Setting contrast with Spears and Munsil disc - AVS Forum
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post #1 of 484 Old 04-02-2010, 07:38 PM - Thread Starter
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Is there another pattern on this disc to set/verify contrast, other than the one labeled "contrast"? I'm having trouble getting the "contrast" test pattern to work correctly. Thanks.
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post #2 of 484 Old 04-03-2010, 08:38 AM
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Greetings

How about trying to understand it instead of looking for another pattern? The instructions are on the disc too ... cursor up and the instructions show up.

Make as many of the boxes show up ... that simple.

Follow the rules of setting contrast.

No clipping ...
No discoloration
No eye fatigue

BAM! ... it's done.

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post #3 of 484 Old 04-03-2010, 01:40 PM
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Originally Posted by Michael TLV View Post

Greetings

How about trying to understand it instead of looking for another pattern? The instructions are on the disc too ... cursor up and the instructions show up.

Make as many of the boxes show up ... that simple.

Follow the rules of setting contrast.

No clipping ...
No discoloration
No eye fatigue

BAM! ... it's done.

regards

Yet I do sympathize with the OP. Setting Brightness is quite unambiguous, to within a click. But setting Contrast is more subjective, as your criteria themselves indicate. With such criteria I find that I can only narrow it to 5 or 6 clicks. Check the discussion in a similar thread ('setting contrast is driving me crazy', or something like that).
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post #4 of 484 Old 04-03-2010, 01:43 PM - Thread Starter
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Easier said than done. sspears was troubleshooting with me in another thread, but I think he gave up.
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post #5 of 484 Old 04-03-2010, 03:54 PM
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Greetings

We can't set contrast for you because what fatigues us does not fatigue you ... so that part is up to you.

If it hurts your head when you bang it on the wall, perhaps you should stop doing it.

There is no "one right" place to set contrast. Follow the rules ... hardly that confusing. Just because every setting is not just a yes or no prospect does not make it hard to deal with.

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post #6 of 484 Old 04-03-2010, 05:13 PM
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Originally Posted by Michael TLV View Post

We can't set contrast for you because what fatigues us does not fatigue you ... so that part is up to you.

If it hurts your head when you bang it on the wall, perhaps you should stop doing it.

There is no "one right" place to set contrast.

Well appreciated, Mike. My only point was that setting CR is less well-defined than setting BR, a point that you clearly agree with.
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post #7 of 484 Old 04-03-2010, 07:52 PM - Thread Starter
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I didn't think my question would make anyone angry.
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post #8 of 484 Old 04-04-2010, 08:08 AM
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Greetings

Never anger.

For a more detailed discussion on setting contrast, please go over to the calman help forum and look in the calibration basics area. There is an item on setting contrast and all the rationale too ... especially lots on the fatigue part.

(and no, I'm not going to make a link for you. )

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post #9 of 484 Old 04-04-2010, 10:09 AM
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I have a question regarding clipping. The clipping pattern on the Spears and Munsil BD Benchmark is a nice piece of work. You can use it graphically to identify any clipping.

The part that bothers me, if one looks at something like AVSHD709 instead of Spears and Munsil I can determine at what contrast level a particular color clips. The question for me becomes at what brightness level above white does it not matter very much if say green is clipping? In other words if I start to clip green at 245, should I really care. Yes I can lower contrast until there is no clipping all the way to 253 but at a significant lowering of white level at 235 that is undesirable with this particular set. What are the trade offs. How much are these levels above the 235 used, above 2458, 250 etc?

There is a white 109% saturation pattern on AVSHD709 if the RGB levels if my xy is good at that screen, am I good to go?

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post #10 of 484 Old 04-04-2010, 11:16 AM
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Greetings

Deciding that you want to sacrifice some image detail for the sake of brightness is a slippery slope. Do you want to kill 5% ... 10% ... 20% ... where do you draw that line that it is okay at 15% of the image, but not 16% of the image?

Of course some BD and receiver makers already do you the favor and have units that clip white above 100% anyway.

How much you lose kind depends on the material that you watch. If you watch dark films all the time, you won't miss the detail on the bright end ... ever.

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post #11 of 484 Old 04-04-2010, 12:04 PM
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Quote:
Originally Posted by Michael TLV View Post

Greetings

Deciding that you want to sacrifice some image detail for the sake of brightness is a slippery slope. Do you want to kill 5% ... 10% ... 20% ... where do you draw that like that it is okay at 15% of the image, but not 16% of the image?

Of course some BD and receiver makers already do you the favor and have units that clip white above 100% anyway.

How much you lose kind depends on the material that you watch. If you watch dark films all the time, you won't miss the detail on the bright end ... ever.

Regards

I appreciate your perspective, knowledge ane experience, but isn't that like saying the perfect is the enemy of the good. If the TV is too dim to be watched during the day then what has been achieved. Lets say theorectically everything is perfect but it would not be making much more light than a bright front projector.

Rear projection Televisions are supposed to be set for 30-40 ft lamberts from what I understand but if by eliminating all possible clipping and I end up at 20 ft lamberts that is not a very satisfactory solution either. This is a living room TV to be used both in the day time and in near dark at night.

