The consistency of the white point with the input gray level is referred in the world of display technology as gray tracking. Gray tracking is an issue for Twisted Nematic (TN) TFT-LCD screens which typically show a bluish color shift of the white point when the gray level decreases. This paper discusses some causes of this color shift in TN displays and proposes a method for correcting it by using the existing video card look-up tables (VLUT) in the graphic controller driving the panel. The correction process performs the gamma correction and the gray tracking correction using a single set of three 1D look-up tables. The gray tracking correction uses the luminance and the chrominance information of the R, G, B channels.
For a target gamma and white point, each VLUT entry that corresponds to a certain luminance and chrominance (target color), the method computes the output RGB values of the VLUT such that, the resulted gray has the minimum color difference to the target color. The method proves to be effective in removing the colorcast on the TN TFT-LCD screens. The method is different from a previous published paper from the same author by minimizing the loss of the luminance due to the tuning of the chrominance.