> ...but what happens when I run an image codec that has higher bit value than > the core image chain or QC can handle? I'm not aware of documentation of > "what's going on" in that scenario.
You can't (realistically) have a codec with more precision than CoreImage. CI internally uses 128 bit pixels (32 bits of each component, floating point), which is about as good as it gets (10-bit codecs and _maybe_ 12 bit codecs are high-end). I suppose you could have 32 bit integer components (floating point wins on dynamic range, but not monotonic range like ints do), or 64 bit components, but virtually nothing will deal with that anyway. QC will use whatever GL allows -- in the editor, this is generally 32 bit pixels (8 bits per component), but externally it can be deeper (With native Core Image Rendering enabled on billboards, you should get CI's full precision in the output if the destination can accept it). Color conversion is a more subtle topic -- there are 601 and 709 matrices (that vade's alluded to) for YCbCr -> RGB and back, but there are also RGB->RGB conversions when tristimulus values change, or gamuts change, or when the source changes. This gets complicated more quickly than one might thing. Years ago, color conversions were avoided because they were expensive. They're still expensive, but now they're avoided because everyone needs to be a good citizen, and the longer the processing pipeline gets, the more unlikely it is that everyone does the right thing. When a source provides more data than QC can deal with (e.g., a floating point image via OpenEXR or TIFF or something), it simply discards the low bits. That's unrelated to color correction proper, but it can lead to subtle shifts if other pieces of the pipeline are deeper. There's really nothing QC can do to preserve this data; an 8 bit output context can only store 8 bits. -- Christopher Wright christopher_wri...@apple.com
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