Mia_sky lack of contrast issue

#1

I have a sand surface geometry with a reflective and glossy mia_material applied to it. When I render the scene with an HDR map plugged to an IBL, I get very rich reflections on my surface. But when I use the mia_sky instead I just get very dull and uncontrasted results. I understand that in general HDR gives better results than the mia_sky because it simply has more contrast in it, but the difference here is huge and the HDR map is not a super contrasted one, it’s pretty constant. Notice for instance how in the interior of the sand dunes, the surface looks totally flat in the mia_sky render where in the HDR render, the surface looks completly different with bumps pupping out. So why is the surface rendered with the mia_sky so dull/flat, it doesn’t even show the bumps? What is causing this?

   [[http://sor.typepad.com/.a/6a00d8350600cb53ef01a3fd1a8f9c970b-pi](http://sor.typepad.com/.a/6a00d8350600cb53ef01a3fd1a8f9c970b-pi)](http://forums.cgsociety.org/)
#2

Did you gamma correct the ground color in the sky node?

#3

No, I don’t see the point specially that nothing should be gamma corrected in the sky node since it generates float values. But I did try it just to make sure and nothing changed from slight difference in the illumination pattern.

#4

lack of contrast is caused by key and fill having similar ratios. look at the swatch color of the ground in the sky node, and look at it when it’s rendered. to me it appears lifted, meaning that color swatch, like all others in maya, is not being compensated for a linear workflow. higher values in the ground and sky even out the light since that acts as the fill in this setup. if you don’t want to use a gamma operation since it’s float values just reduce the value until you get the result you want. Additionally, you can adjust the multiplier on the sky separately from the sun and dial in as much fill as you want. If that doesn’t work, perhaps disconnect the exposure nodes and tone map with the view port controls and crank on ‘contrast.’ If that doesn’t work, render to float and grade in post.

#5

Not sure of this, even with a black ground, the surface still lacks definition compared to the HDR.

Check inbox.

#6

I still can’t find what’s causing the lack of contrast in the mia_sky render, tried almost everything. I can only conclude from now on, that mia_sky is good for testing but when it comes to a production render, HDR maps are way better for a more realistic render, specially if one is using displacement.

#7

Your first image doesn’t work unfortunately royterr.

What’s wrong with lack of contrast though in a render? I think it’s better to render “flat” and add your post processing curves later anyway, you’ll get more colours and control out of something like a simple gradient ramp in photoshop even than a hdri or sky if you’re not doing a full on comp and working on the beauty pass of a render.

#8

try this:
http://sor.typepad.com/.a/6a00d8350600cb53ef01a3fd1a8f9c970b-pi

Post or no post is not the issue here. The problem is that details is just not showing up in the mia_sky render, and I don’t see how post will fix this.

#9

Im assuming that you are referring to the physicalsunandsky feature in indirect lighting section of rendersettings because I cant find a mia_sky. I also assume you know that when you engage this feature maya automatically attaches a mia_exposure_simple lens shader node which not only boosts the gamma to 2.2 but also defaults to doing significant tonemapping.
Is the mia_expsoure_simple engaged when you are doing the HDR render as well?

#10

yes and the problem is not the mia_expsoure_simpl.

#11

I see quite a bit more noise in the left side(sunsky version) then the right side(HDR version) implying that render sampling levels were different somewhere.
Would you be willing to share your scene project for a closer inspection?
By the way since the hues of the environments are quite different I viewed your image as just a luminance and that made them look closer in contrast but that doesn’t explain the lack of bump detail in the sunsky version.

#12

Hi royterr,

Thanks for sharing your scenes.
Im actually surprised the renders came out as close as they have. The ibl version is using an ldr image with clouds in the sky a bright sky area and other ground details. The sunsky shader generates a procedural sky with no details except the sky color smoothly ramps between certain hues of blue based on the sun direction or altitude. The ground is by default just a grey color. If you make the sunsky by using the create physicalsunsky button in rendersettings->indirect lighting you will see what this procedural sky looks like when rendered.
Of course, since both maya scenes have a mia_exposure_photographic lens shader doing tonemapping and gamma boosting, the results are non-linear. Which is not part of this issue since they settings seem to be the same in both scenes.

By the way I noticed that there was no sunsky rig in your scenes just the physicalsun and physicalsky environment shaders. Do you not usually use the create physicalsun button to generate a sunsky?

#13

i start with a rig and modify it later on.