1Pnmpsnr User Manual(0) Pnmpsnr User Manual(0)
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6 pnmpsnr - compute the difference between two images (the PSNR)
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10 pnmpsnr
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12 [pnmfile1]
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14 [pnmfile2]
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18 This program is part of Netpbm(1).
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20 pnmpsnr reads two PBM, PGM, or PPM files, or PAM equivalents, as input
21 and prints the peak signal-to-noise ratio (PSNR) difference between the
22 two images. This metric is typically used in image compression papers
23 to rate the distortion between original and decoded image.
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25 If the inputs are PBM or PGM, pnmpsnr prints the PSNR of the luminance
26 only. Otherwise, it prints the separate PSNRs of the luminance, and
27 chrominance (Cb and Cr) components of the colors.
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29 The PSNR of a given component is the ratio of the mean square differ‐
30 ence of the component for the two images to the maximum mean square
31 difference that can exist between any two images. It is expressed as a
32 decibel value.
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34 The mean square difference of a component for two images is the mean
35 square difference of the component value, comparing each pixel with the
36 pixel in the same position of the other image. For the purposes of
37 this computation, components are normalized to the scale [0..1].
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39 The maximum mean square difference is identically 1.
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41 So the higher the PSNR, the closer the images are. A luminance PSNR of
42 20 means the mean square difference of the luminances of the pixels is
43 100 times less than the maximum possible difference, i.e. 0.01.
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47 pnm(1)
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51netpbm documentation 04 March 2001 Pnmpsnr User Manual(0)