Heterochromatic brightness matching with checkerboard patterns.

Heterochromatic brightness matches with checkerboard patterns made up of a white reference and a chromatic test element for various element sizes from 3' to 2 degrees 30' square and with a 5 degrees bipartite field were carried out with a color cathode-ray tube. The brightness-to-luminance (B/L) ratios of six chromatic stimuli were obtained, and the brightness additivity for the mixture of red and green was tested. When the reference and test elements were juxtaposed without a gap, the B/L ratio of the test chromatic stimulus decreased with decreasing element size. Brightness additivity failed for an element size of 30' and a 5 degrees bipartite field. Brightness additivity held for a small element size of 3'. When the reference and test elements were separated by a gap 3' in width, the B/L ratios were generally greater than unity regardless of element size. Under these conditions, the brightness additivity also failed for the smallest, that is, the 3' element size.