Gamma Curve Adjustments - AVS Forum
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post #1 of 14 Old 11-15-2012, 07:48 AM - Thread Starter
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Hi All,

i have a question about gamma calibration.
Exists any problem on adjust gamma using 10p white controls? Moving the r/g/b controls together up or down for increase or decrease luma at specific point.
Works for me, but i don't know if it's wrong.

This is wrong? Or not? Has collateral effects?
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post #2 of 14 Old 11-15-2012, 08:09 AM
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That's exactly how you adjust gamma in an RGB system.
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post #3 of 14 Old 11-15-2012, 08:12 AM - Thread Starter
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Thanks sotti, then i will continue using this method biggrin.gif
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post #4 of 14 Old 11-18-2012, 12:51 PM
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Quote:
Originally Posted by sotti View Post

That's exactly how you adjust gamma in an RGB system.

Alas does not work on Panasonic 10pt system which has a buggy independent 10pt gamma settings.

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post #5 of 14 Old 11-18-2012, 01:34 PM
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Quote:
Originally Posted by ndaa75 View Post

Alas does not work on Panasonic 10pt system which has a buggy independent 10pt gamma settings.

Their system is not an RGB system.

It is an RGB + G system.

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post #6 of 14 Old 11-18-2012, 10:02 PM
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Quote:
Originally Posted by ndaa75 View Post

Alas does not work on Panasonic 10pt system which has a buggy independent 10pt gamma settings.

Please elaborate.

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post #7 of 14 Old 11-18-2012, 11:10 PM
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Quote:
Originally Posted by ndaa75 View Post

Alas does not work on Panasonic 10pt system which has a buggy independent 10pt gamma settings.

On my vt50 it works pretty good, how is it buggy?
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post #8 of 14 Old 11-18-2012, 11:18 PM
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On my vt50 it works pretty good, how is it buggy?

It's buggy because the input single gets modified by brightness and contrast before it gets to the 10 point system.

That means a pattern with level 126 (50%), might get pushed down to 118. Now your 50% pattern modified so it lands between 40% and 50%. Now if you change the 40% control it will effect the measurement of the level 126 pattern. Adjust the 50% control and you'll also change the level 147 pattern (60%).

So it puts you in a tough spot, which is why CalMAN asks you to set brightness and contrast to default locations before using AutoCal.

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post #9 of 14 Old 11-19-2012, 04:53 AM
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sotti,

So is this only an issue with autocal because it makes one pass through the settings where with a manual calibration, the user would likely make several passes to make these corrections?

On the VT50s, adjusting grayscale RGB in equal amounts to effect a change in gamma doesn't cause the same issue for autocal?

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post #10 of 14 Old 11-19-2012, 07:59 AM
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Quote:
Originally Posted by JimP View Post

sotti,
So is this only an issue with autocal because it makes one pass through the settings where with a manual calibration, the user would likely make several passes to make these corrections?
On the VT50s, adjusting grayscale RGB in equal amounts to effect a change in gamma doesn't cause the same issue for autocal?

It's an issue period.

Most Instructors I see teach manual calibrations should start at one end and work your way through to the other.

This catches MANY professional calibrators in the field, we know, we take their support phone calls. But you are correct doing single adjustment multiple pass does seem to give better results, I think I may have mentioned we are continuing to refine AutoCal.

Also the way the VT50's controls work the RGB balance controls have little to no effect on gamma. I'm not entirely sure how panasonic designed their system, but as you remove red, it adds a corresponding amount of green and blue to keep luminance about the same.

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post #11 of 14 Old 11-19-2012, 10:44 AM
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I seriously thought it was meant to work like that, and you just have to do multiple passes like many other calibration things. I manage to get a flat gamma line at 2.22 though. The way I do it is first two point white at 20% and 80%, then I use the gamma module to do 10 point whitebalance and 10 point gamma at the same time, then color, then usually touch up white and then its done, color hardly changes after the whitebalance touchup. I get whitepoint all but 10% below dE 0.8, color all below dE 0.8 except blue, saturation seems really stuck too low, get it to dE 1.3, gamma steady at 2.22.
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post #12 of 14 Old 11-19-2012, 02:04 PM
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Quote:
Originally Posted by Wouter73 View Post

I seriously thought it was meant to work like that, and you just have to do multiple passes like many other calibration things. I manage to get a flat gamma line at 2.22 though. The way I do it is first two point white at 20% and 80%, then I use the gamma module to do 10 point whitebalance and 10 point gamma at the same time, then color, then usually touch up white and then its done, color hardly changes after the whitebalance touchup. I get whitepoint all but 10% below dE 0.8, color all below dE 0.8 except blue, saturation seems really stuck too low, get it to dE 1.3, gamma steady at 2.22.

Similar to my process - I seem to have a nightmare with 90IRE gamma though - not once has it settled to a linear point in respect of the other IRE's, 1 notch on the gamma slider introduces a drastic change but never settles on the target - much prefer the Sammy system if im honest. Heres my latest. TXP55VT30b Calibration.pdf 129k .pdf file
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File Type: pdf TXP55VT30b Calibration.pdf (128.9 KB, 27 views)

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post #13 of 14 Old 11-20-2012, 03:58 AM
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I have the same with 90 ire, 1 tick different setting makes a large difference. I lucked out though, it settles on about 2.20 on my set, close enough for me :P
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post #14 of 14 Old 11-20-2012, 08:58 AM
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Just a general note... there's no such thing as IRE when it comes to digital video. It is widely misused, and often by people who should know better (like manufacturers). IRE is an analog video term that refers to how the analog input voltage translates to measured luminance. Since there's no analog input voltage for digital video displays, IRE simply doesn't exist. In digital video, digital levels (0-254 or 16-235) or % White should be used. When IRE is used properly, there are times when 7.5 IRE could be BLACK.... you don't want to get into that possible confusion factor. Everybody will know what you're talking about if you use % white or digital levels. AVIA discs use IRE correctly and that tends to make them confusing at times for some users because of the issue with 7.5IRE being black rather than 7.5% white. Other discs and hardware I've seen that use IRE are equating it with % white so it's less confusing, but still not technically correct.

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