How To Find Hidden Reefs Using The Color Dodge Effect
Takaroa Atoll - GE Split Image Landsat (Right) and Digital Globe (Left)(1:37,000)
Earlier today I received a question from a viewer - "How do you locate hidden reefs using the color dodge effect? Is it the same effect used in Photoshop?"
Before I attempt to answer the questions let me walk you through a demonstration using a Flickr slideshow and some screen shots. The are relatively self-explanatory.
Finding Hidden Reefs Using The Color Dodge Effect
Now my non-professional opinion on why this effect does what it does with Landsat imagery. I believe the yellow that shows up on an otherwise nearly black-blue ocean surface is due to a shift in pixel value. The pixels that turn yellow are of a different value and that value is transformed into a yellow color using the color dodge effect in Global Mapper. I think the pixel value corresponds to the location of reefs in and very near to atolls and islands. I do not believe that they represent reefs farther away , but within the near proximity of the island, they seem to align with reefs.
I am certain that there is a professional opinion out there that will either explain the Landsat / Color Dodge interaction or not. It seems to work.
Takaroa Atoll with No Blend Effect
Takaroa Atoll with Color Dodge Effect
It sure looks like reefs to me!
Enjoy!
Labels: atoll, color dodge, Digital Globe, Global Mapper, Google Earth, island, reefs
