Light alone is not enough. We need to know what direction the light that reaches us comes from—for that we have eyes. Eyes form images, sorting the flood of photons by direction. Imagine an amoeba under a clear sky, bathed in a flux of billions of photons. Although the amoeba can tell the total amount of energy falling on it, it cannot determine with any accuracy where the photons came from.
Images are the marriage of intensity with direction. Images are patterns of light intensity in which the amount of light on any point corresponds to the direction of origin of the light. Once light has been organized into an image, it can be detected by a retina, a silver-halide emulsion, or electronic camera.
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