I was hoping someone could say that it is very rare for levels above x to be used anyway. Like you said many players clip the whole thing. I am clipping at 240 but it takes me from 20 to 24 ft lamberts what would you do. I am just throwing numbers around. I don't know exactly how much light I would loose if chose to let green clip at 240. But this set will not make 30 ft lamberts in anything resembling a calibrated mode. What choice would you make?

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post #12 of 484 Old 04-04-2010, 12:37 PM
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Originally Posted by gtgray View Post

this set will not make 30 ft lamberts in anything resembling a calibrated mode. What choice would you make?

Buy an appropriate display for your environment. While this may sound a bit glib it's the truth. I wouldn't suggest a projector in your greenhouse (or kitchen) because it's going to be an exercise in frustration.

By the way -- the quantity of valid material above 235/240 is subject to (endless, pointless) argument. Trained filmakers are well aware of the limitations of the medium. 24fps, limited dynamic range, deficient transfers and poor home viewing environments are facts of life. Some directors/cinematographers/editors/colorists may choose to ignore a part of their audience others will be more careful. In either case there are more profound problems to be solved. Like a low luminance display in a "bright" environment.
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post #13 of 484 Old 04-04-2010, 02:06 PM
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hmmmmm
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post #14 of 484 Old 04-04-2010, 03:34 PM
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Buy an appropriate display for your environment. While this may sound a bit glib it's the truth. I wouldn't suggest a projector in your greenhouse (or kitchen) because it's going to be an exercise in frustration.

By the way -- the quantity of valid material above 235/240 is subject to (endless, pointless) argument. Trained filmakers are well aware of the limitations of the medium. 24fps, limited dynamic range, deficient transfers and poor home viewing environments are facts of life. Some directors/cinematographers/editors/colorists may choose to ignore a part of their audience others will be more careful. In either case there are more profound problems to be solved. Like a low luminance display in a "bright" environment.

Tightly controlling the lighting in TV viewing environments has been a standard requirement since the birth of television. The issue of display performance vs. viewing environment conditions is such a fundamental element of understanding how television viewing works, it should be axiomatic (to go without saying). However, both consumers and professionals alike become so focused on the gear that they forget how critical viewing environment/human perceptual factors are. The widely accepted recommendation of calibrating a TV or video monitor to produce 30 to 35 fL at 100% white must be kept in context. That context is what is called in the SMPTE documents and others- 'dim surround' viewing conditions. In other words, brighter viewing environment conditions will require a brighter image from the display. Some displays can operate linearly at such high light output requirements, but many cannot. If a display cannot perform correctly in high ambient light, it is much easier to control the room lighting than re-engineer the device.

No video display that I know of can deliver a reference image in a brightly lit room. Every display made and every viewer alive has definite limitations when competing with ambient light in the viewing environment. Anyone well versed in imaging science should be able to explain why. A brief tutorial explaining how this works is: 'The Importance Of Viewing Environment Conditions In A Reference Display System.' Such principles are taught in formal calibrator trainings by the ISF and THX, Ltd, plus discussed on every home theater setup disc worth its salt. However, even many graduates of such courses forget, diminish, or disregard these principles for a variety of reasons. A viewer educated in these issues can decide where in the video system to make compromises. If ultimate display performance and image fidelity are the desired objectives, high ambient lighting must be avoided. Do not be surprised if a display 'runs out of steam' in some way while being asked to compete with high ambient room lighting.

Best regards and beautiful pictures,
G. Alan Brown, President
CinemaQuest, Inc.
A Lion AV Consultants Affiliate

"Advancing the art and science of electronic imaging"
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post #15 of 484 Old 04-04-2010, 05:35 PM
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I love the philosophical pontificating going on here. I have a viewing environment that has certain limitations. My viewing distance is 14'. That dictates a big display. It is a living room with some daytime viewing, so no front projector. Okay, I am not a multimillionaire so no 84 Panny Plasma.

I chose an 82" rear projector that makes about 32-35 ft lamberts before you beginning to dial it in. Currently I have a Green DE of 5 and all the other colors at 3 or less with a 2.3 Gamma, and a flat gray scale. The set is making 26 ft lamberts. I don't have a high light level in my room. But I am clipping green at somewhere above 240.. The TV looks very good, very natural and balanced and 85 percent of my viewing is at night. Please no technology fanaticism.

I came looking for practical advice on how relatively important green clipping at way above white is but instead the great lords on the high mountains say I bought the wrong display device, or I should turn my living room into a cave.

Thanks everybody, when you go to a customer site and calibrate the end user's display do just say, rebuild your room, buy another house, spend 30k on a 84" plasma or do you make educated compromises on how to best optimize what the customer already has. When NASA was trying to figure out how to get the Apollo 13 astronauts back from the moon, they took the parts they had and said this is it, this is what we have to work with. Not only did the astronauts have the "Right Stuff", the engineers had the "the Right Stuff" too not just in character but laying right there on the table in front of them. It looked like junk at first, but there was a least one solution laying on that table. If the engineers had had more time, I am sure they could have found dozens of reasonable solutions.

They got those guys home. I am not asking for rocket science here, nor I did post in this thread to get some religious fatwa. Sheesh! Just practical advice about the degree of impact from clipping green at 240, while making clear I don't want a 20 ft lambert screen for the sake of having every other test parameter dead on.

Maybe I was naive but I thought all the ISF and THX signatures could have provided more useful practical advice than seen here so far.

