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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 magnitude 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 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 maximum mean square
difference of component 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 possible difference, i.e. 0.01.
SEE ALSO
pnm(5)
netpbm documentation 04 March 2001 Pnmpsnr User Manual(0)
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