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With a little digital assistance, google earth can be used to find 'hidden structure' in the water.

First up, grab "The Gimp" - it's free, and there are versions available for windows, linux and Macs.

More details available from the sig tutorial: http://www.akff.net/forum/viewtopic.php?t=3075

Load up google earth, find the area of interest, then take a screenshot and load it into the 'gimp'.

http://www.akff.net/forum/hosted_images/one_338.jpg

Pop into the Layers menu, choose the Colours submenu, and choose the 'curves' item.

This will bring up a new window - something like this:

http://www.akff.net/forum/hosted_images/two_200.jpg

What we're going to do, is try and 'emphasize' some particular colour ranges. Easy to do, stick your mouse around the middle of the line, and drag it up so that it looks like this:

http://www.akff.net/forum/hosted_images/three_311.jpg

.. and press OK.

Your picture will now look something like this:

http://www.akff.net/forum/hosted_images/four_389.jpg

Now, we want to fiddle around with the highlights/shadows a bit. Go to the Layer menu, choose the colours submenu again, and go to 'Colour Balance'.

Click OFF the 'preserve luminosity' option, then click on "shadows".

  • Slide the Cyan/Red slider to fully red (100)
  • Slide the Magenta/Green slider to slightly magenta (-45)
  • Slide the Yellow/Blue slider to fully yellow (-100)

- Click on "midtones"

  • Slide the Cyan/Red slider to slightly red (30)
  • Slide the Magenta/Green slider to fully magenta (-100)
  • Leave the Yellow/Blue slider alone (0)

- Click on "highlights"

  • Slide the Cyan/Red slider to mostly cyan (-75)
  • Slide the Magenta/Green slider to fully green (100)
  • Leave the Yellow/Blue slider alone (0)

Ok, we should have something like this now:

http://www.akff.net/forum/hosted_images/five_355.jpg

You may want to fiddle with some of those figures, depending on the image. Start there, and work from that as a base though.

All that remains, is to make the reefy areas appear more distinct. We do this with some brightness/contrast:

Layer menu -> Colours -> Brightness/Contrast: Set 'Brightness' to 45 Set 'Contrast' to 80.

The final result should look something like this:

http://www.akff.net/forum/hosted_images/six_658.jpg

The Red/Orange areas are likely to be areas of shallower water/structure. Note that JPEG compression may leave 'square artifacts' on the image, and satellite photos with significant wave activity may not respond as well to this technique.

- Red.

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