This image is the result of the Stack Images transform. The background is noticeably darker than the
first dark frame, and so we have been successful in removing some of the noise components from the
dark frame. But the background is not completely dark, and what is left is bias noise and dark noise.
Hot pixels are still quite obvious.

Using this averaged dark frame, have the option of skipping from this step directly to
the next thresholding step.

However, our "thorough" workflow includes one more preliminary step to reduce the bias and dark noise
components of the image, while (almost) preserving the hot pixel intensity. We accomplish this by
subtracting (using absolute difference) the averaged dark frame from a median-blurred version
of the averaged dark frame.