[Coral-List] photoshop trick for sat imagery

[Allan Smith]

Very useful tips for anyone who wants to use their own raster files 
(airphoto or satellite) of study areas to load into a Garmin mapping 
GPS. Preparing an airphoto  e.g. for a 60Csx gives much better results 
if the contrast and colour saturation of the original image are 
enhanced a lot. This does indeed add more detail for deeper reefs 
which otherwise may not show up on the Garmin because of the 256 
colour limit.

Dean Jacobson wrote:
> Hi listers:
> 
> 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.
> 
> Cheers,
> Dean Jacobson, PhD
> College of the Marshall Islands
> 
> 
>       
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