601/709 DNxHD QT files vs. RGB DNxHD QT files

[Sean]

When importing DNxHD quicktime files, I have the option in Avid of assigning RGB or 601/709 color space to the newly created imports. I've done a test importing DNxHD files and I can see that the 601/709 import option results in a higher contrast image with a histogram that is stretched out wider from blacks to whites. The RGB import test results in lower contrast image with a histogram that is slightly more "congested" in the middle of the range with higher values.

Given that these DNxHD files (from Red footage) have no color correction added yet, I'm wondering what the best starting place might be: the higher contrast 601/709 files with a wider histogram, or the lower contrast RGB option with more compressed histogram.

I should add that final output is NOT for broadcast. It's web and DVD and festival screening.

 

[MichaelP]

RGB assumes that the source file has black at 0RGB and whites at 255RGB. when importing into the system, it will adjust the to meet the digital television SMPTE specification of 16RGB - 235RGB by bring 0RGB to 16RGB and 255RGB to 235RGB scaling everything in between (no cropping).

If you select 601/709 then it assumes that the source images already meet the specification of 16RGB - 235RGB and will do nothing. So if there are values in the 0-16 and 235-255 range they will be kept and you can deal with them as you see fit in the color correction process.

The DVD requirement will require you to know what the RGB range is as some encoders expect 0-255 and other 16-235, and some allow you to indicate what the range is.... just keep track of what you do.

Michael

 

[Sean]

Thanks Michael. From your post at dvxuser I see that I can determine the type of DNxHD in a file by importing the file into Avid using the "as source" option, then Avid won't change what the codec format and I'll be able to tell once imported what the data rate is.

This is the key for me in your answer above: "If you select 601/709 then it assumes that the source images already meet the specification of 16RGB - 235RGB and will do nothing." So I'm concluding that if you WANT to keep the edited footage at a full 0-255, one would select this option in Avid, since it won't try and re-jig the color space to 16-235. Seems counter-intuitive that the 601/709 option is the option you use to keep the picture at 0-255, but that's what I'm concluding from this. (And conversely, the RGB ironically would compress the color space to 16-235--I'd expect an RGB option to give me 0-255 instead).

 

[MichaelP]

Yes, the setting refers to the source, not to what you want to make. It's one of those 50/50 things... Since Avid is trying to ensure proper broadcast, it likes 16-235 and will do that for you if you indicate the sources are RGB.

Same on export. I color correct for broadcast 16-235 but can export as RGB which will take by color corrected sequence from 16-235 to 0-255. I do that when I make Internet formats, etc. Color correct once, export as needed.


Michael

 

[Sean]

Yes, the setting refers to the source, not to what you want to make. It's one of those 50/50 things... Since Avid is trying to ensure proper broadcast, it likes 16-235 and will do that for you if you indicate the sources are RGB.

Same on export. I color correct for broadcast 16-235 but can export as RGB which will take by color corrected sequence from 16-235 to 0-255. I do that when I make Internet formats, etc. Color correct once, export as needed.


Michael

Okay. Interesting. So on export, if I want it to stay in 0-255, I'd select 601/709 so that it doesn't change anything? Not sure what would happen if it's already 0-255 and then I export as RGB. It would "super-stretch" the colors? Because if I imported RGB footage at 601/709, thereby retaining the full 0-255 spectrum, exporting as RGB would try and stretch the 0-255 as though it were 16-235?