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PostPosted: Mon, 24-09-07, 23:10 GMT 
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t00fri wrote:
Cham wrote:
I agree. The star rendering in Celestia currently sucks, and someday, something should be done about it (at the code level), so we can have a more realistic rendering, for ALL stars. The trick I'm exposing is really a "bricolage" (or a kind of "hack") which is applied to a few stars only, so it's not very satisfying.


Absolutely, Martin.

I just wanted to recall the target, which is feasible with the technology of today. In order to
really render stars naturally we DO need

High Dynamic Range Rendering. There is NO way around that.
http://en.wikipedia.org/wiki/High_dynam ... _rendering

Bye Fridger


Fridger, I don't follow you tonight... :?
What HDR have to see with the stars surfaces rendering in X-ray or IR?
Ok for visible light, but even in this case, HDR has not much to see with a specific star itself but much to do with the rendering of a whole scene (fading background stars for example...)


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PostPosted: Mon, 24-09-07, 23:12 GMT 
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t00fri wrote:
...My own time scale is much better defined and certainly less than 2 or 3 years...


Hey, that's good news! :D


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PostPosted: Mon, 24-09-07, 23:35 GMT 
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ElChristou wrote:

Fridger, I don't follow you tonight... :?
What HDR have to see with the stars surfaces rendering in X-ray or IR?
Ok for visible light, but even in this case, HDR has not much to see with a specific star itself but much to do with the rendering of a whole scene (fading background stars for example...)


Well, as I see it, the main deficiency with all the present close-up stars is a far too small available dynamic range in brightness to express an excessively bright star that is a nuclear reactor at work(!), in front of a dark scene... Your eyes must hurt when you look at the glowing ball! ;-)

Look again at the left-hand image...
Image

F.

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PostPosted: Mon, 24-09-07, 23:40 GMT 
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Here is even a respective quote from that Wiki article:

Accurate preservation of light

Without HDRR, the sun and most lights are clipped to 100% (1.0 in the framebuffer). When this light is reflected the result must then be less than or equal to 1, since the reflected value is calculated by multiplying the original value by the surface reflectiveness, usually in the range 0 to 1. This gives the impression that the scene is dull or bland. However, using HDRR, the light produced by the sun and other lights can be represented with appropriately high values, exceeding the 1.0 clamping limit in the frame buffer, with the sun possibly being stored as high as 60000. When the light from them is reflected it will remain relatively high (even for very poor reflectors), which will be clipped to white or properly tonemapped when rendered.

F.

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PostPosted: Tue, 25-09-07, 0:04 GMT 
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Fridger, we agree on the principe, but actually HDR is very useful in common everyday complex scene. In comparison, in our case (space), we have to deal with a light source versus... nothing! (our scenery is far from being complex). HDR create the illusion of brightness using a contrast. Now, in the case of a star, HDR will fade all the background to black, but how HDR will increase the contrast of an already white star on an already black background?

Remember this bug?

Image
Image

(http://shatters.net/forum/viewtopic.php?t=10465)

I'm not talking about the yellowish corona, but about the overall effect. More contrast than this will be hard to do. I don't know for you, but I almost cannot fix the first pict...
This was a bug, ok, but the result was astonishingly good even on my low config AND without using complex technic...


Last edited by ElChristou on Tue, 25-09-07, 0:56 GMT, edited 1 time in total.

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PostPosted: Tue, 25-09-07, 0:44 GMT 
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ElChristou,

I am using the six spheres as is shown in the code. It might not be exactly the way that was stated, but I do have six spheres all skinned with semi-transparent textures all moving according to the code posted with a few tweaks for my own textures of course. So it really is my textures that are showing through and causing what you are seeing. Again, I am going to play with it a bit.

Cham,

A quick question about the sphere models and and the texture. Are the textures being applied to the spheres in Celestia or are they being imbeded into the sphere models in another application. When I applied the textures over the transparent sphere models I have, I get polar pinching. I remade my texture and it now has absolutely no polar pinching. But of course it has other issues. So at this point I can get your code to work, but in a round about way. So I think a little more clarification on the spheres and textures would help.

Don. Edwards


Last edited by Don. Edwards on Tue, 25-09-07, 20:24 GMT, edited 1 time in total.

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PostPosted: Tue, 25-09-07, 4:31 GMT 
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ElChristou wrote:
HDR will fade all the background to black, but how HDR will increase the contrast of an already white star on an already black background?


