Most text characters are converted into binary using a code called ASCII (American Standard Code for Information Interchange). The first version of ASCII was published in 1963 and last updated in 1986.
ASCII contains 128 characters, which is enough for most English content. For example, the dollar sign ($) can be represented as binary code of 0100100 (decimal 36); as you can see, it is represented using seven bits of data.
ASCII, however, is not enough for everyone as we have many different languages that use different alphabets such as the Russian alphabet and Chinese characters. For that, a new code was created and it is called Unicode. This new standard assigns a unique number to every character in every language. Each unicode character can take up to four bytes.
All data are stored as binary in computers. How images are represented in binary? To understand how images are stored digitally, first, we need to learn what is a pixel.
What is a pixel?
A pixel (short for picture element) is the smallest element of a display. It is a dot or square in an image that represents only one colour. If we take a close-up of any images, you can see that images are made up of many pixels. To produce a full range of colours, each pixel consists of three LEDs (red, green, and blue). By combining different intensities of the colours, each pixel can display up to 16 million colours, which is way more than 10 million colours the human eye can discriminate.
By ed g2s • talk – Example image is a rendering of Image:Personal computer, exploded 5.svg., CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=807503
By Kprateek88 – Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=4635158
Binary images (monochrome)
Now, let us start with binary images where pixels can have exactly two colours – black and white. Since each pixel only has two states, we can use a single bit to represent each pixel – 1 for white and 0 for black. Here is a 10 x 10 pixels image example generated using our binary image visualisation tool.
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Colour Depth
As demonstrated in the previous example, using 1 bit to represent each pixel can only provide two colour options. Naturally, we can increase the number of bits to represent each pixel and thus expand the possible colour options. For every additional bit we use to represent each pixel, the number of colour options doubles. The number of bits used to represent a single pixel is known as colour depth or bit depth.
For example with 3-bit colour depth, we could create 8 colour variations for each pixel.
True colour (24-bit)
As of today, almost all computer and phone displays use 24-bit colour depth. The term true colour is often used to refer to all colour depths that are equal to or more than 24-bit. 8 bits each is used to represent the intensity of colour red, green, and blue. Using 8 bits for each colour, the value range from 0 to 255.
The resolution of an image refers to how tightly pixels are packed together. It is commonly expressed in pixels per inch (PPI). Higher resolutions mean that there more pixels per inch (PPI), resulting in more pixel information and creating a high-quality, crisp image.
Interactive tool
Hands-on generating images of different resolutions using different colour depths.