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post #16 of 484 Old 04-04-2010, 05:48 PM
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So, recommending that you emulate professional best practices in order to achieve professional image quality/fidelity is pontificating, fanaticism, or rocket science?
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post #17 of 484 Old 04-04-2010, 05:55 PM
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Originally Posted by gtgray View Post

Maybe I was naive but I thought all the ISF and THX signatures could have provided more useful practical advice than seen here so far.

You're welcome.
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post #18 of 484 Old 04-04-2010, 07:28 PM
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Quote:
Originally Posted by gtgray View Post

I have a question regarding clipping. The clipping pattern on the Spears and Munsil BD Benchmark is a nice piece of work. You can use it graphically to identify any clipping.

The part that bothers me, if one looks at something like AVSHD709 instead of Spears and Munsil I can determine at what contrast level a particular color clips. The question for me becomes at what brightness level above white does it not matter very much if say green is clipping? In other words if I start to clip green at 245, should I really care. Yes I can lower contrast until there is no clipping all the way to 253 but at a significant lowering of white level at 235 that is undesirable with this particular set. What are the trade offs. How much are these levels above the 235 used, above 2458, 250 etc?

There is a white 109% saturation pattern on AVSHD709 if the RGB levels if my xy is good at that screen, am I good to go?

Personally I wouldn't trade anything above 235 (100% white), however revealing it may be(?), for loss of contrast/light. Ultimately I use my eyes as the final determination. It'll drive you crazy(gamut/greyscale syndrome) looking at cal graphs for hours on end. I'm a perfectionist when it comes to picture calibration, but sometimes you have to A/B by sight and take what you like, not necessarily whats technically correct. I think this is the reason I haven't recal'd my FP in over a year and a half. I afraid of a relapse.
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post #19 of 484 Old 04-04-2010, 07:33 PM
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Originally Posted by GeorgeAB View Post

So, recommending that you emulate professional best practices in order to achieve professional image quality/fidelity is pontificating, fanaticism, or rocket science?

I take your postings to indicate if you can't make it perfect we have no intention of suggesting increasing one value at the expense of some other setting, which I assume you do in the course of your actual field real world activity on a daily basis. There was not one word her that suggested if I was in your situation I might move this value up, that setting down. Great! I can increase my light control, should I make it so dark I stumble as I try to move though the room during the day.

I was asking for help in achieving better though still compromised image quality. Since all image quality is inherently compromised whether it is due to the the age of viewer, the coating on their corrective lens, some amount of unmeasured color blindness or some other deficiency in the viewing environment or playback equipment or source, it is all compromised. So here is the slippery slope, right! The results are always compromised but we never compromise on the way to achieving our glorius compromised results. Generally the real world comes in to play, not ideology. What I got as advice here seemed a lot more like ideology than real world solutions.

If the only solution is to completely darken the room, or replace the display, that is a set of near nuclear options for me.. Of course I know that the darker the room, the darket the display can be and still get satisfactory results. I have the constraints that I have. There is no dedicated home theater. I have a large display that does not make an optimal amount of light for bright day time viewing in my living room. I imagine there are a few million LCDs out there that don't make good enough blacks to reach an idealized state of calibration either.

I must have been confused about the nature of this medium. While the subject matter is AV Science, I thought this forum was really a social networking site where a certain sense of altruism and passion for imaging informs the dialog ultimately resulting in infomation sharing and an increase in understanding for both the neophyte, apprentice, journeyman and master.

If I were one of those Apollo guys orbiting the moon, and had to rely on the kind of information that came via this thread I would still be orbiting out there 3 decades later.

Turning my living room in to a bat cave is an extreme end point and certainly not justified by either the shortfall in foot lamberts or green clipping above 240 or 245 or whatever it actually is. I guess I am not passionately devout to this art form. I know I should not expect imaging artists and scientists like those in this thread to suggest some intermediate non-purist compromised stategy. From the advice provided I guess the only thing I can do to improve my situation is to call in a contractor and build a room where I can have a front projetor, thanks everybody, thanks very much. I'll be sure to come back after I spent 50 grand only to find out there are few gotcha and it really does not work as advertized. I am sure to get help then. I will have demonstrated sufficient devotion to learn the secret handshake.

While honoring the discipline of the craft the pros here practice I did not ask anybody here to compromise a hippocratic oath. Yes, I think there has been fanatical positioning. There is a 100 percent correct which can never be done. Everything else is somewhat less. Isn't imaging science is about more closely reproducing an artists vision through various levels of optimization given a budget and a host of other constraints.

If the view here is that I was given advice and like any moron newbie I don't want to hearr it, well that is fine. I am sure it is easy for the subject matter experts here to feel that way. I spent years providing support to users and managing highly skilled technicians who did the same. There is something that happens to people. Practicing doctors after a few years often loose their bedside manner. I am well aware that it is easy to feel a certain rightness in knowledge however counterproductive that can be.

I paid for no advice, so if the advice given is pretty much worthless to me then I got what I paid for. Again, thanks everybody!

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post #20 of 484 Old 04-04-2010, 07:43 PM
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Greetings

If it isn't clear yet ... there is reference and then there is preference. If reference cannot work for you, then you do what you need to do to make it look good to your eyes. We cannot see the environment you are in ... nor the gear you are using. We also cannot see the world through your eyes ...

