The View Up Here

Random scribblings about kites, photography, machining, and anything else

Stereo Aerial Photography and False Color

Posted by Tom Benedict on 26/06/2009

It’s always fun to see what can be done with aerial photography: large stitched panoramas, Photosynths, 3D modeling, 2D maps.  One technique that KAP lends itself to particularly well is stereo aerial photography.

With an airplane, stereo photography is typically done by pointing the camera 90 degrees to the direction of flight, and taking a succession of pictures as the airplane flies across the landscape.  Careful choice of frame rate, airspeed, and altitude yields good results.

With a kite, a similar technique can be used:  Point the camera 90 degrees to the kite line, start the shutter going, and carefully walk backwards.  The kite will quickly settle into a stable flight angle with the increased apparent wind speed from the walking, and a nice steady stream of pictures is the result.  This is an example from a recent flight over the contact between two lava flows on the Big Island of Hawaii:

Lava Stereo Pair - True and False Color

The top two pictures are the natural color images as they came off the camera.  The bottom two require more explanation:

Another technique I’ve used with aerial photography is to apply false color techniques to boost certain details, certain colors, or to change the contrast of the image so that particular features will catch the eye.  Most of my experimentation along these lines has been done using an image manipulation program called ImageJ, and a plug-in called DStretch.  ImageJ is a general purpose image manipulation program written in Java.  DStretch is an implementation of the principal component algorithm for contrast stretching that was written by Jon Harman.  It was originally written for bringing up faint details in pictographs, but it has proven to be useful with aerial imagery as well.

In order to get a sense of scale of the image, the thin yellow line in the top pair is a three-section 25′ painter’s pole thath as been collapsed to its shortest length.  My flying partner and I were using it to lower a camera into one of the holes we found in the lava in order to explore the inside.

This probably isn’t the best example of either technique, but it’s the first time I used them in combination.  At some point I’ll write a more in-depth article about building stereo pairs, and a second article about the use of ImageJ and DStretch with aerial photography.  In the meanwhile, enjoy.

Tom

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One Response to “Stereo Aerial Photography and False Color”

  1. I personally seem to agree with all the stuff that was posted inside “Stereo Aerial Photography
    and False Color The View Up Here”. I am grateful for all of the
    actual advice.Thanks for the post,Leandra

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