Image Processing

Gaussian Noise is Added, Poisson Noise is Applied

Poisson and Gaussian noise, pixel values 0 to 5

There is a fundamental difference between adding Gaussian noise and applying Poisson noise. In practice, people often talk about adding Poisson noise anyway, but this is not accurate. I will be looking at this from the image processing perspective in this article, and I’ll show purely visual examples. An application of this could be…

Submitted on 11 January 2014

The PSF of a Pinhole Camera

PSF of a circular pinhole, far away (left) and close by (right)

After introducing the Airy pattern in The Perfect Camera, I will show in this article how the PSF of a pinhole camera looks. A camera with a classical lens focuses the image that would be at infinity on the detector, which means that you actually get (approximately) the Airy pattern as the image of a point source there. This is not true for a pinhole camera, so…

Submitted on 16 August 2013

Tomography, Part 4: Algebra!

The first three articles on tomography focused on analytic techniques, in which the reconstruction problem is attacked using mathematical analysis. When the step to real world scanners is made, the problem is discretized. Both the projections and the reconstruction area are divided into pixels, and a numerical approximation of the true mathematical technique is introduced. The algebraic techniques assume…

Submitted on 9 December 2012