For the JPEG part: That is not surprising, for several reasons: - Depending on if the IDCT (2D cosine-based frequency domain => time domain) is implemented usin

For the JPEG part: That is not surprising, for several reasons: - Depending on if the IDCT (2D cosine-based frequency domain => time domain) is implemented using floating point or fixed-point, the ways roundings are done, 0.5 offsets or not etc, the number of bits of precisions, you will have small errors. - Most JPEGs are in i420 format, that is "for a 16x16 Y block, there is one 8x8 Cb block and one 8x8 Cr block". The upsampling algorithm may differ both in precision and on the choice of the algorithm itself. - Even in YCbCr => RGB conversion, there may be 1-bit differences. More if they used other constants. Note that even between two versions of the same library, you can get different results.