# How Are Colors Formed Digitally Using LEDs?

The number of colors visible on the display screen depends on the bit-depth, i.e., the number of bits used for each pixel on the display screen. A 24-bit depth display can show up to 16 million colors.

Before you start counting the number of LED crayons in your painting set, be advised that it could take a bit more time and patience than anticipated. Counting colors is not so straightforward a process as counting crayons or water colors.

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## What Is A Bit?

How easy it would be to count colors if there were only two—black and white. However, having variety makes life a bit more interesting. See how having more colors is related to life being a bit more interesting and counting being a bit more difficult?The core concept being used here is a bit, quite literally. When you turn the switch ON, the bulb glows. Similarly, when you turn the switch OFF, the bulb goes dark. A convenient way of representing the ON and OFF states of a bulb could be by assigning numerical values.

Let 1 represent the ON state, and let 0 represent the OFF state. The digits 0 and 1 are called BITS. If there were only two colors, then White could be denoted by 1 (ON) and Black could be denoted by 0 (OFF). This is a two-bit color scheme, where the world is only Black and White.

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## A Word On Diodes & LEDs

Life becomes more vivid when diodes come into the picture. A diode (di + electrode) is a device that has two metallic contacts on either side of a non-metallic conductor and conducts electricity in only a single direction.

A power source connected to a diode in the conducting direction (Forward Biasing) allows the current to flow, but the same source when connected in the reverse direction to the diode (Reverse Biasing) wouldn’t produce a current  (this is a simplification of an ideal diode). Thus, a diode can be thought of as a switch, which when turned ON is at 1 state (Forward) and when turned OFF is at 0 state (Reverse).

Some diodes can be engineered to emit light when a current passes through. These are called Light Emitting Diodes (LEDs). When an LED is forward-biased, it emits light (the color depends on the material it’s made of). The LED stops glowing when it’s reverse-biased.

In the decades since the 1960s, the advancement of solid state physics resulted in the development of LEDs capable of emitting Red (R), Green (G) and Blue (B) colors. This marked a significant milestone, for these three colors make up almost all the digital color displays available in the market, from your smartphone to your beloved smart-TV!

## Making New Colors From Existing Ones

While painting, you must have noticed that mixing two colors generates a new color. For example, mixing blue and yellow gives green, whereas red plus white makes pink. A similar principle is also used in generating digital colors. Varying the intensity of R, G and B and mixing them up generates billions of color combinations.

Consider the following cases for a clearer understanding –

CASE 1 – Only one LED is available. Thus, only two states are possible (ON or OFF). This is a 1-bit display. CASE 2 – Invest your savings and buy another LED. Now two LEDs are available, with each LED in either ON or OFF state. Total number of combinations is 22 = 4. This is a 2-bit display.They are (ON ON); (ON OFF); (OFF OFF); (OFF ON). Four colors are possible using two LEDs. CASE 3 – Suppose that someone gifted you a third LED. Then each LED could be combined with the other two in either the ON or OFF states. The total number of combinations is 23 = 8. This is a 3-bit display.They are (ON ON ON); (ON ON OFF); (ON OFF ON); (OFF ON ON); (OFF OFF ON): (OFF ON OFF); (ON OFF OFF); (OFF OFF OFF).

Eight colors are possible using three LEDs.

In general, Number of possible colors, N = Sn, where (i) n = number of LEDs available. (ii) S = number of states possible for a single LED (Either ON or OFF = 2 for conventional LEDs).

## Pixel: The Atom Of The Screen

A digital display screen is made up of thousands of tiny dots called pixels. A pixel is to a display screen what an atom is to an element. It is the smallest unit of the screen. An 8-bit display uses eight LEDs for each pixel (quantities in parenthesis in CASES 1 to 3), so the total number of colors possible in an 8 bit display is 28 = 256! Notice how the number of colors possible increases by an exponent of 2. The greater the number of LEDs, the more detailed the image.

## Working Of An 8-bit Display

Each pixel is colored by 8 LEDs, i.e., each pixel can generate any of the 28 = 256 colors. Increasing the number of pixels per square inch (display resolution) increases the picture detail  (better zooming in capacity). For example, a 5 MP (Mega Pixel) has five million pixels making up the display screen. Each of those five million pixels can render any of the 256 colors in the 8-bit display.

Assume that eight LEDs are arranged color-wise from left to right. On the extreme left is R and on the extreme right is B. G falls in between. The following table shows how colors are assigned to bits. BIT Count (LED Index) is the number of LED from the left.

 BIT Count(LED Index) 0 1 2 3 4 5 6 7 Colour Assigned R R R G G G B B

(NOTE: Color distribution can be varied according to requirements. The above is an example case.)

Another example –

 Bit Count(LED Index) 0 1 2 3 4 5 6 Colour Assigned R R G G B B B

Changing the ON/OFF state and intensity of each LED produces different colors. If LEDs 3, 4 and 5 are turned OFF (i.e., G LEDs are OFF) and the rest of the LEDs are ON (i.e., R and B LEDs are ON), then the color of the pixel would be Violet. The specific shade of violet will depend upon the intensity of the individual R and B LEDs.

Each of the 256 colors is assigned a numerical value from 0 to 255, with 0 representing the OFF state for all LEDs (Black) and 255 representing the ON state for all LEDs (White). The following table lists all colors in the 8-bit scheme.

## Monochromatic V/s Chromatic Display

If each pixel is powered by LEDs emitting the same color, then the image would be monochromatic. If each pixel is powered by LEDs emitting different colors (R, G and B), then the display is chromatic.

True Color 24-bit displays use 8 bits each for R, G and B. Each color is called a channel. Thus, 256 shades for each channel are possible in a single pixel. Total number of colors rendered by a single pixel is 256256256 = 16,777,216. Thus, a 24-bit True Color display can render 16,777,216 different colors.

For comparison, the human eye can detect about 10 million different colors. Basically, the next time you realize that a color is missing from your crayon set, just think back to this article and create any color that you want!

Also Read: How Does A Projector Work?

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