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Pnmpsnr User Manual(0)							   Pnmpsnr User Manual(0)

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

SYNOPSIS
       pnmpsnr

       [pnmfile1]

       [pnmfile2]

DESCRIPTION
       This program is part of Netpbm(1)

       pnmpsnr reads two PBM, PGM, or PPM files, or PAM equivalents, as input and prints the mag-
       nitude of difference between the two images as a peak signal-to-noise  ratio  (PSNR)  This
       metric is typically used in image compression papers to rate the distortion between origi-
       nal 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 maximum mean square difference of compo-
       nent  values that could exist between the two images (a measure of the information content
       in an image) to the actual mean square difference for  the  two	subject  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 pos-
       sible difference, i.e. 0.01.

SEE ALSO
       pnm(1)

netpbm documentation			  04 March 2001 		   Pnmpsnr User Manual(0)
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