I’m just getting into using the compositor in Blender, love how it works, but for some reason I’m getting a problem with using the vector blur. Here’s what I’m doing:
Render out a MultiLayer openEXR file with all the passes that I want to tweak individually (diffuse, specular, shadow, AO, Reflection, Vector, z & combined). I’ve set up full sample anti-aliasing and using RGB, not RGBA.
After rendering out, I start a new blender file which will be used for compositing. I input the image sequence in the compositor, link up all the nodes appropriately to try and get a nice vector blurred motion, but the vector blur cuts off about half of the image.
Hooking up the speed to the final image confirms that, for some reason, even though alpha is turned off from the initial render out, half the image is cut off. Weirder again, if I hook up the alpha, it doesn’t quite match up to what it should.
Being new to the compositor, I’m not sure if it’s something I’m doing wrong, or if it’s a bug… I’m using the latest version of Blender, 2.57, which makes me doubt it’s a bug… I’ve tried looking into this myself, but am stumped. Just doesn’t make sense…
Any help with this would be a huuuge help. I’ve attached the files below:
My guess is it has something to do with the alpha channel. If you aren’t compositing it over anything, get rid of the alpha channel before applying the vector blur. (you could give it a dark backdrop before rendering the EXR sequence, if you want)
Why not do all the compositing together with the render? You could even use an output node in the compositor if you wanted to preserve the original, non-composite EXRs.
Hi benu, thanks for you quick reply. I’m not sure if it’s the alpha channel as I’ve been looking at the vector pass and it’s cut off at the same place (see vector colours below)
I got this by plugging the speed channel in to the image. For some reason, the vector pass isn’t counting the whole of the object’s movement and is being cut off around the mid point of the screen.
I would have included these images in my original post, but there’s a limit as to how many you can use per post…
I originally thought that it was because I had selected RGBA in the first export of openEXRs, seeing as black is counted as alpha transparent and I guess it means no movement in a vector channel. Thought it might have been inadvertently affecting the vector pass.
The final background will be a simple white, but I’d like the option to tweak the individual channels after the heavy rendering has been done. This is why I’m exporting as multilayered openEXRs and compositing them again in a new blender file. This way, if I’m asked to brighten, darken, change colour of blue etc, then it’ll be a quick and easy change. Besides, I don’t see why the vector pass would be fixed if it’s coming directly from the render rather than an openEXR file (unless the writing of openEXR files is broken in my version of blender :S).
If I did do it all in one pass, there is a lot of heavy processing going on, lots of reflections, AO etc, meaning a very long render time if a change is needed. Besides, I’m trying to learn as much as I can about the different render passes and compositing and thought this project was a great opportunity to learn all about it. Has all worked fine apart from this vector pass…
The dark corner isn’t actually black – there’s still information there in 32-bit-EXR land. (And, incidentally, the floor intersects with the letters, which messes with the vector blur a bit.)
