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In communities of people who love e-readers, there are a few topics that pop up again and again — the classic frequent questions. Things like asking for recommendations on bar-type readers, or someone showing off a beautiful planner they found… those cute and delicate kinds of conversations.

Among them, questions about how e-readers actually work also appear quite often. So today, I’d like to talk about this: “Why are black-and-white e-readers considered sharper?”

Black-and-White E-Ink Panel

First, let’s briefly look at what E-Ink — the heart of an e-reader — actually is.
In regular smartphones that use OLED or similar panels, each pixel on the screen emits light by itself.
To “see” something means that light has entered your eyes and its energy has been absorbed by your photoreceptors.
There are two ways for light to enter your eyes:
With a normal smartphone, the light is emitted directly from the device into your eyes. With an e-reader, you see only reflected light — whether that’s sunlight, room light, or the device’s own front light. You see the light after it reflects off the E-Ink panel.
That’s why you can’t see anything on an e-reader in a completely dark room. The device itself doesn’t emit light! (The front light is not a backlight. It shines light *onto the surface* of the screen so that the reflected light reaches your eyes.)

So the easiest way to understand an e-reader screen is this: it’s basically a sheet of paper.

How One Pixel Is Represented

Inside an E-Ink panel are tiny microcapsules — imagine tiny pills. One microcapsule represents one pixel (one dot). Each microcapsule is filled with many white particles and many black particles. Behind each capsule is a panel (TFT) that can apply the needed voltage to that capsule.
White and black particles have different electrical properties. Depending on the voltage applied, certain particles move upward while others move downward. These particles float in a transparent oil-like fluid, so once they move, they stay in place until a different voltage is applied.
That’s why an e-reader can show an image even when the “screen is off.” Some people think “the screen must be on, so it must drain power,” but no — the particles are simply floating in place. That’s your sleep screen.
If the white particles rise 100%, the pixel appears white. If the black particles rise 100%, the pixel appears black. With various mixes in between, the panel displays different levels of gray.

How a Color Panel Like Kaleido 3 Works

A color e-reader simply places an RGB color filter layer on top of the black-and-white E-Ink panel.

The layers (from top to bottom) are:

The black-and-white microcapsules create the brightness values, and the color filter above them adds color.

Ahead we said “1 microcapsule = 1 pixel (1 dot).” On top of each dot, exactly one color filter (R, G, or B) is placed.

Dot 1 = Red Dot 2 = Green Dot 3 = Blue

Depending on the filter design, some systems add a second green, because the human eye derives ‘sharpness’ (luminance) mostly from green. So a common pattern is: Red, Green, Green, Blue — four subpixels per group.

Why Color E-Readers Have Lower Resolution

In grayscale mode, each of the four subpixels can represent its own independent dot.

But in color mode, those four subpixels — red, green, blue (and sometimes an additional green or clear/white) — must work together to form one color dot.

So while grayscale uses all four as separate details, color mode merges four subpixels into one color pixel. That’s why devices advertised as “300 ppi in grayscale” effectively become “150 ppi in color.”

Why Color E-Readers Look Dimmer

Now you might still wonder: “Okay, but how does color actually appear on top of a grayscale panel?”

If the microcapsule shows black, then the pixel is black regardless of the filter. Black absorbs almost all light. No matter which color filter sits above it, the result is still black.

But what about white?

The tricky part is: a white E-Ink pixel cannot appear perfectly white through a color filter. A color filter absorbs all wavelengths except its designated one.

For example, a red filter allows only red light to pass. A white E-Ink pixel reflects all wavelengths, but after passing the red filter, only the red component remains. If the underlying white is bright, it appears as a bright whitish-red. If the underlying white is dimmer (a light gray), it becomes a pastel red.

In simpler terms:

That’s how color is produced on an E-Ink display.

I’ll draw diagrams next time(?). My eyes are closing now…!