pnmpsnr  -  compute the difference between two images (the
       PSNR)


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) dif­
       ference 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) compo­
       nents of the colors.

       The PSNR of a given component is just the mean square dif­
       ference of the component, comparing each  pixel  with  the
       pixel  in  the same position of the other image, expressed
       as a decibel value.  For the purposes of this computation,
       components are normalized to the scale [0..1].


SEE ALSO

       pnm (5)


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