Using Material with Burned-In LUT with ACES
In some situations, editors may receive images that already have a particular LUT “burned in” and have been mastered and approved for a particular output. It is quite common to encounter this with studio logos, archival footage, or content for which only a video master is available. Though not ideal, this type of “output-referred” imagery may still be used in a traditional ACES pipeline.
In order to bring output-referred imagery into an ACES-based workflow, an inverse Output Transform can be applied. For example, if the images are only available from a Rec.709 video master, an Inverse Rec.709 Output Transform can produce corresponding ACES data that represent those exact output values but expressed in a state that allows mixing with more traditionally sourced ACES images. It is important to note, however, that it is impossible to restore data that has already be compressed or clipped to a particular output encoding.
If the footage is starting from a reduced gamut in a display-referenced color space, it will still have a much more limited color depth and dynamic range after being back-converted into ACES. You may still be able to push the color beyond once in the wider color space, but this practice is certainly more of an emergency answer and should be avoided unless absolutely necessary.