DF Unmultiply
(For Fusion5 & 6)
Short info:
This is a set of tools that will "fix"
an RGBA image that has been "Premultiplied" with any color
other than Black.
Long info:
The DF Unmultiply tools are a
collection of settings for DF's "Custom Tool" that will
convert an RGBA image that has been Premultiplied by its Alpha
channel and a non-black Background color, into an image that has been
Premultiplied by its Alpha channel with Black as its Background
color.
Why:
Have you ever spent hours or days on a
render only to find out that you forgot to put in that black "card"
that keeps the camera from seeing the solid color you're using to
calculate Backdrop Radiosity?
(Have you ever worked at a facility
where you've had to struggle with a plate sequence where others have
done this and there's no chance of re-rendering?)
Digital Fusion has become my
compositing package of choice because with it, I can get things done
easily in 1/8th the time needed in other compositing packages I've
used, and with DF, I can do this without needing to use expensive
third-party plug-ins. DF gives me all I need, to do my job, fast,
efficiently and well, right out of the box.
However, DF is geared around images
that have been Premultiplied by their Alpha, with Black as the BG
color. (The Fusion5 Loaders now have an option to "Post-Multiply"
that will let your flows now work with images that have been
generated with a "Straigh" Alpha mask, which is my
preference for rendering the fine structures of hair and fur.)
If you try to composite with an image
that has its transparent and/or antialiased elements rendered against
a BG color other than black, you'll get a (sometimes not-so) subtle
ghosting of a ring around that element, or see the influence of the
BG color through the transparent materials. This is even more
noticeable when you've rendered with motion blur and have the camera
and/or object whipping around.
Up 'till now, this has required a
re-render, or hours-upon-hours of Rotoscoping work on the part of the
compositors.
The DF Unmultiply tools simply reverse
the math used when Premultiplying an image by its Aplha with a
specific Background color.
The result is an image with a Black
background color, and its transparent PIXEls correctly Premultiplied
with it, (fading accurately into Black, as apposed to gray, white,
red, puce, or whatever).
How:
These Tools are to be added to your
Fusion Bins.
(A full explanation of the DF Bin
workings can be found in your DF manuals, but the short version of
how to get these tools up and working is:)
Press to open the Bins
window.
Click on the "Settings"
heading to access the Settings Bin.
Right-Click in the right-hand pane of
the Bin and choose: "Add Item..."
Explore to where you've extractd the
*.settings files from the .zip archive and one-by-one, following the
above steps, Add them to your Settings Bin.
Drag the DF Unmultiply tool you need from
your Settings Bin into your Flow and connect a Loader to its input
and enjoy an image Premultiplied with Black from the tool's output!
What:
Unmultiply_BG_Specify:
This tool requires that you specify the
BG color. It has a BG Generator (that currently is set to 720p, and
will need to be resized to match your input image) connected to the
Custom Tool's Background Input that you will need to set to what you
deem to be the Image's Background color. (The pair of tools are
grouped so all you have to do is feed the Image to be affected's
output into the Group's only input... this directs the image into the
Custom Tool's Foreground Input.)
The other four Unmultiply tools (LL,
LR, UL, UR) can be used if you know that the PIXEl in one of the four
corners, (Lower Left, Lower Right, Upper Left, or Upper Right,
respectively,) will always remain the BG color in question,
throughout the entire run of the Loader. The Image to be affected is
fed into the BG Input for these four Tools.)
All other channels, Z, Z Coverage, UV,
Normals, and x/y Vectors should remain unchanged.
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