This chapter is from the book
This chapter is from the book
This chapter is from the book
Channel Extraction
An image channel is how Photoshop builds image information. A grayscale image is made up of a single channel, and an RGB image is made up of three color channels: red, green, and blue. The combination of these three channels creates the millions of colors we see. For the purpose of restoration work, individual image channels can reveal or conceal bothersome dust and damage in a picture. Frequently, but not always, the noisy or dirty channel is the blue one.
Selecting the Cleanest Channel
The little Lisa image (FIGURE 5.31) suffers from stains from an accidental spill or perhaps uneven developing. Even though the image is black and white, it was scanned as color.
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FIGURE 5.31 The stains in this image can be rooted out by using just one of the image’s channels.
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To see which channel is most useful, do the following (FIGURE 5.32):
Choose Window > Channels to show the Channels panel.
Click the Red, Green, and Blue channels to observe the different grayscale interpretations.
FIGURE 5.32 Exploring the different channels reveals three different interpretations of the image, and one of them barely shows the stain now.
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In this image, the green channel shows the least damage.
TIP
You can also use the keyboard shortcuts listed in the Channels panel to observe the grayscale interpretation of each channel. This is called a channel walk. Press Cmd-3/Ctrl-3 for the Red channel, Cmd-4/Ctrl-4 for the Green channel, and Cmd-5/Ctrl-5 for the Blue channel. Cmd-2/Ctrl-2 returns you to the combined RGB view.
TIP
Scan black and white or monochromatic images in RGB mode, and then extract the cleanest and best channel to work on.
Extracting the Cleanest Channel
With the Green channel selected as the cleanest one, the next step is to turn it into its own file:
Click the Green channel in the Channels panel, and press Cmd-A/Ctrl-A to select the channel. Then press Cmd-C/Ctrl-C to copy the channel.
Choose File > New, and click OK to create a new document.
Press Cmd-V/Ctrl-V to paste the copied channel into the image.
Choose File > Save As to save the newly created grayscale file with a new name.
TIPYou can also select the Green channel, choose Image > Mode > Grayscale, and click OK to the discard the other channels.
A tonal adjustment brightens the image (FIGURE 5.33) and hides some of the remaining damage, but there are still a few marks to clean up. Using methods that will be presented in following sections will result in stain-free image (FIGURE 5.34).
FIGURE 5.33 A tonal adjustment hides more of the remaining damage.
FIGURE 5.34 The rest of the visible damage is removed with the Clone Stamp and healing tools.
Returning the Ambience
The original image had a bit of nostalgia because it looked a little yellowed. Using the channel extraction method returns the image to a true grayscale file, giving it more of a stark look. Adding a little tone will return the old-fashioned feel. Follow these steps, which can also be used for creating a sepia tone.
Convert the image back into an RGB image by choosing Image > Mode > RGB. The image will not look any different. Note that the Channels panel has four identical displays of the separate and combined channels, but now a color tone can be applied (FIGURE 5.35).
FIGURE 5.35 To add the original color tone back into the image, first convert the grayscale image back to RGB.
At the bottom of the Layers panel, click the Create New Fill or Adjustment Layer icon and select Hue/Saturation.
In the Properties panel, select the Colorize option.
Enter 32 for Hue to give the image a brownish cast.
Drag the Saturation slider to 18 to control the intensity of the cast and recapture the older look (FIGURES 5.36 and 5.37).
FIGURE 5.36 Sepia or a similar colorization can be added with a Hue/Saturation adjustment layer when the Colorize option is selected.
FIGURE 5.37 The original color tone has been put back into the grayscale image.
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