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Change Detection in two still images

Posted on 1998-09-24
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Last Modified: 2010-04-27
Is it possible to do a pixel by pixel comparison between two still images of TIF file format. After comparing, can I highlight the differences in a new window so that the changes between these two images which are taken at the same spot but at a different time. How do I do this?
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Question by:wmlim060298
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mark2150 earned 200 total points
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I wouldn't try and do it on the files directly (you could simply do a binary file compare if it were *that* easy!). generally I think you'ld load 'em into a couple of picture frames and then compare the pixels there. You can then set the pixels in a 3rd picture frame according to the absolute value of the difference. The drawbacks are that it would be slow as mud and that it would be TOO sensitive.

Depending on the source of the images you're generally going to find too much of a delta even from consecutive video frames for pixel-by-pixel to give you much value. (I'm presuming that the original source of the data is video - correct me if i'm wrong...)

Anyway, one of the techniques to reduce the frame-by-frame noise in the image is to discard color depth. The more bits of color you have the noiser the image is going to be. Your chances of having all 2^24 colors exact between two images is slim to none. If you reduce your color depth from 24 bits to 8, 6, or even 1 bit, your comparator will be much less suscepable to "trivial" changes.

One way to measure change is to sum the absolute value of the differences and then divide by the number of pixels in the image. This will give you a "delta per pixel" figure of merit so you won't be snowed by a large change in a small area.

I could write something if you ship me a pair of images. Send to:

Mark_Lambert@ntsc.navy.mil

What are you looking at?

M

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