Realtime gamma tracking - AVS Forum
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post #1 of 27 Old 01-24-2012, 03:11 AM - Thread Starter
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I'm interested in correcting the gamma on my JVC HD350. I use HCFR but I don't see how I can correct the gamma in real time. Right now I have to do a grayscale measurement after each change and since the JVC controls aren't that easy it can get tedious. Anyone knows how I can solve this problem?
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post #2 of 27 Old 01-24-2012, 04:54 AM
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Seems like if you leave at 2.2 its pretty much accurate..Read the following article on this.

http://www.avforums.com/reviews/JVC-...or-Review.html

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post #3 of 27 Old 01-24-2012, 05:18 AM - Thread Starter
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I'm not sure I really agree with the review. I did not find it hard to do the grayscale, on the other hand the gamma is not linear. I think I have .3amplitude difference between the low end and high end. I'm not sure how much this affects the picture but thought I'd ask.
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post #4 of 27 Old 01-24-2012, 05:33 AM
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It's true total gamma and gamma tracking both differ from what the preset says.

Unfortunately I do not use HCFR; I'm only familiar with CalMAN and am just starting to familiarize myself with Chromapure.

The very condensed version of what needs to be done is to start with 100% and work your way down, using graphs that show you absolute RGB balance (rather than the normal relative RGB balance).
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post #5 of 27 Old 01-24-2012, 09:55 AM
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Quote:
Originally Posted by Coolme View Post

I did not find it hard to do the grayscale, on the other hand the gamma is not linear.

Assuming that I am understanding the issue correctly:

In HCFR while viewing the grayscale measures tab, click on the down arrow next to the "Editable Data" checkbox until you see a row of data labeled "Gamma Y". This is the Y value (cd/m2) you need to hit at each % white pattern in order to flatten out your gamma. This value is calculated from the gamma target you've selected in "Advanced/Preferences/References" and the Y value of 100% white.

This will make doing the grayscale a bit more challenging for you
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post #6 of 27 Old 01-25-2012, 01:28 PM - Thread Starter
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Quote:
Originally Posted by djams View Post

Assuming that I am understanding the issue correctly:

In HCFR while viewing the grayscale measures tab, click on the down arrow next to the "Editable Data" checkbox until you see a row of data labeled "Gamma Y". This is the Y value (cd/m2) you need to hit at each % white pattern in order to flatten out your gamma. This value is calculated from the gamma target you've selected in "Advanced/Preferences/References" and the Y value of 100% white.

This will make doing the grayscale a bit more challenging for you

I will have to try this. Is this meant only for the white gamma or also RGB?
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post #7 of 27 Old 01-25-2012, 01:30 PM - Thread Starter
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Quote:
Originally Posted by Chad B View Post

It's true total gamma and gamma tracking both differ from what the preset says.

Unfortunately I do not use HCFR; I'm only familiar with CalMAN and am just starting to familiarize myself with Chromapure.

The very condensed version of what needs to be done is to start with 100% and work your way down, using graphs that show you absolute RGB balance (rather than the normal relative RGB balance).

Is this something I could do with HCFR?
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post #8 of 27 Old 01-25-2012, 04:21 PM
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Quote:
Originally Posted by Coolme View Post

Is this something I could do with HCFR?

Far as I know, ColorHCFR doesn't have any graphs that display in that manner. ColorHCFR also doesn't make it as easy as other software to replace measurements in the graphs (can be done manually). I don't know why they decided to normalize the colors in the Luminance graph, but you can essentially view the same information in different ways. For example you can choose the "RGB" pickbox to the right of your measurements, and then compare the R, G, and B, numbers to the target "gamma Y" line (use down arrow to right of "editable data"). The basic idea is that if R, G, and B match the "gamma Y" line then you are at the target gamma. The same sort of information can also be represented if you open the gamma graph and right-click to turn on red, green, and blue.
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post #9 of 27 Old 01-25-2012, 04:32 PM
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Quote:
Originally Posted by Coolme View Post

I will have to try this. Is this meant only for the white gamma or also RGB?

The "gamma Y" item applies to grayscale in ColorHCFR.
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post #10 of 27 Old 01-25-2012, 04:42 PM
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The gamma Y item in HCFR reflects the target Y for the gamma value that is selected in Advanced>Preferences>References. By matching the measured Y at each stimulus to the gamma Y, the desired gamma will be achieved.

