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I have no idea what you're

> I have no idea what you're driving at here. Are you saying that some DNG-aware
> applications can make use of EXIF

Sure!

I've done simple experiment in two minutes
- image from Canon 50D converted to DNG with Adobe 5.2.0.65 converter
Results
* Black Level tag value: 1023 1023 1023 1023
* Black level repeat dim: 2 2
* White level tag: 13200 (i.e. data is unscaled, 14-bit preserved as is)

But the real Black Level for this image is 511, not 1023.

Right RAW processor should:
- think: "this is Canon! we should calculate black level by left side of black mask"
- ignore black level tag from DNG
- calculate black level by averaging black (masked pixels)

If you strip all vendor-specific metadata from this file you will get unacceptable nonlinearity in shadows.

-- Alex Tutubalin