Color Sequences for Univariate Maps: Theory, Experiments and Principles

ABSTRACT

Pseudocoloring for presenting univariate map information on a graphic display system is investigated. The kinds of information available in maps are divided into two classes: metric information denotes the quantity stored at each point on the surface, and form information denotes the shape or structure of the surface. Theoretical principles are proposed to predict which color sequences will be effective at conveying value and form information respectively. According to this theory, a scale that approximates the physical spectrum should be good at conveying value information, because of the reduced effects of simultaneous contrast. It should be poor at conveying form information, however, because the brain prefers form information to come through the lightness-processing channel. Conversely, a gray scale should be poor at conveying value information and good at conveying form information, according to the same theory. These predictions are tested in a series of psychophysical experiments that test five color sequences. The results show that simultaneous contrast can be a major source of error when reading maps, but only partially confirm the form hypothesis. Guidelines are given for designing color sequences to be effective in both conveying form and value information. An experimental color sequence is presented to illustrate these guidelines.

REFERENCES

• 1: 1. C. Ware, "Choosing a Colour Sequence for Univariate Maps," <i>Proc. IEEE Conf. on Systems, Man and Cybernetics</i>, Vol. 1, New York, Oct. 1986, pp. 41-45.
• 2: 2. W.S. Cleavland and R.A. McGill, "A Color-Caused Optical Illusion on a Statistical Graph," <i>American Statistician</i>, Vol. 37, No. 2, May 1983, pp. 101-105.
• 3: A M Heath , R B Flavell, Colour coding scales and computer graphics, Proceedings of Graphics Interface '85 on Computer-generated images: the state of the art, p.307-318, January 1986, Montreal, Quebec, Canada
• 4: 4. P.K. Robertson, and J.F. O'Callaghan, "The Generation of Color Sequences for Univariate and Bivariate Mapping," <i>CG&A</i>, Vol.6, No. 2, Feb. 1986, pp. 24-32.
• 5: 5. J. Tajima, "Uniform Color Scale Applications to Computer Graphics," <i>Computer Vision, Graphics and Image Processing</i>, Vol. 21, No. 3, 1983, pp. 305-325.
• 6: 6. C. Ware, and W.B. Cowan, "Changes in Perceived Colour due to Chromatic Interactions in Striped Test Fields," <i>Vision Research</i>, Vol. 22, No. 11, 1982, pp. 1353-1363.
• 7: 7. L.M. Hurvich, <i>Color Vison</i>, Sinauer Associates, Sunderland, Mass., 1981, 328 pp.
• 8: 8. C. Ware and W.B. Cowan, "Chromatic Mach Bands: Behavioural Evidence for Lateral Inhibition in Color Vison, <i>Perception and Psychophysics </i>, Vol. 41, No. 2, 1987, pp. 173-178.
• 9: 9. G. Wyszecki and W.S. Stiles, <i>Color Science: Concepts and Methods, Quantitative Data and Formulae</i>, John Wiley & Sons, 2nd edition, New York, 1982.
• 10: 10. F. Kingdom and G. Moulden, "Digitized Images: What Type of Gray Scale Should One Use?" <i>Perception</i>, Vol. 15, No. 1, 1986, pp. 17-25.
• 11: 11. Commission Internationale de L'Eclairage (CIE), "Recommendations on Uniform Color Spaces, Supplement #2 to CIE Publication #15," Paris, (E-1.3.1), 1971.
• 12: William B. Cowan, An inexpensive scheme for calibration of a colour monitor in terms of CIE standard coordinates, Proceedings of the 10th annual conference on Computer graphics and interactive techniques, p.315-321, July 25-29, 1983, Detroit, Michigan, United States
• 13: 13. K.Y. Mullen, "The Contrast Sensitivity of Human Color Vision to Red-Green and Blue-Yellow Chromatic Gratings," <i>J. Physiology</i>, 359, 1985, pp. 381-400.
• 14: 14. S.M. Anstis and P. Cavanaugh, <i>A Minimum Motion Technique for Judging Equiluminace in Colour Vision: Physiology and Psychophysics </i>, J.D. Mollon and L.T. Sharpe, eds., Academic Press, London, 1983, pp. 156-166.
• 15: 15. R.L. Gregory, "Vision with Isoluminant Color Contrast: 1 A Projection Technique and Observations," Perception, Vol. 6, No. 1, pp. 113-119.