HDR Help

[Ecuadorian]

Hey people, I found another free tonemapping program that's more stable than RealCamera and works in Windows 7. It's called Picturenaut. You can save your render as .hdr and then do the tonemapping in Picturenaut. You can also use it to convert .exr image syou find on the web to .hdr for use in Twilight.
http://www.hdrlabs.com/picturenaut/index.html

[Chris]

sIBL (made by the same people as Picturenaut) is another great package / application. I use it a lot to generate "smooth / blurry" hdr images that work better to provide diffuse light (though may not make very good backgrounds).

[olishea]

here is another free tone mapping application.

works on mac too

http://qtpfsgui.sourceforge.net/download.php

[Boofredlay]

Oli, thanks for your lengthy reply on the last page. It is all starting to make sense now. It was the tone mapping that I was not doing. (tone mapping is changing the gamma and exposure right?)

[Ecuadorian]

Please excuse me if what I'm about to write turns out to be totally false. I'm no expert, but this is what I think "tonemapping" means.

If I understand correctly, "mapping" in computer terms is assigning how one group of data corresponds to another. For example, we talk about keyboard "mapping", meaning how characters are assigned to the physical keys in your keyboard. In this case, the first group (characters) is larger than the second group (physical keys), so when "mapping" one to another we have to resort to modifier keys.

When we talk about "tonemapping", the first group is also larger than the second one, because it's a high-dynamic range image, and thus has a LOT more colors than what can be represented in normal bitmaps, some way darker and some way brighter. So the tone mapping is how the program is going to take that large group and assign it to a smaller group, similar to how we took lots of characters and assigned them to a smaller group of keys, or how cheap hotels cram several guests in the same room. To achieve this in images, the usual technique is to compress the dynamic range. This is usually not done in a linear way, but rather in a logarithmic way, to better simulate how our eyes respond to light. Still, if the variations between bright and dark areas is too high, some parts of the tonemapped image might appear "clipped"... pretty much the same thing you would obtain when taking a photograph of a similar real subject. For example, when raising the exposure to do an interior shot, it is natural that the exterior becomes almost white, as it is being over-exposed. I find this natural and nice, but some people don't like it, so they invented the dreaded...

Adaptive compression. Which is basically using different exposure values for different parts of the image, trying to achieve "correct" exposure for each part. This, when not handled with care, produces the truly hideous "HDR look" you see so much on Flickr photos tagged as "HDR"... where you have the oddity of the sky looking as bright as the objects it illuminates. Thankfully, Twilight does not do adaptive compression AFAIK, but if you think you can do it tastefully, save the .hdr and open it in a program such as Photomatix, or simply save .jpg's wit different expusure settings, open them as layers in GIMP and use masks to reveal/hide the parts you want of each one.

Now, the gamma control, as I understand it, is just manipulating the curvature of the function used in the tonemapping, similar (but not equal) to manipulating "curves" in photoshop.

Now I'm waiting for an expert to come and offer a better explanation.

[Boofredlay]

My brain hurts

[David_H]

I guess I don't understand HDR rendering. How is it done? how is it set up?
Thanks in advance.

[Ecuadorian]

To use these, you simply change your sky to either "spherical sky" or "sky probe", according to the type of image you have, and click the button to load the image. Most of the time, you might want to turn off all other lights, including the sun, as the .hdr is supposed to provide all illumination, often simulating a studio, as the free ones Oli linked to:
[urlhttp://zbyg.deviantart.com/art/HDRi-Pack-1-97402522]Collection 1[/url]
Collection 2
(Download link is to the left, and looks like an orange screen)
The ones in this collection must be loaded as spherical skies.

Other hdri's simulate the light coming from the sun, sky and environment, as the ones in the Dosch collection. These are also loaded as spherical skies.

Here are a few free ones that must be loaded as sky probes:
http://www.debevec.org/probes/

[Chris]

In all honesty, the debevec probes are not that great for renders (My opinion only). You can find some really good ones here: http://www.hdrlabs.com/sibl/archive.html (They aren't probes, they are spherical)

[olishea]

boofredlay: theres a lot of mumbo jumbo concerning tone mapping. basically it spices up your images.

its just like photoshopping your image but before its finished rendering. you can do like 5 different versions of the same image all with different exposure/gamma/blacks/whites and then choose your favourite.

I could tell you didn't tone map that chess scene of yours.....but I didnt dare photoshop it as not to offend.

For some scenes linear mapping looks better than simple mapping.....just test and see what looks best.

Generally the gamma value (1.00) with simple tone mapping is fine but I tend to reduce it slightly to 0.95 or 0.9 and I also up the exposure a bit (again how much depends on the scene-just use your eyes there is no science to it). This will add more contrast and make the image 'punchy'

Linear tone mapping is like playing with levels/curves in photoshop. Generally you should reduce the black value (makes them deeper) and up the white value (makes them brighter). again this just adds contrast and balances the image.

Remember to save a few different version of the same image....you can mix all your images together to get the perfect blend (if you can be arsed).

I cant say it enough....just do a few tests and remember you can tone map while it renders or after its stopped so have a bit of fun!!