One man's too bright is just right for another.

Do what you gotta do ... and if you figure out a way we can experience the world through your eyes ... please let us know.

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post #21 of 484 Old 04-04-2010, 07:48 PM
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Quote:
Originally Posted by coolrda View Post

Personally I wouldn't trade anything above 235 (100% white), however revealing it may be(?), for loss of contrast/light. Ultimately I use my eyes as the final determination. It'll drive you crazy(gamut/greyscale syndrome) looking at cal graphs for hours on end. I'm a perfectionist when it comes to picture calibration, but sometimes you have to A/B by sight and take what you like, not necessarily whats technically correct. I think this is the reason I have recal'd my FP in over a year and a half. I afraid of a relapse.

Thank you so much. It is the kind of practical advice I was looking for. Even if you had told me the opposite of what I hoped to hear, I would still have been very appreciative.

I hope this calibration OCD thing developing in me can be controlled and not get out of hand. I want this to remain a hobby and not a hobbly like putting clipper ships in bottles. I already went through an audio phase and a still camera/color dark room obsession a few decades ago. My uncle has a bunch of audio patents and I know how all consuming these technical hobbies can get. At some point you are designing for Mr. Golden Ears, with cost as no object and you find there are no or very few actual customers buying the stuff and you are mostly trying to impress reviewers and your peer designers.

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post #22 of 484 Old 04-04-2010, 08:45 PM
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Quote:
Originally Posted by gtgray View Post

I take your postings to indicate if you can't make it perfect we have no intention of suggesting increasing one value at the expense of some other setting, which I assume you do in the course of your actual field real world activity on a daily basis. There was not one word her that suggested if I was in your situation I might move this value up, that setting down. Great! I can increase my light control, should I make it so dark I stumble as I try to move though the room during the day.

I was asking for help in achieving better though still compromised image quality. Since all image quality is inherently compromised whether it is due to the the age of viewer, the coating on their corrective lens, some amount of unmeasured color blindness or some other deficiency in the viewing environment or playback equipment or source, it is all compromised. So here is the slippery slope, right! The results are always compromised but we never compromise on the way to achieving our glorius compromised results. Generally the real world comes in to play, not ideology. What I got as advice here seemed a lot more like ideology than real world solutions.

If the only solution is to completely darken the room, or replace the display, that is a set of near nuclear options for me.. Of course I know that the darker the room, the darket the display can be and still get satisfactory results. I have the constraints that I have. There is no dedicated home theater. I have a large display that does not make an optimal amount of light for bright day time viewing in my living room. I imagine there are a few million LCDs out there that don't make good enough blacks to reach an idealized state of calibration either.

I must have been confused about the nature of this medium. While the subject matter is AV Science, I thought this forum was really a social networking site where a certain sense of altruism and passion for imaging informs the dialog ultimately resulting in infomation sharing and an increase in understanding for both the neophyte, apprentice, journeyman and master.

If I were one of those Apollo guys orbiting the moon, and had to rely on the kind of information that came via this thread I would still be orbiting out there 3 decades later.

Turning my living room in to a bat cave is an extreme end point and certainly not justified by either the shortfall in foot lamberts or green clipping above 240 or 245 or whatever it actually is. I guess I am not passionately devout to this art form. I know I should not expect imaging artists and scientists like those in this thread to suggest some intermediate non-purist compromised stategy. From the advice provided I guess the only thing I can do to improve my situation is to call in a contractor and build a room where I can have a front projetor, thanks everybody, thanks very much. I'll be sure to come back after I spent 50 grand only to find out there are few gotcha and it really does not work as advertized. I am sure to get help then. I will have demonstrated sufficient devotion to learn the secret handshake.

While honoring the discipline of the craft the pros here practice I did not ask anybody here to compromise a hippocratic oath. Yes, I think there has been fanatical positioning. There is a 100 percent correct which can never be done. Everything else is somewhat less. Isn't imaging science is about more closely reproducing an artists vision through various levels of optimization given a budget and a host of other constraints.

If the view here is that I was given advice and like any moron newbie I don't want to hearr it, well that is fine. I am sure it is easy for the subject matter experts here to feel that way. I spent years providing support to users and managing highly skilled technicians who did the same. There is something that happens to people. Practicing doctors after a few years often loose their bedside manner. I am well aware that it is easy to feel a certain rightness in knowledge however counterproductive that can be.

I paid for no advice, so if the advice given is pretty much worthless to me then I got what I paid for. Again, thanks everybody!

As I clearly said, "A viewer educated in these issues can decide where in the video system to make compromises." Excuse the pun, but you need to lighten up.
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post #23 of 484 Old 04-05-2010, 01:26 AM
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My advice in these situations is to try it and see what you prefer.

I personally prefer white to disclose all the way up and I can usually tell fairly readily when I'm watching a display that is clipping any lower than about 252.

Its worth bearing in mind how images work at this point. If you had a theoretical image with near infinite dynamic range your eyes would run out of ability to discern variation towards white before the image did. Ergo if you view an image with limited dynamic range you should be giving you visual system as many "rungs" as possible for your eyeballs to clamber up before the limitations of the image become apparent .

Imagery that exhibits noticable white clipping just screams synthetic at you probably to a far greater extent than grayscale error or gamma for example.

