The Czenakowski distance (sometimes shortened as CZD) is a per-pixel quality metric that estimates quality or similarity by measuring differences between pixels. Because it compares vectors with strictly non-negative elements, it is often used to compare colored images, as color values cannot be negative. This different approach has a better correlation with subjective quality assessment than PSNR.[ citation needed ]
Androutsos et al. give the Czenakowski coefficient as follows: [1]
Where a pixel is being compared to a pixel on the k-th band of color – usually one for each of red, green and blue.
For a pixel matrix of size , the Czenakowski coefficient can be used in an arithmetic mean spanning all pixels to calculate the Czenakowski distance as follows: [2] [3]
Where is the (i, j)-th pixel of the k-th band of a color image and, similarly, is the pixel that it is being compared to.
In the context of image forensics – for example, detecting if an image has been manipulated –, Rocha et al. report the Czenakowski distance is a popular choice for Color Filter Array (CFA) identification. [2]