Ok, so i have browsed the forum but havent quite found the answer im looking for so decided to post.
I have a title animation, just animated meshes & Masks with added vector blur in the compositor
so far so good.
now im really new to the compositor and havent quite got my head around the render layers and combining them so i want to use after effects to add a background texture to the whole thing.
how do i give the text render an alpha value? so where there is no text or blur its transparent?
also i was thinking about adding some texture to the text in AE, could i convert the text layer into a black & white track matte as well??
So far i have checked RGBA & Rendered a test png image, didnt work.
also there is nothing going into the alpha channel of the output node, which i think is the problem, but the only alpha output is from the initial input prior to the vector blur, which i believe with cause troubles right?
anyway, thanks for any help & let me know if this doesnt make sense,
First and most important: In render settings, shading select Straight Alpha mode.
This way your RGB channels will not multiplied by Alpha.
Unfortunately when you enter Vector Blur Node - RGB will be multiplied by Alpha, but we can fix it. After Vector Blur we can convert Alpha mode from premultiplied to straight.
If we chose premultiplied alpha mode - RGB will be multiplied twice: First time during render, second time by vector blur node. That’s why we should use straight. Don’t use premultiplied, don’t use Sky
In order to render this setup so that alpha is preserved, you need to check RGBA in output.
First of all, hi community! This is my first post here but I’m reading for quite a while now!
Actually I have more or less the same problem. I’m just using a glare node instead of vector blur.
I tried to follow the described steps but didn’t succeed.
I set Alpha to “Straight Alpha”
I used the Alpha Convert Node with ‘premul to key’ option. Somehow I assumed that this would get the alpha that is ‘baked’ into the rgb-channels back to the alpha channel! But that was not the case. For sure there is a lack of basic understanding here…
(I tested this by splitting the rgba-channels and the alpha-channel was still the same as the one from the inital renderlayer)
Actually I must be wrong somehow cause I don’t know how such “alpha-recovery” should work without harming the object-color itself as well…
I’m really a bit down right now
Any further help would be so appreciated! I invested several hours in this now…very frustrating if you think you finished the work and ‘just’ need to save the image
Here is my (test-case) blend-file, it would be so great if someone could fix this so I have the cube + glare on a on top transparent background.
Use “convert Alpha” only when using vector blur. This is a workaround. If you render straight alpha - the output should be straight alpha. This is not what happens when you use vector blur. Image is being premultiplied inside this node and premultiplied result is blurred. That’s why you have to un-multiply afterwords. I will analyze this glare behavior and let you know, but I’m 99% sure that here you shouldn’t use convert alpha node.
I don’t quite understand that. Is this a workflow only when going to after-effects? Or are you saying this should be done in Blender too? because alpha-overing an un-premultiplied vector-blur gives wrong results in Blender.
I personally would use this method in blender as well. What is wrong with un-premultiplied vector blurred image?
Try to take the result of my setup and mix it with anything else using “Mix” node. Let the result of this setup be the second input and let’s turn on “Include alpha of second input”. Is there anything wrong with the result then? I think that it’s fine. What am I missing?
Ah, didn’t try mix node. I usually use the AlphaOver-Node, because I thought that’s what it was made for.
Putting the vector-blur output right inside that node it looks fine, but not if un-premultiplying.
In fact Alpha over does the same as my setup as I see it. It un-premultiplies and then mixes. At least that’s the way I understand this.
So if you un-premultiply, then use alpha over - you in fact divide by alpha twice, but if you put unchanged vector blurred image there - all is fine.
I tend to do it my way because I feel that I don’t fully understand how Alpha over works and I feel that I don’t have full control over my results.
Sometimes I even don’t use “convert alpha” but “mix” node to manually divide RGB by alpha.
I like to work on straight images as long as I can, so that no potential misinterpretations of alpha occur. I simply don;t trust blender in this matter
I had a look in the node, but that is too much for my little brain: http://www.pasteall.org/25453
I did not yet have any bad surprises with AlphaOver though.
hey so thanks everyone for all your help really appreciate it
Here is an image of my Node set up and viewer in the background, the render looks identical.
what would i need to do to get this without that white edge, and to get an alpha channel?
this convo is a bit above my head lol
But i have set it to RBGA and also straight alpha and rendered as a PNG
so yeah as i said i want it to go to after effects without the ‘black’ background essentially lol. i havent really explored the compositor yet so am not very good with it…
Not good. Seems like we have bigger problem than I thought. This object doesn’t move right? And yes - this outline is scary. It shouldn’t be there if my theory is right, but it seems, that I made some mistake.
I do a lot of compositing in After Effects. When I add vector blur I do it a bit differently. I first composite stuff in After Effects without vector blur, then come back to blender and add vector blur to ready composited in AE image.
Didn’t analyze your scenario deeply enough, because for me - vector blur is always the last, last, final, last step
Well basically all i want to do is add a cool textured background to it.
the reason i decided to do this in AE is because i have annimated masks that take chunks out of the background, so although i would like to solve this problem as i will want to render out footage with alpha channels at some point, if i can get around it by figuring out how to have the masks not effect the background that would be ok, because i can just create the background in AE then put it on a plane behind the animation…correct?
ok so i made it work by using sampled motion blur…takes longer but is ok for a test like this
however i am trying to convert it into a video format from PNG. which format can i use that will keep the alpha? so far avi codec didnt work. because when i add a solid colour underneath the black background remains.
this was not the case for the still PNG’s. will i have to put it together in AE? or is there a format that will keep the alpha?
really appreciate it