Color space confusion

[John Rofrano]

Don’t I need to end up with computer RGB for any file uploaded to YouTube?

That’s correct.

But the color space article implies that the MPEG2 codec expects 16-235. Does that mean it will clip levels outside that range to full black / white?

Yup, which is why you should not be using MPEG2 for YouTube videos. For YouTube delivery, place the Sony Color Corrector filter on your master video bus with the “Studio RGB to Computer RGB” setting. Then render to Sony AVC which will retain your 0-255 color space and upload that to YouTube. You should use one of the “Internet” settings under Sony AVC which are specifically designed for YouTube-like delivery.

~jr

http://www.johnrofrano.com
http://www.vasst.com

[Paul Goelz]

Now ya tell me 😉 I’ll try that workflow and see how it goes. Thanks! I’ll be curious to see if it renders faster or slower to Sony AVC vs. MPEG2. I have to use NeatVideo on most of my old stuff and it is veeerrryyyy slow to begin with.

Paul

[Paul Goelz]

Later that very same day…..

Worked fine. Thanks. It still amazes me how utterly complicated and initially incomprehensible digital video editing is. It is, after all, just a series of still photos shown in rapid succession.

BTW, I didn’t bother with putting a separate color corrector on the master video track. I just set the waveform monitor to computer RGB levels and used the color corrector on the video track to set levels like I usually do. It was a bit confusing at first because the waveform monitor was set to computer RGB but still displayed reticle markings above and below 100%. But since the waveform never went beyond 0-100% I assume the “headroom” isn’t really there in the computer RGB waveform display.

At the same time I calibrated both my monitors as best I could and now everything seems to track much better, especially because using computer RGB levels, the preview window is also correct.

Paul

[Paul Goelz]

OK, I’m back with another question or two.

I rendered a couple projects to Sony AVC and uploaded them to YouTube. And discovered that YouTube treats them differently than it does MPEG2 uploads for some reason.

They all started out as 720 X 480 and rendered as such. But the MP4 uploads ended up slightly lower resolution than the identical project rendered as MPEG2 and uploaded. I have not looked at the files closely yet…. it may be that they rendered differently.

But I also noticed something else after I rendered a couple seconds of one of the projects to MPEG2 and MP4 using a couple different bitrates each and uploaded them to YouTube. The bitrate affected how YouTube displayed them too. The higher bitrate MP4s displayed with lower resolution. Again, it might be how they actually rendered…. there may be differences in the size of the video vs. the frame size when it renders.

But the last thing I noticed was that there was essentially NO LEVEL DIFFERENCE between the Sony AVC and the Main Concepts MPEG2 renders. They were both rendered from the same project, which was set for computer RGB levels. The MPEG2 was slightly darker but it was so slight that I had to run them both side by side on the same monitor to see it. I’d say maybe 1% at most. So what’s all the fuss about using the correct levels for MPEG2 vs. Sony AVC? There doesn’t seem to be an observable difference in levels, and if anything the MPEG2 was a bit sharper than the Sony AVC at 6Mb/s.

I then created a project with generated media “pluge and porches”. I rendered that to Main Concepts MPEG2, Sony AVC and DV-AVI and found zero difference in levels between any of them when they were added to the timeline and examined with the waveform monitor. I did note, however, that on the preview screen all shades of grey were easily visible. But when played back using Medial Player or QuickTime, only the 10% level was visible. The two below that were solid black. This behavior was identical for all three renders (MPEG2, MP4 or DV-AVI). What am I missing?

Paul

[Paul Goelz]

Let me summarize for clarity. Or at least try 😉

I created a project with two seconds of generated “pluge and porch” with the levels set for computer RGB (0% = black and 100% = white). All shades of gray were visible in the preview window.

I then rendered this to three different output formats…. MPEG2 with the YouTube preset, Sony AVC with the YouTube preset and to DV-AVI.

All three renders were placed on the timeline and the preview window and the waveform monitor confirmed that the levels were identical to the original.

All three were played…. the MPEG2 and DV-AVI in Media Player and the Sony AVC in the Quick Time player. All three showed the lower two shades of gray to be black as if the player was expecting NTSC video levels.

This seems to indicate that any level issues I am having are in playbeack and not in rendering, regardless of the codec used??

So…. what to do? Is the easy answer to simply re-adjust my levels to NTSC with 7.5% setup? Easy to do, but is that the correct way to do it? It kinda makes sense, since I have a two part goal…. upload to YouTube and also burn to DVD. Setting levels to 7.5% = black would seem to accomplish both goals?

Paul

[John Rofrano]

When I render Sony color bars with a pluge to Sony AVC with and without the Sony Color Corrector filter set to “Studio RGB to Computer RGB” setting, I get VERY different output. Especially when using Quicktime player to play the .mp4 files. I’m not sure why you are not seeing this too.

