> Quote - So, I've generally been a convert to using gamma correction for a while now, but every now and again something crops up that makes me wonder if there arn't still a few issues with how it's been implemented in Poser (specifically render GC). > > The thing that bothers me most is what happens to the shading at the terminator between light and shadow on a model. It seems to my eyes that GC overly sharpens that transition right at the terminator, leaving a harsh line. We've discussed this before but I couldn't track down the thread.

I do not think it is overly sharpened at the shadow border. GC does make a rather sharp border, that is true. But this sounds reasonable to me. If you were to assign a different greyvalue (subjective measurement) to each pixel on a line along the equator of the sphere (red line in the illustration), you should get something like the curve on the right. It is essentially a cut-off circle, because if the sphere is a lambertian reflector, its brightness is the cosine between the surface normal and the lightvector, and in the special case of the circle, it is the same as distance to the light. So there must be a relatively sharp shadow border.
Of course, this does not automatically mean, that it looks good, even if it is realistic. It is only realistic for a specific material, which must be a very good diffuse reflector on one hand, on the other hand it must be perfectly smooth to be have a close to lambertian surface. If you look at the sphere and think of a plaster ball it might not look right, because in reality a plaster ball would not be smooth enough to be a good candidate for the default lambertian diffuse shader.

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To illustrate, in the above test I have two primitive spheres, one low and one very high res (I thought there may have been a geometry issue but apparently not), lit very simply with one infinite light (similar occurs with spotlights) at 100 percent intensity with RT shadows enabled. The balls have a simple diffuse/specular material setup, one ball coloured blue. Each image was rendered using exactly the same settings except for the GC and TM options (the TM options were set at 2.2, although it's usually recommended to use them at lower settings). No IDL or SSS was used.

The results actually startled me a little, as not only did the non GC image have a better transition at the terminator, but the GC 2.2 image appears to have shading artifacts running along it (shows clearly on the coloured ball).

I am not sure what shading artifacts you exactly mean, but on the dark side of the blue ball, there seems to be a zone that is not pitchblack like it should be, but has some very dark grey. It seems to have something to do with the specular shader of the sphere, as far as i can tell. I tried with Poser2010 and it has that not-quite-black area too and it disappears when i disable specular.

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The TM renders have a much better transition to me, but since TM is a post filter it seems more difficult to work it's use into a linear workflow (or maybe I'm not understanding the functionality).

In the end it is you who decides on how harsh the shadows should look in your image, so you can do anything. But you should be careful when using tonemapping (and GC too) on your image; when you have more things in your scene than just spheres, other parts of the image will be effected by the tonemapping, too, and these might be parts where you do not actually want it. Anyway, if you are using a linear workflow, it probably means that you use a compositing program or something like that to process your image after rendering, and probably tonemapping and GC is best done at that later stage (if possible).

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I'm considering a bug report to SM regarding the GC artifacts, but I want to run it by you guys to see if it's reproducable.

I'm running PP2012x64 SP1 for this test.