Binary Representation of Images
Candidates should be able to:
- explain the representation of an image as a series of pixels represented in binary
- explain the need for metadata to be included in the file such as height, width and colour depth
- discuss the effect of colour depth and resolution on the size of an image file.
How can an image be represented in binary?
Data in computers is stored and transmitted as a series of ones and zeros (also known as Binary).
To store an image on a computer, the image is broken down into tiny elements called pixels. A pixel (short for picture element) represents one colour. An image with a resolution of 1024 by 798 pixels has 1024 x 798 pixels (817,152 pixels).
In order for the computer to store the image, each pixel is represented by a binary value. We call this representation of colours a “bit-plane”. Each bit doubles the number of available colours i.e. 1-bit would give us 2 colours, 2-bits would give us 4 colours and 3-bits would give us 8 colours etc.
In a monochrome (two colour) image, like the example below, just 1 bit is needed to represent each pixel e.g. 0 for white and 1 for black.
Data in computers is stored and transmitted as a series of ones and zeros (also known as Binary).
To store an image on a computer, the image is broken down into tiny elements called pixels. A pixel (short for picture element) represents one colour. An image with a resolution of 1024 by 798 pixels has 1024 x 798 pixels (817,152 pixels).
In order for the computer to store the image, each pixel is represented by a binary value. We call this representation of colours a “bit-plane”. Each bit doubles the number of available colours i.e. 1-bit would give us 2 colours, 2-bits would give us 4 colours and 3-bits would give us 8 colours etc.
In a monochrome (two colour) image, like the example below, just 1 bit is needed to represent each pixel e.g. 0 for white and 1 for black.
Images are stored in scan lines. Each line is encoded from left to right, top to bottom. The image here would receive the following binary values:
000000
010010
010010
000000
011110
000000
010010
010010
000000
011110
000000
In an image that uses 4 colours, 2 bits are needed for each pixel. The following example uses two bits to store the following colours:
00 – White; 01 – Black; 10 – Yellow; 11 – Blue
00 – White; 01 – Black; 10 – Yellow; 11 – Blue
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101010101010
100010100010 101110101110 101010101010 100101010110 101010101010 |
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More Examples
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Pacman ghost bitmap
Why does metadata need to be included in an image file?
In order for the computer to correctly display the image, the computer needs to know the following:
We call this extra piece of information “metadata”.
- Height and width of the image – so each line of the image starts in the correct place.
- Colour depth – so the correct number of bits are used to represent the colour of each pixel.
- Resolution - so the image displays at the correct size.
We call this extra piece of information “metadata”.
Want to know more?
To find out more about how a computer represents an image using binary, click on the links below:
To find out more about how a computer represents an image using binary, click on the links below:
- GCSE Computing revision (Binary image representation) - http://mattg99.wordpress.com/2011/05/21/gcse-computing-revision-binary-image-representation/
- CS Unplugged (Image representation) http://csunplugged.org/image-representation
- BBC: Cracking the code (How pictures can be represented in the form of binary) - http://www.bbc.co.uk/programmes/p0166rgs
Tags: How can an image be represented in binary?, how is data represented in binary?, What are bitmap images made up of?, binary representation of images
