Monitor Parameter Adjustment

How to visually determine your monitor's gamma parameter

The following table contains columns of color triples at different intensity levels for each of the three color channels. The center patches and the two surrounding patches may look different. The following steps may be used to determine a monitor's gamma parameter:
  1. Turn off the room lights if you want "colorimetric" settings. Use your normal working environment if you want "working environment" settings (whatever that means).
  2. Switch your browser to full screen display.
  3. Adjust your monitor's brightness setting such that black areas are black and the lowest intensity color patches are barely visible. You may use a CVD low intensity test image which contains very low intensity steps. Nine of the ten low intensity patches should be visible.
  4. Adjust your monitor's contrast setting as high as possible. You may use the CVD high intensity test imagewhich contains very high intensity steps. Nine of the ten patches should be different from the highest intensity white.
  5. For each color channel scroll the table horizontally until you find that column where the visual difference between the center and the surrounding patches is smallest. The respective number printed in that column is your monitor's gamma parameter for that channel. If you need a single gamma parameter for all three channels choose the column with the smalles over all difference between center and surrounding patches for all color channels.
There are some more video test images contained in the CVD home page.

 

 

 

 

 

1.30 1.40 1.50 1.60 1.70 1.80 1.90 2.00 2.10 2.20 2.30 2.40 2.50 2.60 2.70 2.80 2.90 3.00 3.10

 

 

 

 

 

1.30 1.40 1.50 1.60 1.70 1.80 1.90 2.00 2.10 2.20 2.30 2.40 2.50 2.60 2.70 2.80 2.90 3.00 3.10

 

 

 

 

 

1.30 1.40 1.50 1.60 1.70 1.80 1.90 2.00 2.10 2.20 2.30 2.40 2.50 2.60 2.70 2.80 2.90 3.00 3.10

 

 

 

 

 

How does it work?

Suppose the gamma function is L = E**g with E being input voltage and L being luminance output. Then the input voltage necessary to create pixels with luminance L/2 can be computed by L/2 = (E**g)/2 = (E/(2**(1/g)))**g using the gamma parameter value g. Thus a patch where each pixel has input voltage (E/(2**(1/g)))**g has halve of the luminance of a patch where each pixel has input voltage E. A patch with halve of the luminance of the homogenous patch with input voltage E, however, may also be created by only controlling every second pixel with voltage E and setting every other pixel to zero luminance. If the gamma parameter g is correct then both patches should look equal if the viewing distance is large enough. Also, it is crucial to avoid crosstalk between pixels and thus the usual method is not to control every second pixel but to control every second video line by input voltage E and every other line by zero input.

The method above assumes that there is no incident light from secondary illuminant sources on the screen. This usually is a wrong assumption. To take this into account one has to use a different gamma function with more than a single parameter.