ProRes transcode in ACES 2065-1 ?

Hi there

I’m working in post production

I wanted to try a complete ACES workflow between DI and VFX.
But the EXR file was too heavy for us.

so i tested with prores4444(ACES2065-1)

But Highlight clipping occurred compared to the EXR.
(When setting Acescct color space and ODT 709)

I wonder why


ACES2065-1 is a linear encoding. This data isn’t suited for a limited integer format. You will have to choose a different format to output to. ACEScct can be an option but I’m not fully sure if that remains accurate enough if you have really high dynamic range scenes like from CG. Another alternative could be an intermediate in the camera native log encoding of your project’s camera.

Thank you so much, Shebbe!!

When ACES2065-1 Linear encoding converts to an integer

I don’t think I know much about the reason for the highlight clipping.

Do you have any recommendations for this knowledge?

I’m not the best at explaining it… but when you have scene linear values these can reach far above 1.0 floating point. Whenever you store floating point information into an integer format it will only store the values within the range of 0 to 1.0 to it’s available bits. 1.0 means the maximum value for that channel. Like 1023 for 10bits or 255 for 8bit. So while that part of the transformation will look correct, any value that was above 1.0 will become clipped.

In theory you could scale all the scene information down to fit the 0-1 range for your 10bit file but that means that the brightest exposure stop would posses half of the available bits and the lower you go the less bits are dedicated to it. That’s why we have log encodings, to more evenly fit the captured stops so we can have equal quality and control across the captured dynamic range in these smaller formats.

The first 15mins of this great talk from Daniele Siragusano covers this.

Was the EXR uncompressed? PIZ compression is lossless and results in file sizes smaller than a DPX. Also 16-bit half float rather than 32-bit.

use dwab/dwaa exr files, you can dial in compression as you want , making stuff as big a a prores is easy