CGTalk Questions about Gamma / Human Perception
 03-31-2013, 03:32 PM #1 Freuling New Member portfolio Ariel DDDDD, Israel   Join Date: Nov 2011 Posts: 2 Questions about Gamma / Human Perception I am very new to 3D graphics, and I am struggling to understand the concepts of Gamma, Linear, Log, Exponential... I apologize if this this has been asked a lot; I did read about gamma correction but I still have some things I want to clarify. So first, a capturing device records in linear format, then a gamma of 2.2 is applied to compensate for the 0.454 gamma of the monitor, thus making it linear again, am I right so far? Now say we have a gradient, divided to 10 shades, 0 being the lowest value, and 255 the highest. The values go like this (equal size steps of 28.33): 0, 28.33, 56.67, 85, 113.33, 141.67, 170, 198.33, 226.67, 255. But when I think of light as like candles, if I have 10 steps, each step I light another candle, the difference between the first step (unlit candle) and the second is huge, and between the second and the third is double, but the difference between the 9th and 10th is very small. Is it something to do with human perception not being linear? Would a creature with linear vision perceive these steps as equal steps? Why the values in the color picker are not exponential? For example 1 to 255 in 10 steps as: 1, 1.85, 3.43, 6.34, 11.74, 21.73, 40.21, 73.43, 137.77, 255. Is it just to make it more comfortable or something? I don't get it... =[ I really need an in-depth explanation for those things... share quote
04-01-2013, 06:03 PM   #2
colesslaw
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Sherrie Law

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First of all I am no scientist, but I will try to explain my understanding of this.

Quote:
 Originally Posted by Freuling So first, a capturing device records in linear format, then a gamma of 2.2 is applied to compensate for the 0.454 gamma of the monitor, thus making it linear again, am I right so far?

Yes and no. Yes the capturing device is always capturing light data as-is, in this case linear. However the gamma of 2.2 has more to do with file encoding (data-compression) than to do with compensating for the monitor. The human eyes cannot distinguish high spectrums of light very well, so it is a waste of data to store those values in a file when we cannot see them. A gamma of 2.2 is for crushing the bright values and so we are only storing the darker spectrum of light (the images become "washed-out"). Most images (like JPEGs) are encoded with sRGB which is equivalent to the gamma 2.2, and the sRGB color profile is attached to the image to tell the monitor how to handle this type of file. The monitor will apply 0.454 to crush the dark spectrum again so the image is no longer "washed-out".

Quote:
 Originally Posted by Freuling Is it something to do with human perception not being linear?

Yes human perception is not linear.

Quote:
 Originally Posted by Freuling Why the values in the color picker are not exponential? For example 1 to 255 in 10 steps as: 1, 1.85, 3.43, 6.34, 11.74, 21.73, 40.21, 73.43, 137.77, 255. Is it just to make it more comfortable or something?

Not sure why you want the color picker range to be exponential... but in general linear numbers are easier to work with?

Here is a good read for linear workspace:
http://www.seazo.no/linear-workflow
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 04-01-2013, 06:03 PM #3 CGTalk Moderation Lord of the posts   Join Date: Sep 2003 Posts: 1,066,481 Thread automatically closed This thread has been automatically closed as it remained inactive for 12 months. If you wish to continue the discussion, please create a new thread in the appropriate forum. __________________ CGTalk Policy/Legalities Note that as CGTalk Members, you agree to the terms and conditions of using this website. share quote