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Old April 28th, 2014, 02:18 AM   #1
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Vegas 12 preview screen

If one sets the preview device preferences to "Adjust levels from studio RGB to computer RGB" does this only show up as such on the preview screen or does it transfer to the rendered material?

Thanks
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Old April 28th, 2014, 04:57 AM   #2
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Re: Vegas 12 preview screen

The way I understand it is that if you have this 'Adjust Levels' box checked the output to a second computer graphics monitor will approximate how it should look on a correctly set up TV when Preview on External Monitor is selected.

Just to test what is happening put some PAL or SMPTE bars on the time line with the 'Adjust Levels' box unchecked. When you select preview you should see your bars on the second monitor but now look at the bottom of the bars and you should see the bottom quarter of the display showing 'black.' You will also note that this black isn't very black and you will also see the three pluge bars towards the right hand side showing super black, black and bottom grey. The first and third bars should be sitting about 40-millivolts below and above black which is at 0 volts black.

This is obviously not how your levels should be displayed on a TV. Now go back in and check the 'Adjust Levels' box and go preview again. If your output monitor is adjusted correctly you should now only be able to see the third + 40-millivolt bar and the black areas of your bars should look closer to true black. On a correctly adjusted TV you should only ever see this third bar. If you see the black and super black bars standing out the monitor levels are incorrect.

In other words with this box checked when you preview your program you can see just how your blacks and whites look on a TV. If your program blacks look crushed then they probably are.

To answer your question does it affect the render levels the answer is no.

Chris Young
CYV Productions
Sydney
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Old April 28th, 2014, 07:55 AM   #3
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Re: Vegas 12 preview screen

Chris, the biggest problem in Vegas is the way that it deals with video levels from various sources. Some are 16-235, some are 0-255, others are somewhere in between and it's up to us as editors to figure things out and make it all look good.
Here are two recent threads on the Sony Vegas forum that will either clarify things or further muddy the digital waters.

Vegas video levels - debate possible changes

What min/max levels does your cam shoot?
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Old April 28th, 2014, 10:37 AM   #4
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Re: Vegas 12 preview screen

Maybe this extension for Vegas Pro 12 (and 13) is useful.
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Old April 29th, 2014, 01:33 AM   #5
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Re: Vegas 12 preview screen

Quote:
Originally Posted by Mike Kujbida View Post
Some are 16-235, some are 0-255, others are somewhere in between and it's up to us as editors to figure things out and make it all look good.
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Mike ~

Sorry if this sounds like a bit of a rant but it bugs me that so many aspiring editors lack the basic knowledge of 'levels', the technical basis on which the video industry is built on. Lack of knowledge not through their own fault but brought on purely by the lack of training. It's hardly surprising though with many organisations not wanting to train people and self taught editors having to grapple their way through theses issues.

Various sources is not a new problem. Back in linear edit suite days these problems existed. Footage came in with peaks up 1.09 volts. Badly set up cameras had vision below black. Computer graphics arrived with 0-255 levels, broadcast graphics arrived with 16-235 levels. It was just as much a shambles back then as it is now. This is all part of an editors lot understanding this, it's part of his / her craft. How can you be classified as an editor if you can't comprehend that it is part of your job description to understand the signals and technology used in this industry. The problem these days is no one wants to train people so we have many editors who are pretty clueless technically but very skilled and inspired artistically. In 90% of cases we find they are self taught.

Regardless of what arrives in the shop it's up to the editor to analyze fix / correct, however you want to put it, all material to meet whatever output delivery specs he / she has to meet whether using Premiere, FCP, Avid, Vegas or whatever.

Vegas can handle all video levels correctly if you understand Vegas and the way it works with various video levels thrown at it. . That's why we have WFMs and V Scopes. A WFM will quickly tell an editor whether a signal is based on 0-255, 16-235 or 16-255 If editors don't use them then they are making a rod for their own backs. Once it is established what signal levels a particular piece of material is coming in at you then its up to you manipulate it to suit your output requirements. The difference these days is that web delivery has no 'fixed standards' to adhere to so many editors have just created material with little reference to any standards. It is hardly surprising that many of them get confused between broadcast and PC standards when its required to differentiate between them.

