Notes on Contrast-Adjusted Maps

The Problem

The normal Google Maps graphics often have very faint lines that are difficult to read for many people, and especially difficult for people with vision problems.

A Solution

This page displays Google Maps with enhanced contrast. The brightness level at which the contrast is most enhanced, and the amount of enhancement, are adjustable with sliders. The default works well for many map pages.

Arial ("satellite") images are not affected.

Technical Notes

Contrast adjustment is done with a sigmoidal function as in ImageMagick. This is an S-shaped curve that stretches contrast by a larger amount at one point in the brighness range (the "mid" point). Since Google Map images seem to have a lot of detail hidden in fine variations of very light colors, the sigmoidal contrast enhancement can target this range and separate these colors to enhance detail.

The web page loads a Google Map using the V3 API and looks for loaded map tiles. For every image on the page that looks like a map tile it applies a sigmoidal contrast adjustment and replaces the image bitmap.


This is a standalone project intended mostly for printing maps since the standard Google Map pages are nearly unreadable when printed, at least on my printers.