View Full Version : Volumetrics Question

01-07-2008, 01:13 PM

I have a setup of a Spot light pointing up with volumetrics turned on.
when I make a render it looks good on a black background, but when I want to use it as a transparant image I saved it as a png32 file.
This is where I get stuck, it doesn't save the volumetrics.
Which is why I wonder why doesn't show up, but if I save it a bitmap it works fine.

Can anyone help me?

01-07-2008, 01:18 PM
You'll have to render an alpha image as well to get the transparency. As far as I know (someone correct me if I'm wrong), rendering as a .png won't save the "empty" portions of your image as transparent.

01-07-2008, 01:31 PM
Yeah I did try that too, the Alpha file was just filled with black, a white color should show the alpha regions but it's not...

I have tried placing a dummy box in it to see what I am doing wrong, the box is indeed shown in white on the alpha image but not the volumetrics.

01-07-2008, 05:03 PM
This happens when your transparency curves are too aggressive. if you have a high luminance and low opacity, it will show up in render but not in alpha.

volumetrics is all about ballancing opacity, luminousity, density and color over a particles life span. you must have an adequate amount of opacity to see the alpha and you must have an adequate amount of density to drive the opacity.

you need to keep playing to find the magical sweet settings. i could tell you what they are but whats the challenge in that?

01-08-2008, 03:04 AM
Thanks Stooch,

I already noticed when I changed the opacity value, it showed up in alpha.
But the color of the volumetrics changed so I have to balance that out.

Now to find the perfect balance :)


01-08-2008, 08:08 AM
you need to keep playing to find the magical sweet settings. i could tell you what they are but whats the challenge in that?

Ooh, you mean, Stooch, you mean...

If you still need some help Artia...SORRY!!!! :D

01-08-2008, 09:05 AM
Nah hes right, you learn a lot more by experimenting yourself.
And sometimes a push can do a lot :)

There also many settings in the property window, I get lost in the sea of information and if I don't know what it means. I can stil do it but stil not understand :s

01-11-2008, 04:18 PM
:) i cant sit here and tell you the settings blindly. it depends on your scene, lighting (if you are using lights to light voxels - for shadows) and the number of particles being emitted
and spacing between particles
and the blending modes you want to use

the possibilities are endless. :)

overdrive density, it helps if you are using density driven gradients (hint, i use em alot)

01-12-2008, 11:42 AM
I want to add that PNG files can cause some stange problems.
I know I turned to them because lots of people said the same about my beloved TGAs, but I DID have some weird issues with PNGs that disappeared when I went back to TGAs.

Mr Rid
01-12-2008, 04:11 PM
I suspect the problem is that your original render of a volumetric light had no opacity and therefore no alpha contained in the png32. I would not fiddle with opacity, and you should not need the alpha. But when you load that png32 image back into LW to apply as transparency map, the blank alpha is canceling your luminance info and so it affects nothing. In the Image Edior, under Source tab, set the Alpha Channel to 'Disabled.' Or just save your original render in a format that does not contain an alpha, since the alpha is not needed for transparency mapping.

I have been tripped up a number of times by an alpha imbedded within an image that I didnt realize was there (someone else generated it) and had to remember to disable the alpha in the Image Editor.

I sometimes pre-render volumetrics and then map them on cards in a scene to speed things up, but there can sometimes be undesirable edges especially with hazy voxels. It may never be apparent in most instances, but using the luminance values of an image as a typical transparency map is not exactly the same as keying an image with an alpha like in a compositing program. There is a post multiply that takes place in an alpha key that I have never found a way to recreate in surfacing with transparency maps. I tried countless ways of combining/multiplying transparency maps and alphas but it never quite looks the same. But in your case, a simple volumetric light should be no problem. It is usually with more detailed textures like smoke that the edges dont key well in the transparency channel.

Mr Rid
01-12-2008, 04:27 PM

I dont know any advantage to using PNGs as texture maps unless they are first reduced to 8 bit greyscale or 256 color in Photoshop. And I have seen weirdness with PNGs only when using LW's Image Editor to alter the image- it may or may not appear right when mapped. But PNGs can be a huge RAM saver that most animators still dont seem to understand.

98% of color texture images can be reduced to 256 colors and will appear exactly the same, yet will take up a third as much RAM in LW. You may occasionally get banding in images that have very subtle color gradiations, but most of the time it works very well. And 8 bit greyscaling of black & white images will have no artifacting at all. I make 8 bit versions of ALL image maps, and save them as lossless PNGs in order to save time loading scenes (makes a big difference if you have hundreds of Mbs of image files) and conserve RAM as well as drive space. I have worked on projects where heavy scenes were maxing out ram on workstations. 8 bit PNGs saved the day.