Preview 3D LUT - FPGA feature
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3D LUT support for preview video output

what does "preview" mean excactly? what is simplified/left out/estimated?

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Given that the sensor's data is effectively unknown, a “preview” could be interpreted to mean a few different things:

  1. A generic 709 that correctly transforms the sensor's data into meaningful values. That is, it requires defining the primaries relative to the sensor in relation to 709 / sRGB, hence the need for a 3D LUT which is the only method to adjust the saturation intents.
  2. A more creative 709 view that might offer slightly crunchier blacks and a softer rolloff. Some vendors take a little creative liberty with their 709 output. Still requires as 3D LUT.
  3. A unique preview LUT, or series of LUTs, as designed by a cinematographer for an estimation of looks for lighting usage on set. Would require a primaries transform to whatever display type chosen, and therefore 3D.


Bertl added a comment.Jan 24 2015, 9:20 PM

@sebastian mostly it means that we probably won't have the resources to run a 3D LUT on full data, especially not on 150+ FPS 4K data in realtime, and it isn't necessary either, as this is better done in post.

I doubt you'd be able to do any processing on 4K (above 30fps) or high speed data would you? It'd be straight raw out.

To be honest I'm not really sure what 'preview' means in this context the Axiom has no monitor or recorder so everything is output for recording.

This also means LUTs could be pushed onto a monitor recorder - the Convergent Design Odyssey and Atomos Shogun both support LUTs.

You could possibly work with the frame grabber to pull a 25fps stream out of the high speed for a monitoring output of those set ups.

At 'normal' speeds and HD resolution 3D LUTs should be no problem. Ideally you'd want a few options. At least a corrected 709 image and a cinelog. Ideally the option of user defined LUTs too.

You'd also, ideally, be able to route different LUTs to different outputs ie Log to HDMI 1 for recording. Corrected 709 to HDMI 2 for monitoring. Finally you'd also want to be able to switch between two LUTs (eg log to 709) at the click of a button: I often do this while shooting as I monitor the 709 but often flick to a log to check I'm not clipping highlights.