GNU Astronomy Utilities

8.1.2 If convolving afterwards

In case you want to convolve the image later with a given point spread function, make sure to use a larger image size. After convolution, the profiles become larger and a profile that is normally completely outside of the image might fall within it.

On one axis, if you want your final (convolved) image to be \(m\) pixels and your PSF is \(2n+1\) pixels wide, then when calling MakeProfiles, set the axis size to \(m+2n\), not \(m\). You also have to shift all the pixel positions of the profile centers on the that axis by \(n\) pixels to the positive.

After convolution, you can crop the outer \(n\) pixels with the section crop box specification of Crop: --section=n+1:*-n,n+1:*-n (according to the FITS standard, counting is from 1 so we use n+1) assuming your PSF is a square, see Crop section syntax. This will also remove all discrete Fourier transform artifacts (blurred sides) from the final image. To facilitate this shift, MakeProfiles has the options --xshift, --yshift and --prepforconv, see Invoking MakeProfiles.