If editors working for TV don't know how to read and understand their measurement tools or understand what those instruments are saying then they had better learn pretty quickly otherwise broadcast delivery requirements for both vision and sound will cause them a lot of grief as they get asked to re-edit material. It's in their own best interests to learn. It's a continual learning process, like the recent loudness levels of the CALM requirements.

Sorry again if it sounds a bit of a rant but after twenty-six years of running a business that supplied weekly TV programming and still does but not weekly I am saddened to see so many aspiring editors stuck with a lack of understanding what are basically some of the most fundamental rules and tools of the trade. In 99% of cases this is because they haven't been taught correctly from the get-go.

It is great that forums like this exist so that people like Mervin can hopefully learn some of what is required to become a good 'technical' editor as opposed to just an artistic editor. The craft of editing encompasses both ends of the spectrum. Hopefully some of us older duffers may be able to feed back some of what we have been taught and learnt.

Chris Young
CYV Productions
Sydney
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Old April 29th, 2014, 02:56 AM   #6
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Re: Vegas 12 preview screen

well said chris!!!!

understanding waveform / vector scopes should be the stuff editors are made of, not using every fx in the box and wondering why things go belly up on preview.

once upon a time i'd get a betasp tape and had that as my ONLY jumping off point - that said, it's not been made any easier by the plethora of proprietary codecs, camera formats and levels, etc., that manufactures seem so keen on inventing and promoting nowadays....
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Old April 29th, 2014, 03:01 AM   #7
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Re: Vegas 12 preview screen

Oh yes. Sigh. Unfortunately out there even lots of broadcasting engineers doesn't get all these things right, extracting single parts of given standards while ignoring the rest and also don't seeing the big picture. It often starts with jumbling reference levels and peak levels …
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Old April 29th, 2014, 07:03 AM   #8
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Re: Vegas 12 preview screen

Quote:
Originally Posted by Christopher Young View Post
broadcast graphics arrived with 16-235 levels.
I still don’t understand why they chose to limit the output like that. It makes no sense photographically, as it takes away a stop. Nor does it make any sense mathematically, as way too many effects are best computed in the full mode using floating point math, with reference black being 0 and reference white being 1. For example, raising the values between 0 and 1 (i.e., exponentiation) returns values still confined to the 0-1 range. But raising the values within the video standard not scaled to 0-1 but to a limited range within >0 and <1 will return results within the 0-1 range, so changing the contrast (to name just one example) will get you outside the video range.

I know I am going against the grain of this forum, but I wish all cameras used the full range of 0-255. Then all editing should be done with the 32-bit floating point full 0-1 range. Even if the camera gives you the video range, you should expand it to the computer range while editing. Only when outputting the final result should one convert to 16-235 when editing for broadcast video.

Let’s not forget that broadcasting is not the only goal of editing. If you want to go to film, for example, you need the full range or even more (see ACES, for example) because film can handle more stops than television.
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Old April 30th, 2014, 05:48 AM   #9
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Re: Vegas 12 preview screen

Adam ~

I also wish all cameras used ‘full swing’ 0-255 8-bit PC levels. Life would be infinitely easier in post.

There is a very good reason why many camera signals and broadcast graphics units are limited to 16-235 it’s because that equates to the 1v P-P video signal. That’s come about because early video systems were based around the 1v P-P video signal from acquisition to delivery. This signal was around way before modern readily available computer technology appeared. It was based on a 1 volt peak to peak signal of which .7 of a volt was reserved for the vision component and .3 of a volt was reserved for blanking, syncs, and later when color arrived, the burst signal. Back in the 'old' days the whole transmission chain was built around this 1v P-P signal level. The trouble is the old days are still here when it comes to TV. Sad to say we have to acknowledge that if working for broadcast TV, DVD or Blu-Ray output as they ALL expect to see 1v P-P signals. So whether we like it or not the 16-235 restricted swing 8-bit RGB levels of the computer is still required.

What does this mean to us today? The convergence of video and computing technology started to take place in the analogue era but then started to accelerate with the advent of digital video. Hence the conundrum of two totally different ways of handling and displaying these signal levels confronted us. How do we mix them we asked? Well let’s superimpose the studio video signal on top of the computer RGB signal. Let’s take NTSC as our yardstick.

The sync pulse is 40 I.R.E. units, the peak picture amplitude is 100 I.R.E. units and so a standard one volt black and white peak-to-peak video signal is 140 I.R.E units (40 SYNC + 100 LUMINANCE [WHITE] = 140).

