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Is there a way to get point density and a transparency film to work. Point density works when in normal film but when I turn transparency on, it is nowhere to be seen.

Martynas Žiemys
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node
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1 Answers1

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If point density is visible in RGB (set the viewer channel to "Color" only) it means that pixels in transparent areas should emit light, despite they don't occlude the background.

That's perfectly fine for an associated alpha image, and it means it can be conmposited straight away with an alpha over operation in the compositor.

Just go to the compositor and use an alpha over node to composite your plate over a solid background (black or gray should work) and check the result.

If that worked it means your plate is perfectly fine for compositing, although the viewer won't show the emissions in transparent pixels.

This is caused by a longstanding bug (sadly still present in 2.8) that makes the viewer pre-multiply images (that are already associated, resulting in a double up), making transparent emissions disappear. They are there, but the broken viewer doesn't show them.

Gez
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  • how do i set the wiewer channel to color only and can you make more specific what you mean by compositing over solid , do you mean without tranparency or should i ad an solid object.? – node Jan 14 '19 at 17:55
  • The image viewer has a group of six buttons in the bottom for selecting what channel is displayed (Color and Alpha, Color, Alpha, Red, Green, Blue). The second one shows the image without transparency, it's useful in cases like this.

    With "Compositing over solid" I mean going to the compositor, add an Alpha over node to blend the rendered image (with transparent background) over a solid color. The output of that alpha over has to be connected to a viewer node in order to view the result.

     – Gez Jan 14 '19 at 18:05
  • btw, it looks like you're not familiar with Blender's compositor. Are you producing this image with transparent background to be composited using Photoshop or other external program? Keep in mind that luminous transparent effects can't be done in a single pass with unassociated alpha (this means that PNG won't be able to store the rendered image with transparent effects and like the viewer will discard the luminous effects). – Gez Jan 14 '19 at 18:11
  • It´s supposed to come an animation, mayby this case is to complex to manage by explaining. but i think im a little wiser now :) – node Jan 14 '19 at 18:43
  • could you clarify some more,., it renders the point dencity ,but the alpha channel show´s only empty. , i used render results as the image , but then when i try to overlap it with alpha over it shoes just black, i have a other picture that the alpha over can show but the backround picture , but when sliding the fac the picture with the point dencity is black, not even the color channels that show the working point dencity are nowhere to be seen. switched routing from the pictures to the alpha over but it does nothing and tryed to use only the images alpha channel but nothign seems to work. ? – node Jan 15 '19 at 13:40
  • If it's a pure emission it means it won't occlude any of the background. Alpha should be completely black while RGB has colour information. A simple alpha over blend over a solid colour should reveal the point density. But if you ckeck the "Alpha Premul" checkbox you'll get the same result as in the viewer. Could you please share a simple .blend flle showing the problem so I can help you fix it? – Gez Jan 16 '19 at 18:57