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The "page flash" on the kindle

The "page flash" on the Kindle 4 - the sudden turning of all the pixels black and then white, before the page is displayed - occurs every 6 page turns. It seems to be necessary because a certain amount of 'dirt' accumulates inbetween - bold letters (and also normal text) seem to leave traces pixels around the edges of the letters after they have been wiped after a page turn. The 'flash' wipes these pixels out and makes the page look crisp again.

I don't know if this is a flaw in the driver software, or a shortcoming in the e-ink display itself (that leaves the traces).
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