I am generating multispectral images using Raw (.NEF) photos with the colorchecker passport 91-3% standards. However, when I go back to measure the RGB values for a mean reflectance in my multispec image, the mean is always way too low (i.e. the (91% reads as 89%, the 59% reads as 56%, etc.). Any thoughts as to what may be causing this error?
Maybe it’s because of the standard being somewhat glossy? Does the issue repeat under different angles of taking the image or different directionality / diffuseness of your illuminant? Having an illuminant with a sufficiently broad spectrum should also be considered. I hope this helps?