ElChristou, even your sun pic is unrealistic - at that distance the screen should just be completely white! (Any known sensor - human eyes included - will just be completely saturated). Somehow I don't think many users will dig a white screen instead of a picture of a star - while of course physical accuracy with rigourous HDR is important, in some instances human expectation is going to win out. This is why the current approach with giving stars fake glare textures may continue to be useful.

An alternative, may be to apply rigourous HDR but also introduce the concept of ND filters (like those used in photography to reduce the amount of light entering the lens)..


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PostPosted: Tue, 25-09-07, 7:35 GMT 
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I think in the above pictures, the most important point to HDR is what it can do for the reflection of light on water surfaces. If you look at the one picture, the one with small puddles, you can see that one shows a lighting effect we have in Celestia, and the other what it can be with HDR. It might not seem like much, but you can see these effects in other apps it really makes them impressive.

Don. Edwards


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PostPosted: Tue, 25-09-07, 10:50 GMT 
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Don. Edwards wrote:
A quick question about the sphere models and and the texture. Are the textures being applied to the spheres in Celestia or are they being imbeded into the sphere models in another application. When I applied the textures over the transparent sphere models I have, I get polar pinching. I remade my texture and it now has absolutely not polar pinching. But of course it has other issues. So at this point I can get your code to work, but in a round about way. So I think a little more clarification on the spheres and textures would help.


Don, the textures (fluid1.png and fluid2.png, respectively for the models fluid1.3ds and fluid2.3ds) are applied in a 3D modeler, not in Celestia.

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PostPosted: Tue, 25-09-07, 14:48 GMT 
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dirkpitt wrote:
ElChristou wrote:
HDR will fade all the background to black, but how HDR will increase the contrast of an already white star on an already black background?


ElChristou, even your sun pic is unrealistic - at that distance the screen should just be completely white! (Any known sensor - human eyes included - will just be completely saturated). Somehow I don't think many users will dig a white screen instead of a picture of a star - while of course physical accuracy with rigourous HDR is important, in some instances human expectation is going to win out. This is why the current approach with giving stars fake glare textures may continue to be useful.

An alternative, may be to apply rigourous HDR but also introduce the concept of ND filters (like those used in photography to reduce the amount of light entering the lens)..


Of course, you are right, but what I wanted to illustrate is that we can already obtain a very bright effect without HDR.
Now, here and example of what HDR should do in our case:

Image

Now I'm wondering if it's what we really want... :? (imagine at the distance of my first previous pict... full white screen!!)


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PostPosted: Tue, 25-09-07, 17:55 GMT 
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Christophe,

I think this is a pretty impressive demo! It clearly illustrates that in many respects in Celestia the lighting is still very poor. In the absense of atmospheres the sun and its rerflections must REALLY be rendered brilliantly almost such as to make the eyes hurt...

Bye Fridger

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PostPosted: Tue, 25-09-07, 18:58 GMT 
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t00fri wrote:
Christophe,

I think this is a pretty impressive demo! It clearly illustrates that in many respects in Celestia the lighting is still very poor. In the absense of atmospheres the sun and its rerflections must REALLY be rendered brilliantly almost such as to make the eyes hurt...

Bye Fridger


It's not a demo, it's a mosaic from real shots during Apollo11 (what explain the odd glare). Now if we go for this kind of ultra realistic lightening via HDR, we must be conscious that almost 60 to 80° all around the light source will be really faded by light...


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PostPosted: Tue, 25-09-07, 19:04 GMT 
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ElChristou wrote:
t00fri wrote:
Christophe,

I think this is a pretty impressive demo! It clearly illustrates that in many respects in Celestia the lighting is still very poor. In the absense of atmospheres the sun and its rerflections must REALLY be rendered brilliantly almost such as to make the eyes hurt...

Bye Fridger


It's not a demo, it's a mosaic from real shots during Apollo11 (what explain the odd glare). Now if we go for this kind of ultra realistic lightening via HDR, we must be conscious that almost 60 to 80° all around the light source will be really faded by light...


Well, a demo might also be a photograph, DEMOnstrating some particular issue under discussion ;-)

Cheers,
Fridger

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PostPosted: Tue, 25-09-07, 19:53 GMT 
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Another demo then :wink: (forgetting the lens flare)

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PostPosted: Tue, 25-09-07, 20:30 GMT 
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Cham,

Thanks for the clarification about the models and textures. As I said I di get it to work without the textures being imbeded, but it still needs work.

Don. Edwards


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