Tag Archives: point sampling

Resolution, Sensors, Sharpness

The Effect of Sampling on Image Resolution

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We understand from the previous article that the process of digitizing an optical image with a photographic sensor can be thought of as two subsequent operations:

  1. filtering (convolution) of the optical image on the sensing plane by the pixel’s finite effective active area (aka pixel aperture);
  2. point sampling the convolved image at a given fixed rate and position, often corresponding to the center of each pixel.

Both affect resolution in different ways: the former can be thought of as modifying continuously the analog optical image, as seen below right; the latter as possibly introducing interference (aliasing) into the result.

Figure 1. Digitizing an optical image corresponds to convolution with pixel aperture followed by Dirac delta sampling at the center of each pixel (red dots).  Highly magnified images of two simulated stars separated by the Rayleigh limit: the stars are resolved after just the optics to the left; and unresolved after smoothing by an ideal square pixel with 100% Fill Factor to the right.

In this page I will explore how the act of digitizing that image – the process of sampling – fundamentally alters what we can resolve.   In the next one we will discuss the impact on resolution of  pixel-shift modes available in current mirrorless cameras. Continue reading The Effect of Sampling on Image Resolution →