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Hi,Every Master!How are you!
Today, I encounter a problem on background.
the problem like this:
1. I did not set any background in the scene,and after setting the materials,I rendered the scene, get such result:
Attachment:
TestSceneLightNoBackground2.jpg
TestSceneLightNoBackground2.jpg [ 94.17 KiB | Viewed 1457 times ]

Upper is the scene that I didnot change any items in Sun and Sky.just choose the Sun and Sky,Use sketchup's sun system.
2. I feel I should add a background to make the scene much better,so,I chose a background picture ,just like this one:
Attachment:
Background.jpg
Background.jpg [ 41 KiB | Viewed 1457 times ]

Wa, this picture gets a very good color ,so take it as background,the scene must be very good.
So, I chose it as the environment map of the scene.
But ,after the rendering,I get such result:
Attachment:
TestSceneLightHasBackground1.jpg
TestSceneLightHasBackground1.jpg [ 64.55 KiB | Viewed 1457 times ]

3. I found sun and sky can set the sun's position,so ,I set a position for the sun in the scene, and I get such result:
Attachment:
TestSceneLightNoBackground1.jpg
TestSceneLightNoBackground1.jpg [ 87.02 KiB | Viewed 1457 times ]

Compare upper three Scene rendered by indigo, I get some problem:
1. in the scene that has no background ,I get a very good indoor effect,and the light way is very accurate,but without background,I always feel losing something.
2.in the scene that has a background,I found the shadows were gone,No shadows of the pillars on the ground. And the background get a very light vision,the color does not meet the original picture. and the position does not meet my requirement. the leftup corner must be blue sky,but the scene shown a sky with cloud.
3.in the scene that changed the sun's position,no background and the light just like at twilight,show us a orange scene.
What is the problem exist? How can I control the background and sun light accurately.
the background how can I set its position in the scene and how can I get its original good color ?
And the important Point, How can I set the background without losing the shadows of those stuff? just get a right sunlight way with a background?
Please answer me ,every Masters! thanks a lot firstly!


Last edited by FiveAG on Fri Jun 04, 2010 12:51 pm, edited 1 time in total.

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In Indigo, external lighting and background are a single thing.

So when you set the background (case 2), this disable the sunlight. Instead, the external lighting is calculated from your background image, which is wrapped on a sphere surrounding your scene, and emitting light. As this background image has no strong lightspot, the resulting light is quite diffuse and you get no shadows. By the way, you will not get nice results by using standard (rectilinear) pictures for the background. You need a spherical picture (classically called envmap or environment mapping), this would be better.

In case 3, you switched back to skylight, and set a position close to twilight. Hence the lighting.

If you want skylight and background image, you need to render it with a sunlight (no background) and composite it with another tool (like photoshop)

That's both an advantage and a drawback : environement and outside light are the same thing. Doing otherwise would be a non-physically based hack.

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galinette wrote:
If you want skylight and background image, you need to render it with a sunlight (no background) and composite it with another tool (like photoshop)


..OR you can model a curved surface onto which you'll apply your background, as you like from you point of view. So you'll have sun/sky, you'll preserve glass reflections and you get a nice background, Some people here would suggest you make the background image an emitter, so you can set it to emit a small amount of light not to appear like sort of a dead poster or something :lol:

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Can I understand your meaning like below?
1.In indigo ,the software can calculate the sunlight's position automatically through the background image, can't it?
2.the indigo100's idea looks very good,but I feel it gets another problem. Whether the curved surface can block the sunlight? If it can block the sunlight,I feel it will be very difficult to control the position of sunlight. I feel make it an emitter will be a better idea.Because it can simulate the sunlight,but How large the power it will be will meet the power of sunlight to make the scene looks much real?


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1) Not exactly. In fact, when you use a background image (better : an environment map), indigo uses every pixel value of the image as a lightsource. If there is a bright green area, the environment will emit a bright green light from this direction, etc... This is not exactly "auto calculation of the sun position" but the use of the whole environment map as an emitter.
I use this for making realistic lighting of objects, by taking full spherical hdri images of a room, for instance. Then I render just the object, using the room picture as envmap. The object is then rendered perfectly as if it was in the real room.


