Why not calibrate grayscale from 100 to 40 or 100 to 30? - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 20 Old 04-23-2015, 10:50 AM - Thread Starter
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Why not calibrate grayscale from 100 to 40 or 100 to 30?

When calibrating color I remembered that white during grayscale calibration was pretty much spot on with xy coordinates and Y. I chose to do only a 100% saturation color cal, so I began to wonder if it would be beneficial to try to calibrate grayscale at 100 to 30. I'm assuming that 30 being on the dark end may be stuck with delta E just below 3. Has anyone done this?

Almost forgot 2 point grayscale is my only option.
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post #2 of 20 Old 04-23-2015, 11:51 AM
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a full scale run should be made not just
20/80, 30/70 etc.
depending on how the gamma runs, 0/100 just may give the best
entire run.
point is, the entire run is important. having 30/70 perfect at the expense of
the rest is half azz.

since the controls are for 0 and 100, the entire run should always be looked at.
hope that makes sense.

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post #3 of 20 Old 04-23-2015, 01:07 PM
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Quote:
Originally Posted by DisplayCalNoob View Post
When calibrating color I remembered that white during grayscale calibration was pretty much spot on with xy coordinates and Y. I chose to do only a 100% saturation color cal, so I began to wonder if it would be beneficial to try to calibrate grayscale at 100 to 30. I'm assuming that 30 being on the dark end may be stuck with delta E just below 3. Has anyone done this?

Almost forgot 2 point grayscale is my only option.
LG is done at 100~30 while others such as SONY's are done at 80~30. What you want to keep an eye out for is how well it tracks linearly. After making adjustments and you do a re-read of the the grayscale, look to see how much of the other numbers re-adjust (70 & 90) and (20 & 40). If the display tracks poorly linearly only the 80 and the 30 will be effected, while everything else remains unchanged. If the display tracks well linearly there will be an effect through out all of the numbers. More of a reaction the better the display probably tracks linearly.

On a two point system, gamma calibration is not really possible. The best you will be able to do is find the best present setting for gamma.

The 80 point is usually chosen because it is about the middle of the upper half of the grayscale, while the 30 point is around the middle half of the darker half.
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post #4 of 20 Old 04-23-2015, 02:40 PM - Thread Starter
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My last calibration, I got 80-20 down below a delta E 2pt. The upper end below 1, so I'm in good company. So I take it therewouldn't be any visual benefits, going for 100?
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post #5 of 20 Old 04-23-2015, 03:04 PM
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Originally Posted by DisplayCalNoob View Post
My last calibration, I got 80-20 down below a delta E 2pt. The upper end below 1, so I'm in good company. So I take it therewouldn't be any visual benefits, going for 100?
Unless the manufacturer calls for different values it is safe to assume that a two point calibration is 80~30.
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post #6 of 20 Old 04-23-2015, 03:08 PM
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Originally Posted by DisplayCalNoob View Post
My last calibration, I got 80-20 down below a delta E 2pt. The upper end below 1, so I'm in good company. So I take it therewouldn't be any visual benefits, going for 100?
I don't get your issue.
you want all levels to be as close to ref as possible.

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post #7 of 20 Old 04-23-2015, 03:32 PM
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Here is a workflow that you can try the thing it is for a Samsung TV. I did some editing to it to suit my needs for my Panasonic.

Start with TV in Movie Mode; reset to get to baselines (contrast, gamma, enhancements off, etc).
Adjust brightness with a low APL pluge pattern. Adjust backlight for LED and Cell Light/Contrast for Plasma for target luminance.

Adjust 2 pt white balance, using 80 % white for the high end adjustment and either 20 or 30% (your preference, could also be determined by your meter's low end sensitivity) at the low end.

Re-check brightness with low APL pluge.

Take a full 10 or 11 step greyscale run. If gamma is close to target, then proceed. If not, then select a different gamma setting to find one that's closer, and re-check brightness. Then re-measure. Repeat as necessary. After correct gamma preset is found, re-check 2 pt white balance, and then re-check brightness.

Then do the 10 pt adjustment, starting at 100% and working your way down.

Check the minimum and maximum luminance values adjust the Contrast and Brightness if needed.

Take another 10 or 11 step measurement. You will find areas that need further improvement, so you will have to repeat until you are as close as you want to be or until you reach the point of diminishing returns.

