David L. MacAdam

Dr. David L MacAdam joined the colorimetry section of the Physics Department of the Eastman Kodac Co, Rochester, NY. In July 1936, He did research on the methods of colour measurement employing a spectrophotometer and on the application of these methods to a study of the accuracy of colour reproduction in colour photography and printing.

Dr. MacAdam extended the theory of colour photography based upon the characteristics of human vision and spectrophotometric characteristics of dyes and pigments. He also conducted an investigation of visual senitivities to small colour differences and the influence of visual adaption to colour on perceptions of colour and colour photography and colour television

Using an ingeniously designed colorimeter, MacAdam arranged that by turning a single control knob, the colour of one half of the 2° visual field was varied along a straight line in the CIE chromaticity diagram, while its luminance was held constant. The matching field was surrounded by a 42° diameter surround field having a chromaticity similar to that of CIE illuminant C and a luminance of 7.5 millilambert. Repeated colour matches were made between the variable light and a fixed light of the same luminance occupying the second half of the visual field. The chromaticity of the fixed light was located on the given straight line in the CIE chromaticity diagram. The standard deviations of the settings were determined, a setting being specified by the distance in the chromaticity diagram between the variable and the fixed chromaticity points. MacAdam's extensive auxiliary experiments on just-noticeable colour difference indicated that for the same observer these are proportional to the corresponding standard deviations of colour matching, the just-noticeable difference being about three times as large as the standard deviation.

	Ellipse representing just noticeable differences of chromaticity. Based on experimental results obtained by MacAdam's observer PGN.

For the variable light several straight lines intersecting in a common fixed chromaticity were used in turn, and the resulting standard deviations of colour matching were plotted as distance Ds along these lines measured from the central fixed chromaticity point. The end points fell closely on an ellipse whose size, shape, and orientation changed when the whole procedure was repeated with a new fixed chromaticity point

Discrimination ellipses in 1931 CIE Chromaticity Diagram as observed by MacAdam's observer P G Nutting.
Centre		Ellipse parameters
x0	y0	103a	103b
0.160	0.057	0.85	0.35	62.5
0.187	0.118	2.20	0.55	77.0
0.253	0.125	2.50	0.50	55.5
0.150	0.680	9.60	2.30	105.0
0.131	0.521	4.70	2.00	112.5
0.212	0.550	5.80	2.30	100.0
0.258	0.450	5.00	2.00	92.0
0.152	0.365	3.80	1.90	110.0
0.280	0.385	4.00	1.50	75.5
0.380	0.498	4.40	1.20	70.0
0.160	0.200	2.10	0.95	104.0
0.228	0.250	3.10	0.90	72.0
0.305	0.323	2.30	0.90	58.0
0.385	0.303	3.80	1.60	65.5
0.472	0.399	3.20	1.40	51.0
0.527	0.350	2.60	1.30	20.0
0.475	0.300	2.90	1.10	28.5
0.510	0.236	2.40	1.20	29.5
0.596	0.283	2.60	1.30	13.0
0.344	0.284	2.30	0.90	60.0
0.390	0.237	2.50	1.00	47.0
0.441	0.198	2.80	0.95	34.5
0.278	0.223	2.40	0.55	57.5
0.300	0.163	2.90	0.60	54.0
0.365	0.153	3.60	0.95	40.0