View Full Version : compositing sprites ?

05-12-2009, 11:49 AM
I have a very big long setup scene with some surfaces covered in bright twinkly crystals, HD instance is doing the crystals but to get constant almost random 'flare' of the crystals catching light sources I'm using very short lived particles emited from the surfaces with hyperxoxel sprites of a lens flare.
The problem is that the pfx files are so massive that I have only 2 machines out of 35 render nodes that can load the whole scene, so I need to render the sprites separately and composite (in Speededit).
But how? - I have very, very little experience in compositing!
- I can turn all the other objects to mattes and get a very quick render which is just the flares against black, but I can't see an easy way to 'add' that to the 'unflared' render.
can't find any way to get out an alpha chanel

05-12-2009, 06:38 PM
Add is exactly what you need, but some apps assign different names to the function, f.e. it's called Screen in Photoshop. And you don't need an alpha channel.

I don't know if Speededit is layers or nodes - if it's layers, put the flares on top with that layer set to Add. If it's nodes, find an Add node and there should be two connections on it, try it both ways and you'll find it.

05-13-2009, 04:16 AM
I may be thick or something, but I can't see any way to make SpeedEdit 'add' the4 contents of a layer without an alpha channel.
I only have LW and Speededit to work with.

05-13-2009, 04:43 AM
As Dr. Cross so succinctly state some time ago, "It is not a compositor."
You would be better off compositing in LW, particularly if you need blending modes as SE has none of what you are looking for.

You might use the luma keyer to achieve your effect or even the chromakeyer. Doing it with an unmultiplied alpha is going to be your best bet. A multiplied alpha, iirc, will leave the black fringes (or whatever color your material is on) around your clipped material.

You can get it done with what you have. You just have to change your approach someway; lw is the closest tool you have to a true compositor but SE is much much much faster with the process, though cumbersome.

05-13-2009, 05:45 AM
Thanks UnCommonGrafx, but I'm afraid that's left me totally in the dark, the only way I can find to get those 'sparkles' is to us the HV sprites (the sprite image I'm using is a LW generated lens flare - the actuall effect I'm imitating is of course thousands of lensflare type artifacts with the reflections as 'sources') Despite my best efforts, the sprites generate no alpha. At the moment I have everything except the sprites as a (black) matte object, that way I don't see sprites through objects.
The attatched image shows (left to right) render without HV, render with HV, HV only, HV added in photoshop.

05-13-2009, 10:33 AM
What Robert means is to use LW as the compositor; bring both image sequences into an empty scene and comp them there. You could even use a desaturated copy of the rgb as an alpha, but you may have to tweak it; but I still don't think you need one. There are a couple of free compositors, one in Blender and one called Jahshaka.

Your test in Photoshop looks fine, a little bit brighter but that's easily adjustable.