File Formats Flashcards
What is ASCII?
American Standard Code for Information Interchange
How does ASCII work?
It uses 7 bits to store 128 different characters
What characters does ASCII store?
letters, numbers, symbols (“alphanumeric”) and special commands
What is a character set?
Collections of characters that a computer recognises from their binary representation
How many characters can extended ASCII store?
256
What is the use of Unicode?
It has over 1 million possible characters, so it allows the use of different languages and emojis
What is a bitmap image?
It is an image made up of small parts called pixels that are each assigned a colour eg JPEG, Gif
What is a vector image?
It is an image made up of lines and shapes. Each shape/line has properties like line thickness/colour. Often used on webpages and graphics
What are the main differences between a vector and bitmap image?
A vector image is scalable. You can zoom in on a vector image without losing resolution, but in a bitmap image, the pixels are enlarged when you zoom in
What is colour depth?
Each colour value of an image is stored as a binary number. The greater the number of bits allocated to store that number, the more colours to choose from e.g. if you have 5 bits you have 32 different colours
What are pixels?
A picture element - the smallest point in an image
What is resolution?
Resolution is a measure of pixel density, measured in dots per inch (dpi) - eg a resolution of 72 dpi has 5184 pixels per square inch
What are the dimensions of an image?
Dimension of an image is the number of pixels wide by height. We call this the size of an image
Formula for size in bits?
Size in bits = width x height x colour depth. Divide by 8 to get size in bytes
What is an audio sample?
An audio sample is a measure of amplitude at a point in time
What is the sample rate?
The number of samples taken in a second, measured in Hertz
What is sample resolution?
Bit depth - The number of bits available for each sample. The higher the resolution, the higher the quality of the audio. A sample resolution of 16 has 2^16 = 65,536 possible values
How to calculate the size of sound files?
Sample rate x sample resolution x seconds
What is compression?
It is the method computers use to make file sizes smaller by reducing the number of bits used to store the information
Why do we compress files?
Storage space is very valuable on a computer. Reducing file size allows data to be transferred more quickly over the internet. It allows faster download and upload times. It allows faster streaming eg JPEG MP3
How does lossless compression work?
It compresses files by finding repeated patterns in the data and creating a data dictionary. It can be restored to the original. No quality is lost. Eg ZIP PNG
How does lossy compression work?
It compresses files by removing redundant data. Cannot be restored to the original. Some quality may be lost, but usually parts you can’t see or hear
How does lossy work on images?
It compresses by reducing colour depth, running a compression algorithm that will reduce colour ranges or brightness to a level that will not change the viewers perception of the image
How does lossy work on sound?
It is compressed by reducing the bit depth of the samples, removing sounds too high, low or quiet for human hearing. Also, if two sounds are played at once, the quieter one is removed, converting a WAV to MP3 file. This gives about a 90% reduction
