Leveling -- A Comedy of Errors

musicvid10 wrote on 2/9/2015, 11:07 AM
This ridiculous exercise is here to amuse and enlighten those just dipping their toes in the swamp, to the multitude of errors that can and are introduced by downstream "fixes" for so-called "fullrange yuv," which in itself is an oxymoron, if not an extremely common one.

This is RGB Shirley, also called Fullrange Shirley. If there weren't a lot of analog TVs that would choke on her, everything would be dandy. If you can't see gradation between 0-16 and 235-255, drop back in when your monitor is calibrated correctly. Calibrize is cool, Spyder is amazing in concert with a trained pair of eyes.


This is YUV Shirley, happy and correctly stored at 16-235. She will, by design, play back the same as RGB Shirley above, but represents a compromise because she will play on older TVs correctly, too. We didn't used to see her much in the wild, except when their were first-tier flag errors (more to come on that).


This is Clipped Shirley. We see her a lot, because most cell phones, DSLRs, and pocket cams shoot "Fullrange YUV," which I said is an oxymoron. It's a sad commentary that many (most?) uninformed consumers actually prefer this mutation, because that's what they're used to seeing, almost everywhere. This first thing an informed viewer will see is a clipped image, with 0-16 and 235-255 completely blocked up, leaving blotches in the hair and facial tones.


This is overcorrected Shirley, happens when correct YUV Shirley gets flagged as Incorrect Fullrange Shirley, run through a converter, then gets played back on one of the players that recognizes the flag. This happens a lot actually, because the "converters" that do this assume it's cellphone video, and have no way of knowing if it's already been corrected. Just ran into this again last week.


This is "almost" the worse case. YUV Shirley flagged as Fullrange, run through a converter, flag recognized by player, and the smart kid left the Dynamic Contrast hardware filter on to boot. It actually happens, and the inevitable complaint is that the encoder messed up. The encoder, for those who don't understand by now, is the only thing that WASN'T messed up by operator error.


OK, so smart kid thinks he'll just adjust the contrast and brightness to "fix" it. Let's say he actually gets it back to 0-255 playback levels. Only catch is, he's lost almost 40% of native bit depth, so it looks kind of like pre-16 bit monitors, or maybe Swiss cheese (note the histogram.) The banding at HD resolution is nothing short of horrible. Is this really what he wanted? How would YOU go about undoing all the misinformation that led up to this? Will this kid work part-time at a ski resort for the rest of his life?


The moral?
Deliver only16-235 YUV, not a kludge, and hope for the best. The rest of the nonsense actually presents a compelling case of the cure being worse than the ailment.
YUV delivery media include .mpg, .mp4, m4v, DVD/BluRay, AVC/h264 x265, and a few nonstandard AVI. Best.

Comments

farss wrote on 2/9/2015, 1:33 PM


Which Shirley is this?

Bob.
musicvid10 wrote on 2/9/2015, 2:03 PM
It looks a lot like my Shirley leveled the way you recommend (and as I used to) for 16-235; apply Computer RGB for edit, then remove filter for render. I can tell because luminance/chroma are not hard-clamped as in the second example above, but loose, which many broadcasters still accept.

Show me the thread where you got the image (my dropbox uid is 20519276) and I may be able to pin it down a little better.

farss wrote on 2/9/2015, 2:44 PM
[I]" Show me the thread where you got the image (my dropbox uid is 20519276) and I may be able to pin it down a little better."[/I]

I just did a screen grab from your original post in this thread.
I applied a Levels Fx set to cRGB>sRGB followed by the Sharpen FX set to "light".
It shows how easily using histograms to judge levels can fool people.
The waveform monitor shows quite clearly that Shirley is correct YUV sRGB levels.

Bob.

S35 wrote on 2/9/2015, 2:54 PM
Many thanks again for sharing this...

If I'm doing color correction on an HDTV, I don't need to apply Computer RGB for editing, right?
musicvid10 wrote on 2/9/2015, 2:58 PM
Bob,
Heh. Yes I said it looks like YUV levels. Do the same test with your sharpness filter first in the chain, and the levels filter dead last, as I've always recommended. Should be very close to my second example (strict digital broadcast levels).

"I applied a Levels Fx set to cRGB>sRGB

It's not the histogram at question, it's your filter hierarchy. Waveform monitor may just not be as good at revealing that bit of slop, and indeed it didn't used to matter, at least not with NTSC [-20,120] IRE tolerance.


wwjd wrote on 2/9/2015, 3:12 PM
I've noticed the Sony Levels plug is not as accurate as the AAV ColorLab one. Color lab IS hard 16-235, Sony one is... meh... somewhere close enough. This was using Sony's built in histo.
farss wrote on 2/9/2015, 3:28 PM
[I]" It's not the histogram at question, it's your filter hierarchy."[/I]

My filter hierarchy was done that way to demonstrate why using histograms to judge levels is not a good idea.

If Shirley was already sRGB with some sharpening added and a kid looked at the histogram he could easily think he needed to add a levels correction.
That's why the industry doesn't rely on histograms, it uses Waveform, Vectorscope and maybe RGB Parade.