If, at the same time, one adjusts the RGB Level bars each to be as close as possible to 100%, both grayscale tracking and gamma can be adjusted.

EDIT: Of course, continuous measurements must be used to make the adjustments as I described above.

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post #11 of 27 Old 01-26-2012, 01:30 PM - Thread Starter
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Quote:
Originally Posted by LarryInRI View Post

The gamma Y item in HCFR reflects the target Y for the gamma value that is selected in Advanced>Preferences>References. By matching the measured Y at each stimulus to the gamma Y, the desired gamma will be achieved.

If, at the same time, one adjusts the RGB Level bars each to be as close as possible to 100%, both grayscale tracking and gamma can be adjusted.

EDIT: Of course, continuous measurements must be used to make the adjustments as I described above.

Larry

I think I have a vague idea of what I'm supposed to do. I am a beginner at calibration so please be patient. In order to align gamma for W and RGB it is a good start to have an accurate grayscale. If I understand the methods explained here I'll have to adjust the RGB values as well as the individual gamma controls. If I have a gamma target of 2.2 I can do continuous measurements and try to get gamma Y to target. How do I then proceed to do the same for the other colors. The RGB chart will give me an indication of the grayscale values and gamma? If I balance my RGB, my gamma is not necessarily right. I know how to read the graphs for gamma but I need to find a way to do it real time.
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post #12 of 27 Old 01-26-2012, 04:02 PM
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Coolme,

First get a good a grayscale. Then tackle gamma.

Use the green control up or down in the 10 point interval to get Y close to the desired gamma Y value. Then change red and blue by the same amount. Repeat until success is achieved. (Increasing the RGB will increase the Y values and will reduce the actual gamma -- decreasing them will decrease Y and increase the gamma)

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post #13 of 27 Old 01-26-2012, 04:57 PM
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Quote:
Originally Posted by Coolme View Post

How do I then proceed to do the same for the other colors.

Most people don't try to calibrate in this manner, and it's not part of ColorHCFR.

Quote:


The RGB chart will give me an indication of the grayscale values and gamma?

Gamma is not represented on the RGB chart in ColorHCFR. The RGB chart just represents the balance of red, green, and blue in the grayscale. If red, green, and blue are balanced you have gray.

Quote:


If I balance my RGB, my gamma is not necessarily right.

Gamma is related to brightness. The grayscale from black to white is intended to be at gray (equal red, green, and blue). The levels between black and white are intended to be shown at different brightness levels. Gamma simply says how bright the levels between black and white should be.

ColorHCFR will calculate the intended grayscale brightness with "gamma Y", which is also represented on the luminance graph as the reference line. For example for a 2.22 gamma if you look at the luminance graph and mouse over the reference line you will see that 50% gray should be 21.46% of the brightness of white (assuming black has no brightness). If your 50% gray is brighter than 21.46% then your gamma at that point is lower than 2.22, and if your 50% gray is darker than 21.46% then your gamma at 50% gray is higher than the 2.22 reference.
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post #14 of 27 Old 01-27-2012, 04:52 AM - Thread Starter
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Quote:
Originally Posted by LarryInRI View Post

Coolme,

First get a good a grayscale. Then tackle gamma.

Use the green control up or down in the 10 point interval to get Y close to the desired gamma Y value. Then change red and blue by the same amount. Repeat until success is achieved. (Increasing the RGB will increase the Y values and will reduce the actual gamma -- decreasing them will decrease Y and increase the gamma)

Larry

Ok got it. But what about white gamma, should I make any change to it?
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post #15 of 27 Old 01-27-2012, 04:58 AM - Thread Starter
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Quote:
Originally Posted by alluringreality View Post

Most people don't try to calibrate in this manner, and it's not part of ColorHCFR.



Gamma is not represented on the RGB chart in ColorHCFR. The RGB chart just represents the balance of red, green, and blue in the grayscale. If red, green, and blue are balanced you have gray.



Gamma is related to brightness. The grayscale from black to white is intended to be at gray (equal red, green, and blue). The levels between black and white are intended to be shown at different brightness levels. Gamma simply says how bright the levels between black and white should be.

ColorHCFR will calculate the intended grayscale brightness with "gamma Y", which is also represented on the luminance graph as the reference line. For example for a 2.22 gamma if you look at the luminance graph and mouse over the reference line you will see that 50% gray should be 21.46% of the brightness of white (assuming black has no brightness). If your 50% gray is brighter than 21.46% then your gamma at that point is lower than 2.22, and if your 50% gray is darker than 21.46% then your gamma at 50% gray is higher than the 2.22 reference.

