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I have question of Mantra. If I make two area lights in scene and set color to white and intensity to 0.5 I get very bright render. I do not understand why this happens. My shader is clay and only diffuse with color white and intensity 1. Area lights have normalize light intensity checked. I think the brightest color of render must be maximal 1.0 but I get over 2.0. Even for one light with intensity of 0.5 render is to bright. Why is this?

Thank you!!!

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Brightest color of render is not 1.0. That's why. It would severely limit the possible render results.

Thank you Erik! I know brightest color is over 1.0 but I do not know why? I think it should not be over 1.0 with settings I use. If I have one light with intensity of 0.5 and shader with only diffuse of 1.0 the brightest color should be 0.5 or do I misunderstand it?

Thank you!

Edited by renderfan
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Thank you Erik! I know brightest color is over 1.0 but I do not know why? I think it should not be over 1.0 with settings I use. If I have one light with intensity of 0.5 and shader with only diffuse of 1.0 the brightest color should be 0.5 or do I misunderstand it?

Thank you!

EDIT: Scratch what i wrote in this message first. Not totally sure on the answer for your question. What renderer btw? PBR or MP?

Edited by Erik_JE
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.. . I think the brightest color of render must be maximal 1.0 but I get over 2.0. Even for one light with intensity of 0.5 render is to bright. Why is this?

..

i have never heard that as a 'law' .

anyway , id suggest you turn off Normalize Light Inten .. and combine resizing of area light with light's intensity .

to have final and finer control look also the last tab Attenuation options .

.cheers

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I misunderstood your question. Not 100% sure about this but I would say it's because of diffuse reflections. With a diffuse intensity of 1.0 it will reflect all of the incoming intensity which adds up in some places.

Thanks Erik, but I think this is wrong result! The render produces more light than it exist. For example if I have sheet of paper in white and one spotlight with intensity of 0.5 the rendered paper must be 50% grey not again white. I looked in shader and energy conservation is checked even if I do not need it with only diffuse output.

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i have never heard that as a 'law' .

anyway , id suggest you turn off Normalize Light Inten .. and combine resizing of area light with light's intensity .

to have final and finer control look also the last tab Attenuation options .

.cheers

Thank you Zarti, but I believe the render should not produce more enery as light exist in scene. With one light of intensity 0.5 how is it possible to get brightness of 1.0. where does the extra light come from?

Thanks again

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I did test with other lights. It is not only area light but also with pointlight and spotlight I have same result!

I do not know if this is wrong result or I do musunderstand it. Any explanation is welcome!

Thank you!!

Edited by renderfan
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Thank you Zarti, but I believe the render should not produce more enery as light exist in scene. With one light of intensity 0.5 how is it possible to get brightness of 1.0. where does the extra light come from?

Thanks again

Well it have something to do with diffuse intensity being 1.0. There is nothing "real" about that cause it don't lose intensity. My theory is a little rusty but i am 99% sure it boils down to this.

EDIT:

http://www.sidefx.com/docs/houdini11.1/nodes/vop/surfacemodel

Diffuse Intensity part. Check your attentuation.

EDIT2:

Basicly if you have two surfaces of diffuse intensity 1.0 they can reflect all their light intensity upon the other creating high values.

Edited by Erik_JE
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i think that predicting the final intensity of light over a surface might be accurate when you have point lights .

but , im not sure how that can be measured in the case of area lights ..

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Well it have something to do with diffuse intensity being 1.0. There is nothing "real" about that cause it don't lose intensity. My theory is a little rusty but i am 99% sure it boils down to this.

EDIT:

http://www.sidefx.com/docs/houdini11.1/nodes/vop/surfacemodel

Diffuse Intensity part. Check your attentuation.

EDIT2:

Basicly if you have two surfaces of diffuse intensity 1.0 they can reflect all their light intensity upon the other creating high values.

Thank you Erik! This does help but if I set attenuation to physical correct and move pointlight near surface I have again same problem. Surface renders much brighter then light intensity. I find it hard setup render and tweak settings if output is like that. Maybe this is normal with PBR renderer but for me it is hard to understand how Mantra works.

Thank you again!!

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Thank you Erik for reply!

I did test with Vray and Mantra to match output on both renderer. It is simple scene with one geometry light with texture and only diffuse shader. I have problem to get same result. With Mantra area around light is to bright and I do not see texture on light. If I turn down light intensity then the render is to dark.

Erik, I think you maybe have same problem with your scene HERE

Any help welcome.

Thank you!

post-6984-133200660671_thumb.jpg

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My scene is a mixture of problems :) But not really that one.

You still havent answered if you use PBR or MP?

One thing you could try is to allow more diffuse bounces. It default to 0 for MP and 1 for PBR.

Sorry! I am using PBR with 3 diffuse bounces.

Thanks!

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I did new test with comparing Vray and Mantra in regards to THIS post.

I use file and settings for render from Side Effects site here:

http://www.sidefx.com/index.php?option=com_forum&Itemid=172&page=viewtopic&t=20382&highlight=pbr

http://www.sidefx.com/index.php?option=com_forum&Itemid=172&page=viewtopic&t=21548&postdays=0&postorder=asc&highlight=pbr&start=0

Mantra is much slower in my test and it is still noise. I really like Mantra but for GI i think it is simple to slow.

Any tips and tricks are appreciated.

Thank you!!!

post-6984-133235569789_thumb.jpg

post-6984-13323557102_thumb.jpg

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Thank you Erik for reply!

I did test with Vray and Mantra to match output on both renderer. It is simple scene with one geometry light with texture and only diffuse shader. I have problem to get same result. With Mantra area around light is to bright and I do not see texture on light. If I turn down light intensity then the render is to dark.

Erik, I think you maybe have same problem with your scene HERE

Any help welcome.

Thank you!

i guess your light-intensity is outside the 0-1 range and thats the reason why you get these overexposed areas around your light. you should render out the image in 32 bit and do tonemapping and color grading in comp. for previews you could use a simplified tonemapper to get a better feeling how the final image will look like.

file is attached.

hth.

petz

tonemapping.hipnc

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