<target_file> is the file name of an image for which detection probability should be computed (e.g. distorted image) and <mask_file> is the file name of an image that is a reference (e.g. original, not distorted). The order in which both images are passed to the vdp is important and may affect the results.
The format of input images and output map is pfs. Use one of the readers from pfstools package to read images into vdpcmp.
Use the original (non high dynamic range) version of the VDP. Since the original VDP has not been maintained for ages, this option is depreciated. HDR VDP should provide better results and can work with LDR images as well.
Multiply luminance values of both target and mask by <val>. Using such multiplier is necessary if the images contain only relative but not absolute luminance values (cd/m^2). In case of low dynamic range images that have been converted from sRGB color space to XYZ (--linear switch of pfsinppm), --multiply-lum should be set to the maximum luminance of the display (see also man page of vdp).
DEELEY (default) - OTF from 'Deeley, R.J., Drasdo, N., & Charman, W. N. (1991). A simple parametric model of the human ocular modulation transfer function. Ophthalmology and Physiological Optics, 11, 91-93'. It takes into account pupil size, which depends on adaptation luminance. This is suggested OTF function for the VDP.
MARIMONT - OTF from 'Marimont D.H. and Wandell B.A., 1994. Matching colour images; the effects of axial chromatic aberration. Journal of the Optical Society of America A, 11 (no 12) 2113-3122'. It takes into account pupil size, which depends on adaptation luminance. (note: the integration performed in the current implementation is not accurate. This can lead to artifacts in the filtered image).
SPENCER - PSF from Spencer et al. SIGGRAPH'95 paper
NORMANN - PSF from Normann et al. IEEE Trans. on Systems, Man and Cybernetics '83 paper (note: this function can be wrong (typo in the paper?), therefore it is not recommended to use it).
WESTHEIMER - PSF from Westheimer "The eye as an optical instrument" in Handbook of Perception and Visual Performance. This function is also used in Sarnoff Visual Discrimination Model.
NONE - no OTF preprecessing
WATSON, VDP - Watson cortex transform (default)
SIMPLE - no multichannel processing, only a single channel
VDP can predict visible differences for pixels that are identical because of inaccuracies of visual band filters. To avoid this, as a final step HDR VDP compares two input images pixel by pixel and if the corresponding pixels are almost identical (difference < 0.0001), it sets the prediction for that pixel to 0. Use --no-abs-fix to disable this behavior.
The following options define viewing conditions. Because passing a complete set of options to specify viewing conditions is rather tedious, the better way is to use -vc option of the vdp command (see the man page for vdp).