Calibration of a color monitor for visual psychophysics

Abstract

It has become common for stimuli used in visual psychophysical experiments to be presented on high-resolution color cathode-ray tubes (CRTs) such as the Barco CDCT 6551. These enable a flexibility of color, spatial-frequency content, temporal-frequency content, duration, size, and position that is not provided by most other media. CRTs are, however, not perfect; they suffer from the effects of temporal instability, spatial variability, lack of phosphor constancy, gun interdependence, and gun nonlinearity. This paper describes methods of assessing these aspects of monitor performance with respect to how significant each may be in psychometric terms. Although every application of CRT use in visual psychophysics is different, some general rules can be formulated to help ensure that unwanted effects are kept to a minimum. For the CRT used in this study (Barco CDCT 6551), a warm-up time of 30-45 min is necessary before chromatic and luminous stability ensues. Restriction of individual gun outputs to within 10%-90% of the possible range ensures that the effects of gun interdependence and lack of phosphor constancy are negligible. Calibration methods dealing with the linearization of gun output are also discussed.CRT (cathode-ray tube) technology offers a unique opportunity to display a variety of visual stimuli. The advantages offered by CRTs over other media include flexibility of color, size, position, and presentation duration as well as spatiotemporal frequency content of the stimuli. A major disadvantage of the CRT is that the maximum light output achievable is limited, compared with other display techniques such as Maxwellian view. This is still well into the photopic range, as is borne out by observing that images are in fact colored on CRT screens. Color CRTs have three channels, so it is possible and desirable to describe their output in terms of a mixture of three independent primaries, although, as will be shown, strict independence is not achieved. In order to determine the limitations that may exist in applying CRTs to the study of the human visual system, we have undertaken a thorough study of the colorimetric aspects of a Barco CDCT 6551 monitor that was used in our laboratory. We believe that this high-resolution color monitor is likely to be used in other laboratories and that the information provided in this paper will be useful to others. Moreover, the techniques described here can be applied to other brands and models of CRTs and should provide a useful reference for those unfamiliar with this technology or colorimetry. 1This work was supported byARC Grant A79030414 andNH& MRC Grant 890568 to A.J.Y. We thank George Smith for his consultation and helpful comments on the manuscript. We also thank two anonymous reviewers for their very useful comments. Address correspondence toA. Metha, Department ofOptometry, University ofMelbourne, Parkville YIC 3052, Australia.In the present study, we consider several aspects of monitor performance: temporal stability, spatial variability, phosphor constancy, gun i...

Tell me, what did you see? The stimulus on computers

“…If the data are published, these calibration routines should be better reported in the method sections. Metha et al (1993) and Olds et al (1999) give some examples for display calibration techniques. Brainard (1997) has a nice bibliography on psychophysics that lists many articles related to monitor calibration.…”

“…In addition, these values will be different for each of the primaries, so each primary needs to be calibrated independently (see Olds, Cowan, & Jolicoeur, 1999, for a procedure for determining the gamma ofa system). These values are not fixed until the display has warmed up, usually about 20-30 min (Metha, Vingrys, & Badcock, 1993).…”

Using MATLAB with the Psychophysics Toolbox to present the heterochromatic fusion nystagmus stimulus

“…The contents of this file would vary on the basis of individual monitor characteristics. For information on creating such a linear CLUT, the reader is referred to Metha, Vingrys, and Badcock (1993) and Olds, Cowan, and Jolic ur (1999).…”

“…This is due to the fact that for the vast majority of monitors, the relationship between RGB values and luminance is nonlinear and instead follows a gamma function. For more information on monitor nonlinearityand related issues, the reader is referred to Metha et al (1993) and Olds et al (1999).…”

Assessing the monitor warm-up time required before a psychological experiment can begin

“…Despite their advantages, however, computer monitors also have a number of limitations that must be taken into account before they can be used in psychological and neuroscientific experiments (Bauer, 2015;Elze & Tanner, 2012;Klein, Zlatkova, Lauritzen, & Pierscionek, 2013;Metha, Vingrys, & Badcock, 1993). Doing so is complicated by the fact that the specific stimulus (Goris, Wagemans, & Wichmann, 2008), the stimulus presentation software, the specific monitor technology (Foerster, Poth, Behler, Botsch, & Schneider, 2016;Poth, Foerster, Behler, Schneider, & Botsch, under review) and even the individual monitor (e.g.…”