help with blended materials? trying to do smoke. SOLVED

[Vampyre]

i'm trying to do a scene with a ciggarette. I figure the best way to do the smoke (the only way i could think of) was to draw the smoke on a bitmap, adn use it as a blend mask between a diffuse and a null material. but its behaving strangely. the colors are clipping really early.

to illustrate the problem, i made a bitmap that is nothing but a blend from black to white. i then made a blend material using a null and a white diffuse, and mapped the blend with this bitmap. here is the result.

the origonal blend .png is the top rectangle. the resulting blend mapped material is the bottom rectangle. notice how indigo starts to convert very dark grey colors to a solid color very quickly?

i've tried compressing my smoke picture down into this range, so that its very dark, but it still looks really clipped. does anyone have any suggestions? i'm open to starting from scratch and going about this another way if i can get convincing cigarette smoke another way.

I'm also posting an image of the problem image in question

[Kram1032]

What are your A B C values for the blend map?
Did you also try this under more normal light conditions? (That blue background looks really strange to me...)
Did you try to tweak settings like BiDir? - Maybe, it's a problem with that, again...

[Vanessa07]

Can yous share your .blend are show us the .igs

[fishbowl]

The ultimate help I could give, is use Kerkythea for clip map based renders. It's much more forgiving regarding convenient things like that & there's less geometrical/lighting jerking about involved.

[Vampyre]

The A B and C values are the blendigo default, 0,1,0. bidir is set to on.
I first noticed the problem when trying to blend the smoke into a real scene, im posting an image of the smoke from that scene, as well as the test rig blend file for you guys to have a look at. its packed, u may have to unpack it to get it to render. thanks alot for all teh input.

I hadn't heard of Kerkythea, i'll look into it.

[Vampyre]

I figured it out, i'm elated. i increased the gamma setting for the blend map, simple as that. as u can see it looks much better now, i thought i'd post the results incase anyone else has this problem

[Kram1032]

oh, interesting...
actually, that gamma should be at 1 for such a map, but seemingly, 2.2 is the default, even for such a kind of a map...

[Roger]

Great! Now let's see a smoking render!

[Woodie]

Make sure that your object is using UV to apply texture. By default blender is using object.

[Vampyre]

the render is comin, it'll be here... eventually. i'm at 28 hours now, looks like it'll take another 40 or so. and yeah ,they are uv mapped.

i think i know what caused the strange behavior. indigo expects a color blend map, so when i feed it a RGB image with grey values, it adds red green and blue together. so if thats the case, the proper way to fix it, is to set gamma to 3, instead of 2.2

[Kram1032]

no, I actually thought about it:
2.2 is fine, except using a mac-screen, where you need 1.8.
It's because the blend only looks smooth at 2.2. 'cause your screen looks like that.
at 1, it wouldn't.
(simply make a standard smooth gradient and then set it's gamma to 0.454545454545454545..... (doesn't need that accuracy^^), to see, what Indigo saw )

[Vampyre]

i'm curious now. I don't really have any idea what you mean .could you please elaborate?

Im not sure what my screen has to do with how indigo reads the bitmap. Im sure your right, im just not following along. is indigo programmed to compensate for screen brightness and thats whats causing the result?

[Kram1032]

not directly your screen, but all the programs, you may use to get a gradient.
They're usually all set to Gamma 2.2.
In Photoshop, you can change the way, Gray is projected or understood to 1.0 or 1.8 etc. but most programs simply assume, you're using a screen with gamma 2.2

[Vampyre]

when i made the test rig, using the blend in the gimp, i set the left color to 0,0,0 and the right color to 255,255,255.. wouldn't that create a linear blend no matter what screen i have?

[Kram1032]

well, yes....
A linear blend, when you look at it with gamma 2.2
gamma moves the grey-point, so if your screen was set to gamma 1.0 and gimp would create a blend for 2.2, it would look (I think) brighter in the middle, while if the gimp would create a gamma 1.0 blend while your screen is 2.2 (which it should be), you'd get a too dark blend.