robkar97 Posted January 23, 2008 Share Posted January 23, 2008 I can't get the ambient occlusion to function with the mental ray "arch + design" materials when using "mr photographic exposure control" (and using photomeric lights)... A single "mr area light" 1500 cd washes out every trace of AO... Turning the light off doesn't help since exposure control make the image extremely dark. :-( I've even set the Shadow color to rgb 0, 0, 0 and Custom Ambient light color to rgb 255, 255, 255 and the Max Distance to way high (3000 mm). The model (a chair) is about 500 mm high. It would be nice to skip the step of manually doing a separate ao pass and do a multiply blend layer in Photoshop for simple viz jobs (and animations!). Any ideas? Robert Link to comment Share on other sites More sharing options...
Justin Hunt Posted January 23, 2008 Share Posted January 23, 2008 Have you tried different exposure settings? If your image is too bright then dial down the exposure and vice versa, thats what its for. For AO usually larger max distances can have two effects, If its in an enclased room then the distance should be less than the floor to ceiling height, otherwise the ceiling (or floor) will be calculated and result in overly dark AO If its not in an enclosed room then overly large max distance will lessens and spread the AO thus be less noticable. By making the ambient light colour pure white you will be adding ambient light to the object making it brighter. leave it black. Its the shadow colour thats important, to make the AO more noticable darken this colour. However making it too dark can look wrong. JHV Link to comment Share on other sites More sharing options...
robkar97 Posted January 23, 2008 Author Share Posted January 23, 2008 Thanks Justin! I had not understood the meaning of the ambient light color until now! I guess I'm asking too much from the AO, trying to get things it wasn't designed for. Link to comment Share on other sites More sharing options...
MasterZap Posted January 24, 2008 Share Posted January 24, 2008 I can't get the ambient occlusion to function with the mental ray "arch + design" materials when using "mr photographic exposure control" (and using photomeric lights)... A single "mr area light" 1500 cd washes out every trace of AO... First of all, are you trying to use the AO as additional ambient light, or as a refinement for FG? The default mode is FG refinement only, so it won't give you any "light" (unless you add an ambient light value) only add *details* to existing FG. Turning the light off doesn't help since exposure control make the image extremely dark. So change the exposure, if that is your problem!?! I've even set the Shadow color to rgb 0, 0, 0 and Custom Ambient light color to rgb 255, 255, 255 and the Max Distance to way high (3000 mm). The model (a chair) is about 500 mm high. I assume you mean 1.0 1.0 1.0 and not 255 255 255... these oldschool 255 integer colors aren't used in mental ray. Also, if you really want to add ambient light in a physical mode (if you are using the photographic exposure control in max 2008 in the 'cd/m^2' mode) your "ambient light" needs to have an intensity that makes sense. 1.0 1.0 1.0 equals 1 cd/m^2, which is pretty much black. But since it's mental ray, 1.0 isn't the upper limit for color values. Put in 1000.0, and if you run out of range in the color spinners (somebody limited them to 1000.0 I think, I dont know why) pipe a color through the "Output" shader, and add a multiplier. However, an alternative to that is to switch from the "cd/m^2" mode in the photographic tonemapper to the old "physical scale" mode. By tweaking the "physical scale" you change the "physical meaning" of the oldschool intensity "1.0". So if you set your ambient light to "1.0 1.0 1.0" and set the physical scale to 1500, that would equivalent to 1500 lux of illuminance, i.e. it would rival your 1500cd light at 1 meters distance. It would be nice to skip the step of manually doing a separate ao pass and do a multiply blend layer in Photoshop for simple viz jobs (and animations!). You should never do that. Because a simple multiply will do the AO also in the directly lit area. This is wrong and will only make your render look "dirty". Yes, I know it's an oldschool recommendation frmo days of yore, and yeah it can "look neat", but it will invariably give your render an "ambient occlusion look", not a realistic look. Don't apply AO to the direct illumination, it sucks. /Z Link to comment Share on other sites More sharing options...
robkar97 Posted January 24, 2008 Author Share Posted January 24, 2008 Hi there Z! It's cool that a fellow Swede is involved with mental ray! Thanks for your extensive comments. I think I got most parts. The part of pushing RGB beyond 1.0 was new to me. Very nice, like most things with mental ray. All the best Robert Link to comment Share on other sites More sharing options...
Scott Dombrowski Posted January 24, 2008 Share Posted January 24, 2008 Hi there Z! It's cool that a fellow Swede is involved with mental ray! Saying Master Zap is involved with Mental Ray is like saying Einstein had an interest in physics. Completely true, but somewhat understated. Link to comment Share on other sites More sharing options...
MasterZap Posted January 28, 2008 Share Posted January 28, 2008 Saying Master Zap is involved with Mental Ray is like saying Einstein had an interest in physics. Completely true, but somewhat understated. ROFLMAO! But thanks! /Z Link to comment Share on other sites More sharing options...
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