Hi Jolyon, Hi Cedric,
Is it possible to get negative values when converting an image from cone catch to RNL Chromaticity? I can\\\’t understand what negative values would imply and if these would interfere with my results (e.g. would this change the delta-S?).
Yes, values will often be negative in RNL chromaticity space. The origin is the achromatic (grey/black/white) point. For example, the human cones are listed in order from longwave to shortwave (LW, MW, SW), and creating RNL chromaticity images for human cone catch images will mean the X channel is red-green (all positive numbers being red, all negative numbers being green I think). The Y channel is then red-green versus blue (i.e. blue-yellow), so again positive and negative refer to blue or yellow colours.
The lovely thing about this space is that you can use Euclidean distances to work out the delta-S (JNDs) between any values.