pnmpsnr(1) [redhat man page]
pnmpsnr(1) General Commands Manual pnmpsnr(1) NAME
pnmpsnr - compute the difference between two images (the PSNR) SYNOPSIS
pnmpsnr [pnmfile1] [pnmfile2] DESCRIPTION
Reads two PBM, PGM, or PPM files, or PAM equivalents, as input. 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, pnmpsnr prints the PSNR of the luminance 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 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, 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. SEE ALSO
pnm(5) 04 March 2001 pnmpsnr(1)
Check Out this Related Man Page
IDIFF(1) General Commands Manual IDIFF(1) NAME
idiff - compare two images SYNOPSIS
idiff [options] image1 image2 DESCRIPTION
The idiff utility is invoked as follows: idiff [options] image1 image2 Where input1 and input2 are the names of two image files that should be compared. They may be of any format recognized by OpenImageIO (i.e., for which image-reading plugins are available). If the two input images are not the same resolutions, or do not have the same number of channels, the comparison will return FAILURE imme- diately and will not attempt to compare the pixels of the two images. If they are the same dimensions, the pixels of the two images will be compared, and a report will be printed including the mean and maximum error, how many pixels were above the warning and failure thresholds, and whether the result is PASS, WARNING, or FAILURE. For example: $ idiff a.jpg b.jpg Comparing "a.jpg" and "b.jpg" Mean error = 0.00450079 RMS error = 0.00764215 Peak SNR = 42.3357 Max error = 0.254902 @ (700, 222, B) 574062 pixels (82.1%) over 1e-06 574062 pixels (82.1%) over 1e-06 FAILURE The "mean error" is the average difference (per channel, per pixel). The "max error" is the largest difference in any pixel channel, and will point out on which pixel and channel it was found. It will also give a count of how many pixels were above the warning and failure thresholds. The metadata of the two images (e.g., the comments) are not currently compared; only differences in pixel values are taken into considera- tion. For a complete description, see /usr/share/doc/libopenimageio-dev/openimageio.pdf.gz. OPTIONS
--help Print help message -v Verbose status messages -a Compare all subimages/miplevels Thresholding and comparison options -fail %g Failure threshold difference (0.000001) -failpercent %g Allow this percentage of failures (0) -hardfail %g Fail if any one pixel exceeds this error (infinity) -warn %g Warning threshold difference (0.00001) -warnpercent %g Allow this percentage of warnings (0) -hardwarn %g Warn if any one pixel exceeds this error (infinity) -p Perform perceptual (rather than numeric) comparison Difference image options -o %s Output difference image -od Output image only if nonzero difference -abs Output image of absolute value, not signed difference -scale %g Scale the output image by this factor SEE ALSO
iconvert(1), igrep(1), iinfo(1), iprocess(1), iv(1), maketx(1), oiiotool(1). AUTHOR
OpenImageIO was written by Larry Gritz and the other authors and contributors. This manual page was written by IRIE Shinsuke <irieshinsuke@yahoo.co.jp>, for the Debian project (and may be used by others). May 19, 2012 IDIFF(1)