Photoshop provides a number of tools for colorizing, but the most useful for selectively coloring Mountain High Maps is the lasso tool.
Using the lasso tool
1. Open the base version of your map image and change it to RGB color mode.
2. Open the “Channels” floating palette by selecting “Palettes > 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 that appears, name the channel “Ocean mask” and click “OK.” The map image window will now go blank, this being an “empty” new channel.
4. Open the corresponding mask for the map you are using, 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 on it). Choose “Paste” from the “Edit” menu. This will paste the map mask into the blank channel.
7. Make the base map channel visible by clicking on the word “RGB” in the Channels palette (or type Command-0).
8. Choose “Load Selection” from the “Select” menu. In the dialog box which appears, select “Ocean mask” from the “Channels” pop-up menu, and check the “Inverse” box. Click “OK.”
9. Making sure that the background color is set to white, choose “Cut” from the “Edit” menu (or press Command-X). This copies the Ocean floor to the Clipboard, leaving just the land relief visible. Although it is not absolutely necessary to remove the Ocean floor (you can use the “Layers” feature of Photoshop for storing areas of map you don’t want to affect), doing so makes selecting land areas a lot easier.
10. Apply your chosen color to the land relief by using one of the methods described earlier. We have used Hue/Saturation to define a green color, with values of 90 for Hue, 60 for Saturation, and +20 for Lightness:
 
11. Double-click on the Lasso tool in the Toolbox. This will reveal the Lasso Options dialog box. Enter a value into the “Feather Radius” box – the bigger the number, the more gradual the feathering. We used a value of 10 for this map, but if you are working on a high resolution image, the value will have to be much greater.
12. Now use the Lasso tool to select an area of land relief on your map.
 
13. Use your preferred method of defining a color. We have used Hue/Saturation to define an ochre color, with values of 50 for Hue, 70 for Saturation, and 0 for Lightness. Save your color settings by clicking the “Save...” button in the dialog box, so that you can apply the same color to other parts of your map, if necessary.
 
14. Again using the Lasso tool, select an area of land relief within the area you selected in step 12. Define a color and save it for later use. We have used Hue/Saturation to define a purple color, with values of –30 for Hue, 70 for Saturation, and 0 for Lightness.
 
You can go on building up multiple layers of color by using this technique:
 
15. You may now want to put back the ocean floor, which you copied to the Clipboard in step 9: Choose “Load Selection” from the “Select” menu.
16. Choose “Paste Into” from the “Edit” menu. The ocean floor, in gray, will appear. You may now want to colorize the ocean floor.
17. Again, choose “Load Selection” from the “Select” menu. Use your preferred method of defining a color. We have used Hue/Saturation to define an blue color, with values of –160 for Hue, 80 for Saturation, and +70 for Lightness. Save your color settings so that you can apply the same color to other maps.
 
You may want to give the ocean floor multiple colors, as you did for the land relief. If so, before pasting the Clipboard contents into your selection (step 16), create a new document (choose “New” from the “File” menu, then press “OK” in the “New” dialog box – the new document size will be exactly the same as the most recently copied selection), and paste the ocean floor into it (press Command-V). Alternatively, use the Layers feature of Photoshop to store the land areas, while you colorize the ocean floor. Do your selective coloring in exactly the same way as described in steps 11 to 14 – but using different colors, of course! When done, copy the ocean floor (press Command-A, then Command-C), and execute steps 15 and 16 above.
 
You can also use Photoshop or third-party filters to apply some dramatic effects to the colored land or ocean areas.
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