Some people have suggested that if you are going to disclose whites all the way up to the dynamic range limitations of the the format why not disclose everything towards black?

Really simple answer to this: in an ideal world yes show it all!

You should disclose everything and have the response curve of the display handle things in such a way that the image still looks good and even notionally correct.

Maybe gtgrey should contruct a lut that throws away any notion of clipping whatsoever and relies solely on the curve of the the lut to present variation towards black and white.

So why do we have this convention of clipping everything below 17 on display rather than have the display show it all?

Another simple answer ...limitations of display and camera tech from when the standards were designed propagating down the years. Todays displays are still quite limited in performance in terms of how precise they are towards black and indeed across a measly 8bit video intensity scale.

So if you have a display that is somewhat contrast limited how do you handle it?

Rule number 1 view it in a dark environment ( personally I don't regard there being such a thing as a video display that isn't designed to be viewed in a dim environment).

If thats not possible then think about clipping the whites further down closer to 235. I personally can't stand this but to each their own and lets face it if you are watching in an enviroment that warrants this sort of setup its hardly reference to begin with...so knock yourself out.

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post #24 of 484 Old 04-05-2010, 05:43 AM
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I have a question regarding clipping. The clipping pattern on the Spears and Munsil BD Benchmark is a nice piece of work. You can use it graphically to identify any clipping.

The part that bothers me, if one looks at something like AVSHD709 instead of Spears and Munsil I can determine at what contrast level a particular color clips. The question for me becomes at what brightness level above white does it not matter very much if say green is clipping? In other words if I start to clip green at 245, should I really care. Yes I can lower contrast until there is no clipping all the way to 253 but at a significant lowering of white level at 235 that is undesirable with this particular set. What are the trade offs. How much are these levels above the 235 used, above 2458, 250 etc?

There is a white 109% saturation pattern on AVSHD709 if the RGB levels if my xy is good at that screen, am I good to go?

The goal of many is to utilize all the tools at your disposal to calibrate your display as accurately within the limitations of your display and viewing environment.

Unfortunately, the limitations can be very real. It doesn't do you any good to utilize theater environment settings in a room with a lot of ambient light, and compromises sometimes have to be made.

If when your properly calibrated display is yielding 25-30 ftls, but at this level, is having difficulty keeping up with the room's lighting, your picture may appear too dark, which may obscure any details you were trying to preserve in the first place, and your viewing experience will suffer.

One of the pitfalls of setting contrast too high can often be clipping white, and in a lot of cases ruin grayscale. But again, more important than anything else, is to make viewing enjoyable. Once it is no longer enjoyable, no matter how accurately calibrated your display is, you will hate the result.

The compromise is to start out with your display's properly calibrated settings, and then deviate from them to the point necessary. In your case, increasing contrast to the point where viewing content is enjoyable in a bright room, even at the sake of losing detail at the high end, but hopefully not too much.

Nothing wrong with that.

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Originally Posted by Mr.D View Post

I personally prefer white to disclose all the way up and I can usually tell fairly readily when I'm watching a display that is clipping any lower than about 252.

How can you tell? Can you tell with actual program material or do you need test patterns to see the difference?

If video levels are only 16-235 and DVDs and Blu-ray Discs all have video levels, what is the real world significance of showing above 235? What would be the point of sacrificing valuable light output just to be able to show levels that are not supposed to exist in video content anyway? If it can be done without making any compromises I don't see any reason to clip above 235 intentionally, but otherwise it seems to be rather pointless and detrimental advice.
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How can you tell? Can you tell with actual program material or do you need test patterns to see the difference?

If video levels are only 16-235 and DVDs and Blu-ray Discs all have video levels, what is the real world significance of showing above 235? What would be the point of sacrificing valuable light output just to be able to show levels that are not supposed to exist in video content anyway? If it can be done without making any compromises I don't see any reason to clip above 235 intentionally, but otherwise it seems to be rather pointless and detrimental advice.

Which is why I am so perplexed by all this. I have no issue that I can see in the in 16-235 other than that my Chroma5 and ChromaPure indicate to me I have a Delta Error of 5.7 on green mostly a luminance error. I don't see how I can tweak around that. At least I have not figured out how yet.

The green clipping I see is on the clipping pattern on the Spears and Munsil BD , and yes lowering the contrast a sufficient amount will avoid this clipping that I probably can never otherwise see in content programing.

This whole thing feels a bit like if a tree falls in the forrest and no one is there to hear it fall, did it really fall. This is where I expected the subject matter expert to argue that I will see it.

So as far a s I can tell If I never bought the tool I would not even know I had the problem. Perhaps I am trying to overtreat the symptom. Again all I wanted was help with was gaging its relative importance to overall image quality. It seems to be an article of faith here tha all levels above white must be shown and their should be no primary clipping. I mean I can't see any coloration issues on the same test BD in the contrast pattern screen wheter I go all the way to the last box, the gray looks the same neutral timt.

I am sure my DE of 5.7 on green is another symptom of the same root cause that makes green clip well above white. I am sure the picture would be better if I did not have the DE, I can't say that eliminating the green clipping in high whites would be that beneficial or make that much difference whether done by by magic or by severely limiting the light output.

