Metadata
Introduction
Apart from information about each pixel in an image, an image file also holds information about the image as a whole. This extra information is known as 'metadata'. The word 'metadata' pops up all over the place in computing and it usually refers to 'data about data'. In the context of images, it means the extra data we store about the pixel data that makes up an image.
What information is held in metadata?
When an application such as a web browser or word processor wants to open a picture, it needs to know more than the information held about each pixel. For example, it needs to know:
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- the height and width of the image
- how many pixels there should be in a square inch (the resolution)
- how many bits are being used to define the colour of each pixel (colour depth).
The application needs to know this information so that it can display the picture properly. In addition, however, there may be other information held as part of the image file, other metadata. These might include:
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- who owns the copyright to the image so that someone knows who to contact if they want to use the image
- when the image was created so that a user can see if the image is up-to-date
- keywords (tags) so that the image can be easily searched for on the Internet
- what software was used to create the image so someone can try the software for themselves if they were impressed with the image.