L_BM_GAMMACORRECT

Send this message to adjust the intensity of colors in an L_BITMAPCLASS window's bitmap by changing the gamma constant that is used to map the intensity values.

Intensity values ideally follow a logarithmic progression, because the eye perceives changes in intensity as being equal when the ratio of change is equal. For example, we would see a change from 0.1 to 0.2 as being equal to a change from 0.2 to 0.4.

Gamma is a standard constant that is used to calculate the progression. For most CRTs the gamma constant is in the range of 2.2 to 2.5.

Parameter	Meaning
wParam	Specifies whether the window should be redrawn to reflect the image changes. Use 1 to redraw the window, or 0 not to redraw it.
lParam	The low order of the lParam parameter should contain an unsigned integer that represents the gamma value. Because this is an unsigned integer, it is 100 times the actual gamma value. For example, use 235 to set a gamma value of 2.35.

Returns

SUCCESS	Function was successful.
< 0	An error occurred. Refer to Return Codes.