HDRI Color+Spatial Distortion in Iray
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I've been trying to render a simple image of a figure jogging—the geometry is the figure (Genesis 2), the hair, shoes, shorts and top. There are no lights in the scene and the headlamp is off. I've tried four different HDRI maps, most or all of which I've gotten from commercial HDR vendors (HDRmaps.com for most of them), and I know they're good files (I've used some of them successfully in Modo). But when I render, I get a hard line with a strong yellow cast above the midpoint, and a greenish-blue cast beneath it. As well, the lower half bends towards the center, creating a distortion line.
I tried restarting, but this still happens. I tried a new scene with just a sphere primative and I still got it (although with the different camera angle, the split line is towards the top).
Why is this happening? And, on a related note, does anybody know of a good tutorial for incorporating HDRI lighting with backplates? Most of the commercial HDRI images I've bought include backplates, but I've never managed to integrate them well.
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Thanks. That solved that problem. Now I have a shadow problem, but an inconsistent one that's baffling me.
In the first attachment (the night setting), the shadow is completely wrong—wrong direction, wrong softness. In the second (daylight), the shadow is correct—right direction, right softness. Both renders use the exact same settings, with only the HDRs switched. There aren't any lights in the scene, so they should both get light from the images. that's obviously not happening correctly in the first image. Any ideas? I like that image (and have some backplates for it, which, unfortunately, I don't for that fantastic second one).
I think it must be something wrong with that HDRI. Here is a link to an image in my gallery that uses the same HDRI, and has the same shadow problem, although I never noticed until you pointed it out.
I didn't think that was technically possible for an HDR to be wrong like that, but with two renders getting the same broken shadows, it must be. Thanks, that makes me feel much better (although sad that I probably can't use that HDR anymore).
The reason it is wrong is the brightest light element in the night image is on the right of the image. Unfortunately the shadows in the image are showing the light coming from in front but if you look at the bottom right corner you can see the shadows begining to come from the right. There isn't a lot you can do with that. Try turning the dome; or turn off the ground plane; or move the jogger farther back or forward until the shadows match. Unfortunately it is a badly taken image for an HDRI background but may be fine for lighting only.
Can an HDRI efectively mimic light falloff? In the real scene the light from each lamp is decaying, so the shadows change as the locally dominant light source changes, but the HDRI can encode only the brightness of the light at the camera position and has no effective falloff across the scene "stage", as far as I understand. That would be a limitiation of HDRI, not necessarily a bad HDRI shot.
By bad I mean the photographer has taken the picture with the main light source to his right and off camera which means that anything put into the image and receiving light gets it from there and not the lights that are giving the shadows in the main image. If he had moved back or forward a few meters then the light sources may have been in the right place to give proper shadows to anything placed within the scene. That is why I would move the HDRI, the jogger or both.
What setting is this? Do you mean Draw Dome? I can't find "virtual" anything in any of the Iray Render Settings panels / tabs.
Surely the picture is a dome and will include all of the lights, otherwise it wouldn't be there to cast light. There may I suppose be an issue with the way the tone mapping was handled causing the light to the right of this view to appear brighter than it should to match the environment.
It is more about the positioning of the figure within the dome that will dictate the direction of the shadow. That was why I was suggesting moving the jogger position within the dome or move the dome until the shadows matched. If the jogger is too far forward in the dome she will be picking up the light from the brightest source but she may be positioned too high in the image so the shadow will be different to the shadows in the background because she is too high above the ground. Moving the jogger either backwards or forwards up or down may fix this.
It is Visualize Finite Dome. I wasn't at a computer where I could check the exact name when I wrote that. That's why I said "something like".
As I thought. I downloaded the HDRI and the main light source is the street light in the middle of the road and the only way to get shadows showing in the proper place is the figure and camera positions with regard to that light.
Night time HDRis are much harder to get 'right' because of things like that. I suppose one could open it in Photoshop and reduce the 'wrong' light...
The other problem with this HDRI is that the roads are wet and there is a lot of reflection on them which doesn't show up from an object which is added.
Yes, that's probably what I was meaning when I burbled about the light won't generalising across the whole stage.
Does Visualize Finite Dome do anything? When I click it, I don't see the finite dome, which makes positioning the HDR to match a backing plate hard. I don't have a Nvidia card, though, so if it's an Iray visualization thing, I wouldn't see it.
Here's how the final image turned out, using a matching back plate. It took me a long time to get it positioned right, but I'm happy with the result.
After clicking on Visulize Dome; in Perspective click on the terrain to choose it then on the Square with the + in it, this should take you outside of the dome where you can see it.