~jr

http://www.johnrofrano.com
http://www.vasst.com

[Paul Goelz]

I think you mis-understand. I rendered the SAME levels (computer RGB) to the three codecs and got the same results from each. Each one, when the rendered file was placed on the timeline yielded precisely the same levels as the source. So far, so good.

The problem I am trying to work through is that while the waveform monitor seems to be saying that I am outputting and rendering computer RGB levels…. and the rendered files CONTAIN computer RGB levels, when those rendered files are played back outside of Vegas, they seem to play back as if they were expecting studio RGB. That doesn’t make sense given the fact that the same file placed on the timeline shows computer RGB levels. Why doesn’t it play back that way?

One possibility is that my monitor is not calibrated properly and I am simply chopping off the last 7.5% when I play a file in Media Player. However, it displays a built in test pattern (part of the nVidia control panel) correctly. And the Vegas preview window (viewed on the same monitor) correctly shows all gray steps down to the lowest on the pluge…. 1% maybe?

Is there any way I can check my monitor calibration with tools available in Vegas or Photoshop? For example, how about I grab a frame from the pluge and examine it in Photoshop. If it contains the correct levels but they don’t display correctly on my monitor when the file is played, is this just a monitor issue?

Or am I totally mis-understanding the basics….. when presented with a file containing pluge and porch, SHOULD I be able to see all the grey levels during playback on a PC monitor? Like I said, it plays it back as if it was expecting studio RGB…. the 1% (?) and the 7.5% steps are totally black. All others are visible.

Another possibility is that I am not correctly setting or interpreting the waveform display. Both boxes are unchecked. I am assuming that sets it up for computer RGB and in fact, I cannot drive the waveform below 0 or above 100 with the color corrector tool even though the scale extends beyond 0-100.

Thanks for bearing with me. I’d like to get this right.

Paul

[Paul Goelz]

OK, after some experimentation it looks like I have some answers to my own questions.

1. I tried rendering various levels to three different codecs and then placing the renders on the timeline, looking at the levels and comparing them with the original. Of the three codecs I tried (MPEG2, Sony AVC and DV), all three output exactly the same levels that you input. Computer RGB in = computer RGB out, studio RGB in = studio RGB out. This seems to be in opposition to the colorspace article / tutorial?

2. When I played these apparently correct files outside of Vegas, the levels were shifted downwards and everything below about 7.5 IRE was black.

3. When these files were uploaded to YouTube and then played, the levels were shifted downwards and everything below about 7.5 IRE was black.

4. My local playback error turned out to be because the nVidia driver for my G-210 video card defaults to a setting that either allows the playback application to change the video levels or changes them when it knows a video is being played (can’t tell which is true). This caused much confusion because a frame grab showed the correct levels but actually playing the video in a player shifted the levels downward. When I changed the nVidia driver to use fixed levels for everything and then calibrated those video settings, my playback looks the same as it does within Vegas or as monitored on my second monitor. It also matches the frame grab (a jpeg file).

5. The YouTube level shift seems to be either YouTube or their Flash player messing with the levels. For videos uploaded to YouTube in MPEG2 format, it seems you need to use standard video levels with 7.5 IRE setup (or studio RGB) to get a correct playback.

Since my primary target is both YouTube and DVD, it seems to make sense to use studio RGB levels within my projects and for all renders and render to MPEG2. That way, my renders are compatible with both as-is.

Comments?

Paul

[John Rofrano]

Since my primary target is both YouTube and DVD, it seems to make sense to use studio RGB levels within my projects and for all renders and render to MPEG2. That way, my renders are compatible with both as-is.

Comments?

If that works for you, then go for it. I wasn’t aware that YouTube applied any intelligence to it’s processing and processed MPEG2 and different than MPEG4 but if they do then what you want to do will work.

~jr

http://www.johnrofrano.com
http://www.vasst.com

[Paul Goelz]

Well, according to my experimentation so far, YouTube seems to assume incoming video is at studio RGB (NTSC with setup?). Their player seems to assume that 7.5IRE = black when playing back, regardless of the actual levels in the file (in other words if it sees video below 7.5% it clips it to black instead of shifting to computer RGB). I downloaded the transcoded MP4s but I can’t remember what the levels were…. I’ll have to do that experiment over.

I have checked several times and the various codecs definitely accept any incoming levels and preserve them in the output.

Since YouTube transcodes the entire file before it displays it in full quality, it is too bad they don’t at least sense incoming levels and transcode appropriately.

I do note that I uploaded an HD clip a while back that was in computer RGB and it looks perfect on Youtube. Not sure what to make of that. Maybe they assume computer RGB for HD files?

Paul