Testing vs an image texture (made it in Inkscape, packed), black World and Emission, orthographic camera, Raw view transform, 16bit Color Depth, tiff and tiff (no compression, so I’m not posting the 5,626k render): according to GIMP’s Color Picker the Color Ramp patches are a perfect match to the rendered image texture.
MacBethChart_010.blend (157.8 KB)
Yeah, me too – couldn’t’ve done it without you guys, thanks again!