ProRes to DNxHD

Hey guys, me again!

Having some issues with converting ProRes clips to DNxHD within Resolve. the clips convert fine and the quality is superb - but there is a REALLY noticable shift in the gamma (I believe).

Here is the original clip



and here is the clip, after being converted to DNxHD (mov wrapper)



There is no difference in colour when rendered to Uncompressed MOV, either.

This is not a problem with my display, as the clips themselves seem to be at fault. I can only imagine it's something to do with colour spaces - is there a way to alter the settings for rendering DNxHD? I don't get this shift when rendering to Uncompressed. I'm on a PC so I can't try ProRes. Or perhaps another way of fixing this?

Cheers,
Allan.

To make things more interesting, this problem doesn't occur if I render the file from ProRes to Uncompressed in Resolve, and then convert the Uncompressed file to DNxHD - it ONLY happens when I go from ProRes to DNxHD in one hop. But I don't have the room to be uncompressing all my footage before I convert it to DNxHD.

To make things more interesting, this problem doesn't occur if I render the file from ProRes to Uncompressed in Resolve, and then convert the Uncompressed file to DNxHD - it ONLY happens when I go from ProRes to DNxHD in one hop. But I don't have the room to be uncompressing all my footage before I convert it to DNxHD.

How are you processing the conversion? What tools are you using? What settings? This will help someone point you in the right direction.

The problem occurs with every flavour of DNxHD, in every combination I can think of - even when varying the levels, etc. Currently I'm just using Resolve to process the conversion. I converted to .mov Uncompressed YUV 422 to get a colour correct version of the clip. At the moment I haven't graded the clip at all, just testing workflow, so there's no LUTs or anything to get in the way. I'm rending it as a single clip, typically with the levels set to Data. I'm sorry - I'm not sure what more information I can give you. I feel like I've tried every DNxHD combination available, and the shift is still there, and REALLY present.

But if I convert the file to Uncompressed, the problem isn't there.

And if I convert the resulting Uncompressed file to DNxHD, the colour is all perfect, the way it should be.

Al.

Hi I had some time today so took a prores hq clip converted it to dnx 220x in resolve with video levles. I opened both up on PC display on Quicktime and the PRO res file was raised up compared to DNX file. However I ama linked to both files in avid and they were identical on scopes. I have seen prores files on pc monitors look raised possibly due to the gamma difference between MAC and PC. So it is strange that your dnx file is raised and not the prores.

The problem occurs with every flavour of DNxHD, in every combination I can think of - even when varying the levels, etc. Currently I'm just using Resolve to process the conversion. I converted to .mov Uncompressed YUV 422 to get a colour correct version of the clip. At the moment I haven't graded the clip at all, just testing workflow, so there's no LUTs or anything to get in the way. I'm rending it as a single clip, typically with the levels set to Data. I'm sorry - I'm not sure what more information I can give you. I feel like I've tried every DNxHD combination available, and the shift is still there, and REALLY present.

But if I convert the file to Uncompressed, the problem isn't there.

And if I convert the resulting Uncompressed file to DNxHD, the colour is all perfect, the way it should be.

Al.

It looks a case of data level/video level. (keep in mind that due to firewall I cannot see the images)

In ingest, set the level of the clips to [video level] (explicit scaling) and the export to [video level] (explicit scaling) as well. and see if it works.

If you leave to [auto] and you have in any point in the chain 444 you might get it wrong.

Hi mate, thanks for the reply. I have already tried setting the levels explicitly, sadly that didn't help. The only way I seem to be able to fix the problem is render it to Uncompressed, then rerender THAT output as DNxHD.

C'mon guys, no-one able to solve this?

I would use test signals, like a gray scale ramp and SMPTE color bars, then do some test file renders and troubleshoot the settings to see where the problem is occurring. There's lots of places where things can be set wrong. Once you have the right settings, save that as a Preset and (in theory) it won't happen again.

Generally speaking, looking at anything in Quicktime Player is an "all bets are off" proposition. Quicktime as a whole is already horrible, and Player just makes it worse. However in this particular case I think you're running into an unfortunate behavior of Avid's DNxHD Quicktime codec.

