Care is necessary when switching the xybinsize and using regions defined in saoimage.
To extract a sub-image at high resolution one can reset xysize. Images are constrained to be square and so xysize requires the dimension, in output pixels, of the side of the output image. Each output pixel is of the size determined by xybinsize. To do this, set xycenter in raw pixels. In detector cordinates they are 0.934 and 0.600 arcsec per pixel, for the PSPC and HRI, respectively.