I'm planning a Bryce 5 animation of hot air balloons flying by twilight.  Not having used Bryce in quite a while, I find that I'm having a problem with simulating the internal glow of a balloon when its burner is lit.

I initially thought I could put a light inside of the balloon (which I would turn on and off periodically) and then play with the balloon's surface texture to allow some of that light through, but the only way I've been able to do this is to make the balloon partially transparent, which has the undesirable effect of making the whole balloon transparent.  It should be opaque save for the effect of the internal lighting "leaking through".

I also tried discarding the internal light object and instead increasing the ambience of the balloon itself with a yellowish ambient color selected, but that doesn't seem to be visible in darkness, even with ambience set to 100.  (Is Bryce ambience not truly ambient?  I would expect a 100% ambient object to show up very brightly in the dark.)

Can anyone point me in the right direction here?

A hot air balloon is not solid, a bit of transparency should be ok.  If not the light can't be seen.
You could try a hollow balloon and make the inside an even color to help with the light.  The outside can be multicolored but have orange or something as the inside color.  
I haven't tried this but it may be something along those lines.

I just tried several materials with ambient at 100 with no sun and a black background and it was bright.  
What material are you using? 

 

I don't think hot air balloons are transparent to any significant degree: look at en.wikipedia.org/wiki/Hot_air_balloon for some example photos of what I mean.  Anyway, if I add just barely enough transparency to the balloon to allow a little bit of the inside light through (not enough to achieve the desired effect), I can already see the pattern on the opposite side of the balloon, as well as the horizon beyond, and I think that's very wrong.  :(

I did just figure out my ambience problem - my ambient color in Sky Lab was black.  Thanks for trying it for me, though.  (slapping self :)

I'm now wondering if it might work to put a solid, highly ambient copy of the balloon bag just inside the main balloon bag, and then add some transparency to the outer bag?  That way the slightly transparent balloon still couldn't be seen through.  And if I base the outer bag's transparency on an alpha texture that is less transparent in darker areas, perhaps it would prevent the "washed out" effect?  Does that sound like a workable approach, or can someone suggest a better one?

or make a primitive in the 'shape' of a flame, then put a light in that? The balloons aren't transparent, but are opaque enough that the flamelight shoots through when lit.

What has been the problem has been emulating the gentle glow that fills almost the entire bag when those burners light off in the dark, and the existence of a "flame object" doesn't seem like it would be of any help in that.  That's such a cool thing to see in person that I'd like to realize it as closely as possible in my animation.

I tried the idea I'd proposed in the last paragraph of my previous message, and it comes kind of vaguely close, anyway.  I'd still like to get closer, but at least I feel like I'm in the ballpark now ... maybe it will do the trick after some additional refinement.  However, I remain open to any brilliant notions that anyone might have.  I'm still working with a sphere primitive for testing it today, but before the end of the weekend I figure to try a render with one of my actual balloon models ... when I do, I'll post the results for your comments.

The ambient inner bag sounds great.  That's kind of what I was thinking but your way seems the most promising.  Maybe you can rig it up so the ambience is stronger near the flame and gets less farther away.  I will wait for your render, and experiment a bit myself.

I was thinking of something similar: i.e., adding a gradient mask to the alpha texture used for the outer bag's transparancy to lessen the effect at distances further from the burner.  But perhaps adjusting the ambience of the inner bag itself in this way would indeed be more effective.  Good thoughts!

Thanks for all of the input!

Did you try using True Ambience?
Set all of your material ambient levels low, except the parts you want to glow; set them high. Use a high global ambience.

Ooo ... I had completely forgotten about the Render Options dialog.  I just tried enabling True Ambience, and it definitely improved the results of my "inner ambient bag" method a LOT.  Thanks for that!

Sometimes for light spread on a translucent material you can try checking "blurry transmissions" in render options or alternately you could add a sandy bump to a material with a height less than 3 and scale the sandy texture to 600 or above. The downside is that this costs some render time.

ok, usually, the most realistic solutions are received by emulating real life as realistically as possible. So first lets look at a few reference shots. The whole effect is based on light so lets first analyze it under a few different lighting circumstances

Here's balloons by day. As you can see they look fairly untransparent but you might notice there´s a low contrast between shadowed and light area´s. This means the balloon probably has a translucent propperty rather then a transparent propperty. This is not something bryce does by default, but we can work around it later. Also notice that the flame´s light effect on the balloon is quite unnoticable in bright daylight.

Now lets look at an evening pic. The light in the evening is much less strong, allowing to better see the effect. What we notice straight away is that the flame is obviously shooting off the white scale of the photo (the white balance clips the brightness of the flame to white), so it must be by far the brighest point in the scene. The balloon and the sky share about the same amount of light. there's no strong key sunlight anymore so the main light source in this setting is behaving like an ambient low-intencity fill light. Taking into account the low intencity fill light, and the high intensity flame, its clear that the illumination at the base of the balloon is fairly dim. The amount of light from the flame that's blocked out by the balloon is probably still pretty high! also the effect doesnt spread very far, so a strong fall-off on the flame's light source will be essential in bryce to simulate the same effect. Perhaps with a gradient ramp and range for extra controlability?

