1.2 Text, sound and images

## Text

### ASCII

- The standard ASCII code character set consists of 7-bit code that represents the letters, numbers and characters found on a standard keyboard, together with 32 control codes
- Uppercase and lowercase characters have different ASCII values
- Every subsequent value in ASCII is the previous value + 1. e.g. “a” is 97 in ASCII, “b” will be 98 (which is 97 + 1)
- Important ASCII values (in denary) to remember are as follows:
- 0 is at 48
- A is at 65
- a is at 97
- ASCII uses one byte to store the value
- When the ASCII value of a character is converted to binary, it can be seen that the sixth-bit changes from 1 to 0 when going from lowercase to uppercase of a character, and the rest remains the same. e.g.
### Unicode

- ASCII does not contain all of the international languages, thus Unicode is used to solve this problem

- Unicode uses 16 bits / 32 bits to represent per character.
- Unicode has 65 536/4 294 967 296 characters // approx. 60/70 thousand/4 billion characters
- For the first 128 values, it is the same as ASCII.

- Unicode supports up to four bytes per character, storing multiple languages and more data.
- **To represent text in binary, a computer uses a character set, a collection of characters and the corresponding binary codes that represent them.**
#### How the text is converted to binary to be processed by the computer.
- A character set is used such as Unicode/ASCII
- Each character has a unique binary value
#### Explain the differences between the ASCIl character set and the Unicode character set
- ASCIl has limited/fewer characters // Unicode has a more characters ASCII covers a limited set of languages/fewer languages
- Unicode includes many/more languages/emojis
- ASCIl requires 7/8 bits per character
- Unicode requires up to 16/32 bits per character
- ASCIl has 128/256 characters
- Unicode has 65 536/4 294 967 296 characters // approx. 60/70 thousand/4 billion characters
#### Explain how the word 'RED' is represented using a character set
- Unique binary/denary number given/stored for each character
- The code for R is stored, then the code for E then D in sequence
## Sound
- Sound is analogue, and for it to be converted to digital form, it is sampled
- The sound waves are sampled at regular time intervals where the amplitude is measured, however, it cannot be measured precisely, so approximate values are stored
### Explain how the analogue sound is recorded and converted to digital
- (The analogue sound is) recorded using a microphone
- The sound wave is sampled measuring the amplitude
- Each amplitude has a unique binary value 
- The sample rate is set
- ... that is the number of samples taken per second 
- The sample resolution is set
- ... that is the number of bits used for each sample
- Each sample taken is converted to binary
### How is Sound Recorded
- The amplitude of the sound wave is first determined at set time intervals
- The value is converted to digital form
- Each sample of the sound wave is then encoded as a series of binary digits
- A series of readings gives an approximate representation of the sound wave
### Sampling Resolution:
- **The number of bits per sample is known as the sampling resolution (aka bit depth)**
  - ... that defines the number of different amplitudes that can be recorded 
  - ....that determines how loud the sounds are that can be recorded
- Increasing the sampling resolution increases the accuracy of the sampled sound as more detail is stored about the amplitude of the sound.
- Increasing the sampling resolution also increases the memory usage of the file as more bits are being used to store the data.
### Sampling Rate
- **The sampling rate is the number of sound samples taken per second, which is measured in Hertz (Hz)**
- A higher sampling rate would allow more accurate sound as fewer estimations will be done between samples.
#### Explain why recording sound with a higher sampling resolution creates a more accurate recording.
- More bits allocated to each amplitude
- Amplitudes can be more precise
- A wider range of amplitudes can be recorded
## Images
### Bitmap Images
- Bitmap images are made up of pixels
- A bitmap image is stored in a computer as a series of binary numbers
### Pixel
- One square of one colour // the smallest component of the image
### Colour Depth
- The number of bits representing each colour is called the colour depth.
- An 8-bit colour depth means that each pixel can be one of 256 colours (because 2 to the power of 8 = 256)
- A 1-bit colour depth means each pixel can store 1 colour (because 2 to the power of 1 is 2) - ( This is done as the bit can either be 0 or 1, with 0 being white and 1 being black)
- Increasing colour depth
  - A greater range of colours can be seen/used
  - Image will be closer to the actual content of the image/real life 
  - The image will have more detail
  - increases the size of the file when storing an image
### Image Resolution
- The number of pixels wide by the number of pixels high

### File Header/Metadata
- Data about the bitmap image (e.g. 
    - number of colours, 
    - File format/File type 
    - File size 
    - Dimensions, resolution & colour depth of the image 
    - Date and place when the photo was taken 
    - Time and date when the photo was changed 
    - Camera settings when the photo was taken 
    - type of data compression )
### Describe how a digital image file is stored by a computer
- Image is made of pixels
- Each pixel stores one colour
- Image has a set number of pixels wide by pixels high
- Each colour has a unique binary value
- The binary value of each pixel is stored in sequence
- File contains metadata to identify how the file should be displayed 
- ...metadata can be the colour depth / resolution