Gamma 2.2 : a lot of doubt :(

[Vympel]

Hello,

i have many doubt on this argument: the gamma: what's exactly?

I my research i found that the CRT monitor has a non linear respons of the colour.

1° QUESTION - Why the monitor has this behavior? What rappresent the 2.2 number?


http://perso.orange.fr/colorid/iso_album/gamma_courbe.jpg



Gamma is mathematical operation (power) used to adjust a image, this function normally preserve the back and white points (prevents cliping). The monitors have this behavior for a better exhibition of colors (our eyes works non linearly , it imitates the way with that the people see the colors). The number 2.2 represent the inverse exponent (1/2.2) used in the gamma function, the correct number (whithout inversion) is approximately 0.45. This number is just an approach of the one more complex expression, that it defines the sRGB color space

2° QUESTION - In Windows XP the colors hat i see in my CRT are correct? Or i need to color correct?

3° QUESTION - If they are correct, who have corrected them?



The monitor have a standard, but with time the accuracy of color can be reducted. To keep the accuracy you need adjust the color profiles of your OS and use the settings of monitor like brightness and contrast to keep the precision

4° QUESTION - Why many persons go to monitor calibration ? Which benefits can give of monitor calibration??

People that work to determined segments (film, print) need to see the images in your monitors equal in the final output

5° QUESTION - Photos on my digital camere, or scanned images, are il linear space or not?

Probably this camera use the sRGB color space (a industry standard)

6° QUESTION - How i can calibrate your monitor for 2.2 gamma output. Or better, my monitor (Sony trinitron CRT 21") is already automatically calibrated to this number?

This monitor is calibrated, but to survey the precision of color you can use softwares and hardware to calibrate the monitor


And now the more important question...

7° QUESTION - In 3dsmax Customize/Preferences/Gamma dialog there are meny parameter. How I can use them?

read the help?

[jasonsco]

Pretty good reply, Vympel. The most important thing here is that our eyes work non-linearly (which you pointed out). This is important because of you decide to make an image half as bright, in linear color space, half the value won't look like half to our eyes. An image that is half as bright to our eyes is around 18% as bright.

[payton]

ok, guys.
seems like you know the basics about gamma. maybe you can help me with this question.

lets say i will shoot the holy "18% grey card" which looks middle-gray for us with a videocamera. the card will get gamma corrected with a gamma of appr. 0,45 while shooting and the rgb values will be something about 128 per channel in 8-bit. everything fine until now.
assuming that i use a crt with the appr. inverse gamma of about 2,5 the gray will be re-darkened and will look like the 18% grey card at the beginning. our eyes, as mentioned above, with a gamma of approx. 0,45 brightens the image and we interprete it as "middle grey"

let me know if i missed something until know...

that all sounds pretty nice and logical. but now my gamma-hell starts. can´t sleep right now because of that...

as far as i understand rgb values of 128 must look like middle grey. but all the gamma test-charts (http://www.graphics.cornell.edu/~westin/gamma/ward.png) around are showing clearly that rgb values of about 190 will be like middle-grey.

why??????? please help me. im getting crazy about that.

thx in advance,
payton

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