Graphics Programs Reference
In-Depth Information
5.
In the Source 2 area, you'll experiment to find the right com-
bination. The red channel is a good place to start, because
it looks very different than the blue channel. It's also a good
idea to experiment by clicking the Invert button to reverse the
channel. Calculations is all about trial and error, but since it
works so well, taking a little time to experiment is worth it.
6.
Combine the red and blue channels by using Blending. From
the Blending menu, try different blending modes. Blending
modes control how two different images or channels blend
together based on their color and luminance values (for more
on blending modes see Chapter 9, “Using Blending Modes”).
Different source images will need different modes. Experi-
ment by clicking through each mode on the list. You may also
want to try deselecting the Invert check box when working
with other images. In the Independence Hall image, the blue
and red (inverted) channels combine most effectively using the
Vivid Light blending mode. This will create a new channel that
has a clean separation between the building and sky.
7.
Click OK to create a new channel. The channel, called
Alpha 1, should be selected in the Channels panel. Photoshop
turned off the RGB channels for now.
8.
Choose the Brush tool and set the foreground color to white.
9.
Paint over the trees so the sky becomes pure white.
