Graphics Reference
In-Depth Information
and green make yellow. With the addition of a weak blue channel, this
means that the color opposite from blue—yellow—is stronger.)
Looking at some of the shapes in the waveform monitor, we can try to
see if the corresponding parts of the image are white or black and figure
out what we need to do to get them to be balanced white or black. Notice
that the far left side of the red and green channels on the RGB Parade
are higher than the blue channel. On the red and green channel, that
portion of the trace comes up to about 40IRE. On the blue channel, it's
at about 25. To pull this part of the waveform up, click on the blue curve
about 25 percent of the way up the diagonal line and drag it straight up
( Figure 4.46 ) . We'll watch the blue channel of the RGB Parade, but we'll
also watch the video image. That part of the waveform is on the left side,
so we need to be looking at the left side of the video image as well. We're
also pulling up part of the image that is fairly dark, so we want to keep
our eyes on the shadows on the left side of the video image.
I was able to get the blue channel to match the red and green chan-
nels, but when I did, I noticed that the shadows in the pine tree in the
background to the left became very blue. So I undid that correction.
What I know about the real-world scene is that the extreme left side
of the image is actually the siding of my house. That siding is painted a
warm tan color (reddish yellow). The bluish tinge to the shadows gave us
the clue that we didn't want that part of the waveform to match.
Let's try something else. Looking at the RGB Parade waveform, we
can see that even though we have the brightest part of the blue channel
up as high as it can go, the rest of the blue highlights aren't as strong as
the highlights in the red and green channels. Knowing that the bench has
a lot of white in it and the garage door in the background is also probably
white tells us that we need to bring up the highlights of the blue channel.
Grab a point on the blue curve about 75 percent of the way up the diag-
onal line and drag it upward. We're trying to get the area on all three chan-
nels to look about the same at 75IRE. Before doing this correction, there's a
kind of a “peak” in both the red and green channels at about 75IRE. Bring
Fig. 4.46
 
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