View Full Version : Rendering : Using Motion Vectors to apply blur in post

03 March 2004, 11:23 PM
Hi Forum

I am trying to find someone who has some experience with using the 'keep motion vectors' option in Maya software. The default workflow for this is to render the image with this option ticked and then used the blur2d.exe to apply motion blur as a post render effect. I have been told the one can render a frame with the motion vectors as an rgb image which can then be blurred in a 2d application does anyone know how to do this ??


03 March 2004, 12:30 AM
I also would like to know how to do that!

03 March 2004, 01:57 AM
in digital fusion (which is our comp app) theres a krokodove plugin called motion vector blur which can do for the blur2d tool, if you have problems with it, i can elaborate on the correct syntax, since we use it on occasion when maya freaks out (happens with fast animated objects with texture projections on them)

im hitting the hay, let me know if you need assistance


03 March 2004, 09:28 AM
i dont know about plugins or tools that can read the motion vector data from a maya IFF file so far, which i still think is strange since it is one of the best ideas since the invention of sliced bread.

when i am using it i do it the following way:
- i start rendering all my passes as usual.
- when i need Z info and/or motion blur for parts of it, i usually render them seperately in one IFF file.
like that you can have a very fast rendering motion blur and z-depth pass, because you dont need lights or anti aliasing. just assign a surface shader and the render is hell fast.
- then i comp the elements in shake without the motion blur. like that you dont walk into the problem of having all the artifacts of motion blur rendering.
(e.g. you have a background and a foreground that you comp without the motion blur.)
- when all this is done i render the compositing into files that now get the motion blur with blur2d.exe. like that moblur can be tweaked very well.
- if all that needs further comp work you can reload the blurred files in shake and continue.
not really the best workflow but better than rerendering motion blurred files all the time.
if someone can do it: a shake plugin that applies the moblur is very welcome :)

have fun



03 March 2004, 10:34 AM
the way i do it, is i render out the image using the the save motion vectors option. When those are render you can then open up the command prompt and type "blur2d.exe -h" minus the quotation marks and that will list all your flags for your blur2d utility, it even gives you examples, which help alot.

my example:

open command prompt (startmenu/accesories/commandprompt
C:\blur2d.exe -n 1 100 1 -l 4 -f "enter file location here"

then push enter. What this will do is blur your file sequence from frame 1 to 100 at 1 frame intervals, with a blur length of 4 using the file you entered the location for, you could also find your file in my computer or explorer and drag the .iff file where you want to type location and it will automatically type it. The only kicker for an image sequence is that the files need to named "filename.iff.#" the numbers cant have padding as far as i know so just 1,2, etc and when you enter the file name for the sequence just enter the name no numbers(filename.iff) then it will create a whole new sequence named "filenmae.blur.iff" or something like that and you can view that in fcheck then save it from there where ever you want as whatever file you want. Hope i helped, i was looking for the same thing about 2 weeks ago and after about a day figured it out with a little help from cgtalk.


03 March 2004, 10:46 AM

there are 2 more flags that are not in the blur2d.exe -h help that you will need:
where -v specifies the file sequence that holds the motion vector information and -c is the color info sequence.
so you dont need to take the motion blur from the same file as the color which is what i described above



03 March 2004, 05:30 AM
Thanks for all the replies.

Alexx has kind of hit the nail on the head. I am looking for a way of reading or accessing vector data.

BTW Very nice info about the extra flags!!

What I am trying to do is apply the motion blur in shake rather than using blur2d.exe. I find blur2d a bit arbitrary.

I really want to take advantage of a shake idBlur Macro (from which allows a user to specify the input data and the resulting blur to be applied with a very fine degree of control.

the problem with the .iff is it comes out all nasy and compiled and I cant acess this info.

I am sure there is a way to write a shader either, PRman of mental ray, that will generate vector data in rgb format a normal map .... maybe there is a TD out there with some time on their Hands ??

03 March 2004, 10:47 AM
after some searching i found an old piece of software that might be a beginning:

this is a plugin (for maya 4.0!!) that creates a new MEL command called:
syntax is:
motionVector -i "file containing motion vector data" -o "file with motion data as rgb information"

that thing is very unfinished afaik. i got it from alias some years ago.
since i dont have any time for stuff like that and i am not a good coder for CPP, i hope someone else can use it to create what we need.

the sourcecode is in the zip file as well.

motionVector ( )



03 March 2004, 09:58 PM
wow thats just brilliant Alexx.

I can't thank you enough. I will try and get my brother to have a look at it as he is a programmer. Otherwise I might just try and find someone who is willing to give me some time.Hopefully I will have some R&D time comming up.... if i get it up dated and working I will post the results along with a tutorial on my workflow in Maya and shake.

Thanks again



03 March 2004, 12:54 AM
Hey Aneks,

I know Shake 3.01 support the .mt file format (Mray motion)


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