Quote:
Originally Posted by psbernitz
Does a colour screen actually increase the contrast?
Because right now every ereaders background is gray, the font is black but can colour screens make the background purely white?
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Edit: Short answer is that, full colour makes the greyish white even greyer on eInk!
The background is a milky liquid the tiny black balls are in. If the balls in a cell stick to the front then it's black.
Colour is usually by a filter printed on the front of the screen/cells. So it makes the white 2/3 rds dimmer (greyer) if the filter was 1/3 rd of spectrum for each pixel. In practice that would not be possible and the R G B mix technique to give white and
decent colour saturation and range of hues requires that each R, G, B subpixel blocks about 7/8ths of spectrum at least. Then since the light is reflected off the milky white liquid, the coloured light is attenuated twice by the filter. Not a problem for LCD, just increase the backlight.
So decent white, not too grey needs poorer filters (more transparent) which results in poor range of colours and pastel shades. Otherwise you need twice the front light power of an LCD backlight. Though direct sunlight will work well with no frontlight.
It's basic physics and the trick of how fake RGB colour takes advantage of how our eyes work if you have average colour vision.
Printing, film negatives and colour slides use C Y M (cyan, yellow and Magenta. Also black on printing) in layers rather than side by side R G B dots. So White (or black on negatives) has no dye/colour and lets all the light through.
No electronic C Y M layer technology yet exists. LCD twists polarisation of light and uses polarising film, so it varies from transparent to black, though a single colour is possible, the physics doesn't allow layers that vary from transparent to complementary colour, so all LCDs are monochrome with RGB filters on top.
Plasma, VFD, CRT, real LED and OLED/AMOLED use R, G, B emission, though OLED/AMOLED are not real LEDs so often also have filters too.
DLP come in two kinds. They are essentially tiny mirrors for each dot. They either use a colour wheel to add colour to a monochrome display illuminated by a white light, or use three chips with images combined by prisms. The three chip solution can use filtered white light or R, G and B LED or laser sources.
There are also real laser projectors. They have the interesting property that the image is in "focus" at any distance without focusing it. They use two stages of spinning mirrors a bit like a laser printer except much faster and the image drum is replaced by frame scan polygon mirror drum or some other deflection method.