Last Sunday I dove in the Dive Haven Query for the express purpose of producing a photo merge of the diesel shovel that was submerged in 44 feet of water there when the quarry was flooded over 30 years ago. A photo merge as its name implies is a merge of 2 or more photos. Usually photo merges are used to combine a series of landscape shots to show a complete view.

A while ago I saw a photo merge of a sunken WWII submarine, the U-352, wow, what a shot! You could see small divers all around it and the entire wreck, courtesy of a photo merge:

http://www.chris3d.com/photography_u352.html

Just about the time I saw this photo, I heard about the sinking of the Oriskany and an idea was born, I want to do a photo merge of the Oriskany.

However, you just don't take a bunch of shots and then use Photoshop to magically knit them together. If the photos aren't in the same view plane, at the same angle, or aren't at the same distance or changing by a constant ratio to the target as far as distance, then your attempt may not work at all. I have been practicing with my underwater housing and camera, one of my attempts is shown above.

For a constant range photo merge the plane of pictures needs to be constant, same angle, same distance from the target object. For a perspective photo merge the distance and should decrease/increase at a constant rate and constant angle.  If either of these conditions are not met the photo merge will probably not be successful without manipulation of the images for size and angle. The camera should also be kept on a level plane in relation to the target. In addition the exposure needs to be as close as possible to identical for each photo, or, the gradient of exposure needs to be constant (the light/dark ratio should be constant for each level of the shots.)

The plane of the images should be constant whether the plane is constant in relationship of the target or varies, either getting closer on the front or the back of the target.

It seems it is more difficult with a small, close subject that with a large target at a larger distance. When an object is close, any small change in the view angle produces detectable changes in the parallax of the photo, changes in perspective and shadow. These changes in perspective make it tough to merge photographs. Also if the change in depth for a given object is a large percent of its size (for example, the shovel in my photo is about 20-30 feet tall and is in 44 feet of depth. Having the object of your photo merge run that gamut of depths makes the color gradient due to depth severe, making a seamless merge difficult.

Anyway, I am still practicing for my Oriskany pictures and am really looking forward to March when I can put my practice into practical use.