ImpulseNoise

Impulse noise are bad pixel in otherwise correct image.

The pixel doesn’t have to be saturated. There are multiple types of bad pixels and can be caused by different reasons.

Filtering it:

• always
• two steps
  • detect - determine, which pixel are bad
  • correct - correct bad pixels, use surrounding pixels for this correction

Detection can be done in different ways

1. You know coordinates of those bad pixels
   • Caused by hardware failure - chip issues
     • The chip can be tested
     • Number of bad pixels increase over time
2. Issues in scanned film
   • There are number of bad elements (dust, scratches)
   • ICE - Image Correction and Enhancement - uses IR (850 or 950 nm)
   • The scanner passes IR through the film, which is transparent to IR, but dust or scratches are not. The scanning chip is sensitive to IR and therefore, you get layer of imperfections, which can then be processed
3. Bad pixels at random locations, which are not known, but we determine them mathematically
   • Statistical test, that the pixel is bad
     • You need test criteria to test the hypothesis
       • $o_{i,j}$ stands for the surrounding of the pixel $a_{i,j}$

Correction:

1. Single-pass -