A well known problem with taking underwater pictures is that the pictures have a tendency to lack in contrast and especially in color. A lot of pictures turn out to be a variation in blue. The deeper you go the bigger the problem gets. There is a simple solution but that is a solution that costs a lot of money: buy powerful underwater strobes. Another solution is to do (extensive) post processing to bring some color and contrast back. Often the only solution if even powerful strobes are insufficient to lighten the whole object.
Recently I went diving to get some pictures of a deep wreck, the tugboat that was used to transport the car wrecks of the Car Pile at Vaersenbaai in Curaçao. The tugboat lies deep, even below sport dive limits. The deepest point of the wreck is at 52 meters but the top is at 45 meters.
There are some prerequisites outside your sphere of influence. At that depth you need sufficient natural light, so you have to wait for a sunny day. Also the visibility needs to be good. Apart from these two factors you need to prepare your camera for such a challenge. Per definition there will be a limited amount of light at such a depth so you have to choose for a higher than normal ISO value. How high is dependent on the amount of noise you accept in your end result and is also dependent on the size and quality of the sensor. A DSRL definitely has an advantage, but such a camera is outside the financial limits of a lot of divers. I used my older camera, the Sea&Sea DX-1G for this picture. The other settings that determine your lighting are the lens opening and exposure time. For this kind of conditions I always use a fully open lens. Depth of field is not important because it is a shot from relatively far away so everything will be in focus even with a wide opening. As exposure time I use the lowest possible value where I am reasonably sure that I can hold my camera steady. With image stabilization I can get to 1/25sec. This is the only time that I trust my camera to do all these settings for me. I have put my camera on auto ISO with a maximum of 800 ASA and automatic determination of opening and exposure time.
Also use a wide angle lens or your zoomlens at the widest setting so that you can get as close to your object as possible. This limits the amount of water between you and your object.
I used my DX-1G in its dedicated underwater housing with a wide angle wet lens (120 degree view), no external strobes. The settings for this picture came out at ISO 295, which is very reasonable, F/2.5 and 1/35sec. Apparently there was sufficient light even at this depth. My camera has a RAW setting which allows for white balance correction after the picture has been made. If your camera doesn't allow RAW pictures the best you can do is use custom white balance to set the best white balance before the shot.
The picture above is the result of the shot before white balance correction. It is the unprocessed RAW picture. Blueish as can be expected, low contrast but well exposed.
This second picture is is minimally processed in the RAW editor. The white balance has been corrected as far as possible and the exposure is lowered a bit (-0.35 stop).
A problem with using a high ISO-value is that the amount of noise increases. This is a 100%-detail of the picture showing a fair amount of noise.
After applying noise reduction the result is better although the noise is still visible. I use an external plugin for Adobe photoshop for noise reduction, noise ninja. The built-in functions for noise processing are far less efficient in reducing noise while keeping good sharpness.
Then comes the most important step. Trying to get some of the color back while increasing the contrast. Low contrast means that not the full dynamic range of the sensor has been used by the exposure. This is easily visible in a histogram of the picture. There are parts to the left and to the right of the curve where no pixels are present. The most common solution to increase contrast is by extending the curve of the histogram till it fills the complete range by moving the left and right triangle to the right, respectively left till they touch the histogram. But to get some color back you have to do that per color channel. Open the Level adjustment and choose not for the default value of RGB but do the processing per R, G and B channel. That results in the above picture with a far better color balance and contrast.
The remaining steps are finishing touches:
First I have applied a bit more vibrance to the picture by means of a vibrance/saturation layer. Especially the blue water is a bit more vibrant.
The last step is a little increase in contrast by means of a curves adjustment layer. That is a personal preference.
An interesting aspect is how far you should go to get a realistic result. In my last picture the sand is white which is the actual color of the sand. The blue cast of the original picture is completely gone. Does this picture give the impression of the depth at which it is made? In fact not. This is picture that could have been made at a depth of 10 meters. Actually it is made at a depth of 45 meters looking down. A way of suggesting this depth is by leaving some of the blue cast in the picture. I leave it to you to decide what you would have done.
A picture is better than 1000 words so here is a link to a smaller version of the processed picture with all the adjustment layers present. Even at 1024x768 pixels this file is still 12 MB. Open the file in Photoshop to see what I have done in each layer. And play with it to get a feeling of what you can do yourself.
Original unprocessed image
White balance correction and reduction of exposure by 0.35 stop
Noise of the original image - 100% detail
After applying noise reduction with Noise Ninja
Levels adjustment layer to correct white balance and improve contrast
Vibrance increased
Contrast increased a little bit
