offset||Unset for initial guess of 0|
|options=expand||Unset to vary everything and x|
|and y expansions separately|
In the following example, we FFT a CLEANed image and form the amplitude and phase images of the Fourier Transform.
|rin=ic4296.icln||Input real image|
|center||Use ref. pix. for centre of transform|
|order=#||Order of polynomial|
|coeffs||Unset not to see coefficients of fit|
|email@example.com||Fit over this region|
It may be that you would like the image to be written out with histogram equalisation applied, rather than it just being computed but not saved by the display task. The task imheq will do this for you. You can specify the intensity range in which pixels will be included when computing the histogram. It is useful to use this if you have outliers significantly from the bulk of the distribution. imheq will equalised each plane of a cube, and by default, use the image minimum and maximum of that plane. If you set options=global it will take the minimum and maximum from the whole cube instead.
If you set the device keyword, imheq will draw a plot of the image histogram and discretized cumulative histogram (see help file). The latter is essentially the transfer function that is applied. This plot is drawn after every plane of a cube.
|nbins||Default for 128 histogram bins|
|range||Default is image min to max|
|options||Unset for plane by plane equalisation|
|device=/xs||PGPLOT device for histogram|