CRT colorimetry. part I: Theory and practice

Abstract

The rrlationship was derived for computer-controlled color CRT displays between spectral radiant exitance emitted and digital counts. The derivation was historical and could be traced to pioneering work in photographic sensitometry, vacuum tube physics, and broadcast television. By performing radiometric measurements relative to a display's maximum exitance, the model simplijied to a two-stage model. The jirst stage was a nonlinear transformation relating normalized digital-to-analog converter values to device-dependent monitor tristimulus values using model parameters of gain, offset, and y . The second stage was a linear transformation where the device-dependent monitor tristimulus values were transformed to device-independent CIE tristimulus values. By using the model, colorimetric characterization accuracy of better than 0.5 CIELAB color-difference units for 125 colors sampling the display color gamut was achieved by measuring the CIE tristimulus values of only eight colors. The model had equivalent performance to methods using extensive measurements and table lookup. 0 1993 John Wiley & Sons, Inc. CCC 0361 -231 7/93/050299-16 299Video voltage. Voltage of red, green, and blue analog video signals from host computer video-signal generator. These are assumed to be linearly quantized from DAC values dr,dg,db using a standard similar to EIA RS-170. The red, green, and blue video signals are assumed to be independent of each other and of pixel position. Minimum and maximum video signal voltage. EIA RS-170 specifies values of about 0.05 and 0.71 V.These are assumed to be the same for all three channels and for all pixels.Grid voltage. Voltages applied to first control grids for red, green, and blue CRT guns. These voltages are amplified from video voltages vr,vg,vb with gains ar,ag,ap and offsets b,,bg,bb. The grid voltages are assumed to be independent of each other and of pixel position. Cutoff voltage. These are the values of vG,,. v~,~, and vG,b that correspond to zero beam currents jrJgrjb. DAC values. Discrete integer values converted to red, green, and blue analog video voltages v,,vg,,vb by the computer video-signal generator. The digital-to-analog conversion (DAC) is assumed to be linear.These DAC values are computed by the video-signal generator using image and lookup table (LUT) data. In computer graphics literature, image data, LUT data, DAC data, and CRT tristimulus values are all called R, G, and B. Previous literature about CRT colorimetry has referred to these as "digital counts" or "DAC values." DAC quantization depth. Number of bits used in digital-to-analog conversion of d,,dg,db to vr,vg,vb.Common quantization depths include 1, 2, 4, 6 , 8, 10, and 12 bits. Channel gain. Gain factors used in amplification of video voltages vl , vg, vb to grid voltages v~,~. v~,~, VG.6. These gains are assumed to be constant regardless of video voltage or of pixel position. Channel offset. Offset factors used in amplification of video voltages vr,vg.vb to grid voltages v~,~. v~,~, v~,~. These offsets are assumed...

Digital color imaging

“…Berns et al [125] report an accuracy around 0.4 using only eight measurements for determining model parameters. However, the gamut of CRT tubes is limited by the phosphors used, which causes significant color errors for colors that lie beyond the gamut.…”

ADICT: Accurate Direct and Inverse Color Transformation

“…Here, to estimate T we need to reconstruct h l in addition to M [2]. This involves measuring color output at k uniformly sampled channel inputs i l when inputs to the other two channels are zero.…”

Computational models for fusion of texture and color: a comparative study

“…CRT display. The characterization of the display was carried out using the gain, offset, and gamma ͑GOG͒ model, 16 and the RGB values of the texture images can be transformed to the corresponding CIELAB values according to the model. For each pixel, its color difference ⌬E ab * to the mean color is calculated in the CIELAB space.…”