Thanks for the explanation. I will give it a try. Although this is just part of the story since I'm dealing with 4 variables at each point (For every color + white). Maybe I can use the info posted above.
Is there any alternative to hcfr that is not too expensive that will make my life a little easier?
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post #16 of 27 Old 01-27-2012, 05:25 AM
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Quote:
Originally Posted by Coolme View Post

Thanks for the explanation. I will give it a try. Although this is just part of the story since I'm dealing with 4 variables at each point (For every color + white). Maybe I can use the info posted above.
Is there any alternative to hcfr that is not too expensive that will make my life a little easier?

This is not that hard.
In Calman with a 10 point control the easiest way is to look at the Target Y number and the actual Y number while you are adjusting the RGB. Keep the target and the actual with in a few points of each other and gamma will be perfect. There is no continuous read for gamma even in Calman, because it is calculated and requires all 10 samples to work (I assume). If you change one point you have to read all in the Gamma area.
However, if you do it looking a the Target and Y of the RGB charts it simple. Make sure you read 100% first, then 0, the up or down the scale. You need the 100% so the target Y will be populated.
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post #17 of 27 Old 01-27-2012, 05:45 AM
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Quote:
Originally Posted by Coolme View Post

Is there any alternative to hcfr that is not too expensive that will make my life a little easier?

I know CalMAN doesn't normalize the luminance graph, so the luminance graph in CalMAN more intuitively represents both the gamma and grayscale balance on a single graph. Graphs are just a representation of the numbers shown on the ColorHCFR measures tab. Like I commented in my first reply, personally I prefer to display the information as RGB (instead of xyY), which CalMAN doesn't offer (see note). If you look at the information as RGB on the measures tab in ColorHCFR the idea is just that you want to do two things:

1) Set gamma by trying to match RGB with "gamma Y".
2) Set grayscale balance by trying to make the RGB numbers nearly equal.

Note: I think the CalMAN RGB numbers are normalized.
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post #18 of 27 Old 01-27-2012, 06:11 AM
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Quote:
Originally Posted by alluringreality View Post

Note: I think the CalMAN RGB numbers are normalized.

What does this actually mean?
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post #19 of 27 Old 01-27-2012, 07:28 AM
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Quote:
Originally Posted by alluringreality View Post

I know CalMAN doesn't normalize the luminance graph, so the luminance graph in CalMAN more intuitively represents both the gamma and grayscale balance on a single graph. Graphs are just a representation of the numbers shown on the ColorHCFR measures tab. Like I commented in my first reply, personally I prefer to display the information as RGB (instead of xyY), which CalMAN doesn't offer (see note). If you look at the information as RGB on the measures tab in ColorHCFR the idea is just that you want to do two things:

1) Set gamma by trying to match RGB with "gamma Y".
2) Set grayscale balance by trying to make the RGB numbers nearly equal.

Note: I think the CalMAN RGB numbers are normalized.

CalMAN does have absolute and relative options on all of the charts including RGB. So yes the RGB chart can be used for grayscale in relative mode or gamma/grayscale in absolute mode.

So you will see in the charts below the Relative shows your RGB is balanced at 10 and 20 percent for grayscale. But if you look at the Absolute is also shows your luminance is low at 10 and high at 20. Which means your gamma number at 10 is higher than it should be and lower at 20.

Absolute RGB

Relative RGB

Changing the RGB mode
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post #20 of 27 Old 01-27-2012, 10:52 AM
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Quote:
Originally Posted by airscapes View Post

What does this actually mean?

Using the terms in the reply from derekjsmith, normalized just means relative, rather than absolute. The absolute RGB graph from his reply is basically the same thing that I was talking about doing by looking at the RGB data, where in ColorHCFR you just try to get the RGB numbers close to the "gamma Y" numbers. Mainly the only reason I started representing the grayscale as what he is calling absolute RGB is because it makes it easy to measure clipping near white on certain displays. If you turn up the contrast control while looking at such RGB data the color that is clipping will remain the same brightness, while the other colors will continue to increase as you turn up contrast.
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post #21 of 27 Old 01-27-2012, 03:21 PM
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Geez, guys. The OP doesn't even understand the basic terminology. Some of your comments are analogous to a lay person asking me to explain redshift in astronomy and me going into a detailed explanation of Minkowsk space or even Schwarzschild geometry.

