Does using a LUT on log footage reduce dynamic range?

[avpromedia]

Some video/cine cameras shoot in log format to give wider dynamic range, but they look wash out if used as-is. Some people apply a LUT in premiere pro to convert them back to rec 709.

But doesn't that reduce the dynamic range back to rec 709's 5 stops, which defeats the purpose of shooting in log format?

[R Neil Haugen · Accepted solution]

Log was conceived as a way to record both wider dynamic range (light to dark) and/or wider colorspaces into the file. Allowing the user to "normalize" the log image to "linear" display space later, in post. Understand, it was never intended by any camera maker that the flat log-look image would be used as a final image.

The normalization process can be done with LUTs, manually, or via  the (typically superior) algorithmic based processes like now adopted in Premiere when you couple auto-detect log with auto tonemapping, with your sequence set to Rec.709.

For quite some time, most any capture used for "SDR" ... Rec.709 ... has meant collapsing some of the camera dynamic range into the dynamic range available in Rec.709 by the standards specifications. Whether it is done by the camera itself during the recording, or the user later in video post.

So no, it doesn't defeat "the purpose of shooting in log" ... not at all. That purpose is to capture the wider space/range, and allow the user then to control the display of that image data within whatever space they choose.

I work for/with/teach pro colorists. Most pro colorists have yet to deliver a single paid HDR job. HDR is still very much the Wild Wild West, with competing formats none of which are universally accepted by all devices that list themselves as  "capable" of HDR display. Most of the ones that can do HDR formats don't do any of them particularly well.

And many devices still don't do HDR at all.

So all that log-encoded media in professional workflows is still going out as Rec.709 via broadcast or streaming services. Intentionally so.