Computing - Topic 4 Flashcards
What is colour depth?
The number of bits used for each pixel.
How do you calculate file size in bits?
image resolution (width x height) x colour depth
What is metadata?
The information stored in an image file which helps the computer recreate the image on screen from the binary data in each pixel.
Usually includes the image’s file format, height, width, colour depth and resolution.
How do you work out how many colours can be made using the colour depth?
2^n where n is the number of bits per pixel.
What is lossy compression?
It works by permanently removing data from the file - this limits the number of bits the file needs and so reduces its size.
Used on MP3, AAC and JPEG
What is lossless compression?
It makes the file smaller by temporarily removing data to store the file and then restores it to its original state when it’s opened.
Used on FLAC, ZIP and PNG
Why do we compress data?
Smaller files take up less storage space on a device.
Streaming and downloading files from the Internet is quicker as they take up less bandwidth.
It allows web pages to load more quickly in web browsers.
Email services normally have restrictions on the size of the attachment you can send.
What are the pros of lossy compression?
File size is greatly reduced, meaning more files can be stored.
They take up less bandwidth so can be downloaded and streamed quicker.
Commonly used
What are the pros of lossless compression?
Data is only temporarily removed so there is no reduction in quality.
They can be decompressed.
It can be used on text and software files.
What are the cons of lossy compression?
Loses data permanently.
Can’t be used on text or software files.
Lossy files are worse quality than the original.
What are the cons of lossless compression?
Only a slight reduction in file size so the files still take up quite a bit of space on your device.
What is a two-dimensional array?
A one dimensional array where each element is also a one dimensional array.
What is sample rate?
How many samples you take in a second - usually measured in Hertz.
What is sampling?
The process of converting analogue signals to digital signals.
How can you improve digital sound data?
Take samples more regularly, e.g. every couple of milliseconds.
How does sampling work?
The amplitude of the wave is sampled at regular intervals. The amplitude can only take certain values depending on the bit depth.
What is bit depth?
The number of bits available for each sample.
How do you calculate the file size in bits of a sound file?
sample rate (Hz) x bit depth x duration (s)