If you re-import the Resolve-generated DNxHD Quicktime back into Resolve and compare it to the ProRes, do you get the luminance shift? Or what about Premiere, or VLC Player? None of them actually use the DNxHD Quicktime components, they have their own internal encoders/decoders -- IE you don't actually need to have the Avid DNxHD Quicktime codecs installed separately. However, when you're playing one with Quicktime Player, you do.

When you encode DNxHD with Avid's Quicktime codec, you tell it if you're feeding it RGB levels (0-254) or 709 levels (16-235) and it saves that in a proprietary atom (ACLR) in the Quicktime. Their codecs can in turn use that to change how they decode. If you select 709, it leaves the incoming levels alone; If you select RGB, it converts the incoming 0-255 to 709 range 16-235. When decoding, if it's marked RGB, the decoder stretches the 16-235 back out to 0-255 so it looks right as RGB. But if it's marked 709, it leaves them alone. And I think that's what you're seeing...

Digging into the Resolve-made DNxHD Quicktime it looks like it doesn't write the Avid atoms (and why should it? Avid doesn't document any of this that I'm aware of.) If you're set to 'Video' levels (or probably Auto) you've encoded at 709 range which is correct. But apparently, lacking the ACLR atom, Avid's codec assumes it's 709 (which it is) and leaves the levels alone -- which is I think what you're seeing in Quicktime Player, where the blacks are high and the whites are low.. it's not converting it back to full-range 0-255 for display on your computer monitor.

However, the actual compressed data inside the Quicktime is fine. It's just Avid's own DNxHD Quicktime decoder showing it (arguably) wrong. As mentioned, if you re-import into Resolve or Premiere or Flame or show it in VLC, they should all look correct. Even if you AMA Link it into Media Composer it should be fine, for the same reason -- when you AMA Link it you're bypassing the Quicktime codec, Media Composer decodes internally, knows it's 709 levels and does the appropriate conversion to your monitor (or not if it's going out SDI to a monitor, etc.)

Why, I do believe you've hit the nail on the head! I can't believe I didn't look this up myself. Is there a way of getting a Quicktime based decoder that works better so I can edit without the gamma shift? I edit in Premiere you see.

THANK YOU.

Well, I apparently lied a bit. Now that I'm back in the office with access to all my stuff, I've spent some time testing this again today.

When I said Resolve doesn't write the Avid 'ACLR' atom, I was wrong -- it IS writing it. I have no idea why I wasn't seeing it over the weekend at home, but I had so many test files I'd generated that I guess I was looking at the wrong thing at some point at 3am. In any event, it doesn't change the results (in this case...)

As far as Premiere not showing the right thing when I originally said it should, well I was wrong there too. Premiere does have its own DNxHD decoder as I said (as of like CS4 or CS5 anyway, I don't really recall exactly) -- but in sitting here testing it, I can only conclude that it's broken, at least with Quicktime-wrapped DNxHD. It seems to always treat the data as if it were RGB, and re-scales the levels to 16-235 (when internally it's already at those levels) giving you the same washed-out look you do with Quicktime Player.

However it seems like if you render to DNxHD as MXF instead of Quicktime from Resolve, Premiere gets that right. So that appears to be the solution here.

*sigh* I will try to bring this up with Adobe to see what's going on inside Premiere, but it's almost impossible to talk to an actual human being who knows anything at that company.

My copy of CS6 doesn't seem to read MXF files, am I doing something wrong?

Oh.. no, looks like CS6 doesn't. I guess CC might have been the first time internal DNxHD appeared too. I swore it was earlier than that, but I still have CS6 installed at home and just tried and indeed it doesn't work.

So I guess you're stuck.

Before conversion, you should ensure that it has little quality drop. On the other hand, you can choose converter with high definition. Whatever, hope you can find ways to get rid of your confusion.

Before conversion, you should ensure that it has little quality drop. On the other hand, you can choose converter with high definition. Whatever, hope you can find ways to get rid of your confusion.

JJ are you back!!!

For an 'outside Resolve' transcode from ProRes to DNxHD on the PC, try Wayne Norton's ClipToolz Convert v2.xx. It will also allow ProRes encodes on the PC. Free un-restricted download at http://www.hdcinematics.com