Thanks cckens for your great tutorial on hdri. I now know how to modify my digital pictures to become useful hdri images. But I have a problem with shadows. I thought I could build a few rough shapes and use them as "shadow catchers" so my 3d objects cast shadows on the background, but this doesn't seem to work. Is it just finger trouble? Help. How can I make shadows if shadow catcher will not work?

groucho, Can't tell if you're trying to get shadows on the HDR or on a backdrop image... Could use a glimpse of what you are trying to map shadows onto, though. From what I can see in C3, you have the HDR image in the background and that can't really catch shadows. I'm going to try to see if I can't generate a test for shadow catchers. You may have to add a neutral backdrop and key it out in another app... Something I'll have to look into. Glad you got something out of it! Ken

OK, here's what I found out. Testing with a known HDR image that casts shadows... HDR images DO NOT produce raytraced light as a spot, distant or bulb light do. This seems to be an integral component in producing the shadow catching effect. I tested with both the standard distant bulb (which produces the shadow) and the by making that light invisible and using an HDR that seems to cast shadows. In the case of the HDR, the shadow-catcher showed up in the render... all of it, not just the shadow. So it seems that this, groucho, is a no-go for using that particular function. I may be able to find a workaround but this may take a bit. Somebody sound off if they've already found one! Thanks Ken

I always figured that people where using invisible (fake) planes underneath their objects to cast shadows on from HDR images? Maybe they were using backdrops instead, and had distant lighting turned on? I'll have to check the images again to see what exactly is reflected off the objects. www.shonner.com

I think they use visible planes with textures on them...

I have only played this last week with HDRI.. but actually I may have fuond an answer to your problem by accedent... I had left a spot light in an image.. and it made shadows.... was kinda nice effect....just point it where you want the shadows and render away...maybe adj brightness of both the hdri and the light? try it and let us know :) hope it helps

god i'm a bad speller/typer... oh well you get the idea

I often use hdri and then add a single spot for additional lighting/shadows. Seems to be a nicer effect, and usually I can switch off indirect lighting (with HDRI generating a fake GI effect) and get a quicker render. :)