Scale and bias operations can be used to adjust the colors of images. Also, they can be used to select and expand a small range of values in the input image. Scales and biases are applied at several locations in the pixel transfer pipeline. In general, scales and biases are controlled with eight floating point values (a scale and a bias for each channel).
The first scale and bias in the pixel transfer pipeline is part of base OpenGL and is specified with glPixelTransfer<pname>, <value>(<pname>, <value>) where <pname> specifies one of GL_RED_SCALE, GL_RED_BIAS, GL_GREEN_SCALE, GL_GREEN_BIAS, GL_BLUE_SCALE, GL_BLUE_BIAS, GL_ALPHA_SCALE, or GL_ALPHA_BIAS. Other sets of scale and bias values are associated with the color matrix extension (SGI_color_matrix) and the convolution extension (EXT_convolution), both of which are part of the imaging subset of OpenGL 1.2.