CentOS 7.0 - man page for pnmpsnr (centos section 0)
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Pnmpsnr User Manual(0) Pnmpsnr User Manual(0)
pnmpsnr - compute the difference between two images (the PSNR)
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 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
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.
netpbm documentation 04 March 2001 Pnmpsnr User Manual(0)
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