(The resolution of the human eye is one arcmiunte at 10 inches, then the maximum resolution of the human eye is found as follows:
You find the circumference of a circle of radius 10 inches, which comes to 62.83 inches. One 1/21600th (or 1/60th of a degree) of this is 0.002908 inches, the minimum possible perceptible distance by the human eye at 10 inches.
Based on the above data for the resolution of the human eye, let’s try a “small” example first. Consider a view in front of you that is 90 degrees by 90 degrees, like looking through an open window at a scene. The number of pixels would be 90 degree * 60 arc-minutes / degree * 1/0.3 * 90 * 60 * 1/0.3 = 324,000,000 pixels 324 megapixels).
At any one moment, you actually do not perceive that many pixels, but your eye moves around the scene to see all the detail you want. But the human eye really sees a larger field of view, close to 180 degree. Let’s be conservative and use 120 degree for the field of view. Then we would see 120 * 120 * 60 * 60 / (0.3 * 0.3) = 576 megapixels.
The sensitivity of the human eye in ISO equivalent in the dark adopted eye in ISO is 800.
So: although the human eye and brain when combined can resolve massive amounts of data, for imaging purpose, 150dpi output is more than enough to provide adequate data for us to accept the result as photographic quality
