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Old April 2nd, 2008, 05:53 AM   #1
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LCD for color correction --- when will it be good enough???

I was reading another thread (http://www.dvinfo.net/conf/showthread.php?t=118075) and really got to thinking about this... I hear a lot of people saying that you should only use a broadcast monitors for color grading. I'd like to hear from the collective group on what would be a good criteria as to when will LCD monitors be ready for color correction work???

To my way of thinking... if an LCD can meet the requirements of the specified gamut you're working to (primaries, white point, grey scale, etc) why would it not be acceptable for grading??? If it's more than just faithfully reproducing the color space, then what is it???

So I guess what I would like to know is what measurable parameters, when met, would be sufficient to say that an LCD is acceptable???

Mark

Last edited by Mark Keck; April 2nd, 2008 at 06:27 AM.
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Old April 2nd, 2008, 01:45 PM   #2
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In my opinion, the Sony BVM-L (ballpark of $30k with input cards I believe) looks pretty good. Sharper than CRT, blacks not quite as good on dark scenes. But most people can't tell it apart from the Sony BVM CRT (depends on distance though).

I'd also look at the eCinemasys monitors... they look like a better buy than the Sony monitors.

LCD display technology is getting better very fast... it's only now that it looks like they are good enough.

2- LCDs have historically had some limitations like:
- Blacks not that good (they still aren't that good)
- Colors are off
- Limited viewing angle
- Response time and motion portrayal not that great
- Need to de-interlace the image
- The image may not be that uniform
- Bit depth

Many of those points aren't issues now.

3- I'd still get a broadcast monitor over a computer monitor. Computer monitors can be affected by video overlays, probably won't handle interlacing right, etc.
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Old April 2nd, 2008, 04:53 PM   #3
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Thanks for the input Glenn.

I always like to be able to use the best tools I can get or afford, but I don’t think most people have anywhere close to 30k to drop on a monitor. How about something more realistic???

The list you provide are fair complaints against LCDs, but I would like to come up with quantifiable parameters that are measurable so as to be able to say “yep, this is a reasonable solution that’s also affordable”.

Let’s take them one at a time:

- Blacks not that good (they still aren't that good): I would agree… it’s a trade off. I’m thinking that this would translate to contrast ratio. Assuming that the manufacture’s number is inflated, what would be a good “true” contrast radio that could be measured???

- Colors are off: Obviously this would translate to calibrating the display to the required spec (ie: Rec709 for HD), most of the newer displays provide the controls to make most of the necessary adjustments. Also, I assume you can calculate a dE that tells you how close you are to being dead on. But what would be a good spec that says you’re close enough??? Also, how accurate of equipment do you need for the process??? Would a i1 type device be accurate enough or do you have to step it up a notch or two???

- Limited viewing angle: Granted, this can affect color on the off axis, but I would accept this as a trade off. Those who make a living at this probable can’t.

- Response time and motion portrayal not that great: Ok… how fast do you need??? Some of the newer panels are in the 2-4 ms range.

- Need to de-interlace the image: This might be a gotcha, I would think most of the newer displays with HDMI inputs should be able to handle this as this is more of a TV connection vs a PC connection, but I really don’t know.

- The image may not be that uniform: I think this will always be a problem with cheap displays. I’m not proposing bottom fishing here, so I move up the food chain a bit.

- Bit depth: How many bits are enough??? 8 is a gimme, I think 10 would be do-able via aja box or equivalent. I’m not familiar enough with the digital interfaces (HDMI or DVI) to know if they would support 10 bits on the LCD, I’m thinking not. If you have to convert to analog to get this then it seems to me to defeat the purpose.

- Computer monitors can be affected by video overlays: Do you mean overscan??? If so, I’ve seen several that have a 1:1 pixel mode, assuming it works, this should be ok.

Mark
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Old April 2nd, 2008, 10:36 PM   #4
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Mark,

I understand that you're looking for quantifiable answers. And I'd LOVE to give them to you. Just like I'd LOVE to find a camera that takes great pictures under all lighting conditions with just a single AUTO button.

But the reality is that right now, things can only be simplified so much - particularly in a world where you're trying to make nice pictures under so many, MANY variable conditions. Take the recorded signals, and pass them along over so many MORE variable conditions, and then view them on even MORE variable conditions.

The whole point of the professional CRT monitor what that is was FAR from being a regular TV. The system of color bars, blue gun, pluge, etc, was to make it possible to have some consistency from place to place, shoot to shoot.

