xenial (1) pnmpsnr.1.gz

NAME

       pnmpsnr - compute the difference between two portable anymaps

SYNOPSIS

       pnmpsnr [pnmfile1] [pnmfile2]

DESCRIPTION

       Reads  two  PBM,  PGM, or PPM files, or PAM equivalents, as input.  Prints the peak signal-to-noise ratio
       (PSNR) difference between the two images.  This metric is typically used in image compression  papers  to
       rate the distortion between original and decoded image.

       If  the  inputs  are PBM or PGM, pnmpsnr prints the PSNR of the luminance only.  Otherwise, it prints the
       separate PSNRs of the luminance, and chrominance (Cb and Cr) components of the colors.

       The PSNR of a given component is the ratio of the mean square difference of the  component  for  the  two
       images  to the maximum mean square difference that can exist betwee any two images.  It is expressed as a
       decibel value.

       The mean square difference of a component for two images is the mean square difference of  the  component
       value,  comparing each pixel with the pixel in the same position of the other image.  For the purposes of
       this computation, components are normalized to the scale [0..1].

       The maximum mean square difference is identically 1.

       So the higher the PSNR, the closer the images are.   A  luminance  PSNR  of  20  means  the  mean  square
       difference  of  the luminances of the pixels is 100 times less than the maximum possible difference, i.e.
       0.01.

SEE ALSO

       pnm(5)

                                                  04 March 2001                                       pnmpsnr(1)