Shading correction method, photographic printer and index print production apparatus

A photographic printer, comprising:

• a printer unit comprising a main exposure optical system and a subprint unit;
• said main exposure optical system comprising a main exposure light source emitting exposure light through a color correction filter and a diffusion cylinder, and onto negative film to provide exposed light, said exposed light being exposed onto a first portion of said printing paper;
• said subprint unit comprising:
• colored light sources providing colored lights to dichroic mirrors, each of said colored light sources providing a respective one of said colored lights
• said dichroic mirrors synthesizing said colored lights to provide synthesized source light,
• an LCD panel, having pixels receiving said synthesized source light, and providing transmitted light to a transmitted light amount sensor detecting differences in light transmittance among said pixels, and to an exposure lens,
• a memory storing correction data, and
• a subcontroller controlling said colored light sources, said LCD panel, and said transmitted light amount sensor, said main exposure optical system providing said exposed light to said subcontroller as a frame of image data;
• said subcontroller driving said pixels of said LCD panel to successively display colored images, each of said colored images relating to a corresponding one of said colored lights and being based on said frame and said correction data;
• for each of said colored images, said subcontroller controlling said colored light sources to successively provide said corresponding one of said colored lights;
• and
• said exposure lens exposing said transmitted light onto a second portion of said printing paper;
• wherein said subcontroller controls said colored light sources according to at least one of a light emission time and a current value, and said correction data compensates for said differences in light transmittance for each of said colored images.