Radiosity, Logarithmic Exposure Control, and Bitmaps

[Guest Matthew Boorstin]

Howdy, I'm looking everywhere for an answer to this issue:

 

I'm rendering a radiosity solution, which of course works best with logarithmic exposure control. HOWEVER, I just tried mapping a bitmap image to be used as a poster on the wall, and logarithmic exposure causes the image to be rendered incorrectly. It is not just washed out; the suggestion to reduce it's RGB values will not work because logarithmic appears to be performing a curves adjustment on the RGB values, in effect solarizing the image. How in the world can I place a bitmap image in a radiosity solution that will look correct? I'VE TRIED EVEYTHING!

 

I've gotten hints from other newsgroups that placing bitmaps (full ones meant to be seen as an image, not as a texture) in radiosity solutions is actually something that you just can't do in Viz 4. Is this true? I can't believe it....

 

Thanks in advance!

[HeDaCoM]

hi. First of all. to tell you that you have came to the right place

could you post some images of the problem ? Reducing the RGB level of the texture to 0.5 or 0.6 should solve the problem. And why you need logarithmic exposure? Are you doing an animation? If not, you could try with automatic exposure.

[Guest Matthew Boorstin]

Hector, thanks for the quick reply! I'm trying to set up a place to post some images. In the meantime, have some questions about your suggestions.

 

1. I'm using Logarithmic exposure because this is a radiosity solution using out-of-the-box photometric lights, and everything I've read suggests logarithimic exposure. Plus, I've tried rendering the solution with Automatic exposure and the room is completely underlit (It looks perfect using logarithmic, with the exception of bitmaps).

 

2.Why would you use a different exposure for animations than for stills? They're all the same frames. (I've heard this suggested before, so it must be something I'm not aware of)

 

3. I've completely played with the output levels of the mapped graphic and this simply will not solve the problem. What I've been trying to explain to the discussion groups is that the image itself is being altered, it's not a lighting level. Try this: Find a personal picture that you're intimately familiar with so you'll know if the image looks different. Map it to a simple square in your model. Point a single light on your square (doesn't matter if it's photometric). Render it using normal exposure and it looks fine. Render it using logarithmic and the image looks wrong.

 

I have an idea why this is happening, I just don't know how to fix it other than to simply not use bitmaps. It's performing a logarithmic function on the RGB curve data. In other words, if you've ever worked in Photoshop, it's turning the RGB curve data in the bitmap from a straight line into a curved line, completely skewing the value imformation of the image.

 

I can't be the only person who was ever used a bitmap and logarthimic exposure together, so I'm assuming I'm missing something.

 

Pictures to follow! Thanks!

[Frank]

Is the affect indirect checked in the Logarithmic settings. This mite fix your problem

[Guest adrian_dav]

Originally posted by matthewb:

Howdy, I'm looking everywhere for an answer to this issue:

 

I'm rendering a radiosity solution, which of course works best with logarithmic exposure control. HOWEVER, I just tried mapping a bitmap image to be used as a poster on the wall, and logarithmic exposure causes the image to be rendered incorrectly. It is not just washed out; the suggestion to reduce it's RGB values will not work because logarithmic appears to be performing a curves adjustment on the RGB values, in effect solarizing the image. How in the world can I place a bitmap image in a radiosity solution that will look correct? I'VE TRIED EVEYTHING!

 

I've gotten hints from other newsgroups that placing bitmaps (full ones meant to be seen as an image, not as a texture) in radiosity solutions is actually something that you just can't do in Viz 4. Is this true? I can't believe it....

 

Thanks in advance!

i had the same issue. logarithmic exposure control works very well when the overall solution is roughly on target(turn off all exposure controls). i had some luck when i was turning shininess down to 0 and gave the diffuse and ambient colors a full black. you could change the texture after calculating the radiosity. copy the bitmap to the self-illumination channel if you need it to look closer to the original image.

 

good luck!

 

adrian

http://www.adriandavidson.com

[Guest adrian_dav]

Originally posted by HeDaCoM:

hi. First of all. to tell you that you have came to the right place

could you post some images of the problem ? Reducing the RGB level of the texture to 0.5 or 0.6 should solve the problem. And why you need logarithmic exposure? Are you doing an animation? If not, you could try with automatic exposure.

you are right: logathimic exposure control is the only exposure control that does not use a histogramm to calculate the exposure and avoids therefore flickering by not evaluating the animation frame by frame.

so far it has been my impression as well, that logarithmic exposure control is the only way to adjust a scene that has an overexposed radiosity solution.

automatic exposure works best if your scene is roughly on target. and yes: he should just adjust the lights and re-calculate the scene and use the automatic afterwards.

 

best,

 

adrian

http://www.adriandavidson.com

[Frank]

They goning to the Exposure control and in the Logarithmic Exposure Control Parameters pull down make shore that the Affect Indirect Only box is checked. If that Doesn't fix it you my have a light in the room that may be to strong for the image so it may need to be excluded.