I guess that was my point in asking the pros here. If I can't see an effect or consequence of the green clipping other than the test. Elininating the clipping might be the equivalent of waving a rubber chicken around while listening to may favorite rain dance music. So how much priority should I give the green clipping over what seems to me a more pressing that is the sets lmited overall luminance.

I guess I should not fret so. My worst case scenario would likely still yeild more light than a front projector. In fact there are probably lots of folks with front projectors bemused by my frustration that I clip green 27 ft lamberts.

I have a DVDO Duo and the current beta CMS software does not yet provide for multiple profiles. So it is not easy for me to have a day time calibration, and a night calibration, let alone for each source for day and night.

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post #27 of 484 Old 04-06-2010, 02:12 AM
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How can you tell? Can you tell with actual program material or do you need test patterns to see the difference?

Bit of both really. I use test patterns to confirm I'm not clipping "anything" above 235 (its quite difficult with bright displays to actually see the last couple of steps up to 254 with a mid level apl...your eyes are not so great at differentiating levels towards peak white). Don't worry if you are clipping off 254 for example.

On program content (BD , dvd and dtv) I can usually tell almost immediately if its clipping above 235.



Quote:
Originally Posted by PlasmaPZ80U View Post

If video levels are only 16-235 and DVDs and Blu-ray Discs all have video levels, what is the real world significance of showing above 235? What would be the point of sacrificing valuable light output just to be able to show levels that are not supposed to exist in video content anyway? If it can be done without making any compromises I don't see any reason to clip above 235 intentionally, but otherwise it seems to be rather pointless and detrimental advice.

16-235 are reference levels not limit points ( as I'm sure has been discussed to death round these parts).

The mystery of the 16-235 limit has been floating about for years and I regularly come up against it in the workplace. Its often trotted out by people who are hugely experienced and respected in other areas and you will be able to find lots of comment and opinion masquerading as fact that seems to support the 16-235 limit especially in the semi/pro broadcast forums. People have a tendency to latch on to numbers and then misquote them without realising how they are applied in the real world.

If you have a look back through some of the comments by stacey and others regarding this issue you will find references to video range from well respected sources that explicitly mention the need for excursion beyond the reference range.

Thats all well and good but what does that mean in reality?

Remember what I said about how images work. If you have a display with a notionally massive contrast range you want to map material to it in such a way as to give your eye as many steps up the point where your eye cannot differentiate changes in brightness. Otherwise it looks clipped ( or more clipped than is necessary in the case of video which will always look clipped to a certain extent with certain types of material).

Similarly if you think about it if the display was capable of depicting tiny brightness changes towards black you could also display range below 16 and still maintain a notionally healthy visual black level even to the point where the brightness differences below 16 were pretty much undetectable to your eye , the point is the level is still there.

If you think about how a high dynamic range displays and imagery works it might make it clearer ; imagine you are outside a cave in moderate sunlight. If you look towards the sun your visual system hits a point where you cannot differentiate any increase in brightness level ( hopefully you have also not burnt your eyeballs out) if you look towards the cave you can't really see much differentiation towards black inside the cave as your eyes are essentially washed out by the ambient light levels , if you walk into the cave suddenly you can see more variation towards black. The relative black and white peak levels have not changed just your visual systems ability to differentiate them. If you have a display and material that presents high dynamic range its closer to how your eye is presented with brightness variation in the real world : its a total range that your eye is unable to differentiate all off in all situations your eye slides up and down the range according to environment .

Thats all very well but what about video?
If you accept that there exists level outside 16-235 your next question is what does it contain...garbage/noise , nothing or useful image intensity steps. Well it has to contain something otherwise why have reference points that aren't at the maximal limits of your available dynamic range ( although even then anyone that creates imagery and knows what they are doing never bangs off the end stops of their available intensity range but thats a slightly different issue).

So if you accept its 16-235 but with headroom/rolloff/excursion ( last one not so helpful a term) then what is the additional stuff for?

Clamping off noise in a technically imperfect engineered system:

Yes sure but the noise doesn't just bang in right after the ends of the reference range. The whole point is not to be able to guillotine off the noise but have a nice smooth organic roll off into the end stops of the dynamic range whilst losing the noise. Hard clips in images ( video or otherwise) are never good, pleasing imagery is all about smooth transitions.

So 16-235 is the reference range but what does that mean.
Simply its the bit you really need to keep , however it doesn't conversely mean that you should take a knife and just chop off the rest . How you deal with it is a function of your display capabilities and viewing environment as has been stated again and again.

Lets expand out the pot a bit.

Most video we are concerned with watching has originated from film in most cases ( or originally captured with more intensity steps than are ultimately presented to the end viewer..even stuff shot on video to be honest). So its "bigger" than the video it ends up as.

A negative film scan is usually 10bit. 0-1023 code values. A film scan also has a defined reference range although in this case its linked to the density steps (film imagery is a density range rather than an intensity range , the difference is mostly semantic as its still essentially a recorded intensity range despite the mechanics) .

black ref coincides with the Dmin point at code value 0098
white ref coincides with the Dmax point code value 0685

These are the points that will appear notionally black and peak white if you strike a one light print straight off a negative , they relate to the intensities you will actually see ( film is a bit fuzzy as its a chemical system so you actually see some variation above 685 and below 98...hint think why films generally looks nicer than video).

