Table 2.

Mean and SD of the residuals (absolute values, in %) of linear regression models between visual and optical erythema evaluation, relying on different erythema indices (EI: RG–EI_RG, GR–EI_GR, BRG–EI_BRG, BG–EI_BG, and a*) and image-sampling methods (ISM: PT–60 pixels, SQ2–two small squares, SQ1–one big square).

ISM\EI	RG	GR	BRG	BG	a*	Mean
PT	11.7 ± 0.7	11.7 ± 0.6	11.6 ± 0.5	12.7 ± 0.6	12.1 ± 0.3	12.0 ± 0.7
SQ2	11.9 ± 1.0	11.9 ± 0.8	11.6 ± 0.8	12.6 ± 0.8	12.3 ± 0.5	12.1 ± 0.8
SQ1	12.2 ± 0.7	12.3 ± 0.6	12.0 ± 0.5	12.9 ± 0.9	12.4 ± 0.3	12.4 ± 0.7
Mean	11.9 ± 0.8	12.0 ± 0.6	11.7 ± 0.6	12.7 ± 0.7	12.3 ± 0.4