Keywords
ASPECT
Set this keyword to retain the image's aspect ratio. Square pixels are assumed. If WINDOW_SCALE is set, the aspect ratio is automatically retained.
INTERP
If this keyword is set, bilinear interpolation is used if the image is resized.
WINDOW_SCALE
Set this keyword to scale the window size to the image size. Otherwise, the image size is scaled to the window size. This keyword is ignored when outputting to devices with scalable pixels (e.g., PostScript).