View Full Version : Depth of Field & Compound Blur

01 January 2004, 10:48 PM

This is kind of a follow on from numerous posts in the past about successfully getting a DOF effect in combustion from Maya. Ok so I've got a sequence of targas for both my colour and ZDepth pass.

I read that I should use the Zdepth to drive a compound blur on the colour pass. I've got this far and it all works ok.

The problem I am having is controlling the effect - what I would like to do is have the focus of my scene in the kind of midground. So how can I blur out both the lightest and darkest parts of the ZDepth? Ideally I would like the most blur to be in the foreground, non or a tiny amount in the midground and then more blur in the background (though not as much as in the foreground).

How can I achieve this? At the moment if I exaggerate the effect, my blur is extreme in either the lightest or darkest parts of the ZDepth image but not both.

Or am I being self defeating in trying to use the ZDepth in this way? Should I just settle for the kind of effects its giving me? (ie: is that what you would expect in a true dof effect?)


01 January 2004, 12:33 AM
What you can do is put a colour corrector operator (just use a Histogram, Curves, or Brightness Contrast) to the Z-Buffer layer.

If you then point your Compound Blur operator at the CC operator, you can alter the Z Position of the blur (ie the focus range) by altering the CC operator. Increase contrast & you will shorten the focal range, clipping the whites or blacks will move the start or end focal point in Z space...

If you use x2 copies of the Z-Buffer layer (one with an invert operator before the CC operator) you can use x2 Compound blurs, one to do the foward blur, one to do the background blur.

01 January 2004, 01:30 AM
Awesome Chris that really helped.

One more thing, to get a convincing DOF effect would I have to key the value of the blur over time or can I almost set and forget?

To me it looks ok but then I dont know exactly if it's 100% accurate.

As a little background, I've just got a camera move which begins by looking at the background of the image and then gradually dollies out to reveal the mid and then ultimately the foreground. The end of the animation is my final composition so I ultimately want this to look the best. Should I set my values to get a good effect at this point and then let the rest do whatever? (it's like a 6 second move). Or, should I choose various points througout the animation and set keys to get them correct and let the software interpolate?

Or any other suggestions on how to go with this?


01 January 2004, 03:10 AM
I'd do it with a couple of keyframes (with some ease in & ease out) just set your CC values at the end, & beginning. If you have too many keyframes in there its going to look like youve got some newbie DOP doing the camera work whos jumpy doing the focus pull ;)

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