Wednesday, August 22, 2012

Ghosts in the ROM...

The photo at right was found in the system ROM of an ancient Macintosh SE.  It's part of an “Easter Egg” left in the ROM by the system's developers, some of whom are in this photo.

Geeks of a certain age will recognize a now almost-forgotten technique in this photo: dithering to get gray scale.  The photo actually contains nothing other than black or white pixels – the appearance of various gray levels is created by varying the relative prevalence of either white or black pixels over a given area of the photo.  Dithering is a bit harder than it might appear to be at first glance; the obvious approaches lead to grid patterns showing up as artifacts in the photo.  To make it look “natural”, the dithered pixels have to be randomized, as they are in this photo.  Pure black and white photos can be stored very efficiently, one bit per pixel, which I'm sure is why this technique was chosen here.

Read the whole story...

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