77 lines
2.3 KiB
HTML
77 lines
2.3 KiB
HTML
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<HTML><HEAD><TITLE>Man page of pnmpsnr</TITLE>
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</HEAD><BODY>
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<H1>pnmpsnr</H1>
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Section: User Commands (1)<BR>Updated: 04 March 2001<BR><A HREF="#index">Index</A>
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<A HREF="/cgi-bin/man/man2html">Return to Main Contents</A><HR>
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<A NAME="ixAAB"></A>
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<A NAME="lbAB"> </A>
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<H2>NAME</H2>
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pnmpsnr - compute the difference between two portable anymaps
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<A NAME="lbAC"> </A>
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<H2>SYNOPSIS</H2>
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<B>pnmpsnr</B>
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[<I>pnmfile1</I>]
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[<I>pnmfile2</I>]
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<P>
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<A NAME="lbAD"> </A>
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<H2>DESCRIPTION</H2>
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Reads two PBM, PGM, or PPM files, or PAM equivalents, as input.
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Prints the peak signal-to-noise ratio (PSNR) difference between the
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two images. This metric is typically used in image compression papers
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to rate the distortion between original and decoded image.
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<P>
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If the inputs are PBM or PGM,
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<B>pnmpsnr</B>
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prints the PSNR of the luminance only. Otherwise, it prints the
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separate PSNRs of the luminance, and chrominance (Cb and Cr)
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components of the colors.
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<P>
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The PSNR of a given component is the ratio of the mean square difference
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of the component for the two images to the maximum mean square difference
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that can exist betwee any two images. It is expressed as a decibel value.
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<P>
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The mean square difference of a component for two images is the mean
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square difference of the component value, comparing each pixel
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with the pixel in the same position of the other image. For the
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purposes of this computation, components are normalized to the scale
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[0..1].
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<P>
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The maximum mean square difference is identically 1.
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<P>
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So the higher the PSNR, the closer the images are. A luminance PSNR
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of 20 means the mean square difference of the luminances of the pixels
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is 100 times less than the maximum possible difference, i.e. 0.01.
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<P>
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<A NAME="lbAE"> </A>
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<H2>SEE ALSO</H2>
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<B><A HREF="/cgi-bin/man/man2html?5+pnm">pnm</A></B>(5)
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<P>
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<HR>
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<A NAME="index"> </A><H2>Index</H2>
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<DL>
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<DT id="1"><A HREF="#lbAB">NAME</A><DD>
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<DT id="2"><A HREF="#lbAC">SYNOPSIS</A><DD>
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<DT id="3"><A HREF="#lbAD">DESCRIPTION</A><DD>
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<DT id="4"><A HREF="#lbAE">SEE ALSO</A><DD>
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</DL>
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<HR>
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This document was created by
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<A HREF="/cgi-bin/man/man2html">man2html</A>,
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using the manual pages.<BR>
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Time: 00:05:24 GMT, March 31, 2021
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</BODY>
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</HTML>
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