Render format for Colour Grading

[Job Ter burg]

I’ve sent same-as-source Quicktimes to grading facilities. Worked fine.

You say it looks oversaturated and soft, were you judging that on a Rec 709 monitor?

Avid works in 709. When you export from Avid, export with 709 levels, and in the native pixel aspect ratio. That way, your QT’s may look greyish on a computer monitor, but that is because Rec 709 has black at 16 and white at 235 (8bit values that is).

[Jay Moffat]

Yep, on HD monitor Rec709, comparing to the original footage…

I’d not have though rendering out to Rec709 would be the ideal as you’re essentially clipping values before the grade. no?

Jason

[Job Ter burg]

No, if you export from Avid with the 601/709 button selected, you are telling the export module that the source is already 709, so it leaves it untouched.

If you export with the RGB button selected, it will stretch 16-235 over 0-255, clipping of any whites over 235. Not a good idea if you need to grade indeed.

Not sure what you are comparing and how the footage has been brought in. HDV is usually captured digitally (FW or HDSDI) and that should leave all levels untouched during capture. If you export same-as-source and 709, you are basically not changing anything, leaving the original intact.

Are you sure you are not being bitten by some gamma issues within QuickTime?

[Job Ter burg]

I meant to write: “if you export from Avid with the 601/709 button selected, you are telling the export module that the destination is 709, and the source is already 709, so it leaves it untouched.”

[Jay Moffat]

I think that’s probably the issue then, they have exported as RGB which would probably account for the issues…unsure about any QuickTime issues, shouldn’t be unless there is an PC Avid/QuickTime to MAC QuickTime issue…we’re grading in Apple Color, the Avid is on Windows.

Not sure it accounts for the softness though… We were wanting to avoid outputting ‘same as source’ due it being HDV, there was a concern that the quality would not hold up for re-rendered clips with speed changes etc, so we wanted an uncompressed export. Any advice on an uncompressed for format from Avid for cross platform use?

Thanks for the feedback

Jason

[Job Ter burg]

If it were up to me, I would transcode the HDV source clips to an actual Avid DNxHD codec and use that to send to color grading. I prefer to work in DNxHD because it holds up so much better in post anyway. Plus, before any processing, you are upscaling thin raster to full raster, which is nicer to work with.

Alternatively, export the edited sequence as some form of DNxHD. DNxHD145 should suffice, since you are coming from 25 Mbit/s. Make sure you have the DNxHD codec installed on your Mac. It’s a free download at avid.com/codec.

Blowing up HDV to Uncompressed seems like a huge boost of empty data to me.

[Bouke Vahl]

I second the DNxHD idea.
But i’m pretty sure you will have a gamma issue.
No problems, just start with a gamma shift of .8 (or 1.2, i forgot) on each clip. You have to render anyways…

I cannot explain softness. It should be exactly what it is…

Bouke

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[Jay Moffat]

The softness issue is pretty perplexing it could have been the RGB vs Rec709 issue perhaps. But in general, outside of the HDV issue I’m really looking for how you guys, as Avid users, which I’m not, send material for grading, and from what I see it could well be the RGB vs Rec709 export issue, the codec being slightly secondary.

The reason I ask for Uncompressed is that I know that at least what I get is as good as it’s going to get. The DNxHD file they sent me from the HDV sequence was terrible, then again it could have been an operator issue. I did notice a huge shift in the levels too, it produced a very washed out image on the mac, compared to the original HDV footage, which is also in addition to the softer image, why we re-conformed.

Thanks for the replies

Jason