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I recently got interested in an electronic paper. One design that I liked was the one from Mirasol, Interferometric modulator display.

enter image description here

However, what I don't understand, is the following: Their subpixels are either ON (color) or OFF (black). Therefore, I am wondering how they can produce lighter and darker colors?

By lighter and darker colors, I mean that the color intensity is tuned. For instance for red:

enter image description here

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  • $\begingroup$ Have a watch of this youtu.be/3BJU2drrtCM?t=7m39s $\endgroup$
    – Jonathan R Swift
    Mar 16 '18 at 14:22
  • $\begingroup$ It works exactly like print works. Printers also can generally only do ink or no ink. and intermediate colors are done with subpixels called halftone patterns. $\endgroup$
    – joojaa
    Mar 20 '18 at 21:05
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If I understand that picture correctly, the brightness is a function of how many subpixels are turned ON in a given image frame. Your eye integrates all the photons it receives, so if all 16 red subpixels are ON, you'll perceive "red" but also perceive "very bright." If only one is ON, you still perceive "red" but will see "very dark."

edit to add:

It occurs to me that the perceived color could in theory be adjusted by toggling the pixels' states at, e.g., 240Hz to be ON for only part of a video frame. However, this has not been achieved in actual devices, and in any case would defeat one of the desired features of this technology, which is to maintain a color image without drawing additional power (the pixels hold state until addressed).

For those who don't know much about the retina, some info:

There are color cones, typically 3 types, each of which is sensitive to a different band of frequencies. The combination of signals from these cones is what the brain processes to sense a color. Along with these are rods, which are more sensitive detectors but are monochromatic (only report total intensity). Combine the intensity signal with the color signal to get teh final perceived shade.

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    $\begingroup$ so, what you are saying, is that in fact Mirasol could only dim a color in 16 steps ? Maybe that's enough though... I don't have an answer to that. Do you ? $\endgroup$
    – james
    Mar 16 '18 at 20:47
  • $\begingroup$ @james, yes, your eyes will pick up the average intensity of the 16 sub pixels. You may want to add that the colour pallette in the question is not possible using only red pixels and will require the green and blue pixels as well to create the lighter shades of red $\endgroup$
    – ChP
    Mar 18 '18 at 20:55
  • $\begingroup$ @james 16 steps is not enough to make smooth gradients even 256 shades of grayscale gradients really is not enough, its very close though. This is why next gen colorspaces are going to be 10 or 12 bits per channel. $\endgroup$
    – joojaa
    Mar 20 '18 at 21:09

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