Forgive me if my terminology is poor. I’m using a glare composite node to create streaks that make some gold coins “gleam”.
When I render the image I can see the streaks clear as day and they extend beyond the coins over the background. But when I use the F3 command to create a png file of my rendering, the streaks are only visible where they overlap the coins. They no longer extend out over the background. I’m trying to create a png file of the tumbling coins with a transparent background that I can drop into CorelDraw but the gleams get cut off at the edge of the coins. Attached is a screenshot of the settings, the render window, and the resulting png file.
I was hoping someone might be able to tell me what setting needs adjusting so the streaks appear outside of the coins in the png file (ie having some alpha value over the background)
click premul or key, not sky. that will save your color information as non-transparent, so you can see the color in another package and still use the alpha channel. see my book page 252
Glad to see you’re still at it down under 
Still no luck I’m afraid. Here is the .blend file. The streaks created from the composite node don’t seem to have any alpha value.
Attachments
Chinese Coins.blend (118 KB)
ah yes, you are correct, the streaks are an artifact and they are color only. so, you have a few choices. see pg 340-346. Since you already have black there, use the luminance key node (fig 11-31) and key on black. Note the really low sittings in the figure and mentioned in the text. The next easiest would be to set your world background blue or green and use the other matte nodes to then greenscreen it out, leaving you with a an alpha image that is based on color.
Thanks old buddy I’ll give it a whirl. Hope all’s well with you.
Still no luck I’m afraid. The streaks appear but they are mixed in with the background and actually darken whatever object I overlay them on instead of blending the pale yellows and white of the streaks.
I have played around with lots of different methods using the alpha inputs etc but can’t seem to get it.