This is just pertaining to the greyscale and nothing about calibrating color but it should get you started.
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post #8 of 20 Old 04-23-2015, 05:40 PM
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Originally Posted by randal_r View Post
If the display tracks poorly linearly only the 80 and the 30 will be effected, while everything else remains unchanged. If the display tracks well linearly there will be an effect through out all of the numbers.
Correct me if I'm wrong, but my understanding is that the so-called 80/30 two-point calibration simply means that the calibration aims to minimize the errors at 80 and 30, and let the other points fall wherever they do. It does not mean that the Gain adjustment affects 80 more than it affects 90 or 100. Unless there's severe clipping, the Gain adjustment always affects the high end the most. Similarly, the Bias adjustment affects the low end the most.
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post #9 of 20 Old 04-23-2015, 06:50 PM
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Originally Posted by Dominic Chan View Post
Correct me if I'm wrong, but my understanding is that the so-called 80/30 two-point calibration simply means that the calibration aims to minimize the errors at 80 and 30, and let the other points fall wherever they do. It does not mean that the Gain adjustment affects 80 more than it affects 90 or 100. Unless there's severe clipping, the Gain adjustment always affects the high end the most. Similarly, the Bias adjustment affects the low end the most.
They say a picture is worth a thousand words. Right now my wife is starting to bug me to get off of the computer so I am going to try and explain the concept through a video. Go to the time frame 56:30 and watch until 1:07:30. Note how the narrator makes reference to the tracking of the display. I have dealt with displays that have horrible tracking and only the 80~30 where correct and all of the rest of the points still remained chaotic.

There is no argument that the gain will have an effect on the bias and vice versa. What I am trying to convey is that once the 80~30 are showing each to be at the 100% for there corresponding points, you should see for those points the RGB converging together while all the rest of the points may appear chaotic. It is not until when a re-read of the whole grayscale that the rest of the points should correct their values. Again, this is on a display that reasonably tracks linearly. If the display doesn't track linearly there will probably be very little change.

The object of the two point grayscale calibration is very well illustrated in the video. Get 80~30 correct and everything else should come together. If you listen to exactly what the narrator is saying you can almost hear the legal disclaimer.

The poor tracking condition is found more in the less expensive displays.


Watch the video and comment. I am interested on your thoughts.
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post #10 of 20 Old 04-23-2015, 09:44 PM
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Originally Posted by randal_r View Post
Watch the video and comment. I am interested on your thoughts.
Thanks for the video; it's very informative - and is completely consistent with the statements I made in my previous post, i.e.,

"the so-called 80/30 two-point calibration simply means that the calibration aims to minimize the errors at 80 and 30, and let the other points fall wherever they do". This means:

- If the tracking is linear, adjusting 30 and 80 to 0 delta-E, will "automatically" result in a low delta-E at the other points
- If the tracking is poor (non-linear), adjusting 30 and 80 will affect the other points just as much, but the delta-E for those points will likely still be high, or even higher than the pre-adjustment values.

Nothing in the video supports your statement "If the display tracks poorly linearly only the 80 and the 30 will be effected, while everything else remains unchanged."

Thus, with the same two-point controls, one could also choose to optimize 90 or 100 instead of 80. The controls are not "hard-wired" to affect 80 only.

Last edited by Dominic Chan; 04-23-2015 at 10:15 PM.
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post #11 of 20 Old 04-23-2015, 11:25 PM
 
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This stuff is all wrong. 100% of it. Sorry... the whole thing about calibrating at 80% and 30% or whatever... it's just wrong. The whole point of grayscale calibration is to find the combination of settings that produce the smallest errors over the entire grayscale. That means you run the entire grayscale after adjustments, not just 2 points. That way nothing gets past you. You don't want 80 & 30 perfect with huge errors at 50 and 20. This all means that you may have to CAUSE some errors at 80 & 30 in order to have lower overall errors everywhere else in the grayscale.


The whole 80-30 thing is an old concept from CRT days that's not particularly useful today. You could use it (today) to get your grayscale in the ballpark, but once 80 & 30 (or whatever your 2 points are) have minimal errors, you then have to start running the entire grayscale and tweak settings to get the best overall results across the whole grayscale, not just at 80 & 30. But most displays' grayscales are relatively "in the ballpark" already with digital displays so doing 80-30 or whatever really is going to waste more time than it's going to save.


