Author Topic: Support for linear lighting ?  (Read 2380 times)

Kim Baumann Larsen

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Support for linear lighting ?
« on: February 18, 2011, 11:34:58 pm »
February 18, 2011, 11:34:58 pm
Hi developers,

 

First I must say I am very impressed by your product - but shadows in brightly sunlit scenes are way too dark...

 

Any plans to implement linear lighting with LUTs (Look Up Tables) in Lumion ? That would be at least a 32-bit color high dynamic range rendering pipeline resulting in gamma-correct, linear color space output.

 

The cutting edge game engines like Unreal 3 and CryEngine along with I believe most games coming out of EA, Activision and Naughty Dog work this way. The Uncharted Engine is another one that uses linear with LUTs.

Coming from a linear light workflow in arch viz  (stills and films) and VFX since a few years now, I have to say that anything BUT a linear light approach is plain wrong and does not look as good as anything rendered with.

 

This is not only about what is right or not, it is about creating a more realistic and ultimately a better look with Lumion. Without a linear light approach to rendering the math will not add up: shadows will be too dark, highlights will burn out and be oversaturated, light falloff will be incorrect, gradients on surfaces will be unrealistic, and GI will be too dark to name but a few issues.



On explaining linear light workflow - it is not done in a flash - for those not familiar with this topic check out the below podcast, blogpost and videos:

http://www.lysator.liu.se/~zap/lwf/

http://filmicgames.com/archives/299

http://vimeo.com/8119194


 

Cheers,

Kim

Marvil

    Reputation: 1
Support for linear lighting ?
« Reply #1 on: February 20, 2011, 06:17:40 am »
February 20, 2011, 06:17:40 am
I second that.

You can get MUCH better images with range that 32 bit output gives you for post work.

Support for linear lighting ?
« Reply #2 on: February 21, 2011, 10:06:26 am »
February 21, 2011, 10:06:26 am
Kim Baumann Larsen said:


Any plans to implement linear lighting with LUTs (Look Up Tables) in Lumion ? That would be at least a 32-bit color high dynamic range rendering pipeline resulting in gamma-correct, linear color space output.

 




 

Remko knows the answer to this question, but in the mean time, if you haven't already, do check out his latest experiments with tone mapping:

More tonemapping and engine tweaks

I should also hasten to say that the full version of Lumion has changed significantly since the Demo version was published on 31-11-10, so assuming that you're using the Demo version results may differ quite a bit from the full version. That being said, I personally agree that the default settings in Lumion tend to produce too dark shadows and too bright clouds (compared to Vray for example) but this is easily rectified if you adjust the shadow brightness/cloud brightness settings by pressing CTRL in the Weather section (or by clicking on "Home" -> "Always Advanced Mode on"). In any case, you can expect the visual quality to improve even further in Update 2.

Support for linear lighting ?
« Reply #3 on: February 24, 2011, 11:39:46 pm »
February 24, 2011, 11:39:46 pm
What he is talking about is that 'normal' image files all have exponential color values. The reason for this is twofold:

1) This is a better distribution of the 256 levels of intensity since the eye is more sensitive in the low range

2) The standard is chosen so it exactly compensates the response of CRT monitors so the signal could be sent directly to the screen without any conversion.

 

Now when you start to do math with images you need to take this into account. Your monitor gives you a warped view of reality. If you view an image and it looks like an even distribution you need to think about the fact that all monitors do not display images as they are.

 

So, before you do the math just convert all images like they should be. They will look wrong on your screen but that's your monitor playing tricks on you. Lumion is smart enough to remove gamma from all textures you give it, then do all calculations linear and finally output a nicely rendered images with gamma re-applied.

 

Removing the gamma is as simple as converting the Lumion frames to a float file format and applying a gamma correction of 0.4545455. That will give you MUCH better results when you start adding post processing effects. You can do this with the output lumion currently provides.

 

The second part of the story is Tone mapping. This is a function which exposes the large dynamic range of color values into a visually pleasing range which fits in a 8 bit texture. If we were to remove tone mapping you would end up with images that are pretty useless unless you have software that can do the tone mapping for you. Also note that this software (a plugin for example) also needs to do the exposure. For best results you do all your effects over the raw image and then to tone mapping and gamma correction. I'm not sure many people know how to do this though. I don't even know if there are plugins available that can do this in editings software.

 

 I do reccomend to remove the gamma correction if you can. I would be suprised if software like premiere would not already do this automatically. Browsers for example don't do any gamma correction when they scale images. You can try this by making a 1x1 pixel black and white grid image and let your browser scale it down. Most browsers wont display a 50% gray image!

Marvil

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Support for linear lighting ?
« Reply #4 on: February 26, 2011, 05:52:40 am »
February 26, 2011, 05:52:40 am
Thanks for the insight Remko/Morten. Very helpful info.

I finally managed to figure out how to open 32bit .dds format in photoshop, which did indeed provide a much better tonal range for editing. The fact that one can output 32 bits from realtime software is unexpected and quite amazing!Surprised

 On the downside, the dds plugin from nvidia only works in the 32bit version of photoshop. Aftereffects also cannot open dds. Any plans for .exr output from Lumion?

Aaron

    Reputation: 80
Support for linear lighting ?
« Reply #5 on: February 28, 2011, 11:48:22 am »
February 28, 2011, 11:48:22 am
Marvil said:

On the downside, the dds plugin from nvidia only works in the 32bit version of photoshop. Aftereffects also cannot open dds. 

 


CS4&5 64-bit support now Wink

http://developer.nvidia.com/ob.....ugins.html