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For HDR, first apply one of these to linearize the tone curve:
- Avata2_D-Log_M_to_PQHDR1000
- Avata2_D-Log_M_to_PQHDR10000
Then after that apply this LUT if you also want color correction:
- Avata2-D-Log_M_Rec2020_CC
For SDR, first apply the color correction if you want it:
- Avata2-D-Log_M_CC
then apply one of these to linearize the tone curve into the gamma space of your choice:
- Avata2_D-Log_M_to_Gamma_2.2
- Avata2_D-Log_M_to_Gamma_2.4
- Avata2_D-Log_M_to_Rec709
- Avata2_D-Log_M_to_sRGB
- Avata2_D-Log_M_to_LinearGamma
Tone curve linearization is extremely precise as it's based on 73 measured input and output light values, in fact it's so precise that when I tried to save it as a 3D LUT, it noticeably lost precision in extremely dark scenes. This is why I separated the gamma correction and color correction into two separate LUTs.
Color correction was performed using XRite Color Checker Passport visible at the end of the video. Half using Resolve's automatic color checker based color correction tool, and half manually by hand using all the scenes in this video as a reference. Since number of patches on color checker is rather limited compared to full spectrum of colors, such color matching is half science and half art. This means that this color correction is not objectively perfect, unlike the gamma correction LUTs, which was another reason to separate them into two separate LUTs.
Since D-LOG M desaturates the image by default, color correcting such image means we get to recover some saturation values that are outside the range of sRGB/rec.709 primaries, which is useful for HDR deliveries.
For those who don't know:
- 2D vs 3D LUT:
2D LUT is grayscale-only, but supports much higher grayscale resolution of up to 65536 points, which is what these Avata 2 LUTs are using.
3D LUTs can do color transforms, but as a result their maximum grayscale resolution is 65 points (R 65 x G 65 x B 65 = 274 625 points across the whole RGB color space), which is what the two color correction (CC) luts are using. These two CC LUTs ONLY do color transform, they do not touch the gamma.
- Linear tone curve vs linear gamma:
Linear tone curve is not the same as linear gamma. Gamma refers to the curve into which the data is saved so that it can more optimally be encoded and written down in order to save storage space. When videos are displayed, gamma is inverted similarly how a zipped file is unzipped.
Linear gamma really just means no gamma, it's similar to not zipping the file, but instead of large file size it will result with quantization artifacts (low quality image) if saved like that in 8 bit precision for example. It's usually used in compositing or as intermediary when doing color/gamma space transformations.
Tone curve on the other hand is a curve that is not inverted when displayed, nor is it meant to be, but it is instead a transformation that is baked into the video in order to make the image look more pleasing, and usually with the purpose of reducing the washout effect that bloom has on the dark areas of the image.
One size fits all is not an ideal approach here, especially if working with multiple different cameras, as even when all the footage is converted to same color and gamma space, different underlying tone curves will still cause footage from different cameras to look different.
This can be inherently avoided by working with raw video, but that's usually not available on drones and action cameras. Linearizing the tone curve with a technical LUT can then be thought of as turning the video into a closest possible equivalent of a raw video file, without it actually being raw. The data in the video then faithfully reflects the light intensities that the camera sensor saw. Linearizing the tone curve means undoing the edits that camera introduced internally.
29 сен 2024