So whats outside the reference range? The Dmin is the point where the film essentially can't get any darker because of its chemical nature ( fact it does actually go darker hence the need for a reference level above the end stops of the range)

The Dmax is the point that registers as white and the clearest the print can get. Fact it actually goes higher than this hence why its the 90% white point not the end of the range. (allowing for fuzziness is an important part of most engineered systems...absolutes are usually frowned on...its all about tolerance)

Film negative also has massive headroom in the whites (its why it looks nice people). Everything above 685 is useful image that can be made visible by bringing it down to the Dmax point (think about video ...think about that range above 235 , think about how images work).

Luckily for me I work with film day in day out so I'm very familiar with material in mainstream blockbusters before it gets transferred into video (often I even have to convert stuff to video for client temps).

Historically the default method to convert a film scan to video is to chop it off at 98-685 and map this to ...16-235 (you will find white papers on this) and give it a gamma twist.
This creates video imagery that looks like garbage with 99% of imagery and has never been how you really convert film to video and still make it look nice.

If I have a picky client they normally ask me to match to video rushes that have already been generated through a proper film to video pipeline by the colorist(s). I would say 99% of the time pretty much everything from 95-1023 on the original negative has been mapped into 1-254 on video. At the high and low limits of the video it will have been very crushed together by necessity but the point is it hasn't simply been chopped off.

If I have to come up with something myself I never chop it off according to the reference limits. I grade it subjectively on a calibrated video system using quite arbitrary curves to give nice range in the blacks and whites but with a pleasing level of overall contrast. According to the image content I may clip off values outside the dmin dmax range.. like I say it depends on image content... a guy in a cave probably won't have much level if any above 685...if he lights a candle its a different story , likewise someone silhouetted in front of a raging inferno may not have any level below 250 ( doesn't mean I won't drag it down a bit to give better contrast).

I'm hoping most of what I've posted will be somewhat relevant, the key thing is to stop seeing images and video in terms of strict reference ranges. The ranges have a purpose ( usually to differentiate from formats that have different ranges) but they are not absolutes when it comes to how the imagery should look.

Video is a pretty pathetic intensity range and your eye likes big ranges. Video is not like the real world and most displays do not get anywhere near the levels of intensity variation your eye is used to seeing on a daily basis.

Back to whether to clip at 16-235 or not...

Lose everything below 17 to black: your display is unlikely to show level below this point in a useful manner.

Keep everything up to 254 as even with the maximal range on display video will often look clipped to your visual system regardless and you might as well mitigate this as much as is possible.

If your display in conjunction with environment is so lacking in contrast performance that keeping everything above 235 results in a visually unpleasant experience then chop some of the range above 235 off to free up some of the contrast.

If you prefer to watch with a hard clip in place at 16-235 fine knock yourself out no-one is going to kill you for it but please don't confuse this as being of absolute correctness.

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post #28 of 484 Old 04-06-2010, 04:21 AM
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Bit of both really. I use test patterns to confirm I'm not clipping "anything" above 235 (its quite difficult with bright displays to actually see the last couple of steps up to 254 with a mid level apl...your eyes are not so great at differentiating levels towards peak white). Don't worry if you are clipping off 254 for example.

On program content (BD , dvd and dtv) I can usually tell almost immediately if its clipping above 235.





16-235 are reference levels not limit points ( as I'm sure has been discussed to death round these parts).

The mystery of the 16-235 limit has been floating about for years and I regularly come up against it in the workplace. Its often trotted out by people who are hugely experienced and respected in other areas and you will be able to find lots of comment and opinion masquerading as fact that seems to support the 16-235 limit especially in the semi/pro broadcast forums. People have a tendency to latch on to numbers and then misquote them without realising how they are applied in the real world.

If you have a look back through some of the comments by stacey and others regarding this issue you will find references to video range from well respected sources that explicitly mention the need for excursion beyond the reference range.

Thats all well and good but what does that mean in reality?

Remember what I said about how images work. If you have a display with a notionally massive contrast range you want to map material to it in such a way as to give your eye as many steps up the point where your eye cannot differentiate changes in brightness. Otherwise it looks clipped ( or more clipped than is necessary in the case of video which will always look clipped to a certain extent with certain types of material).

Similarly if you think about it if the display was capable of depicting tiny brightness changes towards black you could also display range below 16 and still maintain a notionally healthy visual black level even to the point where the brightness differences below 16 were pretty much undetectable to your eye , the point is the level is still there.

If you think about how a high dynamic range displays and imagery works it might make it clearer ; imagine you are outside a cave in moderate sunlight. If you look towards the sun your visual system hits a point where you cannot differentiate any increase in brightness level ( hopefully you have also not burnt your eyeballs out) if you look towards the cave you can't really see much differentiation towards black inside the cave as your eyes are essentially washed out by the ambient light levels , if you walk into the cave suddenly you can see more variation towards black. The relative black and white peak levels have not changed just your visual systems ability to differentiate them. If you have a display and material that presents high dynamic range its closer to how your eye is presented with brightness variation in the real world : its a total range that your eye is unable to differentiate all off in all situations your eye slides up and down the range according to environment .

Thats all very well but what about video?
If you accept that there exists level outside 16-235 your next question is what does it contain...garbage/noise , nothing or useful image intensity steps. Well it has to contain something otherwise why have reference points that aren't at the maximal limits of your available dynamic range ( although even then anyone that creates imagery and knows what they are doing never bangs off the end stops of their available intensity range but thats a slightly different issue).

