ETM+ Water Mask
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To get just the right water mask we need to use the "Color Range" selection tool, but we need to get the right blend of water colors.
To begin lets get the best color we can for the deep ocean. I've already done this, and this should be a good value, certainly for this image. Alternatively you can use the "Eye Dropper Tool" from the floating toolbar. Move your mouse over the open ocean and left click once. The color of the pixel you click on will be loaded into the "Foreground Color" in the floating toolbar pallet.
Navigate the menu control "Select->Color Range...".
The following dialog box will popup. Drag the "Fuzziness" slider to the far left all the way!
Select the little eye-dropper with the "+" sign below it.
You can now click in many places around the image and add different hues of blue to the sample set for the color range selection.
The more hues of blue you add to the sampled set, the more accurate your selection will become. When you are satisfied that the "Color Range" selection utility will get all the water, or enough of it to be reasonably accurate, then click the "OK" button and let the selection process begin.
In the image below you can see clearly that all the water is properly selected. Zoom in to inspect it if necessary.
Click on the image for a larger view.
Click on the foreground pallet in the floating toolbar and change the color to pure white.
Note the values for "R: 255", "G: 255", "B: 255". Click the "OK" button to complete the new color selection.
With the new color pure white in the "foreground color" pallet, click the little swap arrow between the "foreground color" and "background color". In the image below you can already see that I have moved the pure white to the "background color" pallet.
Click on the image for a larger view.
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