When this colour transform is used, both the input image block and its corresponding prediction use the same conversion. Because the conversion is linear, it is identical to having the transform applied to residuals in the spatial domain when the prediction processes in different colour components are consistent. Thus, in HEVC-SCC (HEVC Screen Content Coding), the conversion is applied on the residual, which makes the prediction process for different colour components independent. It is also noted for intra-coded blocks, when the intra prediction directions for different colour components are not the same, the colour transform is not allowed to be used. This limitation is specified because when the intra prediction directions are different, the correlation among collocated samples across colour components is decreased, making the colour transform less effective. The colour transform also changes the norm of different components. To normalize the errors in different colour spaces, when the above transform is used for an image block, a set of QP (Quantization Parameter) offsets (?5, ?5, ?3) is applied to those three colour component—during quantization. After the quantization and reconstruction, an inverse transform is applied to the quantized residual so that the reconstruction is still kept in the input colour space.

In this application, some issues related CC ALF are addressed.