So if you accept its 16-235 but with headroom/rolloff/excursion ( last one not so helpful a term) then what is the additional stuff for?

Clamping off noise in a technically imperfect engineered system:

Yes sure but the noise doesn't just bang in right after the ends of the reference range. The whole point is not to be able to guillotine off the noise but have a nice smooth organic roll off into the end stops of the dynamic range whilst losing the noise. Hard clips in images ( video or otherwise) are never good, pleasing imagery is all about smooth transitions.

So 16-235 is the reference range but what does that mean.
Simply its the bit you really need to keep , however it doesn't conversely mean that you should take a knife and just chop off the rest . How you deal with it is a function of your display capabilities and viewing environment as has been stated again and again.

Lets expand out the pot a bit.

Most video we are concerned with watching has originated from film in most cases ( or originally captured with more intensity steps than are ultimately presented to the end viewer..even stuff shot on video to be honest). So its "bigger" than the video it ends up as.

A negative film scan is usually 10bit. 0-1023 code values. A film scan also has a defined reference range although in this case its linked to the density steps (film imagery is a density range rather than an intensity range , the difference is mostly semantic as its still essentially a recorded intensity range despite the mechanics) .

black ref coincides with the Dmin point at code value 0098
white ref coincides with the Dmax point code value 0685

These are the points that will appear notionally black and peak white if you strike a one light print straight off a negative , they relate to the intensities you will actually see ( film is a bit fuzzy as its a chemical system so you actually see some variation above 685 and below 98...hint think why films generally looks nicer than video).

So whats outside the reference range? The Dmin is the point where the film essentially can't get any darker because of its chemical nature ( fact it does actually go darker hence the need for a reference level above the end stops of the range)

The Dmax is the point that registers as white and the clearest the print can get. Fact it actually goes higher than this hence why its the 90% white point not the end of the range. (allowing for fuzziness is an important part of most engineered systems...absolutes are usually frowned on...its all about tolerance)

Film negative also has massive headroom in the whites (its why it looks nice people). Everything above 685 is useful image that can be made visible by bringing it down to the Dmax point (think about video ...think about that range above 235 , think about how images work).

Luckily for me I work with film day in day out so I'm very familiar with material in mainstream blockbusters before it gets transferred into video (often I even have to convert stuff to video for client temps).

Historically the default method to convert a film scan to video is to chop it off at 98-685 and map this to ...16-235 (you will find white papers on this) and give it a gamma twist.
This creates video imagery that looks like garbage with 99% of imagery and has never been how you really convert film to video and still make it look nice.

If I have a picky client they normally ask me to match to video rushes that have already been generated through a proper film to video pipeline by the colorist(s). I would say 99% of the time pretty much everything from 95-1023 on the original negative has been mapped into 1-254 on video. At the high and low limits of the video it will have been very crushed together by necessity but the point is it hasn't simply been chopped off.

If I have to come up with something myself I never chop it off according to the reference limits. I grade it subjectively on a calibrated video system using quite arbitrary curves to give nice range in the blacks and whites but with a pleasing level of overall contrast. According to the image content I may clip off values outside the dmin dmax range.. like I say it depends on image content... a guy in a cave probably won't have much level if any above 685...if he lights a candle its a different story , likewise someone silhouetted in front of a raging inferno may not have any level below 250 ( doesn't mean I won't drag it down a bit to give better contrast).

I'm hoping most of what I've posted will be somewhat relevant, the key thing is to stop seeing images and video in terms of strict reference ranges. The ranges have a purpose ( usually to differentiate from formats that have different ranges) but they are not absolutes when it comes to how the imagery should look.

Video is a pretty pathetic intensity range and your eye likes big ranges. Video is not like the real world and most displays do not get anywhere near the levels of intensity variation your eye is used to seeing on a daily basis.

Back to whether to clip at 16-235 or not...

Lose everything below 17 to black: your display is unlikely to show level below this point in a useful manner.

Keep everything up to 254 as even with the maximal range on display video will often look clipped to your visual system regardless and you might as well mitigate this as much as is possible.

If your display in conjunction with environment is so lacking in contrast performance that keeping everything above 235 results in a visually unpleasant experience then chop some of the range above 235 off to free up some of the contrast.

If you prefer to watch with a hard clip in place at 16-235 fine knock yourself out no-one is going to kill you for it but please don't confuse this as being of absolute correctness.

Excellent post! Thank you for taking the time to write it.
-John

ISF Calibrator

Pioneer Kuro Elite Pro-111FD
Pioneer Kuro BDP-320

Displays are like 100% cotton t-shirts. Always buy a size larger than you think you'll need, as they tend to shrink over time.
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post #29 of 484 Old 04-06-2010, 06:17 AM
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On program content (BD , dvd and dtv) I can usually tell almost immediately if its clipping above 235.

Would you qualitatively explain "what you see" when clipping occurs on real program material?

Does the image lose smoothness, detail in the bright areas or something else? Is it certain types of scenes or any scene?
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post #30 of 484 Old 04-06-2010, 08:43 AM
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Excellent post! Thank you for taking the time to write it.
-John

Ditto!
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