pnmpsnr(1)pnmpsnr(1)NAMEpnmpsnr - compute the difference between two images (the
PSNR)
SYNOPSISpnmpsnr [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 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, com
paring 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 ALSOpnm(5)
04 March 2001 pnmpsnr(1)
