Making the Luminosity Map
What is luminosity? Luminosity is very similar to self-illumination but unlike self-illumination it does not depend on the surface's original color. Self-illumination uses a combination of the color in the self illumination map with the surface's
original color for example if you have an object that is light blue and you use yellow color tones for your self
illumination map the areas that the self illumination map affect will have a green color tone (light blue+yellow=green)
Therefore the translucency map that we used before produced areas that had a lighter green tint. But like max's translucency attribute, luminosity does not depend on the color of the original surface therefore areas that those two attributes affect change the color of the surface so if you have a surface that is light blue originally and you use a yellow tone for translucency or luminosity the area that those two attributes affect wont have a combination of yellow and blue like in self-illumination but will look like yellow is on top of blue.
We will use this to our advantage in order to take the thin translucency effect a step further by having lighted areas have a more apparent color change, by making this luminosity map we will be able to control witch areas luminosity affects the most therefore changing the colors of those areas to a degree, in this case we don't want luminosity to affect the center of the leaf much in order to make those areas appear to be thicker, we specially don't want luminosity to change the colors of our
center vain, what we want is luminosity to affect the colors on the edges the most therefore making outer areas appear to be thinner than inner areas. To do this were going to make a map very similar to the reflection level and translucency maps but this time the colors will be black on the center and fade to lighter yellow on the edges. Because we have already done similar maps before I'm going to give brief explanations this time.
Make a duplicate of the translucency map set and rename to luminosity map, change the lightness in hue/saturation of the
center root layer to -100 to make the center vain pure black.
Hide the hue/saturation adjustment layer so the colors don't get in the way, as you did before use gradients to change the colors of the base layer so they go from black on the center to lighter on the edges, use the dodge tool this time to make the outer edges a little brighter. After you finished do the same for the mask layer in the pattern detail layer, use the following image as a reference.
The last step is to unhide the hue/saturation adjustment layer and change its value to a hue value of 58, saturation of 65 and lightness of -10.
This not only completes the luminosity level map but all our 8 painted maps!!, here's a screen of the luminosity map.
Here's a render with the luminosity map in action, I think it's easy to see the essential difference that luminosity plays on our leaf, the leaf's interaction with virtual light looks to be allot more accurate, it now looks like it uses true translucency, witch in hand makes the leaf look more organic.