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post #22 of 27 Old 01-28-2012, 05:06 AM - Thread Starter
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Sorry guys you make too much assumptions about what I know, it's getting difficult to follow. I don't understand for example what 100% is (of what?) to have my target Y. I will try to play a bit with what I understand so far and come back with more questions :-)
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post #23 of 27 Old 01-28-2012, 06:24 AM
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Quote:
Originally Posted by derekjsmith View Post

CalMAN does have absolute and relative options on all of the charts including RGB. So yes the RGB chart can be used for grayscale in relative mode or gamma/grayscale in absolute mode.

I really like this feature in CalMAN.
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post #24 of 27 Old 01-28-2012, 09:13 AM
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Quote:
Originally Posted by Coolme View Post

I don't understand for example what 100% is (of what?) to have my target Y.

100% gray (white) is the brightest measurement in ColorHCFR when you measure a grayscale series. The "gamma Y" line in ColorHCFR tells you how bright the other levels should be between black and white. The "Y" number in ColorHCFR indicates brightness of your measurement. If "Y" matches "gamma Y" then your measurement is at the intended brightness for your target gamma.

If your measured "Y" matches the "gamma Y" then the gamma graph will show your measurement on top of the reference line. Same thing with the luminance graph, if your measured "Y" matches the "gamma Y" then the luminance graph will show your measurement at the reference line. If your "Y" is higher than "gamma Y" (measurement brighter than intended), then the luminance graph will show the measurement above the reference line and gamma will be low for that measurement. If your "Y" is lower than "gamma Y" (measurement darker than intended), then the luminance graph will show the measurement lower than the reference line and gamma will be higher than reference for that measurement.

So "Y" indicates the overall brightness of your measurement, but it's also possible to break up brightness into red, green, and blue parts. The "R", "G", and "B" numbers in ColorHCFR are similar to "Y", and they indicate the brightness of red, green, and blue. If "R", "G", and "B" are equal you have gray. If "R", "G", and "B" are not equal the relationship will be shown as being higher or lower than the 100% reference line on the RGB levels graph. If in a perfect world you were able to get all the "R", "G", and "B" measurement data to match "gamma Y", that would mean that both the gamma and RGB levels would be at their intended targets. If "R", "G", or "B" is higher than "gamma Y" it means the measurement has too much red, green, or blue, and if "R", "G", or "B" is lower than "gamma Y" it means that red, green, or blue is not bright enough for the chosen gamma. If you really want, just buy CalMAN and it will basically show you the same information on the luminance or absolute RGB charts.

Edit: The comments about how "R", "G", and "B" relate to "gamma Y" assume that the 100% measurement (white) is near gray.
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post #25 of 27 Old 02-08-2012, 12:41 PM - Thread Starter
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I forgot to thank you for the extensive answers. I haven't been able to try all the tips yet. I will when I have time and the courage.
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post #26 of 27 Old 11-28-2012, 05:41 PM
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Hi Guys
I read this thread and follow the instruction to calibrate my X70 custom gamma, but I had an issue of the measured Y changes after I calibrate it to match the gamma Y. I started from 90IRE to 10IRE, I adjusted total white for every IRE to meet the gamma Y, but after full calibration, I went back to check from 90 IRE, the reading drops from the number I adjusted around 15%. Then I checked all the readings looks like they all drops after adjustment, except the 10 IRE. What's wrong about this? I really don't have the idea now......frown.gifconfused.gif
I ever reached avg. 2.23 with flat line (not the slope), but the picture tone must set to -16, the picture looks strange in dark scene, so I reset it.
Here is the luminance & gamma chart before I start the custom gamma adjustment

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post #27 of 27 Old 11-29-2012, 09:26 AM
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TBH it's the JVC custom gamma being difficult to adjust. I gave up with my HD350 and used an external VP as it was just too frustrating, especially when I was trying to use HFCR. Now I'm using Chromapure and a Lumagen I can set the greyscale and gamma in about 20 minutes (manually or using autocal) so I expect I'll do the same when my X35 arrives. I thought that the newer models such as X70 had a better, less interactive, custom gamma though (I seem to recall that the HDxxx models never did get a firmware fix to improve it).

Zooming: Been there, done that, bought the lens...
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