[Coral-List] photoshop trick for sat imagery
atolldino at yahoo.com
Mon May 19 03:27:51 EDT 2008
Today I "discovered" a useful way to filter satellite images using Photoshop to reveals relatively deep reefs (below 15 meters). (I am fortunate to have access to 0.6 m Majuro atoll data for ArcMap). I am using Photoshop 6.
Under "images", choose selective color, choose blue, then minimize the black slider. Then choose black, and maximize black slider. Another iteration may be needed. Then, increase contrast and brightness. To avoid blowing out the shallows and land, first save an extra image layer, make your adjustments, and then selectively erase the upper adjustment layer so the original pixels show through.
The results were pretty remarkable; it was like having "X-ray vision"... well-defined deep reefs magically appeared out of the monotonous dark blue lagoon water. This will work only if the stat image was taken an a calm day; a wave chop seems to obscure the deep features.
I discovered this just in time for my coral monitoring season!
I can send some example jpgs upon request.
Dean Jacobson, PhD
College of the Marshall Islands
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