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Calibration - what your eye sees

post #1 of 12
3/1/09 at 10:17pm
Thread Starter 
so I was posed this question by a customer last week and I had no answer for him, but I would like to know if there is one

he is an optometrist and asked about calibration

he said - there are really not that many humans who can see all colors correctly, and some people will see red while others will see burgundy or some other shade of red - that some color blind people wear glasses of a certain shade to tell the difference between colors - we all interrupt colors differently and as we age some colors become more pronounced and some become muted looking

so if I set up the TV to display 6500K 709 rec and so on then if "your" eyes are seeing colors differently than mine do it will not look correct to "you" but it is "correct" as in it meets standards "correctly", but if you see it incorrectly then it is not correct to "you"

there are ways to determine what colors you see correctly and which you dont by comparing them to color gels that are back lit (it has to be back lit not a printed picture because stuff on paper is a "subtractive" means of displaying colors, that is to say that you are seeing the absence of color where as a TV or back lit object is additive color, that is to say you see colors that are produced not reflected) and have been tested with chroma meters then you change the color until the subject says it looks red or green or blue to them - most people are +/- 10% from actual correct colors

that being said those people who say that calibrating there TV made it look worse or they like it better the other way - maybe they are correct, maybe they see colors differently so the result is inaccurate colors for them

most peoples eyse see color differently from the other eye - try this, go into a closet and close the door so you can only see a small sliver if light outside and look through it with one eye and then the other eye without closing the other eye - you will see a difference between them


anyone know about this - the question is

if it is correct as in adheres to a standard and has been confirmed by chroma meters but human eyes see colors differently then whats the point if you cant confirm what the said person who is watching the TV will be seeing, as long as it looks OK to them and isnt over saturated then whats the point?

I assume if you educated them on what over saturated looks like they would be able to figure it out
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post #2 of 12
3/1/09 at 10:37pm
Has nothing to do with what a person thinks it should look like or even if they like what it looks like. It's all about the standards and as you just pointed out you can't trust your eyes to tell you what is correct. If a person wants the display to be calibrated to a standard then it only has a single conclusion the standard. Now if someone wants to change their setting to something they think is right or they like then that has nothing to do with calibration.

I know the above to be true because I suffered from CSCR in my right eye where I lost about 5% of my vision and mostly affected red. So if I look at an image with my left then right eye they are different and I know the left is more accurate because of testing. But I still calibrate my displays to the standard because I'm not the only one watching my display. Plus I know when it has been calibrated to the standards I have taken that variable out of the equation.
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post #3 of 12
3/2/09 at 3:45am
Surely it doesn't matter what you see red, green, blue etc. as?

If you see reds as being bright pink, or green, or not at all, then that colour shift is going to be there whether you're looking at a display, real life, photographs, or anything else.

So it doesn't matter if you can see red or not, you would still have to calibrate to the standards for things to look correct.

If you were to adjust a display to correct for your vision deficiencies, then it wouldn't look anything like real life did. (not that the point of television/film is to recreate reality anyway)

Depending on your colour vision, you may be more or less sensitive to the accuracy of certain colours though.
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post #4 of 12
3/2/09 at 5:03am
This has to be what is most misunderstood about calibration. Calibration is not about "looking good" or "looking right to me", it's about the preservation of the quality of the material produced, from production to the end user.

Think of something like a weigh scale. When used in precision applications a scale is always calibrated against a known reference. Now, different people will most certainly have different perceptions about how heavy an object is depending on physiological attributes and/or how experienced they are in assessing an exact weight simply by feel. The only way we get an objective perception is to weigh the weight on a calibrated instrument. Would anyone question the need for calibration of a weight scale for precision applications?

This is what calibration is, for a video chain and a display, for weight scales or whatever.

Obviously the standards for film production are not strict science but are in part about the Human Visual System and in that sense they are inherently subjective and thus relies on a consensus, but regardless of this the only way to keep the integrity of a material from production to end user is by calibrating against the standards that are in use during production of the material.
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post #5 of 12
3/8/09 at 9:52pm
Thread Starter 
Quote:
Originally Posted by WolfyA View Post

This has to be what is most misunderstood about calibration. Calibration is not about "looking good" or "looking right to me", it's about the preservation of the quality of the material produced, from production to the end user.

Think of something like a weigh scale. When used in precision applications a scale is always calibrated against a known reference. Now, different people will most certainly have different perceptions about how heavy an object is depending on physiological attributes and/or how experienced they are in assessing an exact weight simply by feel. The only way we get an objective perception is to weigh the weight on a calibrated instrument. Would anyone question the need for calibration of a weight scale for precision applications?