And like it or not, NOTHING like that exists today in the world of LCD screens. The analog tools I mentioned above just don't cut it for LCD monitoring. Not when viewing angle and other factors have such a drastic effect on how images are displayed.

Two notes might help you understand why.

I've used DV Monitor from Red Lightening Software on about six different LCD screens over the past year or two. Typically LCD computer screens. It's a very nice tool for monitoring and recording DV in the field and I enjoy using it. But the one area where it (and EVERY other computer based monitoring system I've used fails miserably and that's COLOR adjustment and monitoring.) That's not the software's fault. It's the nature of LCD screens! Red Lightening built in a way lovely way adjust the display's brightness and contrast as you would with bars and pluge on a CRT.

The FIRST time I used it, I'd set the screen to be PERFECT. Then noticed that if I moved my head as little as 2 inches in any direction, the "perfect" reading would suddenly NOT be perfect. The angle of illumination coming from the computer screen would change drastically with viewing angle.

So doing monitor screen "setup" on a laptop was an exercise in futility.

Now I'm talking about relatively expensive editing laptops in the $2000 to $5000 range and I'd expect the screen technology in them to be as good as anything available at modest cost in a field LCD.

Next is an anecdotal test you can do for yourself.

Go to a sports bar in the next week.

Find a nice expensive commercial big screen TV. Preferably HD and preferably one that looks like it's new, and set up properly.

Find a sports channel showing any of the NCAA games.

Find a "highlights" show. And watch the edited work with an eye to skin tones and color reproduction.

After the shoot yesterday that I mentioned in the post in the old thread I was buying my crew a late supper. Nearby such a highlights show was playing in the bar and the crew and I started playing a game I'll dub "call out the lousy color."

We watched from our table as a cavalcade of highlights shots ran across the screen while we pointed out "too GREEN", "too RED", "decent" "too dark" "too Red" etc.

All of those shots were taken by professional crews with great gear.

I won't hazard a guess whether the problem was actual bad shooting, or poor camera shading, problems in different satellite feeds or whether that stuff looked fine on a decent monitor but the big BAR LCD TVs somehow translated subtle signal differences into seriously different pictures.

In 10 minutes, our little group of 3 video professionals, could barely find two March Madness shots in a row where the color looked accurate (or even similar!) at least from the angle of view we had.

THAT SHOULD NOT HAPPEN.

But it does. And it happens more on LCDs and Plasmas then on CRTs in my experience.

So I don't trust them. Period.

I hope some day I can, because like everyone else, I HATE dragging around CRT field monitors.

But it's the ONLY way I know right now to get it consistently RIGHT in field shooting.

Ces't la vie.
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Old April 2nd, 2008, 10:49 PM   #5
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Bill, then can you throw out a few recommendations for CRT's, prefferably at different price points, that you feel can cut the mustard--and HD footage :).

THANKS MUCH!
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Old April 3rd, 2008, 05:15 AM   #6
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For no other reason than I can...........

You guys all come from NTSC land where colour (color) is a myth available for any techie to play with, as it seems to be a total phantom.

The "Never The Same Colour" tag was well earnt, and very well deserved.

HD has killed that cold. NTSC is dead. Yippee.

If you are shooting HD now, wherever, colour (color) correction is practically a thing of the past and only required on gross screw ups.

My experience (which could be totally atypical, admittedly) is that if properly CB'ed on shoot, it doesn't need any CB after, and is good to go.

If, of course, you're still shooting for NTSC, jolly good luck to you - the flourecsent greens were always my favourite scream in Canada.

How you guys put up with that rubbish for so long has me utterly amazed, but that's another story.

Just my 2 cents worth, but if you need to correct HD footage, er, why?


CS
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Old April 3rd, 2008, 06:39 AM   #7
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/\ /\ April Fools?
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Old April 3rd, 2008, 09:56 AM   #8
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Bill,

I enjoy your comments; they remind me that there is a much bigger sandbox out there than the one I play in.

Yes, I’ve noticed the difference in color in sports clips… I always figured that these differences were introduced at the source, it's just too great a difference to be the set. And to think that each of these clips were probably shot by professional crews with as much passion for their craft as you, and most likely graded on CRT broadcast monitors to the best of there abilities. Odds are, nothing I ever shoot will end up on the nightly news and if it ever did it would look more like the Zapruder film than anything you would see on Sports Center. But just as there is a whole world of video outside of my sandbox, there is also a world outside of yours. What I’m trying to achieve is the best I can for the very limited resources I have. By your standard, how are any us weekend shooters to do that without explaining to our kids why it was more important than their college fund???