For sure the waveform monitor in Vegas requires some level of knowledge to use correctly but once you have that you will have way less chance of making the wrong decision.

Bob.
musicvid10 wrote on 2/9/2015, 3:48 PM
Nope. The waveform monitor shows obsolete analog IRE levels, which are easily screwed up / misregistered with a couple of too-handy checkboxes. "Some kid" is going to understand even less about that, despite your considerable experience.

This thread was never a testimonial for the histogram, but a ridiculous example of how exposed user controls have far more dangerous consequences in inexperienced hands than anything you seem to wish to debate. So, really try to get on board, rather than derailing a potentially useful discussion. I encourage you to start new topics on subjects that interest you.

With that I'm back OT, no exceptions.



musicvid10 wrote on 2/9/2015, 6:12 PM
wwjd, nice to know about Colorlab.
s35, that would appear to be right.
MikeLV wrote on 2/10/2015, 11:35 AM
The moral is you'll drive yourself mad trying to get levels "right' and the bottom line is no one but you really cares if they're spot on anyways....
GlennChan wrote on 2/16/2015, 1:17 AM
Musicvid... you are horribly confused and you are spreading misinformation on this topic.

The waveform monitor, vectorscope, etc. in Vegas do not behave anything like a real set of hardware scopes.

Vegas is broken and doesn't follow standards.

Sometimes 0-255 RGB levels in Vegas will produce proper levels.
Sometimes 16-235 RGB levels in Vegas will produce proper levels.
It depends entirely on the codec. It has NOTHING TO DO with whether the footage will be played on an analog TV, computer, etc. (*Assuming that the playback device follows video standards, which most do.)

To use Vegas, you don't really need to know anything about video standards. You absolutely need to know how the codecs behave.
Unfortunately, the manual for Vegas doesn't really explain any of this.
Fundamentally, Vegas has a bad design. Other NLEs handle all this stuff for you. Vegas does not.


Deliver only16-235 YUV
Dangerous and misguided advice.
VidMus wrote on 2/16/2015, 2:27 AM
Steve Hullfish Color Correction Tips



Steve Hullfish Tips & Tricks: Why you should use Waveform Monitors for Color Grading



Steve Hullfish and The Art of Color Grading | Tektronix


How to Edit Video for Compliance to Broadcast Specifications


Why Do We Need Color Correction? | Tektronix


VidMus wrote on 2/16/2015, 6:15 AM
@ GlennChan

I set the waveform monitor for 16 to 235 with the 7.5 IRE not checked. This puts video levels 16 at zero IRE and 235 at 100 IRE on the waveform monitor. I make sure that my final videos are within those boundaries. Any video level above 100 IRE and below 0 IRE will have lost details. Too much video above and below will be reduced to poor quality. I use a second monitor to view the videos with a setting to convert studio 16 - 235 to computer 0 - 255. What I See Is What I get on my final videos.

For me, I cannot get the results I want using the histogram. For me, the correct tools are the waveform monitor and the vectorscope. With Vegas, I use what gets me the final DESIRED results!

I put my videos on the internet and DVD's and so far, I have had 100% complements on the quality of my videos! What I do, works for me!

And that is all I really care about.

KNOW YOUR TOOLS!!!

S35 wrote on 2/16/2015, 7:07 AM
"s35, that would appear to be right."

Thanks for clarifying!
videoITguy wrote on 2/16/2015, 9:55 AM
As I know Glen has commented at length on this before, and supports my experience - inside of VegasPro the codec handling trumps all other tool sets at our disposal.
Hence it would always be wise to explain that and - therefore without that proviso - these discussions get far removed from a general useful guidance of a single set of standards.
musicvid10 wrote on 2/16/2015, 1:07 PM
Beginners at the levels game need a different level of guidance, just as in other threads where unnecessary complexities have been dumped. Like guidance on the most universal delivery standard for now and the immediate future. That's BT601/709, which all of Vegas' yuv encoders invoke, without any of the games I illustrated above. The only "danger" lies in fostering user ignorance, just as stressed in the principal topic.

Anyone who didn't read / doesn't get the irony and absurdity presented at the beginning of first post shouldn't be posting replies here.

In the same vein, anyone wishing to debate scope displays should join Bob's discussion. That's not what this is about.

Baby steps.
Lyris wrote on 2/16/2015, 1:42 PM
That was very interesting. But don't call me Shirley.
GlennChan wrote on 2/18/2015, 9:46 PM
I set the waveform monitor for 16 to 235 with the 7.5 IRE not checked. This puts video levels 16 at zero IRE and 235 at 100 IRE on the waveform monitor. I make sure that my final videos are within those boundaries. Any video level above 100 IRE and below 0 IRE will have lost details. Too much video above and below will be reduced to poor quality. I use a second monitor to view the videos with a setting to convert studio 16 - 235 to computer 0 - 255. What I See Is What I get on my final videos.

Unfortunately there are many ways in Vegas where you can create a situation that is not WYSIWIG. It can be frustrating when you run into unintuitive "gotchas" when you render to other codecs or mess around with the various permutations of the 32-bit floating point modes.

The scopes can be a useful tool. But they won't help you figure out the levels situation unless you already have it figured out in the first place.