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The phrase peak signaltonoise ratio, often abbreviated PSNR, is an engineering term for the ratio between the maximum possible power of a signal and the power of corrupting noise that affects the fidelity of its representation. Because many signals have a very wide dynamic range, PSNR is usually expressed in terms of the logarithmic decibel scale.
The PSNR is most commonly used as a measure of quality of reconstruction in image compression etc. It is most easily defined via the mean squared error (MSE) which for two m×n monochrome images I and K where one of the images is considered a noisy approximation of the other is defined as:

The PSNR is defined as:

Here, MAX_{I} is the maximum pixel value of the image. When the pixels are represented using 8 bits per sample, this is 255. More generally, when samples are represented using linear PCM with B bits per sample, maximum possible value of MAX_{I} is 2^{B}1.
For color images with three RGB values per pixel, the definition of PSNR is the same except the MSE is the sum over all squared value differences divided by image size and by three.
Typical values for the PSNR in image compression are between 30 and 40 dB.
See also
 Signaltonoise ratio
 Video quality
 Subjective video quality
External link
 Program for PSNR measurement in BMP files and video
Categories: Image processing  Noise  Film and video technology  Digital television  Engineering ratios