Ok where does this get us? In our RGB 8-bit world we have 0-255 levels. Stick a pure 255 level solid white on your timeline and what does its peak level read in IRE. It is 109 IRE. Many modern digital camcorders record super-white video levels, or video levels that exceed a digital value of 100 percent. Many record at up to 109 percent. This is computer 8-bit RGB white level 255. Even though these cameras reach 109 IRE whites their black levels will be set to 0 IRE. 0 IRE on the 0-255 full swing RGB level is 16.

A couple of cameras like this come to mind depending on their settings / PPs etc. One is the Sony FS700 which with some of its PP Gammas will give you 0-109 IRE which equates to 16-255 of the full swing RGB levels of 0-255. Another, the new Panasonic GH4 gives you three choices, 16-235, the ‘old’ but still required broadcast 0-100 IRE level, the newer digital 16-255 level and the full swing RGB 0-255 8-bit computer levels. Each range being suited to match certain specific media output requirements. All a little bit confusing for the novice editor who has no or little experience in working across the various delivery requirements for the different delivery methods. So how do we handle this information?

To sum up. Well this is what I do and so far so good and it all seems to work. I could be off base but I don’t think too far off. If you are editing for web delivery and all those little PCs around the world work and grade in the full swing levels of 0-255. That’s the correct thing to do IMHO. Sadly though working in broadcast TV you really have no option but to comply with that ancient old hangover TV standard of 1 v P-P. This of course means working, or at least outputting, in the restricted range of 16-235 if working in the 8-bit digital RGB realm.

If you are now going to work with 10-bit sources with 0-1024 full swing levels in that 8-bit 0-255 space well that’s a different story. 10-bits at 24 bits per pixel equates to 1,073,741,824 discrete colours. This requires very careful handling to shoe horn all that info into the meagre 16,777,216 colors we have in the 8-bit 24 bits per pixel domain. We now have a whole new range of issues to contend with, concatenation / banding issues, being just one of them. This is where the 32-bit floating point math can help us when editing in Vegas. Regardless of whether we are working in 8-bit or 32-bit floating point though we still have to pull and push these levels regardless of how many there are and fit / grade them smoothly into the 8-bit 0-255 world for web delivery or the restricted swing 8-bit 16-235 4:2:0 for broadcast, DVD and Blu-Ray world.

Different story if we are working to comply with DCI ACES film out and working full range especially with log material then we have to work in 32-bit floating point full range in Vegas. Which on an 8-bit native box is a contentious and mathematical fudge at best I think. Work on a dedicated 10-bit processor based 4:4:4:4 box and you can see the difference. I have to qualify that to a degree though because most of the displays we work with cannot come close to showing us 1024 shades of grey per pixel. I often ask myself “Exactly what am I putting out there?”

Edit on regardless I guess.

Chris Young
CYV Productions
Sydney
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Old April 30th, 2014, 09:32 AM   #10
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Re: Vegas 12 preview screen

Quote:
Originally Posted by Christopher Young View Post
Edit on regardless I guess.
Oh, definitely. :)

I understand the need of voltages. But that is analog video. Is anyone still using analog video? Besides, the decision of the video levels in digital seems completely arbitrary to me. An A/D converter could just as easily convert the proper analog signal to 0-255 as it does to 16-235. And a D/A converter could easily convert the full digital range to the proper analog scale.

Digital TV just transmits bits, an MPEG encoded digital stream. Those bits have only two possible values, 0 and 1. It would be just as easy to use the full scale in the digital stream as it is using the limited range.

I guess I just get frustrated when people use words like illegal in this regard and insist that Vegas should work in the limited range. As I said, this is a mathematical nightmare. Everything should be done within the range of 0-1 internally. Cameras that use the full range are always my choice. The broadcast 16-235 range should not enter the equation until the last step when exporting the video to MPEG (and such) and only when it is meant for broadcast.

Yes, it would be nice if we had monitors that can handle more than ten bits. Or, more exactly, if we had video cards that can. For some strange reason Vegas 12 claims my video monitor is ACES, when I am working on a cheap laptop, which I will be using until I get into the mood of fixing my dead desktop computer (I think all it needs is a new power supply, but I have not been in the mood of fixing it for over a year now—I blame my diabetes and my old age on that).

