Wednesday, August 1, 2012

The Making of Another Aerial Composite Image

Over the past few aerial flights I've been trying to perfect a technique that is part photographic technique and part Photoshop technique in order to take high resolution composite aerial photographs.

This is a particularly problematic thing to do because an airplane is always moving - most panoramic and composite images are made using a tripod firmly planted on the ground.

While it's true that I could use a helicopter to make such images, helicopter time costs at least twice what airplane time does.

My last post discusses making a 7 frame panoramic image. This post discusses making a high resolution square image rather than a panorama - using the same technique.

Here's the final image (a shot of a wind farm in the Sacramento River Delta, with Mt. Diablo in the background):

Click to view larger

As in the previous post, the image started by having the pilot make a tight right turn. In this case, we were flying slower (about 75 MPH) and I took 4 shots over a 4 second period - one frame per second. This gave me a much tighter stack of frames than in the previous shoot, and a much greater overlap between images - which I would need.

When you take photographs from different locations, it is impossible to perfectly line up both the foreground and the background elements of each image at the same time. You can prove this simply by looking at near and far objects through your left eye and then your right eye.

In my last post, I was able to get around this partly due to artful blending in Photoshop and partly because the difference in distance between the foreground and the background was not that great.

In this image, I had windmills literally only a few hundred feet away from the plane as well as a mountain 18 miles away. Even with four images, each taken only a second apart, there was no way to do a straight blend of the frames.

As result, I had to blend the foreground and background parts of the image separately in Photoshop:

Foreground Blend
Background Blend
Because the background appears to move less than the foreground as you move, it blends into a smaller composite image than the foreground. To fix that, I re-sized the background blend to match the foreground and merged it on top of the foreground blend, lining up the images as much as possible. It helped that I had a stretch of water in the middle distance to use as a blend line:

The final image is 6700x5400 pixels - about 36 megapixels.

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