[Bf-committers] [GSoC] Improved threadability of Compositor nodes

[Jeroen Bakker]

Hello Matheus,

On 03/20/2016 06:03 AM, Matheus Sousa Faria wrote:
> Hey,
>
> Thanks for the answers! I've been studying the nodes and the techniques to
> finish my proposal. And I have more questions:
>
>     1. What is the difference between directional and vector blur? I saw in
>     the practice the difference, but I want to know conceptually, why to
>     keep both nodes if they create the same effect (Motion Blur)?
Well both were designed for the same use-case. Mimicking motion 
artifacts of typical video footage. Directional blur is a limitted, but 
faster, vector blur has more options, other limitations around the 
border of the image and is slower.

Most of the time in compositing artists can chose which node supports 
their purpose the best. To my knowledge the vector blur node is used a 
lot, the directional blur not that much.
>     2. I was doing some the tests with the glare node and this question came
>     to my mind: What is the difference of fog glow and blur + mix? I generated
>     the same scene using the glare node, and using the blur node with the mix
>     to combine the original image with the blurred one. The result seems the
>     same to me.
Fog uses a convolve kernel with a Hartley Transform. The convolve kernel 
is more precise than the normal blurs. But I can imagine you can get 
visually the same results when using the blur node. It could be written 
as a Bokeh (which is a convolve kernel itself) and use the 
BokehBlurOperation. But not sure about the details as it also does some 
post color corrections...

>     3. And about the technic used in the Ghost Glare, is there any reference
>     to it? I mean a paper or something, the closest thing that I found about
>     this effect are the crepuscular rays[1].
Not sure if that exists. It was written back in 2006? Perhaps Ton knows 
if a specific paper was being used for the algorithm.

>     4. Do you recommend any reference (papers, books, etc) about glares? The
>     things that I found were about the common glare/glow effect[2].
>
>
> [1] http://http.developer.nvidia.com/GPUGems3/gpugems3_ch13.html
> [2] http://http.developer.nvidia.com/GPUGems/gpugems_ch21.html
I do know of some gaming/animation papers that creates very good result.
  - not realistic: 
http://john-chapman-graphics.blogspot.nl/2013/02/pseudo-lens-flare.html
  - relastic but only for point based light sources: 
http://resources.mpi-inf.mpg.de/lensflareRendering/

I most of the time use the latter one for references. It is a difficult 
algorithm, but has very good results. Might be a bit slow on the cpu as 
it generates meshes for rendering.

Jeroen