2. Working in grayscale

Although we have provided the sample map with the sea already masked, you will find that you will have more flexibility and creative opportunities by using the base version in conjunction with the mask. 

The most effective way of doing this is to make use of Photoshop’s powerful “Channels” feature. This takes a little getting used to, but it is well worth spending the time learning – and it doesn’t take long.

Using channels
The concept is really quite simple; each base color of an image has a separate channel – RGB images have three channels (one each for the three video colors of red, green, and blue), plus one extra to show the combined colors, whereas CMYK images have four channels (one each for the four process colors), plus one showing them combined. Grayscale images only have one channel.

However, new channels can be added to an image, and these provide a place where you can store selections, or store masks that can be used to make selections. To see how you can do this: 

1. Open the base version of the sample map (named “2.09 USA(NE)-base select.TIFF” on this disk). 

2. Open the “Channels” floating palette by selecting “Show Channels” from the “Window” menu. Click on the right-pointing arrow at top right of the Channels palette and select “New Channel.” 

3. In the dialog box which appears, name the channel “Ocean mask”  and click “OK” (leave the other settings as they are). The map image window will now go blank, this being an “empty” new channel.

4. Open the mask for the map (named “2.09 USA(NE)-mask select.TIFF” on this disk), and choose “All” from the “Select” menu.

5. Choose “Copy” from the “Edit” menu, and close the mask window.

6. The base map window showing the blank channel should now be active (if not, just click anywhere within it). Choose “Paste” from the “Edit” menu. This will paste the map mask into the blank channel.

You will now use the “Ocean mask” channel to create a selection for manipulating your base map image. The important thing to remember about using channels for selections is that the black areas on the mask channel are those that will remain unaffected on the channel you are manipulating. Or, to put it another way, the white areas of the mask are those that will be affected when you make changes to your image. To manipulate your image:

7. Click on the word “Black” on the Channels palette (or hit “Command-1” on the keyboard”). This will display the base map channel.

8. Choose “Load Selection” from the “Select” menu. The coastline will appear as “marching ants.” This indicates the selected area.

9. Choose “Adjust > Brightness/Contrast...” from the “Image” menu. In the dialog box that opens, move the slider triangle on the Brightness bar until “+95” is displayed in the value box.

10. Click “OK.” The map will now show the oceans in a much paler shade of gray, creating a contrast between land and sea.

Applying effects to selections
The technique of using a selection channel can be employed for a large number of effects. The following steps explain just a few simple effects you can achieve after following steps 1 to 8 above:

If, after step 8 above, you pressed the delete key, you would delete the selected area to reveal the background color, ending up with a white ocean (white is the default color for the background) – the same effect as already supplied on the Mountain High Maps™ sample disk (as the “mskd” version). However, if you hold down the “Option” key while hitting “delete,” the sea will fill with the foreground color.

You can fill the ocean area with a gray tint by defining a tint of black. Do this by openeing the “Colors” palette and using the slider triangle on the “K” bar until it displays the desired percentage. Try 20% black.

You can use Photoshop™ or third-party filters to create dramatic distinctions between land and sea. Try applying the “Noise > Add Noise...” filter with a value of 64, and then lightening it with the “Brightness/Contrast...” control.

Blurring the ocean can give the land an illusion of “floating.” Try giving your image a Gaussian blur of 64 pixels radius, and then lightening it with the “Brightness/Contrast...” control.

End of Chapter 2
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