Please tell me what im doing wrong,
I have had this issue several times. Rendered all of last night with backburner, .png image sequence with alpha. Today i cheked renders, they are all “blank” although they are not 1kb. Rerendering now without alpha, and images are rendered fine. This happened to me before, but I have no idea why, of course I prefer to have alpha channel in my images.
Tried openin the iamges with koshiygaya or photoshop, no luck there also,
thanks
Sounds like a PNG or Backburner issue to me, but we have NEVER used PNG in production so I don’t have any experience with this problem.
Only format allowed at Prime Focus is OpenEXR. Give it a try and see if the same thing happens. If not, the problem is not in Krakatoa.
First off, cool coloring 
Secondly, when rendering in additive mode the alpha channel is left blank since there is no occlusion occurring between any particles (ie. they add together instead of blend together). Perhaps the method you are using to save the images is assuming it needs to multiply the alpha into the color channels and ends up clobbering the color channels (since the alpha will always be 0).
Can you provide some steps through the Max UI for reproducing this issue? Assume I’ve never used Max before, so that there aren’t any assumptions that prevent me from reproducing the problem.
haha, thanks darcy,
well if the alpha is 0 then theres no way for the colors to go through is therE?
hahaha, great to know!!! tHANK YOU!
it is not possible to get an alpha for additive mode? cant it just be evrey pixel that has information that will be used for alpha?
i love my alpha, and .pngs! of course they arent 16/32bit open exr quality, but for 80% of what i do, i just dont need high dynamic range, i can change colors without any loss, i just cant turn it up or down many many stops, which is alright most of the time…
thanks for the tip, i guess i have to save additive without alpha for now–
The Alpha represents the Transparency/Opacity which in the case of Krakatoa is defined by the volumetric density, which controls the Absorption (how much light will pass through the particles when illuminated and how much will be absorbed) and how much of the particles you will see behind other particles when looking through the camera.
When rendering Additively though, Absorption is 0 and all RGB values are just slapped together additively (nomen est omen), so the particles are fully transparent (you can see ALL particles behind each particle, and all their values are summed instead of blended together). The Density value simply modulates the RGB value.
So there is no Alpha in Additive mode, but you can make yourself a fake one by just taking the RGB as grayscale or something. It is up to you, as long as you have some compositing package to tweak the data.
in this case the opacity is defined by the color values being added, but that shouldnt stop an alpha from being there?
jes i can fake it and make it myself, but wouldnt it be nice to have a working alpha for additive?
sure they are added onto each other and 100% transparent in the rendering process, but when you look at the image once its finished, you can stil see parts that are 100% no-see through, and other parts are transparent
i think it would be nice to have that added in, and if for some reason not possible to add a full white matte in the alpha channel, to let each RGB value pass through,
sure we use openEXR in production for movies (Even though they were also using .pngs for 2012 
) but other imageformats with alpha for additive renders should be supported?
and in the comp, sure i can use a “screen” to let it pass through, but if i had an alpha, i could work with bottom and top layers…
does it make sense what i say or is that a stupid idea?
if so just ignore it ^_°
i guess the additive renders force you to “add” it on to other renders in post, which isnt always the case
The whole additively rendered image IS see-through. There is not Alpha (and There Is No Spoon, either 
)
If there was a background image behind the particles, you would see it all through the additively accumulated particles (we just don’t support background images).
And since Krakatoa does not clamp colors, accumulating 100 particles with a color value of 1.0,1.0,1.0 on top of a pixel with a value of 1.0,0.5,0.3 would result in a color value of 101.0,100.5,100.3 if you would save it as OpenEXR. Alpha would have meant “blend N% of the foreground with 100.0-N % of the background”, but an additive rendering would be added to the background, so Alpha makes no sense. Having a colored pixel instead of black background color does not mean that the pixel would cover anything.
I understand what you mean intuitively, but technically you are wrong and there won’t be any Alpha in Additive mode.
ok, no problem
i just looked, setting the alpha to none, obviously does make the images visible in my comp.
So I guess the last question would be, can i save additive renders without a background?
having everything else be transparent?
Don’t they already save without a background? Looks like [0,0,0] to me.
but isnt 0,0,0 a.k.a. Black also a value?
what makes a transparent image transparent?
do transparent images also have a value where its transparent, only the alpha that is hiding it?
i thought an image could hold only values for where its at, and “no” values where its transparent
Black is a value, yes.
There is no value in a typical raster application that represents “nothing”. Not the way we normally think of “bitmaps”.
When doing Alpha Blending, the Alpha channel defines how much of the value in the RGB will be taken in the mix. There, the Alpha defines what is transparent.
But when doing Additive mixing, there is no Alpha and [0,0,0] means nothing, because any value plus 0 results in the same value.
Thus, black is “transparent” when adding your rendering to any other image (no change to the second image), whereas any other color will increase the values of the second image to produce the final image.
If you generate your own Alpha from the RGB to perform Alpha-Blending of the rendered image, then Black will spill into the mix where the RGB value is close to black but is not exactly black. For example, if you take the RGB as Alpha from one of those images you rendered and blend with a fully WHITE image, the while will remain white where the original rendering was black, but when it is not exactly black the Alpha will not be 0 either and a bit of that black will show up in the result… That’s probably what is driving you nuts.
