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Often times, we need to combine various visual elements in the
course of a production. Some areas need to be transparent, to
allow the background to show through, and some need to be solid,
like the live action. The keying tools in DFX combine these
elements together in a seamless fashion.
In this tutorial, you will be using one of the most powerful
tools in DFX - the Chroma Keyer.
Chroma Keying is the process of creating a matte based on certain
ranges of colors or hues. Using the tool's controls, define
what colors and hues are allowed to be transparent and which
Maximize DFX by clicking on the maximize button in the top right
hand corner. From the tool bar, drag a Loader Tool (LD) down
onto the Flow.
On the File tab of Loader 1, click on the file folder on the
right. Locate a folder called Footage. Open the sub-folder called
Med_Back2. Select any one of the files in it. (MedXXXX.dft)
Just below Loader 1, drag a new Loader from the toolbar. Click
on the File tab, and select one of the GuysXXXX.dft files from
the Trooper_1 directory in the Footage folder.
We now have our foreground and background footage. We are going
to composite the soldiers over the background footage that we
loaded with our first loader. Unfortunately, as is often the
case, we don't have an existing Alpha matte for the soldiers.
This is where the Chroma Keyer tool will come in. This footage
is excellent to practice on, because, as in the industry, the
bluescreen background is not perfect, and will require some
tweaking to achieve the effect we want.
From the Tools menu at the top of the screen, pull down to Matte
and select the Chroma Key tool. This should now connect to Loader
If it does not, drag a Cky tool from the toolbar onto the Flow
just to the right of Loader 2.
Double click on the ChromaKey tool to open its Control Header
in the right area of the screen. The first tab contains four
range controllers. Each of these control the range of acceptable
color values for each channel, Red, Green Blue, and Luminance.
Because the original footage was shot against a bluescreen,
it is with this range that we will start. Place the cursor over
the Chroma Key tool and right click.
Select View On and click Large. As was demonstrated in the previous
tutorial, Masks, Paths & Animation, the button bar beneath each
view controls which color channel shown. Double click on the
Alpha channel button to view it.
Before proceeding further, grab the time arrow, and scrub forward
to frame 50. This will ensure that the actors are in frame when
attempting to key them out of the background.
All files are given an Alpha channel in DFX. In this case, however,
unless they had one before, the Alpha will be transparent (black).
View Loader 2 on the Large View and view the Chroma Keyer on
the Small View, with only the Alpha channel visible. By box
selecting areas on the Large View, tell the Chroma Keyer which
colors to remove from the Alpha channel. As you do so, notice
the white areas appearing on the Small View.
These colors are being allowed by the tool, and represent solid
areas in the Alpha Channel.
Continue to box select, but this time use the Alpha channel
visible on the Small View. After having roughly established
the matte, click on the Soft Range slider to fine-tune the edges
of the matte. Finally, click on the Image tab of the Chroma
Keyer and adjust the spill suppression all the way to the right.
The drop down box above it must be set to the color of the screen
that you are keying out.
As with all things, practice with mattes makes perfect, so find
the worst footage possible and do your best to it.
When satisfied with the matte, it is time to join the foreground
and background images together. For this we will use the Merge
From the tool bar, drag the Mrg tool onto the Flow one square
to the right of the Chroma Keyer. At this point in time, it
won't connect to anything. This means that we will have to drag
connections from our other tools onto the Merge tool.
If you hold your cursor over the tool inputs of the Merge for
a moment, a pop up will appear to tell you whether that is the
foreground or background input of the Merge. This is very important
when layering elements, for, if it is not done properly, the
results will not be what you want. Once you have identified
the background input on Merge 1, click and drag from the output
of Loader 1 to the background input of Merge 1.
Click on Merge 1 with the cursor to highlight it. Now press
the 1 key on the keyboard. This is the shortcut to display a
tool on the Large View. 2 will display it on the Small View
and 3 will display it on a monitor attached to your system,
if it is attached to the outputs from the card.
Click on the output of your Chroma Keyer tool and drag to the
foreground input of the Merge 1 tool. The two elements and now
merged, completing this first keyed composite.
Notice that on the Large View the composited image is tinted
blue. Click on the arrow on the Control Header of Merge 1 to
expand it. Move the slider marked Subtractive/Additive all the
way to the left to see the tint disappear.
Step 15 By adding a Saver tool, render out the sequence that
was just composited, or, if you prefer, save the Flow as tutorial
04.flw and proceed to the next tutorial.