There’s got to be a reasonable compromise here. I’m not suggesting that pros like you ever use them… you have better options. But us little guys need a better solution than what we’ve had in the past. The improvements in LCDs make it an attractive choice, but I think all will admit not a perfect one. As long as I know and understand what those limitations are I can accept them, work around them, or try to make a better choice.

Mark

Last edited by Mark Keck; April 3rd, 2008 at 04:55 PM.
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Old April 3rd, 2008, 06:51 PM   #9
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Quote:
If you are shooting HD now, wherever, colour (color) correction is practically a thing of the past and only required on gross screw ups.

My experience (which could be totally atypical, admittedly) is that if properly CB'ed on shoot, it doesn't need any CB after, and is good to go.
1- Sometimes color correction also refers to color enhancement, where you might want to artistically tweak your colors (e.g. film look is one example).

2- Even ignoring color enhancement, most shoots will have a few shots where exposure or white balance is not perfect.

3- There's no reason why HD would change any of this.

NTSC is "never the same color" mostly because of wide differences in consumer TVs. NTSC as a way of transmitting color can cause color inaccuracies since the receiver has to be calibrated, so digital transmission has an advantage there. But in one area HD has less color accuracy because of the whole 601 versus 709 luma coefficients mess.
In any case, consumer TVs will continue to be quite different from one another so we'll still never have the same color.

Quote:
There’s got to be a reasonable compromise here.
For SD, you can get a CRT broadcast monitor starting at around $600. That is definitely the way to go IMO.

For HD, you could:
--Wait for monitors to get better (they are getting better at a very fast pace).
--There are some 1920*1080 LCD broadcast monitors from JVC and eCinemasys for about $4,000. It's difficult to get HD CRTs anymore and they're probably not worth getting (none of them do full HD resolution).
--The cheapest options would be just a computer LCD. You kind of get what you pay for. I'd probably just get a Dell LCD (they are good value when Dell is running a good promotion on them; check hot deals sites).
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Old April 4th, 2008, 06:41 AM   #10
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"But in one area HD has less color accuracy because of the whole 601 versus 709 luma coefficients mess."

Glenn... I know there are differences but I've not heard that there is less "color accuracy"... please explain.

Mark
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Old April 4th, 2008, 07:29 AM   #11
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For the Mac/FCP users there is the Matrox MXO that turns a 24" Apple Cinema Display into a pretty good SMPTE reference monitor.

If there was somethinig for Windows I'd be on it in a heartbeat.

George/
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Old April 4th, 2008, 09:13 AM   #12
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Thanks George. I've seen a little bit about the MXO, but after reading these reviews I think I need to look at it some more. Nice solution. They constantly make mention of it being designed for an Apple display, I wonder if it would work with any other??? Perhaps but suboptimal.

What I'm reading up on right now is the different LCD panel technologies (ISP, PVA, etc), I've not yet seen which type of panel that the ACD use, anyone know???

Mark
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Old April 4th, 2008, 09:41 AM   #13
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I believe its a PVA display. Most of them are. However LCD technology also uses a backlight (behind the panel) which is important for gamut. The backlight is the reason LCD's are generally 'greenish'. New backlight technology has improved on this. Some of the newer DELL displays use this.

The reviewer actually uses a DELL monitor at first, but gets less-than-optimal but "nice" results.

As with the current drivers you can adjust the output, it could work better with other displays that are on par with the Apple Cinema Display. However it has been specifically desiged to work with the ACD and that has no on-monitor controls that can mess up the color (it only has brightness adjustment).

Non ACD monitors usually have a slew of settings that prevent this from being a good solution (when "set wrong").

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Old April 4th, 2008, 02:42 PM   #14
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Quote:
"But in one area HD has less color accuracy because of the whole 601 versus 709 luma coefficients mess."

Glenn... I know there are differences but I've not heard that there is less "color accuracy"... please explain.
HD should be encoded using the Rec. 709 luma coefficients, but some consumer TVs decode HD as if it were encoded with Rec. 601 luma coefficients. They aren't engineered correctly, which leads to major color inaccuracy.

Anyways, this is sort of off topic.
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Old April 5th, 2008, 03:08 PM   #15
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One of the other problems I've discovered while researching computer LCD's for use in color correction is that using the VGA or DVI input limits the tweaking that can be done to calibrate. Most computer monitors only allow brightness, contrast and color temerature adjustments. To get as accurate as possible you really need to tweak hue and saturation as well just like a broadcast monitor. However, I know that some video cards will allow these adjustments. The most inexpensive solution right now may be to go with a high quality 1080p consumer LCD. I've noticed that the image quality has been increasing.
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