Image processing projects

Researchers:

• Jorge Stolfi

Project description

This page describes some experiments in image processing that I have been doing of late. Nothing too deep I am afraid...

Topics:

The three items below describe experiments with various line-enhancement filters, with the goal of improving the legibility of poor-quality images of old manuscripts.

• Weighted rank filter. "Rank filter" is my name for the local histogram equalization filter, that replaces each pixel by its rank among the pixels in its immediate neighborhood.
• Local normalization filter. This filter maps each pixel through a linear rescaling determined by the weighted histogram of values of the neighboring pixels. Namely, selected percentiles of the histogram are mapped to fixed intensity levels, and other values are interpolated.
• Cylindricity filter. This filter computes a second-order local rotational invariant of the image at each pixel, the "cylindricity index", which is maximal for crests and valleys, and minimal for saddles, bumps, and flat areas.
• Line index filter. This filter is an ad-hoc non-linear line detector based on a the relative values of pixels in a 3×3 neighborhood.