Detailed Selections Using Channels
I had some fun writing about the details in my last post about levels so here is another attempt at a mini Photoshop tutorial.
This week I was in the need for a custom graphic of a country map. I didn't want to spend all day trying to draw it by hand but I did have a bitmap image. However this project needed to have the ability to scale so a vector image is what I really needed.
The web is full of Photoshop tutorials and I'm sure I just repeated another sites work but if I keep getting new ideas, I think I will try to make this a regular. By taking the time to experiment and setup these examples, I'm forced to learn.
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For this example, I'm going to use this screenshot of the world I captured from Microsoft Streets and Trips. The goal will be to make a tight selection only around North America and then create a vector path of that shape. |
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The first thing I did was went to the channel pallets and looked at my options. Seen on the left, I selected the Red Channel with the most contrast between land and water and made a copy of it. You can do this by dragging the channel down onto "Create New Channel" at the bottom of the pallet. |
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Make sure you are on the copied channel and then by using levels (Ctrl+L on Windows) I pushed the white and black into the center enough to make the water completely black and the land as white as possible. |
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I then took the Polygonal Lasso Tool and made a quick large selection around North America separating it from the rest of the map. Inverse the selection (Shift+Ctrl+I) and fill the selection with black.
Quick shortcuts:
Press D to set your colors to black and white
Pres X to switch them back and forth
Alt+Backspace to fill with foreground color
Ctrl+Backspace to fill with background color |
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Now that I'm down to just the area I need, the next step is to remove all the text. Using the Magic Want (W), I selected the black area and then inversed that selection. Fill that area with white.
The current results are close but have a number of sharp jagged edges. To fix that, removed the selection (Ctrl+D) and then go to Filter > Blur > Gaussian Blur. I used 0.5. After the edges are smoothed go back to your Levels (Ctrl+L) and sharpen the edges again by bringing in the blacks and whites. |
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Now hold down Ctrl and click the channel we are working on to make a selection. If you go back to the layer pallet and look at the RGB image, there should be an almost perfect selection around all the edges of the map. Click on my example to the left to see the larger image of the selection.
So what next?
Lets go to the paths pallet and create a work path by clicking "Make Work Path from Selection" at the bottom. We now have a vector shape of the selection. |
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I will finish off with 2 possible options
Go to Edit > Define Custom Shape and then give it a name. Photoshop now has a custom shape at your disposal of North America. If you started a new document, selected the Custom Shape Tool (U), you will be able to drop in North America in any color at any size. Remember to hold down shift while scaling to maintain perspective.
Another option is to File > Export > Paths to Illustrator. This will create an .ai Illustrator file for you, ready to open in Illustrator with a vector line graphic. |
