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JackyBoyII
08-24-2011, 08:26 PM
I am trying to light a scene with an image from hdrlabs that I have. It is of a really bright sunny day but when I put it in my scene as a dome light texture it just lights it up slightly. I can't figure out what options to change to brighten it up and make it so it has sharp shadows.

Can someone help with a walkthrough guide of exactly how to set up a scene with a HDRi image with vray in maya.

http://www.hdrlabs.com/sibl/archive.html is where I am downloading the image from. the Desert highway.

I am really struggling so would appreciate any help! Thank you.

cgbeige
08-24-2011, 08:47 PM
you won't get sharp shadows just by increasing the values of a dome/environment light. You need to use V-Ray Rect Lights and make them small and bright for that.

JackyBoyII
08-24-2011, 08:54 PM
But I thought the whole point of a HDRI was that you could use it in your scenen and it figures out the lightest a darkest points and then uses that to light the scene, so it if it has a really bright bit (like the sun) it would light it as if there was a big light there.

for example watching this video by Ronen Bekerman http://youtu.be/Z2G7AFAs6kQ all he does is use an image, and it works.

Or have I just got this completely wrong? sorry for being all a bit noobish, I just can't seem to find much info on this area.

Richard7666
08-27-2011, 01:07 AM
CGbeige will be able to clear this up, but *most* (all?) HDRIs don't have the range of values to produce sharp shadows?

I use an HDRI (instead of using Vray sky) in conjunction with a Vray sun or other Vray direct light. If using a Vray physical camera you may need to increase the 'v' value in Color Gain under the HDRI's file node in Maya.

tharrell
08-27-2011, 05:36 AM
CGbeige will be able to clear this up, but *most* (all?) HDRIs don't have the range of values to produce sharp shadows?

I use an HDRI (instead of using Vray sky) in conjunction with a Vray sun or other Vray direct light. If using a Vray physical camera you may need to increase the 'v' value in Color Gain under the HDRI's file node in Maya.

Basically.... this.

Very, very few commercially available HDRs actually have a reasonable dynamic range or much directionality at all to the light sources. Some are downright terrible (not naming any names, but beware "HDRI" with procedural-looking ground planes) and some have fun stuff like negative colors in the blacks which can result in noise that may take your light dome upwards of 2048 subdivs to get acceptably smooth.

Your best bet is either what Richard suggested above, or skip the physical sun and use a directional light from your sun source at, say, .4 intensity, with your HDR intensity set to slightly underexposed (really depends on the HDR).

The trick with that technique is to make sure that you're adding in some divergence in the shadow rays on the directional light, or your scene will have impossibly sharp shadows and feel a bit miniature as a result.

For a scene that's built at real-world scale (i.e. 1 maya unit = 1 cm), I've found a good starting point is .1 light angle and 32 "shadow rays" (i.e. subdivs) on a directional light.

I also generally don't allow Maya-native lights (directionals, spots, points) to contribute to spec as they're infinitely small light sources and can result in nasty firefly-like flickers in your spec/refl when using adaptive DMC in animation.

Best of luck,

--T

Richard7666
01-22-2012, 04:11 AM
http://www.cgskies.com/resources_tutorial_rendering.php

I take back what I said. Adapting this workflow to Maya gives great results and sharp shadows.

We don't get the Vray HDRI node for some reason, so add the 'texture input gamma' Vray attibute to the HDRI file node to adjust its gamma, and adjust it's 'brightness' by using the 'v' value in the HDRI's Color Balance > Color Gain swatch.

I have Colour Gain value of 600 and Gamma of 1.6 on the 'Lighting' HDRI
and Colour Gain value of 40 and Gamma of 0.7 on the 'Dome' (reflections) HDRI

The values in the tutorial aren't directly applicable because they're for the specialised Vray HDRI file node which as I said Vray for Maya doesn't have :(

visua
01-22-2012, 01:17 PM
Or just use your average gammaCorrection, works like a charm, and I don't agree about
the issue beeing poor exposure range for commercial hdr's. You just need to crank up the contrast of your hdr/exr to bring out those nice shadows by altering the gamma eg.

I've been using this workflow for the past year using all different kinds of dodgy hdr's/exr's with great success.

http://www.nicz.net/domeC.jpg

RagingBull
01-23-2012, 10:04 AM
But I thought the whole point of a HDRI was that you could use it in your scenen and it figures out the lightest a darkest points and then uses that to light the scene, so it if it has a really bright bit (like the sun) it would light it as if there was a big light there.


Think of an HDR as ambient light.
You're likely to still need other lights here and there.

derMarkus
01-23-2012, 02:28 PM
Think of an HDR as ambient light.
You're likely to still need other lights here and there.

Hmm, I wouldn't agree to the first part. Vray samples those HDRis adaptively (in the lightdome, at least), so you will have a lot of contrast in the lighting. If the HDR is set up correctly (as mentioned in the previous posts) you can get nice ('hard')shadows without additional lightsources. Not always, of course, it depends on the shot as always.
But a (CG-) ambient light will just act as an offset for the diffuse term of your shading.

RagingBull
01-23-2012, 02:36 PM
I've always had to add lights/bounce cards to bring extra things out, so I think of it as ambient lighting whether it is technically or not, I find it easier to think of it like that.

visua
01-23-2012, 06:23 PM
One vray domelight with altered gamma, are those shadows sharp enough for you guys? :P

http://www.nicz.net/domeShadows.jpg

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