This is what calibration is, for a video chain and a display, for weight scales or whatever.

Obviously the standards for film production are not strict science but are in part about the Human Visual System and in that sense they are inherently subjective and thus relies on a consensus, but regardless of this the only way to keep the integrity of a material from production to end user is by calibrating against the standards that are in use during production of the material.

yea not sure the weight scale analogy is the best here, but I know what you are saying

it is calibrated against a known reference, yea people inturprit weight differently thats why they use a scale, but if the known reference is precieved incorrectly to the user then its not correct to the user
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post #6 of 12
3/9/09 at 2:24am
Quote:
Originally Posted by leftkidney View Post

yea not sure the weight scale analogy is the best here, but I know what you are saying

it is calibrated against a known reference, yea people inturprit weight differently thats why they use a scale, but if the known reference is precieved incorrectly to the user then its not correct to the user

Analogies rarely ever are (and I know why a weight scale isn't the best), but it at least "visualizes" what one is talking about.

OK, lets use your last sentence. How does the fact that someone perceives the standard reference incorrectly invalidate the calibration to that standard reference?

How would you maintain the fidelity of something produced to adhere to a standard other then calibrating your instrument (in HT it's your video chain) to adhere to that same standard?
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post #7 of 12
3/9/09 at 2:35am
Hi all. Lemme see if I can help here.

Individual comparators are meaningless here. By that i mean you and your eyes. Lets say that you see each color correctly, I see it as a darker shade and someone else sees is as a lighter shade. When you learned what the name of that color was is when you associated that name with what you preceived it to be. Take a red rose. We would all call it red because what we see we learned to be "red".

Another way to look at it is this. If you had all calibrated equipment from a video camera all the way to a display and shot a video of the front of your house it should look the same on the display as in real life, regardless of who is looking.
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post #8 of 12
3/9/09 at 3:51am
Greetings

Calibration is not about looking like real life. The TV is not capable of that. The color palette of the HD system is smaller than the color palette of the human visual system.

Regards
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post #9 of 12
3/9/09 at 10:05am
If a viewer's perception of reds is skewed away from the "norm," his perception of ITU rec. 709 primary red on a calibrated studio monitor will be the same on a consumer TV that has been calibrated to reproduce the same rec. 709 red primary. If an apple on a table under D65 illumination happens to naturally match the same shade of rec. 709 primary red, that same viewer will perceive the color of the apple the same as the video display's red primary. The video system IS able to reproduce natural colors, as long as they fall within the same color space (gamut) that video is constrained to.

Once the basic nature and purpose of video calibration is understood, any optometrist with a logical mind should understand why variations in the color perception of individual viewers doesn't matter. It's not about the viewer at all. It's about adhering to quantifiable, verifiable, reference standards, in order to preserve the integrity of the original program signal (the art): http://www.avsforum.com/avs-vb/showthread.php?t=1021933 .

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 #10 of 12
3/11/09 at 11:22pm
My 2 cents:

If someone sees red different than you or any one does not really matter unless that person suffers from Daltonism (switches colors completely). Even if a person sees different shades than other people for the same image. The brain makes that person feel that everything is normal. For example if you calibrate a set to the same colors that mostly every television is using that person will think that everything is ok. Then again if that person has been watching a tv that is out of calibration for a long time, when you correct the calibration that person will think something is wrong. The same applies to sound. Our brain gets used to colors and sound properties fast. It is just normal brain activity. At some point the brain reprograms it self. For example I used to produce music as a hobby I built a track and if I kept messing with it at some point I though it was right then I switched to a professional track to compare I noticed mine sucked. So don't worry as long as all equipment is displaying the same colors everything is ok use other sets as a reference.
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post #11 of 12
3/14/09 at 12:27am
To answer the optometrist, it is a matter of the accuracy of the instrument to do the calibration, removing the tweaking by eye. If a display is accurately set to D65 with the aide of an accurate meter, it will have the best chance to look "normal" to anyone, no matter what colors they may be deficient in seeing. If the Calibrator is deficient in seeing some colors and tries to adjust the grayscale by "eye" there is a greater potential for error.
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post #12 of 12
3/16/09 at 6:02pm
Thread Starter 
well thanks for your answers and comments

I have showed this to him and he says "wow, there are a lot of smart people on this forum"

but yea it makes sense that if you are used to a color being one way than it should look that way even if you see it incorrectly as long as it looks correct to you - and yea I guess this could only be a problem if you had some warm or cool lighting in real life all the time, but that cant be because it is mostly from the sun so outside things liik the same to you if the display is producing the closest to real life as it can
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