OTOY Forums

Would like to see if anyone has tips on how to increase the strength of a shadow by an object (ie a sphere) against a ground plane when using a HDR as Background Environment.
I am getting really weak HDR shadows.

I know how to select the ground plane material, set it as diffuse, and then set Matte to 'On' in order to have the plane not show up in the rendered scene while preserving the shadow.
And I understand the HDR lighting determines the initial shadow strength.
However, I am interested if there was an artificial/simulated way to somehow combine the shadow making power of the daylight background environment with that of an HDR background environment, in standalone app.

Also, I think I saw that sphere outside of a Target Store, and I think it had a shadow, but I'm not sure...
Anyway, Thanks and Regards!

I'm fairly sure that the quality/strength of the shadow is a lot to do with the quality of the hdri you use. I've found that some are terrible at producing shadows, while others are really good. Don't know what you'd adjust though to make a bad one good.

it is up to your hdri file. if you are happy with the file color,reflections etc. but shadow then you should edit in PS as 32bit sun size and intensity will determinate the shadows as you know.
as a 2nd way; mixing sun+sky is good. once you locate(height and rotation) the sun exactly where it is in hdri image then lock Y rotation.

As said the shadows in many hdri-files are very soft and gentle. The main reason for this is the difference between overall illumination and the maximum brightness of the sun. in many cases the difference is way too low.
this only relates to real 32-bit HDRi Files. Often simple 8bit 360-degree panorama-files are missunderstood as HDRi Files. If you got a real 32bit .EXR or HDR File you can open it in Photoshop. then click on the little white arrow in the left lower corner and set the tool to the 32bit exposure slider. this only affects the preview. lower the slider so you can see the tiny spot where the sun is. then mask that spot and add a exposure-adjustment layer. (the mask of the adjustment layer should now be the mask where the sun is) then add as much exposure as needed. maybe you try a few times. +7 should work in most cases but could be too much aswell
by this way you can archieve hard shadows with any hdri files.

happy rendering!

Also make sure you have importance sampling turned on. I couldn't tell if you have it on in your examples. And you can mix both daylight and HDRI together, that can help as well.

There is old "trick" for doing that.
You can EDIT HDRI, add more brightness to SUN position, just use photoshop and add brightness to center of sun , use PS Brush with high exposure white in center. More strong sun brightness will give you sharper shadow(s)

Here is only video i found with quick explanation.
https://www.youtube.com/watch?v=hsz-HSty4Ig

if You use HDR(i)s, but You don't see them in final shot You can always tune gamma a bit to get more pronounced shadows =) though keep in mind that effects reflections as well..

if You end up seeing Your HDRi - simply tweak it in PS adding bright spot on the higher end (where You light source is). Personally I really like softer look from HDRs, but yeah in some cases it's a bit weak =)

Another "quick and dirty" way of solving this, would be to simply increase the Gamma of the HDRi inside OctaneRender from 1.0 to something around 2.0.
This will however, also increase the contrast and colors of the backplate, so you might not find that soloution feasible...

Notiusweb, long time no see. Another trick is to test HDRIs in PS before even considering putting in your HDRI stash... If you can't crank Image > Adjustments > Exposure to negative high teens (-16 and beyond) and still see dot of sun, it is a poor man's HDRI that isn't made well and with enough exposures.. and should be shit-canned. And it's also been my experience that good interior HDRIs should be capable of cranking down to at least -10 before light sources disappear.

Thanks for all of these great suggestions

Wondering if anyone could elaborate on the following:
-Does the shape of the sun matter (i.e. a plain circle vs a circle with glints, flares, rays, etc.), or is it merely the relative intensity of the white that causes difference in illumination?

Also:

Postby grimm » Thu Jul 16, 2015 10:52 pm
Also make sure you have importance sampling turned on. I couldn't tell if you have it on in your examples. And you can mix both daylight and HDRI together, that can help as well.

-Grimm, are you referring to an in-app mixing of the daylight and HDRI? I apologize, but how is this done, I was not aware that you could do that. The closest I got to that was to try and place an image onto a vertical plane as a 'backdrop' along with the daylight. Thanks!