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Discussion Starter · #1 ·

Hi all,

 

I have a couple of questions and I hope anyone can answer them or point me in the right direction:)

 

The Nexus 5 (Android smartphone;)) community has discovered a way to change their display.

After a while we realized that it was a Lookup-table. But we had another settings that the original LG developer called the white point.

The white point is adjustable from 0 to 255, but it is the range is 0-63, 64-127, 128-191, 192-255. (So 0 equals 64 equals 128 equals 192)

I can confirm this does adjust the white point like you can adjust the white point in the curves adjustment tool in Photoshop CS6 (and previous versions).



 

I just have a hard time seeing the connection between the white point and the colour temperature. Can anyone point me in the right direction? And have you seen settings for the white point like this before?

 

 

Furthermore, as I'm trying to develop an app for the Nexus 5 community that calibrates their screen correctly, I need to find proper images that measure gamma.

There is an app called Display Tester App that provides these kind of images, but I noticed it is flawed for our screen.



 

The gamma image is made up of a background and rectangles. The background is filled with a pattern (0;255 RGB) whilst the rectangle is filled with one colour.

I discovered that the connection between the background and rectangle was the following:

 



 

The outcome of this equation is 186, the value that should match the background if the screen is properly calibrated with gamma 2,2.

The problem is however, that this method only uses 3 values: 0, 186, 255. It's already assuming 0 and 255 are calibrated and then calibrates 186.

This is just one value out of 256. So what I did, is change the background and thereby calibrating another RGB value. This is however flawed, as a background using 0;200, uses the non calibrated value of 200.

 

 

Then I discovered that I could incorporate the White Point in it using this formula:



 

In this formula 2,2 is the gamma, 255 is the difference in background (255-0) and 32 is the white point (The range is 0 to 63, so add 1 up to 0).

 

I can change the outcome of the equation this time without changing the background. This avoids the problem of relying on non calibrated values.

 

My question here is the following: Is this way of measuring gamma correct?

 

 

And just one last question:)

I noticed that calibration software like HCFR gives the user an indication of what the gamma should be. It shows however that gamma should not be 2,2 in the shadows. Is this true?

 
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