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 magnitude of difference between the two images as a peak
22 signal-to-noise ratio (PSNR) This metric is typically used in image
23 compression papers to rate the distortion between original and decoded
24 image.
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26 If the inputs are PBM or PGM, pnmpsnr prints the PSNR of the luminance
27 only. Otherwise, it prints the separate PSNRs of the luminance, and
28 chrominance (Cb and Cr) components of the colors.
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30 The PSNR of a given component is the ratio of the maximum mean square
31 difference of component values that could exist between the two images
32 (a measure of the information content in an image) to the actual mean
33 square difference for the two subject images. It is expressed as a
34 decibel value.
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36 The mean square difference of a component for two images is the mean
37 square difference of the component value, comparing each pixel with the
38 pixel in the same position of the other image. For the purposes of
39 this computation, components are normalized to the scale [0..1].
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41 The maximum mean square difference is identically 1.
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43 So the higher the PSNR, the closer the images are. A luminance PSNR of
44 20 means the mean square difference of the luminances of the pixels is
45 100 times less than the maximum possible difference, i.e. 0.01.
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49 pnm(1)
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53netpbm documentation 04 March 2001 Pnmpsnr User Manual(0)