Image and Sound Representation
Learn about how images and sound are represented on computer systems!
Bitmap images
- Binary data is used to represent images on a computer.
- Pictures must be shown on a screen (or a printer) as a series of dots or pixels.
- These pixels are stored on a computer as a series of bits. Each bit corresponds to a part of the image.
- Images stored in this way are called bit-mapped image files.
- The more pixels in a given area, the better the quality and larger file size.
- The number of pixels in an image is called the resolution of the picture and is essentially a measure of width and height (e.g. an image that is 1024px in width x 768px in height has 817,152 pixels in it).
- The lower the resolution (i.e. the fewer the pixels used in the image), the less quality and smaller file size.
- Colour depth or bit depth is the number of bits used to represent each pixel (i.e. the colour of the pixel) - in other words, bits per pixel.
- The more bits used, the better the quality of the colour because more colours can be encoded, e.g. an 1-bit image can only represent 2 colours, whereas a 2-bit image can represent 4 different colours.
Vector images
- Pictures can also be stored as formulae.
- They define characteristics of points, lines and curves.
- They do not distort when enlarged, because the image is recalculated.
Metadata
Metadata provide extra information about the data in a file.
Image files may contain metadata about:
Image files may contain metadata about:
- the height;
- the width;
- the colour depth;
- the resolution;
- camera used;
- exposure details;
- when the image was created;
- who owns the copyright;
- contact information.
Sound
- Computers only work with digital signals, so the original analogue form that sound takes must be sampled for it to be stored as a file on a computer.
- the quality and size of the file is affected by two factors - sample rate and bit rate.
- Measurements of the analogue sound wave are taken at intervals.
- The more measurements taken, the close the recording is to the original sound.
- The rate that measurements are taken (usually every second) is known as the sample rate.
- So the higher the sample rate, the better the quality of the recording (but also the larger the file size)
- Bit rate refers to the number of bits used to store each sample (similar to bit depth in bitmap images, i.e. the number of bits used to store each pixel).
- The more bits used for each sample, the better the accuracy of the recording (but also the larger the file size).