I originally posted the below on our sister site Gadling.com (which by the way, you should check out). Though I don't like to rehash old posts, this one seems like it would be of interest to our readers so I'll make an exception...

You’ve bought an underwater camera and you didn’t buy an external flash. You took it on a dive trip. You took more photos than you knew what to do with and with the exception of three, they are all green and blue and ugly. There’s no substitute for a good flash, but, there are some things you can do to bring those photos back to life. With the help of a little Photoshop, this guide, and a little practice, you will be amazed.

Why do the photos look so washed out?

It’s immediately obvious that the deeper you go, the darker it gets. That’s part of it but the real problem is how the color spectrum is absorbed at depth.
 
By the time you’ve passed the 15ft mark, the color red is basically gone. That’s why the deeper you go, the more the photos look washed out. At 120 ft, you’ll be lucky to get almost any colors at all. The best option is always an external flash, or, barring that, a red filter, but if you’ve ended up taking photos with neither you’ll need to do some post processing.

Take a look at the photo below. It was shot without an external flash at a depth of about 50ft. As you can see, there is very little color in the image - a slight hint of red on the pillar which looks more like a faded orange than a red. In person, it was popping with color. So, how do you take a photo like this one and make it look decent?
 

Show me how!

Fortunately, the process is simple. I believe the person who first documented this method was David Kusner in an online post. Since then, his method has been tweaked by others. The method below is the best method I’ve seen to date.

•  Make a backup of your existing image just in case. Load or copy the image into Photoshop.

•  Create two duplicate layers by going to the layer function and selecting “duplicate layer”. This will create a total of three identical layers. If you don’t change the name, the layers will be named Layer 1 (the original image), Layer 1 copy and Layer 1 copy 2, as depicted in the image below: 

•  Select the middle layer (Layer 1 copy), and fill it with 50% gray by going to Edit->Fill and selecting “50% Gray”.

•  After you have filled the middle layer with gray, you should see three layers with the middle layer completely gray.

•  Now select the top layer (Layer 1 Copy 2) and change it’s blending mode to Luminosity. Merge that layer down with the middle layer so that only two layers remain. You should see a B/W image of your original image.

•  Create a new layer on top of your existing layers and fill this layer with red. To do this, select your foreground color and set the color to R: 255 G: 0 B: 0.

•  Use the Edit->Fill->Foreground Color to make this new layer completely red.

•  Change the new all red layer blending mode to Multiply. If you’ve done this correctly you should see three layers. A top layer completely red, a middle gray layer and the original layer of your image. 

•  Merge the top layer (layer 2) down into the second layer (layer 1 copy). You can do this by selecting “Merge Down” from the layer menu. You should now have a very dark red image of your photo. 

•  Set the merged layer’s (Layer 1 Copy) blending mode to Screen.

•  Merge that layer down to the final layer.

•  Run Auto Levels by selecting Image->Adjust->Auto Levels.

How’s it look?
 

Much better isn’t it? You can’t add back what was never there, so the color of the pillar isn’t the popping red I hoped for. If the image appears overexposed try playing with the brightness and contrast settings in Photoshop to achieve the desired affect. With a little practice, you’ll be achieving great results in no time. 

Next week we will talk a little more about some other things you can do to photos to make them look nicer. See below for a teaser ….