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...

The colorimetric characterization of computer-controlled CRTdisplays require radiometric measurements with high precihion and accuracy in order to achieve acceptable colorimetric accuracy in defining stimuli generated with this type of imaging modality. Precision und accuracy requirements for photometers, colorimeters, and spectroradiometers were evaluated. When models are used to relate digital counts de'ning a stimulus and resulting spectrul radiant exitance, displays are assumed to exhibit channel and spatial independence. A variety of tests and the results of evaluating four imaging systems are described. From these analyses, measurement accuracy is mainly limited by wavelength scale in the case of spectroradiometers and'lterjit in the case of colorimeters. Measurement precision is limited by the number of signijicant figures f o r fixed-range devices und signal-to-noise limitations for low-luminance stimuli. Display accuracy is limited by u luck of channel and spatiul independence. Display precision is mainly limited by the electronic design of the display and the stability and load independence of the gun ampli'ers. 0 1993 John Wiley & Sons, Inc.

No abstract

This paper describes a visual experiment in which a group of observers made forced choice judgments of the location of neutral in test images presented on a color CRT display and photographic reflection prints. The . CRT and photographic images were presented both separately and side-by-side in a simulated office environment under two conditions of ambient illumination, tungsten and daylight fluorescent. The results indicate that an observer's state of chromatic adaptation during image viewing is mainly dependent on image areas with little or no dependence upon the surrounding environment. With reflection images viewed in normal conditions, observers were noted to automatically discount ambient illumination.When viewing self-luminous images however, observers formed relative judgements only under certain conditions. These results are discussed in terms of their use in choosing white points for color reproduction calculations.