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 | 1 | initial version |
Gamma and brightness are not the same operations. Brightness is a linear operation, gamma is nonlinear; gamma affects only the grays.
However I think there are several different operations to change the brightness of an image:
Add or substract a constant. Take care of the overflow (values above 255 must be truncated to 255; negative values to 0). This is basically your method 2.
A variant would be to work in the HSV color space and change the V channel, then go back to RGB (your method 1).
The drawback of this method is that it clips the image to 0 or 255.
Multiply the image with a constant. This is similar to berak's suggestion, but the formula is a bit different for lightening.
The algorithm is: if the value<1 (darken), then image_out=image_in*value
If value>1 (lighten) then v2=2-value and image_out=image_in*v2+(1-v2)*255
This method won't clip the image. Most programs use this method.
For all these operations you can use direct operations or color lookup (creating LUTs). I didn't test which solution is faster.
| | 2 | No.2 Revision |
Gamma and brightness are not the same operations. Brightness is a linear operation, gamma is nonlinear; gamma affects only the grays.
However I think there are several different operations to change the brightness of an image:
Add or substract a constant. Take care of the overflow (values above 255 must be truncated to 255; negative values to 0). This is basically your method 2.
A variant would be to work in the HSV color space and change the V channel, then go back to RGB (your method 1).
The drawback of this method is that it clips the image to 0 or 255.
Multiply the image with a constant. constant (between 0 and 2). This is similar to berak's suggestion, but the formula is a bit different for lightening.
The algorithm is: if the value<1 (darken), then image_out=image_in*value
If value>1 (lighten) then v2=2-value and image_out=image_in*v2+(1-v2)*255
This method won't clip the image. Most programs use this method.
For all these operations you can use direct operations or color lookup (creating LUTs). I didn't test which solution is faster.
