Focus and Depth of Field
5 messages in this thread
<< I described a couple of ways to do this sort of effect a short while ago,
and if you wish, I'll look to see if I still have those messages somewhere.>>
David,
I would really appreciate that. I thought I remembered a discussion on this
topic before, but I didn't pay much attention to it then. (You know how it is,
you read something that sound interesting, but it has nothing to do with the
project you are currently working on. But the idea sticks in your mind for a
future project.)
I think what I am hearing (reading) from people is that the only way to come
close to this effect would be to use the BLUR IPAS (Or mabye the XAOS one). I
can understand how you could use these to put an entire scene out of focus, but
I am still fuzzy on how you can selectively have one object _in_ focus, and
then change from one object to another.
Good luck finding those old messages. I appreciate the effort.
Alice
>>the only way to come close to this effect would be to use the BLUR
IPAS (Or mabye the XAOS one).
Well, not the ONLY one, but certainly the easiest. A
rack-focus effect using the Blur IPAS (I don't know anything about
Xaos's routine) in its simplest form involves rendering the two
planes you wish to focus to and from as separate elements, with alpha
and using the Split alpha option to keep the alpha separate. You will
then have a series of background frames (no alpha needed for that),
and a series of foreground frames along with the alpha frames.
Now, say you wanted to pull focus from the foreground to the
background. Take the background frames and load them in Video Post (A
working knowledge of VP is pretty important here), and then use blur
to process them, going from blurred at the top of the shot to full
focus at the end. then load the foreground and blur it in the
opposite direction over the range of the pull, then do the same to
the split alpha files for the foreground. Now you will have a new
background sequence, over which you will composite the new foreground
frames, using the split alpha frames as masks. This will leave you
with a final composite that shows a focus pull from the foreground to
the background.
Thats the simple explanation, and of course there are many
variations that can be done. Theoretically you can do the same thing
using an image processor like Photoshop to blur the layers, but
unless you had LOTS of time to run all the frames thru one at a time,
you would need to have a static scene and just composite two stills.
There are some programs popping up that will let you process
sequences of frames, and these would simplify the process of using an
external program to blur the frames.
Well, those are the basics. I hope you get the idea. (if not,
let me know, and I'll go into more detail)
<<(A working knowledge of VP is pretty important here>>
I have a fairly decent understanding of VP, but I do fall short when
it comes to Alpha channels. Would you mind going into a little more
detail on Alpha vs. Split Alpha and why I am using one over the
other?
My understanding of Alpha channels is that in a 32 bit image 24 bits
is the color information, and the remaining 8 bits is transparancy or
"alpha" information. Those extra eight bits can be either included in
the TGA file (32 bit files) or sent to a seperate 8 bit file on its
own, leaving a 24 bit TGA file. Is that the proper definition of the
split alpha? The extra 8 bits as a seperate file?
Alice (on the verge of understanding)
Your explanation is exactly correct. The only reason you need
to split the alpha in this case is because BLUR ignores the alpha in
32 bit images. If you use BLUR to process a 32 bit image and
composite it later, the RGB portion of the image will be blurred, but
the alpha channel will stay sharp, which kinda ruins the effect. If
you split the alpha and run blur on it separately, then use it as an
RGB mask (not an alpha mask) in your composite, then it will work
fine. If you use something else to blur your frames that can process
all the channels in a 32 bit image, like photoshop, then you wouldn't
need to split the alpha.
Thank you David.
I won't actually get a chance to try all this till next weekend when I have
some time to play, but when I do, if I have any problems I'll let you know.
Alice