ICtCp, or Why We Can’t Have Nice Things

Here at the Daejeon Chronicles, we’ve tirelessly championed RAW for a long time now, for a multitude of reasons: it responds better to grading than heavily compressed, low bit rate chroma subsampled codecs and is less prone to banding; sharpening, noise reduction and white balance aren’t baked into RAW files, giving more flexibility in post; 12-bit RAW is preferable to 10-bit log, as converting from one 10-bit format to another, such as when creating the SDR version from the HDR master, introduces errors; and in the case of the Sony a7s III, the RAW files have nearly 25% more resolution than the internal codec, which can come in handy when stabilizing footage or cropping. And lastly, 10-bit log is to be avoided because Y’C’bC’r chroma subsampling causes hue shifts, saturation issues, luminance errors and unwanted noise in HDR. Because so many affordable cameras can shoot RAW nowadays, it’s no longer the insurmountable hurdle it once was.

However, when it comes to video sharing platforms like YouTube and Vimeo, we’re back to using a variant of YCbCr, a color space whose origins can be traced back nearly 70 years, for encoding our video. Practically all consumer video, whether streamed, broadcast or distributed on UHD Blu-ray, relies on 4:2:2 or 4:2:0 subsampling to reduce bandwidth, but it’s not so much the subsampling as the fact that it’s accomplished in a way that is destructive to HDR, ensuring that the viewer will absolutely not be seeing the video as intended, that is reprehensible. The screenshot above gives an indication of how the color transformation of Y’C’bC’r of the HEVC rendered clip distorts color and luminance information. ICtCp is vastly superior to Y’C’bC’r, it’s compatible with HEVC, all Dolby Vision enabled televisions and most displays can decode it, but currently it’s only available on Disney+, Apple TV+, Netflix and Amazon. In an ideal world, the entire imaging pipeline, from the camera to the screen, whether high end or budget production, would be able to take advantage of ICtCp, but we don’t expect to see that happening anytime soon.