Hi ,
I want to keep a linear workflow in Houdini.So using a convoluted .HDR and also a .Tiff . I figured it would be better to pipe it into COPs where I could control the exposure settings. Then pipe the result into a environment map slot on a light .but I cannot seem to find anything suitable to control the exposure of the HDR. Has anyone got any ideas on this ?

Rob

Hi Rob,
I'm not entirely sure, but aren't HDR's and floating point TIFFs always assumed to be linear?
-brian

They sure are ! but I am looking to control the exposure of the HDR somehow in Houdini.

rob

Oh right on, my b.

Normally you can drive shaders directly from a copnet using…

opimg/img1/desired_node

… but this doesn't appear to be the case for the environment map option for lights so I think you're stuck with rendering out whatever result you get in your copnet to a texture file before rendering your scene.


As for which nodes work best for exposure, have you tried playing with the bright cop? Playing with that, and the gamma cop seem to allow me to get almost any result I want.

Cheers Steven for the words . I also thought you could maybe use a levels COP .Mario over at odforce has ever so kindly given me a break down of some code that you could use to increase or decrease the “ brightness” of a HDR image.
With that in mind my idea was to then build it into a shader.

Rob

he

i was actually trying to find a good way to change exposures the other day!
i can't believe that such a SIMPLE thing isn't standard in Houdini!

Actually i feel the whole HDR IBL/reflection workflow needs better support, it's kinda all over the place for me at the moment, or is it just me?

jason

imho the env light should be developed to support separate input textures for casting light, reflections, refractions, background

just checking here, but i take it that you can only see reflections from the environ light when rendering with PBR? it's been bugging me for a while that it doesn't do so in MPR..

jason

Hi Jason my plan is to build the feature into a shader , so you can just load a HDR and then step through the different exposures. I should be able to make a start at the end of the week !. In the mean time there is a thread over on odforce where Mario kindly has posted up some code to do this should you wish to have a crack yourself

PostPosted: Mon Nov 10, 2008 10:10 am Post subject:
imho the env light should be developed to support separate input textures for casting light, reflections, refractions, background

Do you mean more like how the Ray Swtich node can be used in Maya and MR coupled with the IBL node ?.
I would like to know if some of the newer point based techniques used in renderman could be used for lighting in mantra. Can you do brick mapping in mantra ?

Rob

hey Rob

yeah i read the forum yesterday, are you planning on building this into a surface shader?

i personally find using evirn maps at shader level bit of a pain, especially when you have loads of objects in the scene and you want to change the reflection map..

jason

yes, i meant like IBL node in maya, altough IBL sucks too, better to compare it to a ray_type like shader

i personally find using evirn maps at shader level bit of a pain, especially when you have loads of objects in the scene and you want to change the reflection map..

Yes but its fast to render. As all of us know each type of renderer has its advantages and disadvantages. I love lighting and I figure if we can get a defined work flow mapped out it would make life a lot easier. I want to build the exposure settings into a stripped down version of the ambient occlusion shader I made with Marios help.

Rob

I think that the approach to using a shader exposure parameter for the HDR map can be expensive once you get to tweaking other lights? Since you're doing it on the shader, that means that you're going to need to recompute the exposure for every render, no? On the other hand, if the HDR map was modified with the desired exposure, then subsequent renders won't need to do the exposure computation anymore. I understand the attractiveness of having a shader parameter while tweaking the exposure on the HDR map though.