This script is in charge of creating stamps centered at the position provided by the user. However, when the output size is larger than the input image, the output image is not properly centered. To reproduce this problem run the lines below. At the end, it can be seen that the small stamp is properly centered, but the larger one is not.

# Size of the image
w=11

# Generate a noised image, just to distinguish pixels
astarithmetic $w $w 2 makenew 0.1 mknoise-sigma --output=noise.fits

# Put the central pixel with high value.
c=$(astarithmetic $w 2 / 1 + -q)
echo "1 $c $c 4 0 0.0 0.0 0.0 10 0" \
      | astmkprof --background=new.fits --mforflatpix --output=image.fits

# Create two stamps, at the same center position but with different sizes
small=9
large=15
bash psf-stamp.sh image.fits --center=$c,$c --widthinpix=$small,$small \
                  --mode=img --output=stamp-$small-$small.fits
bash psf-stamp.sh image.fits --center=$c,$c --widthinpix=$large,$large \
                  --mode=img --output=stamp-$large-$large.fits

# Check the results
astscript-fits-view stamp-$small-$small.fits stamp-$large-$large.fits