Whatever the logic behind the video levels, I still say all editing should be done in the full range and only the final output should consider the broadcast levels and only when it is meant to be broadcast. When the final use is for computers (e.g., YouTube), I wish the computer software, such as the browsers, would expect the full range. Even more so when talking about digital cinema when ACES should be used.

Adam
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Old April 30th, 2014, 10:32 AM   #11
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Re: Vegas 12 preview screen

That's the point when I say: Don't mix up reference levels and peak levels. According to BT. 709 in an 8 bit signal there are only two values prohibited: 0 and 255 (and the only case I'm aware of when these two values are important is the use of SDI/HD-SDI interfaces). The range from 1 up to 254 is available for video data and so for black and white peaks.
But: Reference levels – which are 16 for black and 235 for white – are quite a different pairs of shoes which actually makes sense in the video world. The limit of 16 because of noise processing. The limit of 235 because of there is a good chance you will have elements which are brighter than reference white (e.g. light sources) and which any display panel up-to-date is well capable to precisely reproduce.

Despite of hundreds of discussions on the theme, Vegas Pro does a pretty good job in handling levels according to BT. 709, with some minor exceptions indeed:
- If you create a generated media it should take care of reference levels (titles, backgrounds, etc.)
- The internal preview should also give you an option to also take care of reference levels (though this is exactly what the extension I linked above does).
- Any compositing based processes inside Vegas (like it's auto background handling) should use a proper way to signify: "Attention please".

Leave ACES behind. It does not yet correctly work in the given OCIO framework.

Last edited by Marco Ba; April 30th, 2014 at 11:54 AM.
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Old May 3rd, 2014, 10:33 AM   #12
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Re: Vegas 12 preview screen

Hi

Is there a way to produce an H264 file that is full range? I know the X264 encoder has options to add meta data that says "hi, I'm full range", and this doesn't affect the actual encoded video but should tell the decoder how to treat the levels. Does this work? Will that meta data survive on a Blu-ray disc to the TV? How does deep color over HDMI come into this?

I'm getting the GH4 which can be told to shoot 0-255, and while yes I can squash that back into 16-235 for output, it would be nice to know I could produce an output with the extra information.

Regards

Phil
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Old May 3rd, 2014, 11:13 AM   #13
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Re: Vegas 12 preview screen

Any device or software which adopts to BT. 709 should carry the data range from 1 - 254 without any metadata needed. Except of HD-SDI (which prohibits value 0 and 255), them should carry 0 - 255. And yes, when exporting as H.264 from Vegas it will survive on a Blu-ray disc and it will be carried over HDMI, but a well calibrated TV display should start its black level from value 16. Anything below will be clipped (though you could calibrate the TV to also display values below 16 if you want, which is not recommended at least). Whereas anything above level 235 up to 255 should be displayed fine.
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Old May 3rd, 2014, 11:49 AM   #14
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Re: Vegas 12 preview screen

Hi

Many thanks for the info, I think I may try a few tests. I always thought a TV clipped at 235 as well, or more likely it would stretch 16-235 into 0-255, so anything above 235 would be gone, otherwise white would only be a light grey on the TV screen.

Usually I've exported from Vegas with strict broadcast levels at 16 to 235 and it has always looked okay, i.e. doesn't look like whites have been lost.

Then again perhaps it has and I've not noticed without an A/B comparison.

Sometimes I think I understand all this level business, other times I'm not sure.

Regards

Phil
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Old May 3rd, 2014, 02:08 PM   #15
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Re: Vegas 12 preview screen

For the display all depends on how you calibrate it, how you set luminance levels for black, white and gamma.

Based on several official papers (ITU and EBU) an LCD's black level is considered to be under 0,7 - 0,5 Nits, white (reference) at about 100 - 140 Nits, whereas maximum luminance level available (I don't mean the peak level which represents RGB 255 but the brightest level the display would be capable to output) almost never is below 200 Nits, so you have plenty of headroom from reference white up to peak white there. Gamma of 2,35 should cover the range up to peak levels of RGB 255.

Of course if your surround is very bright you probably would set the display reference white level to even more then 140 Nits, at the same time you probably would use a display with maximum luminance much higher than 200 Nits (and most LCD displays nowadays offer more than 300 Nits).
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