Do I need to grade HLG video if I plan on using it on an HDR TV?

Teagan wrote on 3/11/2020, 10:10 AM

So I'm switching my workflow to start recording in HLG to future proof my videos and then using color charts and grading to change it to rec 709, which I have ready to go and that's all working perfectly. My main question, even after many videos on youtube that try to explain this, do I need to grade the HLG footage like extending the shadows and highlights (it's extremely compressed right out of the camera) and other things or do I just cut/edit and output it in the HLG format in Vegas Pro (without changing the highlights/shadows) and the video will play normally on a TV that supports HLG? I've seen people say you can just play the raw HLG file on a TV that supports it and the TV, itself, stretches the highlights/shadows, and makes everything look great, but other videos have me grade it - but are those videos only talking about outputting to 709? I'm so confused.

Basically I'm asking how to get HLG raw footage to play correctly on an HDR display that supports HLG.

Comments

Musicvid wrote on 3/11/2020, 12:32 PM

709 is always 2.2 gamma throughout, 8 bit color range.

I haven't seen that particular feature, so I can't tell you if your HLG capable set does the same, or unpacks the curve to full 10 bits.

Teagan wrote on 3/11/2020, 1:09 PM

I'm not sure what you mean, the conversion process to 709 I have almost perfectly done and that's easy, my question is about showing the footage on an HLG supported BT2020 display, if I need to grade the raw HLG or not. When I load it up in Vegas pro or Davinci, the scopes show the brights and the shadows compressed and I'm wondering if I have to grade that to be 100 for whites and 0 for black. Right now it's like 20 for black and 75 for white.

The files are 10 bit 2160p60 HEVC 200Mb/s in HLG scene file from a Panasonic AG-CX350.

Musicvid wrote on 3/11/2020, 4:24 PM

And my answer is, "I don't know, because I don't know if your teevee set unpacks HLG to 8 bit 709 or 10 bit 2020. I have no experience with such a set.

Only your eyes can tell you that. Why don't you throw up a test chart and tell us what it does? Make and model?

Teagan wrote on 3/13/2020, 1:39 PM

Sorry for my laziness, I found out that one of my TVs (actually a very cheap Samsung 4K UN43NU6900 (8 bit + FRC) from 2 years ago) supports HLG input so I put the raw camera HLG file onto a USB drive and put it in the USB 2 port and played it from the TV's built in video player and it looked great I even checked the menu and it was correctly set to HLG (which is usually greyed out).

So it looks like I can grade it for rec709 and put that onto a DVD with help from a color chart and other things and just output the finished file in HLG from Vegas Pro and, without any tinkering, have a UHD master without ANY grading or editing at all.

They say that HLG is backwards compatible, but I can not simply convert my HLG to rec709 and have it be so easy since the TV is the device doing the conversion in real time (stretching the waveform, detecting color information, etc).

I will have to grade it for rec709 delivery (DVD/BD) but if you want the UHD HDR experience, simply leave it in HLG format when you are done cutting and splitting and messing with audio as the TV is the device converting the seemingly-log-looking file to be what you could call HDR. When the HLG file is viewed on a TV or monitor that doesn't support HLG it will look washed out like what a Log video looks like without grading - which was causing my confusion. I have a high suspicion that if I mess with any exposure, brightness or colors in editing that the HLG file will look off, as in the TV's eyes, the waveform that the camera originally recorded in, is perfect.

This just got very interesting as I'm probably going to record in HLG for everything in the future.

 

EDIT: one extra thing, after this discovery I decided to see if I need to grade for rec709 at all so I exported my HLG file to a regular rec709 output (8 bit AVC with AAC) with no grading and it looks fine on the HLG TV (as if I graded it for 709) but its gamma is set to BT.1886 and I can't change it back to HLG. That same file still looks like Log footage on my 709 monitors. I do not know what is going on nor do I know if I can use this to easily convert the HLG footage to 709 without all the grading I'm doing.