Sunday, November 14, 2010

E Ink Color Display - handicapped because of a fundamental color mistake?

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  1. But there's an important difference between the e-ink subpixels and printing ink. Ink overlaps while the filters of each sub pixels don't.

    CMYK inks are chosen because their overlaps need to have a wide gamut, but here there is no overlap of the filters.

    I suspect that the reason the tablet lacks saturation is that the amount of light that makes it out of each subpixel is much less that subpixels on display devices, not because the light is reflected rather than transmitted. Once the light leaves the surface of the tablet it doesn't make a difference to our eye whether it was created there or is reflected from a different source

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  2. Ink does overlap in printing, however that does not mean that CMY filters can't be used. After all CMY inks only overlap once the tones reach a certain density - i.e. once the halftone dots grow to reach a certain size. Up until then they do not overlap. The human eye in both the additive (RGB) and subtractive (CMY) color model integrates the colors of individual pixels to create a color sensation. For example, you can have a cyan pixel beside, or on top of, a magenta pixel and in both cases you will see a blue.

    If the display used CMY filters then it should act in similar fashion to CMYK printing in terms of color gamut and saturation. The color intensity would change according to the ambient light and be dependent on the "blackness" and "whiteness" of the underlying black and white screen pigments.

    Using RGB filters - as would happen if one used RGB inks in presswork - severely limits the gamut. For example, there is no RGB combination of ink hues that will deliver a yellow hue - and yellow is noticeably absent from the images so far shown for this display technology.

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  3. Congratulations on a big "scoop", Gordo. Dead Tree Edition has published a related article (http://t.co/yBnQ4Eb) in hopes that this significant story will get more attention.

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  4. Everything is ok but with one small remark. Colour filters (CMY ink on paper) lay on white paper and filters light which go through them... and it works as we see on magazines, newspapers etc... from years. Now b&w e-paper which works also fine was covered by colour filters, but... real paper does not change from white to black like e-paper do. So maybe white and black particles inside epaper pearls should be CMYK to work fine and without top layer filters?

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  5. It's not that they don't understand the problem ... it's that it is terribly hard to solve.

    For CMYK you need 4 layers. The intermediate layers have to be thin enough to keep the alignment of the CMYK subpixels relatively steady regardless of viewing angle. You have to use actual ink and you have to keep the ink in some reservoir far smaller than the pixel when not in use (which makes keeping the layers thin harder and reduces the brightness of white). Manipulating ink is harder than the electrophoretic particles e-ink is using now (and requires a whole different set of patent licenses). Each layer needs it's own TFT transistors in plane, small enough to be invisible, you can't stack them with the ink layer any more like you can do in BW. All the layers will create a hell of a lot of internal reflection.

    All in all CMYK is where they have to go, but the road there is very hard ... especially when companies like Apple can hypnotize people into thinking a mirror represents an easily readable surface in sunlight.

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