The thing about the whole 80-30 deal is & was... you are NOT done with grayscale when 80 & 30 are correct. But people seem to forget that... or they never understand that from the outset. You can have a HORRIBLE grayscale calibration with 80 & 30 being very accurate. But you'd never know that if you didn't measure the whole grayscale every time you adjust controls.
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post #12 of 20 Old 04-24-2015, 05:48 AM
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Originally Posted by Doug Blackburn View Post
This stuff is all wrong. 100% of it. Sorry... the whole thing about calibrating at 80% and 30% or whatever... it's just wrong. The whole point of grayscale calibration is to find the combination of settings that produce the smallest errors over the entire grayscale. That means you run the entire grayscale after adjustments, not just 2 points. That way nothing gets past you. You don't want 80 & 30 perfect with huge errors at 50 and 20. This all means that you may have to CAUSE some errors at 80 & 30 in order to have lower overall errors everywhere else in the grayscale.
You seem to have missed the point of this discussion. It was NOT trying to describe all the iterative steps required to get the best overall greyscale; the specific question being discussed, was how or whether adjusting 80/30 would affect the other points.

Last edited by Dominic Chan; 04-24-2015 at 06:35 AM.
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post #13 of 20 Old 04-24-2015, 06:37 AM
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Sorry to step into this discussion but I can see where most of you are coming from.

From Doug Blackburn point of view the objective is to introduce the least overall errors to the whole grayscale. This is well apparent when a TV has only a single grayscale calibration point like a Vizio display that I had come across. By what I understanding from your post, it seem that you feel that the 80-30 rule is obsolete. I would have to ask, Why does everyone like SpectraCal, Thx and others still use the 80-30 rule for 2 point calibration?

From Randal's point of view, I too have seen TVs that don't react like the one in the video. The TV was an older one but in no way did it behave like the newer ones do. I also viewed and listened very closely to the narrator in the video and I found points where it was implied that results would differ if the TV did not track well linearly. I did my sisters Samsung TV (LCD), which is about nine years old and I would have to agree with Randal; I too had the same problem. This was all done in a text book manner. Adjust 80, then read the whole grayscale. Then adjust 30, then read the whole grayscale. Repeat, repeat, repeat. I tried adjusting other points and this was of no value. No matter what I did I could adjust a point but the rest points would not fall into line.

From Dominic Chan's view, on TVs that are newer I would agree; adjusting the 80 point would change the values at other points and the same goes for the 30. In my opinion TVs today probably are more linear today then the older TVs of yesteryear. I feel you would be hard pressed to find one that doesn't. I think the video was to show how things will change when linear. Unfortunately, SpectraCal did not show us what would happen if it wasn't linear. Although verbally implied, I would have liked to see the results if it wasn't linear.

There are always exceptions to the rule (or the norm).

Last edited by Phoenix_001; 04-24-2015 at 07:09 AM.
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post #14 of 20 Old 04-24-2015, 08:32 AM
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Sorry to step into this discussion but I can see where most of you are coming from.
From Randal's point of view, I too have seen TVs that don't react like the one in the video.
What the video shows can be very easily misinterpreted. When the adjustment was being made at 80, the video appears to show that 60, 70, 90, etc. remain unaffected, but that is highly deceptive and not the actual case at all. During that step, the pattern generator was displaying the 80% grey level, so the software can only update that single point on the graph since it has absolutely no idea what is happening to the other levels. The other points appear to be unaffected, since they are still showing the pre-adjustment level. It's only after a complete scan is rerun, that you can see the actual effects the other levels.

The TV used in the video is fairly linear on the high end, so things more-or-less fall into place for 60, 70, 90, etc. 100 has a slightly higher error but that's reasonable compromise.

The TV does not have a very linear behaviour on the low end, and the errors at 10 actually increased after calibration (R went from 93% to 88%). That is the point I made in the previous post.
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post #15 of 20 Old 04-24-2015, 09:33 AM
 
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Originally Posted by Dominic Chan View Post
You seem to have missed the point of this discussion. It was NOT trying to describe all the iterative steps required to get the best overall greyscale; the specific question being discussed, was how or whether adjusting 80/30 would affect the other points.

You cannot predict that... different displays are different. The controls work differently and the display's response isn't consistent across brands or models. You measure the entire grayscale each time you adjust controls.


