Posts Tagged ‘colour map’

Dithering

Friday, January 7th, 2011

First of all: Happy New Year!

Over the holidays I’ve been learning about dithering, the process of creating the illusion of many grey levels using only black and white dots. This is used when displaying an image on a device with fewer than the 64 or so grey levels that we can distinguish, such as an ink-jet printer (which prints small, solid dots), and also when quantizing an image to use a colour map (remember the EGA and VGA computer displays?). It turns out that this is still an active research field. I ran into the paper Structure-aware error diffusion, ACM Transactions on Graphics 28(5), 2009, which improves upon a method presented a year earlier, which in turn improved on the state of the art by placing dots to optimize the appearance of thin lines. This got me interested in the basic algorithms, which I had never studied before. Hopefully this post will give an understanding of dithering and its history.

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A colour map to show differences between images

Tuesday, March 31st, 2009

While commenting to a recent blog post by Loren, someone linked to this article at IBM Research. I thought it had some very interesting points, and made me think about the 'zerobased' colour map in DIPimage. It is designed to highlight positive versus negative values, for example when displaying the difference between two images. Using a simple grey value colour map it is difficult to determine what exactly is the zero level.

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