coded pictures. The value ofbit_depth_luma_minus8 shall be inferred to be equal to bit_depth_aux_minus8 for the decoding of the auxiliary coded pictures. NOTE 3 - Alpha blending composition is normally performed with a background picture B, a foreground picture F, and a decoded auxiliary coded picture A, all of the same size. Assume for purposes of example illustration that the chroma resolution of B and F Rec. ITU-T H.264 (01/2012) have been upsampled to the same resolution as the luma. Denote corresponding samples of B, F and A by b, f and a, respectively. Denote luma and chroma samples by subscripts Y, Cb and Cr. Define the variables alphaRange, alphaFwt and alphaBwt as follows: alphaRange = Abs( alpha_opaque_value-alpha_transparent_value) alphaFwt = Abs( a - alpha_transparent_value) alphaBwt = Abs( a - alpha_opaque_value ) Then, in alpha blending composition, samples d of the displayed picture D may be calculated as dy = ( alphaFwt * fy+alphaBwt*by+alphaRange/2)/alphaRange dcb = alphaFwt fcb alphaBwt alphaRange 2) / alphaRange dcr = ( alphaFwt fcr + alphaBwt bcr + alphaRange (2) alphaRange The samples of pictures D, F and B could also represent red, green, and blue component values (see clause E.2.1). Here we have assumed Y, Cb and Cr component values. Each component, e.g., Y, is assumed for purposes of example illustration above to have the same bit depth in each of the pictures D, F and B. However, different components, e.g., Y and Cb, need not have the same bit depth in this example. When aux format is equal to 1, F would be the decoded picture obtained from the decoded luma and chroma, and A would be the decoded picture obtained from the decoded auxiliary coded picture. In this case, the indicated example alpha blending composition involves multiplying the samples of F by factors obtained from the samples of A. A picture format that is useful for editing or direct viewing, and that is commonly used, is called pre-multiplied-black video. If the foreground picture was F, then the pre-multiplied-black video 