Bumpy luminance curve - AVS Forum
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post #1 of 11 Old 04-30-2013, 04:43 AM - Thread Starter
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I'm about to be somewhat frustrated. I simply can not achieve constant luminance curve. I have set the contrast by using this guide: For those struggling with brightness, contrast & backlight settings on LCD's

I have calibrated white balance using 20IRE and 80IRE and obtains the following result:



Luminance:



Someone who can give me a hint about what is going on?
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post #2 of 11 Old 04-30-2013, 08:00 AM
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Possibly contrast is too high, other than that, it looks pretty good.

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post #3 of 11 Old 04-30-2013, 08:37 AM - Thread Starter
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Quote:
Originally Posted by sotti View Post

Possibly contrast is too high, other than that, it looks pretty good.

It was also my guess. I tried, therefore, to lower the contrast, it is to be lowered to 65 versus 89 to achieve a smooth curve. Quite horrible to look at.

I would just add that it is a poor SAMSUNG UE46D5005 with a 2pt white balance. Do you think the time is that I am resigned to it can not be improved?

If I take a measurement on 100IRE is red 99% green 100% blue 94%
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post #4 of 11 Old 04-30-2013, 08:50 AM
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possibly try adjusting at 100% instead of 80%, or find some balance between the two that will raise dE across the board, but make the 100% less noticeable.

You probably also really should look at a contrast pattern like the one on the AVS709 disc to make sure you aren't getting discoloration.

There should be one contrast setting that is the maximum value that doesn't cause clipping, after that adjust the backlight to get more light output.

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post #5 of 11 Old 04-30-2013, 10:36 AM
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Originally Posted by sotti View Post

possibly try adjusting at 100% instead of 80%, or find some balance between the two that will raise dE across the board, but make the 100% less noticeable.

+1.

Many LCD's 2pt adjustments were designed to work at 100% stimulus. The 80% stimulus point, is a bit of a relic from the days when CRT's ruled ... and it didn't always work then either. smile.gif
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post #6 of 11 Old 04-30-2013, 12:25 PM
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Also,, you don't just calibrate at 20 and 80 and walk away. You have to consider the entire grayscale. In fact, you might have to introduce errors at 20 or 80 or both in order to have a better result somewhere else along the grayscale that has a larger error. Your goal is to find the lowest overall/average errors over the entire grayscale, not just 20 and 80. Frankly, I don't even mess with 20 and 80 or 30 and 80 any more. I measure the entire grayscale, then consider what to do with the offset/bias/low controls and gain/high controls, then I remeasure the entire grayscale again. If you only adjust to 20 and 80 you can leave errors elsewhere that you don't want to live with.

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post #7 of 11 Old 04-30-2013, 10:40 PM
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Originally Posted by Doug Blackburn View Post

Also,, you don't just calibrate at 20 and 80 and walk away. You have to consider the entire grayscale.

Agreed ... I was referring (specifically) to my experience stacking 2pt and 10pt adjustments on my LG. In that case, it's actually mandatory that you set the 2pt using 100% stimulus, because the 100% controls on the 10pt become inoperable once you adjust the 2pt's "high" controls. ... I also found that there wasn't a whole lot left to do after the 2pt was dialed in, unless one wanted to go for a BT1886 curve.
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post #8 of 11 Old 05-01-2013, 01:31 AM - Thread Starter
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Thank you for your contribution. I have adjusted the gray scale to achieve a more uniform dE across the board, thanks for the information. smile.gif

Regarding luminance. Blue is still above the target graph. I have a setting named Gamma. SAMSUNG describes the function as follows: Gamma: Adjust the primary color intensity.

Can the setting improve my luminance curve? Someone who can describe the function for an amateur like me? smile.gif
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post #9 of 11 Old 05-01-2013, 12:16 PM
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Gamma doesn't change the "intensity" of the primary colors... at all. Gamma defines how bright each grayscale step should be. That luminance curve you posted... the reference line will change shapes (more or less curvature) when you enter higher or lower gamma targets in your calibration software. I use 2.25 for the gamma target nearly 100% of the time because studios mastering Blu-ray discs are using workstations setup for gamma in the 2.2-2.3 range. When your measured gamma perfectly matches your gamma target, the 2 curves in that graph will be right on top of each other. Small variations there won't be visible in images, but the closer every grayscale step is to the desired 2.25 gamma, the better your images will look.

Samsung gamma controls actually change the luminance of grayscale steps and in doing that, the control will change the shape of the measured curve in your graph. It looks like you have a fairly well-selected gamma setting right now. If you set the Gamma control to a higher number (like 2.5), your measured gamma curve will dip down below the reference curve for your 2.25 gamma target. If you set the Samsung Gamma control for a lower numeric gamma, the measured curve will be above the reference curve defined by your 2.25 gamma target. Higher numeric Gammas will make every measured point from 10%-90% darker than the 2.25 reference gamma (Gamma does not affect the position of 100% or 0%, only the steps between 0% and 100% are affected). When the images look darker than they should because of a too-high (numerically) gamma, images aren't as satisfyingly bright as they should be. When you select a numeric gamma lower than the 2.25 reference gamma target, images will be brighter, but they also lose dimensionality and look "flatter" than they should when gamma is correct.

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post #10 of 11 Old 05-01-2013, 12:54 PM
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Hmmmm...i have a feeling a gamma debate will be shortly brewing...
2.2, 2.22, 2.25, 2.3, 2.35, 2.4, 2.5.
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post #11 of 11 Old 05-01-2013, 06:51 PM
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Quote:
Originally Posted by MSL_DK View Post

Someone who can give me a hint about what is going on?

My opinion is to ignore the red, green, and blue lines on the luminance graph in HCFR. They normalized each of the red, green, and blue lines on the luminance graph. Unless red, green, and blue are approximately equal at 0% (black) and 100% (white) each of the lines on the luminance graph may not have much relation to each other, and the graph might not help you out, especially as a beginner with limited display controls. Your greatest errors are currently near 0% and 100%, so the red, green, and blue lines on the luminance graph likely have little relation to each other. For example blue is low compared to red and green at 100%, as shown on the RGB balance graph, but the luminance graph makes it look like blue matches red and green at 100%. Personally I think other software makes luminance for red, green, and blue a lot easier to comprehend for beginners. HCFR does have the RGB numbers that you can compare to "gamma Y" and each other, and HCFR also has the gamma graph where red, green, and blue actually relate to each other, but unfortunately most new users probably find a good luminance graph far easier to comprehend than trying to make sense of somewhat abstract RGB data and the gamma graph. Personally I doubt if most new users can make any sense out of normalized red, green, and blue on the luminance graph, so my opinion is to shut those items off.


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