Hybrid Log Gamma in Vegas

karma17 wrote on 11/5/2019, 9:03 PM

Very new to HLG and still learning how to edit it. So please forgive my ignorance about it.

I was just curious about one thing.

I don't have any problem color correcting the HLG footage, and so far, everything is going well there.

However, I noticed that if I edit, then render out a clip in HLG, I can't seem to mix it with other non-HLG rendered clips because the HLG clip wants to be in the HLG mode in Vegas. Is this correct?

That you can't mix even rendered HLG clips with non-HLG clips in Vegas unless you are in HLG mode in Vegas? When I bring in HLG rendered clips, they looked washed out until I go into HLG mode and set the color space. Is that because HDR relies on metadata for decoding, even as a rendered clip?

This is screen capture of HLG footage that was graded and rendered in Vegas, but if the rendered clip is brought into Vegas, it will look washed out unless HDR space and color space is set in Vegas.

Any thoughts appreciated.

FWIW, these are my other results, all rendered in Vegas, but I couldn't include HLG clip because it washed out.

Comments

fr0sty wrote on 11/5/2019, 9:56 PM

Make sure you are properly specifying the color space of your clips in the project media properties, such as specifying Rec 2020 1000 nits for your HDR clips. If Vegas is in HLG mode, this should already properly show HLG, assuming you have hardware capable of it.

karma17 wrote on 11/6/2019, 12:00 AM

@fr0sty Thank you.

Yes, so when I'm color correcting the HLG footage, I'm checking off HLG in the Project Properties and then just doing that cascades settings underneath it for 32 bit space and ACEs. Then I'm going into the Media Properties and setting to the Color Space, as you state. And everything's fine. Then I render out the clip, and everything's fine watching it on the VLC viewer.

But if I bring that rendered clip back into Vegas on a timeline with just regular MP4 clips (not HLG), the HLG clip will not display properly and will look washed out until I set up HLG Project Properties and Media.

Usually once a clip renders, I can bring it into Vegas and it will play as it is rendered. And I don't have to adjust any color space for a rendered clip. But it seems like HDR clips are different from any other type of video clip and need the color space set for it to display properly and hence be re-rendered out again.

I guess it just takes some time getting used to this HDR footage and how it plays with non-HDR footage on the same timeline. Is there some fundamental incompatibility between HDR clips and non-HDR clips?

fr0sty wrote on 11/6/2019, 9:56 AM

This is the color space non-HDR footage uses, Rec709:

This is the color space HDR/HLG uses, Rec2020:

In addition to that, you're going from 256 possible shades between black and white/any primary color to 1024.

So yes, the 2 are inherently incompatible when it comes to displaying them on the same timeline, a conversion has to take place at some point on one or the other to make them work together. The BBC and NHK designed HLG to be able to be backwards compatible with SDR by creating a gamma curve that enables SDR sets to ignore the extra highlights 10 bit affords without compromising the image quality when displayed in SDR, but the opposite is not true, and HDR10 also does not have this backwards-compatibility built in. HDR10 on SDR screens looks way over-exposed.

Best practice is to use all Rec2020 (or similar, I use VGamut, for instance, with my VLOG footage)/10 bit content on the timeline when editing HDR or HLG. Those 2 can be mixed on the same timeline with very little conversion required (just an adjustment to the gamma curve). To mix in 8 bit SDR Rec709 video, it all has to be remapped over the new color space, bits per pixel depth, and gamma curve, and it still won't look any better in the end.

Musicvid wrote on 11/6/2019, 10:31 AM

I agree in principle with what's been said.

So I'm curious -- what happens if you open and correct your HLG in an 8-bit project and render as 8-bit? If you can juggle the upper range curves to give a pleasing output, there should be no compatibility issues with your other 8-bit source.

Maybe someone, like you, will come up with a Curves preset to do this generically. I would start with a calibrated display, an X-Rite chart, a means to shoot it in HLG, a precise eyedropper tool, and a couple of months worth of patience with myself.

karma17 wrote on 11/6/2019, 3:21 PM

Thanks!! This is very helpful. Just when I think I have things figured out, I get confused again.

@Musicvid Yes, I will have to keep playing around with it! That sounds like something worth trying.