2)Yes, the background surface will block sunlight. However, you can position it so that the cast shadow is not visible. I don't like that and prefer to use envmaps! I have one here but it is copyrighted. You should try one of these : http://gl.ict.usc.edu/Data/HighResProbes/, just download a .exr version and use it as environment map in skindigo render settings. HDRI envmaps rock (but are hard to make or find...)
Then if you want super-nice skylight & background, I recommend you to buy one such as here : http://www.hyperfocaldesign.com/HDRI/VH ... /index.htm

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..my name is Pibuz, btw :lol:

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I agree 100% with galinette, using normal (low dynamic range) images for lighting will never produce bright sunlight. If you use a high resolution HDRI (long/lat for indigo) it is often also usable as a background.

Here's a couple of links with nice FREE HDRI's
Some nice free hdris http://www.crazy8studio.com/hdr.php
Very high res (more likely suitable for backgrounds as well as lighting) http://www.openfootage.net/?cat=15

Most will come in .hdr format, you can open them in photoshop and save as EXR for use in indigo.

When you're searching and testing HDR images to use, some are made better than others, ie. the sun will have much greater pixel values (contrast) than others, giving more accurate sun-like shadows. Just a matter of testing them.


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Thanks for the links!

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Master. Soup gave us a tutorial on how to composite to environment,it gets some ways to add good background.
download this tutorial,it is very good:
Attachment:
Tutorial_compositing.pdf [819.22 KiB]
Downloaded 156 times


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I feel the two ways must be good for such purpose.
first is use environment map ,second is creat plane and set background to it.
because,sometimes ,we need the surface of Modules can reflect the picture of environment .
as the design of real car's surface,etc.
just like this:
Attachment:
Test1NormalPP22.jpg
Test1NormalPP22.jpg [ 39.44 KiB | Viewed 1347 times ]

the bar reflects the environment map!!
it is very important in a lot of compositions!!!
but use alpha render and PS compositing cannot reach such result.
so , I feel if skindigo designed to be able to use environment map alongside sunlight, the programme will be much more perfect!!!
it will get more sufficent use and effect.


Attachments:
Test1NormalPP22.jpg
Test1NormalPP22.jpg [ 57.26 KiB | Viewed 1347 times ]
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What you are describing is on the to-do list. Using the suns position to bake a sun onto an existing environment map. For the time being, you will have to use a image-editor, such as photoshop, to brighten up the suns position so that it is bright enough to cast shadows.


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Show a Car composition renderered recently:
Attachment:
RenderingCarResult.jpg
RenderingCarResult.jpg [ 398.11 KiB | Viewed 1332 times ]

Always feel it is too difficult to composite the car with background.
In this case,I use the method which create scene that around the car I create the screen which show the background.
Attachment:
TestCarScene.JPG
TestCarScene.JPG [ 41.66 KiB | Viewed 1332 times ]

Because,I feel ,the car's surface must be able to reflect the scene,it will be much real.
but ,this method get a shortcoming originally, it cannot cover the sky.if you are notice the result,you can find the car's upside reflecting blue, that's no any plane covering it.So,it can give us a tricky view that it seems to be real.But i feel it is too difficult to control the background causing such problem.
secondly, the shadow is very difficult to control.
if I change the viewangle a little, I get the scene like below:
Attachment:
RenderingCarResult2.jpg
RenderingCarResult2.jpg [ 461.09 KiB | Viewed 1332 times ]

Notice the leftUpper corner,there is the shadow of the plane.
it is the shortcoming of this method.
I strongly advice the developer :
Please add the capability of adjusting the environment map and sun light.To make the Software become more Perfectly!!!! Thanks a lot!!!:D


Attachments:
RenderingCarResult2.jpg
RenderingCarResult2.jpg [ 461.09 KiB | Viewed 1332 times ]
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Thanks a lot to developers,Hoping for a perfect performance on this in the new version!!!!


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