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:
filtering (convolution) of the optical image on the sensing plane by the pixel’s finite effective active area (aka pixel aperture);
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→
This article and the following one will discuss the effect on resolution of digitizing a continuous optical image.
The sampling process carried out by the sensor results in digital values corresponding to an intensity at each pixel’s location. These so-called Data Numbers are stored ideally as-is in the raw file and are proportional to infinitesimal point samples of a new continuous image: the optical image smoothed by the characteristics of the pixels’ effective active area, known as the pixel aperture function.
Figure 1. Simulated Pixel Aperture Function of a 4um pitch Back Side Illuminated pixel in isolation. Note diffusion beyond the -2/+2um theoretical pixel boundaries suggested by pitch.
