This is thread is a basic introduction to colour correction of underwater photographs using Photoshop. I use Photoshop Elements, but you can do the same things here with the free program called GIMP.
In this demo, I will show how to turn this dull, green color casted photo
into the following much more intriguing image:
Before we start, I should address the ethics of photo editing like this. Nowadays, just about every professional photographer uses Photoshop for doing some photo editing. In fact, such editing even happened long before the digital photography era -- Ansel Adams is on great who did his own editing in the dark room. However, when it comes to nature photography, photo editing is a very sensitive topic. To make a long story short, most agree that you are allowed to edit it as long as it does not make substantial alterations to what you really saw. Now, for the type of editing I'm doing, you might say "hey, wait a minute! This looks substantial to me." And if you think that, that's fair enough. However, there are some facts about how cameras work that you should be aware of. The first point is that cameras (especially digital) are not capturing things the exact same way as you see them in nature. Cameras have algorithms within themselves that make judgments on how to best capture the photo -- for example, the way it guesses white balance (which they never seem to get right for underwater pictures). Moreover, cameras are inherently limited and cannot capture everything your eye can see in one shot. One term known as "dynamic range" describes how a camera can capture fine details in light whites or in dark blacks, but not in both.
What your camera can capture depends upon the light that is reflecting off of the subject. This makes it extra difficult for underwater photographers because different frequencies (colours) of light get lost at different depths. So photographing a fish near the top of the ocean will be hugely different from photographing 10 metres down. The deeper you go, the more colours you lose and the worst your image will be. There are two ways you can make up for that: with sophisticated flash equipment or with good photo editing skills. Here, I'm relying on the latter.
Let's get started. Open your image with Photoshop, and then we select levels (enhance->adjust lighting->levels):
A window like the following appears:
When doing underwater photography images, the trick is to do one colour channel at a time. We start out with red. Click the RGB and go down to red:
Now we are going to adjust the red colour, starting from the left side. We move the black triangle from the far left to the point about at the beginning of the "mountain", like this:
Note that as you move the black triangle, the grey triangle in the middle moves too. Don't worry about that, just look at the black triangle.
Now we choose the white triangle on the far right, and start moving it to the left. But for the right side, based upon experience, I'm a bit more cautious. Rather than moving it all the way to the mountain, I just go to the rightmost part of where I see any part of the graph:
By this time, your image looks like this, which does not look right. But don't panic, everything should come out fine in the end:
The next thing is the green adjustment. Go to RGB again and select green. Do the same thing:
Now the image looks like:
(Still not great, but don't worry yet!)
Finally, do blue:
Now the image looks like:
SURPRISE!!! Not so bad now, is it?
Did we really have to go through all these steps? Why not just click the auto colour adjustment? Well, that hardly ever works well for me. This does.
Let's do a little more enhancements to improve presentation. A crop would be great:
With an additional darkening of some highlights (I'm not sure if you can do this one with GIMP), I end up with:
All of this editing was done quite quickly, and I'm sure if I would have done it more carefully, it would have come out even better. But this post is just a demo. Good luck with your own image editing!!!
