2.1 LINEAR, SHIFT-INVARIANT OPTICAL SYSTEMS
In Figure 2.1, a simple optical system is imaging a clock onto a screen. For simplicity, unity magnification is assumed (that is, the image is the same size as the object). As illustrated in the lower left corner of the image, each point source in the object becomes a point spread function (psf) in the image. The point spread function is also called the impulse response of the system. Each point in the scene is blurred by the optics and projected onto the screen. This process is repeated for each of the infinite number of points in the scene. The image is the sum of all the individual blurs.
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