Now finally we have a night view of the effect. Almost all environment light is gone, so this will be purely your balloon light effect. Perfect to analyze how it works! Again its clear there's a high fall-off in the way the light spreads, and the balloons dont look transparent. The light sent throughout the balloon and shining through seems to be smooth and soft, the wires and the seams block out the most light. What u see here is purely the translucent propperty of the balloon! It's important to remember this, because emulating a scene like this first will allow you to make a good base for your balloons translucent effect. Once it works, u can throw in the diffuse and maybe specular light. I'd avoid using ambience in the textures because translucency tends to reduce contrast and ambience does so too, ambience will kill part of the nice translucent effect as well as reducing the sense of depth.

Excellent reference pictures and good observations.  But now the $64K question remains: how can one create (or simulate) translucent (not transparent) materials/surfaces in Bryce?

Ok, now lets see what we can do about emulating this effect.
We need a few elements:

• Balloon color texture.
• Balloon transparency map. (to make the wires/seams less transparent)
• Bright light source with high falloff.
• Blurry transparency.

Ok, first lets put the color texture of the balloon into the diffusion slot of an empty texture. This will be the base of the balloons texture.
Now we need the balloon to be partially transparent. I know it sounds bad, but it'll be the basis of our translucent effect. Lets put it 30% transparent for now, or use the transparency map to control the transparency.
Make sure there's no ambience or specularity, and no reflections, metallicity or bumps yet. Exit the material editor.

Now place your light source at the position of the flame, and turn the sunlight off, or use a bryce night sky, either way, make sure the flame's the dominant light source.

Now try a square falloff on the light first, it's the most 'true to life' and thus probably a good starting point. Up the light intensity, and play with the lights color a bit to get a convincing light color. notice it's light color I'm talking about here, not neccesarily translucence color.

Now comes the magic, when u have the light shining through looking good. we go to the premium render settings and we turn all premium effects off, except blurry reflections. Change rpp to a low setting for test renders 4rpp-16rpp will do just fine.
Blurry reflections can blur out whatever shines through the transparent surface! thus making it look translucent. It's a powerfull method to simulate translucent surfaces! To control how much the amount of blur, sue the specular halo color in the texture of the balloon. The color can also be used to adjust the translucent color texture, but probably its best kept colorless. feel free to try otherwise though.
Once the effect is the way you want, witch to the lighting u want in ur final scene, and tweak the diffusion intensity and transparency to something that looks like a good balance.
I think something like that should most likely work a treat.

sorry i took a while :-) its in here! use blurry transparency ;-) it'll keep the light comming through, and blur the imagery behind it to make the transparency unnoticable. White specular halo is maximum blur, black is no blur. i usually use 254,254,254 rgb color rather then 255 255 255 to avoid weird effects that occur sometimes...

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Now comes the magic, when u have the light shining through looking good. we go to the premium render settings and we turn all premium effects off, except blurry reflections. Change rpp to a low setting for test renders 4rpp-16rpp will do just fine.
Blurry reflections can blur out whatever shines through the transparent surface! thus making it look translucent. It's a powerfull method to simulate translucent surfaces! To control how much the amount of blur, sue the specular halo color in the texture of the balloon.

Wow, you put a lot of thought into this, and I really appreciate it.  But did you actually mean "blurry reflections", or is it possible that you intended to recommend use of "blurry transmissions" instead?  Because I'm getting just about exactly what you describe with only "blurry transmissions" checked (especially changing the translucency with the specular color ... I never would have known that), whereas the behavior of "blurry reflections" doesn't seem to be matching what you've described.

In case anyone wants to see, here's a quick little test render of a simple parachute-like object that I have been testing with in order to observe the translucent effect on both the inside and outside surfaces.

This render uses blurry transmissions (not blurry reflections) with the specular color set to white.  One difference is that I'm using a negative object that is transmitting a flat white color to the inside of the object, which seems to help with making the inside surface look more realistic.  Both the inside and outside surfaces are using a transparency value of right around 50% in order to test and observe the translucent glow effect more easily.  (There are no lights in the scene other than a radial light at the location of the flame.)

I'm pretty pleased with this result thus far, and deeply appreciate all of the terrific input that people have been offering.

Maybe use a gel for the light color.

Just use the Blurry Transparency option for rendering.  You can adjust the 'blurriness' of the fabric with the second specular value in the material editor.

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Now comes the magic, when u have the light shining through looking good. we go to the premium render settings and we turn all premium effects off, except blurry reflections. Change rpp to a low setting for test renders 4rpp-16rpp will do just fine.
Blurry reflections can blur out whatever shines through the transparent surface! thus making it look translucent. It's a powerfull method to simulate translucent surfaces! To control how much the amount of blur, sue the specular halo color in the texture of the balloon.

Wow, you put a lot of thought into this, and I really appreciate it.  But did you actually mean "blurry reflections", or is it possible that you intended to recommend use of "blurry transmissions" instead?  Because I'm getting just about exactly what you describe with only "blurry transmissions" checked (especially changing the translucency with the specular color ... I never would have known that), whereas the behavior of "blurry reflections" doesn't seem to be matching what you've described.

yea sorry my bad, I meant blurry transmissoins indeed!

I think the best way to simulate what you want is with an ambience texture that has it's parameters animated, or is a quicktime movie.