And 2-point, 10-point, and 20 point controls work differently. 2-point controls always overlap, but the overlap is very unpredictable. Displays with 10 or 20 point controls may or may not have overlap. And the controls may or may not have their largest effect on the % they are labeled (i.e. the control labeled 40 might really control 30% or the range from 20% to 60%. The only way you can know what you are dealing with is to measure the entire grayscale each time you make measurements.


That said, once you have been working with 1 specific display for a long time, you will get more familiar with how the controls work and you can begin to predict what will happen. But when you are in the "getting to know you" phase, all bets are off. Any assumptions you make are likely to be wrong.
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post #16 of 20 Old 04-24-2015, 12:35 PM - Thread Starter
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So ultimately it's up the calibrator to decide what bright end and dark end, he or she will start and end at. I was just wondered if there was any relation to what color saturation levels you are calibrating color(i.e 75% or 100%). Since RGB produces white, at a 100% saturation white is inaccurate because, I just calibrated grayscale at 80/30. White 100 has a delta-E of 4.4
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post #17 of 20 Old 04-24-2015, 02:07 PM
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Originally Posted by DisplayCalNoob View Post
So ultimately it's up the calibrator to decide what bright end and dark end, he or she will start and end at. I was just wondered if there was any relation to what color saturation levels you are calibrating color(i.e 75% or 100%). Since RGB produces white, at a 100% saturation white is inaccurate because, I just calibrated grayscale at 80/30. White 100 has a delta-E of 4.4
I think you might want to re-evaluate that idea. Do your research. There is much information out there if you look. See what the industry suggest versus the individual. For a 2 point calibration 80~30 is the rule , where as with LG it is 100~30. Also keep in mind that the grayscale "x,y" values are the same from 0% to 100% whether the saturation is 75% or 100%. Many times even when the "x,y" are correct you can get deltaE issues from the "Y" value not matching the Target "Y" value. This issue is often overlooked a lot. With a 2 point calibration not much can be done about it but in a 10 point or 20 point calibration system adjustments can be made to rectify this issue.

D65 White Point is created by Green 71.5%, Red 21.3%, Blue 7.2%. Software makes it easier on the users by a process called normalizing so that when we look at the RGB we see each at 100%.

Not knowing what equipment you have or software you are using it is difficult to give any advice or assistance.
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post #18 of 20 Old 04-24-2015, 02:29 PM - Thread Starter
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Here's what I have, Spyder4Pro and I'm using HCFR software. Display is a 2009 Toshiba LED local dimming 46sv670u.
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post #19 of 20 Old 04-24-2015, 06:20 PM - Thread Starter
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Originally Posted by Dominic Chan View Post
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Originally Posted by DisplayCalNoob View Post
So ultimately it's up the calibrator to decide what bright end and dark end, he or she will start and end at.
The 80/30 etc are not the "start" and "end" points of the calibration range; they are simply "representative" points that are being monitored during the initial adjustment. The adjustments will affect the entire range from 0 to 100, so the final results need to be checked and re-adjusted if necessary for best overall response.


I have just calibrated my 5-year old LG LED TV, using the "80/30" 2-point adjustment even though the TV also has the 10-point option. I have attached the Pre- and Post- adjustment RGB graphs; the results speak for themselves. The TV has a very linear tracking, so it would not have made any difference if I had chosen 90/20.


[EDIT: The post-calibration graph was apparently over-written when I made the 10-point calibration. Will re-run and post the correct graph]
I just meant that whatever 2 pt you choose to start grayscale calibration.
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post #20 of 20 Old 04-24-2015, 08:07 PM
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Quote:
Originally Posted by DisplayCalNoob View Post
So ultimately it's up the calibrator to decide what bright end and dark end, he or she will start and end at.
The goal is to get the best "overall" grey scale. I just calibrated my 5-year old LG LED TV, and initially used 80/30 which produced a very neutral grey scale (Delta-E < 1 throughout). However, if I choose 80/20 instead, the overall results would be even better. Both results are attached. The results can be easily predicted by examining the pre-calibration graph.

Since the high end is very linear, I could have chosen 90 (or even 100) instead of 80, and it would not make any difference to the result.
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Last edited by Dominic Chan; 04-24-2015 at 08:25 PM.
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