My understanding from Ray is that -dDOINTERPOLATE is that should turn on interpolation for all images. The documentation in Use.htm concurs. However, running PLANHALF.pdf from Bug 688869, a combination of DCT, CCITTFax and JPX images, I only see it enter the image interpolation code at all for 1 bpc images. $ bin/gs -sDEVICE=pbmraw -o foo.pbm -r36 -dDOINTERPOLATE PLANHALF.pdf It would be nice for display quality if other image depths were scaled down with an intelligent filter.
Interpolation is implemented in a device-dependent way and 1 bpc images are handled separately from other cases. Checking the interpolation parameter in data_image_params() shows that it is always on when -dDOINTERPOLATE is defined. However, Ghostscript can currently interpolate only non-skewed images at 0 and 180 deg. rotation. Most images in the sample file are skewed or rotated. The PDF interpreter and PS code work fine. At most, this is an enhancement request for the rendering logic.
Alex is the owner Image and filter stuff.
Mark an early but user-priority bug a duplicate of newer customer priority bug. *** This bug has been marked as a duplicate of 690246 ***