PSNR

PSNR is measured in decibels. It's defined as

<math>PSNR(I,K) = 20 \cdot \log_{10}{(\frac{255}{\sqrt{MSE(I,K)}})}</math>

with

<math>MSE(I,K) = \frac{1}{M} \cdot \sum_{j=0}^{width-1} \sum_{k=0}^{height-1} | I(j,k) - K(j,k) |^{2}</math>

where M = width <math>\cdot</math> height is the number of pixels in a frame and width, height are the width and height of the frame, respectively, in pixels.

The double-sum term states that (j,k) runs over all pixels of the frame, summing the absolute value of the difference of I, K functions raised to the power of 2.

For more details see: http://en.wikipedia.org/wiki/PSNR .