Table 1.

The RGB Values Used in the PeekCS Test^a

Score Stage	Optotype Gray RGB Value	Background Gray RGB Value	Actual Peek CS Log10 (CS)	Standard Error	Pelli-Robson Log10 (CS)	Contrast
1	0	255	0.006	0.000007	0.00	Highest
2	164	255	0.20	0.00040	0.15	E
3	197	254	0.35	0.000625	0.30
4	216	255	0.50	0.00026	0.45
5	229	255	0.65	0.001225	0.60
6	237	255	0.78	0.00306	0.75
7	242	254	0.96	0.00208	0.90
8	246	255	1.06	0.03935	1.05
9	248	255	1.16	0.0017	1.20
10	250	254	1.40	0.01185	1.35
11	250	253	1.53	0.0184	1.50
12	252	255	1.67	0.00475	1.65
13	246	248	1.71	0.00875	1.80
14	252	254	1.94	0.0034	1.95
15	254	255	2.00	0.0076	2.10	E
16	N/A	N/A	N/A	N/A	2.25	Lowest

N/A, not applicable; RGB, red, green, blue.

^aDesigned for a Sony Xperia Z3 for each Score Stage and the corresponding actual CS measured by a photometer in a darkened laboratory setting. Owing to the finite combinations of optotype and background grays, it is not possible to have an exact alignment between the contrast sensitivities tested with PeekCS and the Pelli-Robson charts. However, the difference between the two tests is never more than two-thirds of the difference between score stages (i.e., 0.10 log units).