Gamma correction

[juliagraphics]

Gamma correction

[timholy]

There's the invert_rgb_compand function; I can verify that repeatedly converting RGB->XYZ->RGB->XYZ preserves the value. But beyond that, I have no comment; colorimetry is not really my area of strength, here I'm acting as a slightly-educated code-janitor.

[rennis250]

I would at least like to see some interface for specifying my own gamma look up tables, as this is something that my colleagues and I always need fine-grained control over. I assume that high-end photography applications would also benefit from that kind of access. Aside from that though, I know next to nothing about color management practices. Do modern image and film formats carry metadata about this?

[KelSolaar]

Do modern image and film formats carry metadata about this?

Images that embed ICC profiles will usually describe the colour component conversion function (EOCF / EOTF) that maps from non-linear R'G'B' video component signal to a tristimulus value at the display.

If by film formats you talk about movie camera output, it is an entire different beast, they may have different file formats and very different conversion functions based on customised logarithmic function, the way to describe that is highly inconsistent.

We have a quite comprehensive amount of those here: https://github.com/colour-science/colour/tree/develop/colour/models/rgb/conversion_functions

And some more tied to RGB colourspaces definitions are available here: https://github.com/colour-science/colour/tree/develop/colour/models/rgb/dataset

Hope that helps :)

[AndrewGibb]

Do modern image and film formats carry metadata about this?

Some brief notes as I stick my head above the parapet of castle Thesis-writing:
In broadcast video, gamma correction functions are defined in standards, and the file format/wire format do not contain metadata specifying the parameters. There is a research project in BBC R&D at the moment which I plan to lobby to transmit data in linear light, and apply gamma at the display.
I've been working with ARRI ARRIRAW and RED EXR files for my thesis. ARRIRAW uses a logarithmic mapping from V_in to V_out, which I have not been able to find a formula for, but they do provide a free look-up table generator on the web. The EXR file format encodes gamma correction within the file format, alongside pixel values in linear light.