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This program is part of

and prints the peak signal-to-noise ratio (PSNR) difference 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,

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 mean square differ-

ence of the component for the two images to the maximum mean square

difference that can exist between 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, 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.

netpbm documentation 04 March 2001 Pnmpsnr User Manual(0)