View Full Version : Alpha's and Lens flares

03-31-2006, 07:00 AM
Is there a way to render lens flares with an Alpha channel? Or do I have to composit in Layout to render the lens flares into the final comp?

I'd rather have all my layers in After FX.

03-31-2006, 07:08 AM
In Image Filters add Flare2Alpha


03-31-2006, 02:45 PM
You might as well want a straight alpha when compositing
(instead of the default premultiplied) so check the 'fader alpha mode'...

04-01-2006, 01:58 AM
Thanks guys. I used the 'Effects/Processing Menu' and added the Alpha2Flare filter.

Since I already render the sequence out over night, what does the 'fader alpha mode' do? Does it improve the quality because it's ended up darker than the first render that had the elements rendered in one pass (I hope you understand that).

The reason I'm compositing is that all the elements haven't been done as I had to re-render the entire sequence when one object had to be replaced!! So I desided to do seperate layers this time.

04-01-2006, 03:22 AM
for some clarification of the fader alpha mode

04-01-2006, 06:03 AM
I did a test render and the flare is way better with 'Fader Alpha Mode' checked! Thank's for that tip, I'll set it up for another render pass, luckly it won't take too long to render the flare only.

04-04-2006, 11:01 AM
I'd like to offer an alternative method. It requires a few more steps, but it saves having to save the Alpha buffer. It's also a little more accurate. Here's how to do it in Photoshop:

Save your image as normal without any image buffers etc. The alpha channel should only represent solid objects. You'll need to do this in two seperate layers. (Note: Because of Photoshop's handling of Alpha channels, you may have to literally save two seperate images. Sorry about that.)
Put your Alpha layer right above the BG Layer.
Invert the Alpha Layer so that 'solid' is black and transparent is white.
Set the transparency mode for that layer to Multiply. Basically what you're doing here is your cutting out the shape of the mesh from the BG Layer.
Take the RGB layer of your image, and place it in a layer above the Alpha layer.
Set the transparency mode to Screen.
Look at the pretty image you just created. :)

So what did we do here? In the simplest terms, we additively* projected these two images together, then used the alpha channel to cut the 'solid' parts of the image out of the background. Since a lens flare isn't 'solid', it is projected onto the BG the same way any other lighting pass is.

Of course, use whatever works best for you. I just found this little exercise to be quite helpful in understanding how compositing works. It opened a lot of doors for me, so I thought I'd share it. :)

*Although the effect of using Screen Transparency is similar to Additive, mathematically Screen and Additive aren't quite the same.

04-04-2006, 01:01 PM
I use post_Alpha2 all the time. Look for it on Flay. It composite all the alpha data in the render. Both Pre & Post processing effects..Works GREAT!! Better than any of the solutions that come with Lightwave.

10-19-2009, 07:26 AM
In Image Filters add Flare2Alpha


ok this is exactly what i need, soup is ON !!!!

thank you soo much :P

ps. err...it may not be a good thing to post a reply because this is like a 3 yrs old thread :3

08-19-2017, 01:41 PM
I have a scene with nothing but lens flares that I need to show in the alpha channel. I added the Flare2Alpha in the Image Editor "Processing" menu but the flares don't show in the alpha.
Maybe something I missed?



08-24-2017, 07:48 AM
background geo, meaning is there something solid behind it which may be obliterating your alpha, you would need to change the render settings in object properties for any object behind the flare to 'unaffected by object' so as not to give you a white background

08-25-2017, 09:51 AM
I do a lot of stuff "in camera" with Lightwave like motion blur and DoF but one thing I would avoid Lightwave flares. They are bad in LW and since they are the second artifacts seen on a camera (first would be dirt on lens and noise on sensor/film stock) they are easy to integrate in post.

In After Effects NanoGator's technique is a great way to add Volumetric lights. Select all objects in scene and "matte" them. Make all volumetric lights white. (Divide them up if necessary for different colors). Use the BandW images as luma mattes with solid color layers in AE. Makes a render last for an hour vs DAYS.