Archive for the ‘Color Management’ Category
Display calibration and profiling are becoming more and more popular thanks to relatively cheap colorimeters and wide gamut monitors. It’s important to know that an application must support color management in order to display accurate colors.
While most of the popular graphics editors, viewers and web browsers have this feature, I haven’t heard about any video players with ICC color management. So, I’ve decided to implement this in one of the most popular open source media players for Windows: Media Player Classic Home Cinema, or simply MPC-HC.
The problem with current color management systems (CMSs) is that they use the CPU. Even with lookup tables and SIMD optimizations, they are quite slow. Way too slow for real-time HD video playback. Fortunately, color management can be implemented very efficiently on the GPU.
The ideal solution would be to write a GPU-optimized CMS from scratch, but that’s a lot of work and I’m too busy right now with my ray tracing stuff. A much easier way is to build a 3D LUT with an existing CMS (I’ve opted for Little CMS), which you can sample in a little pixel shader to transform the pixels. 3D LUTs are frequently used in the film industry and are starting to get serious attention in the gaming industry too.
I’m using a 64x64x64 LUT with 16-bit per channel floating point entries, which provides results virtually indistinguishable from those obtained directly with Little CMS. Trilinear interpolation is crucial, and it’s natively supported for this texture format by most (if not all) GPUs released in the past few years. I’ve also added dithering as a final pass to avoid introducing banding artifacts.
GPU accelerated color management has been introduced in the latest stable version (1.4) of MPC-HC. If you experience some problems with that, you should download a recent SVN build. Make sure to select the EVR Custom (recommended for Vista and 7 users) or the VMR-9 (renderless) renderer in View -> Options -> Playback -> Output. Then, you can enable color management in the View menu as shown above. For a detailed description of the renderer settings, please check out the wiki.