cs revision

Binary being represented as characters.

• The characters that you are reading right now cannot be processed by computers because they don't fit with the two based system that computers understand. To have an alphanumeric character on a computer, each different character is assigned a binary digit.
• character sets: collections of character that a computer recognises due to their binary representation.
• Different character sets can have different amounts of characters.
• This is where ASCII comes in. ASCII is a character set that assigns each symbol, characters or command with a 7 bit binary code. The extra digit of a zero at the start of the code so that the ASCII code of a symbol is one byte.

ASCII, Extended ASCII and Unicode.

• Ascii --> Each symbol is assigned a 7 bit binary code, with a zero at the start of it. Only can represent 128 characters or symbols.
• Extended Ascii --> Each symbol is assigned an 8 bit binary code, so that the amount of characters or symbols that this system can represent is extended to 256 characters.
• Unicode --> Even more extended than extended ascii, as it uses 16 bit and 32 bit codes to represent symbols. This means that Unicode can allow for more symbols and is more reliable in the future because it can allow for more symbols.

How to store images.

• Computers store images in bitmap. This means that the pictures we saved are stored as pixels.
• To read the bitmap, a computer needs a bit more information, in the form of metadata. Metadata usually tells us the file format, width, height , colour depth and resolution.
• The colour of a pixel is determined by a binary code.
• Each pixel uses a certain number of bits. The number of the bits used for each pixel is the co,our depth.
• If the binary code for the pixel was 7 bits, the maximum amount of colours that could be stored would be 128., whereas if the code for the pixel was 8 bits, there would be 256 possible colours that could be stored.
• The formula for the total number of colours is 2 to the power of bits per pixel (bpp)

File size

• (height x width x bit depth) +10% (for metadata) = file size in bytes.
• An image with a colour depth of 8 bits and a resolution of 640x480:
• 640 x 480 x 8=2457600 Height x width x depth
• 10% of 2457600 is 245760 +10% of metadata
• 2457600+245760=2703360 Divided by 8 to get to bytes
• 2703360/8=337920 Divide by 1000 to convert to kilobytes (kb)
• 337920/1000 = 337.92kb rounded to 338kb

Hexadecimal to binary and vice versa

• 16 1
• --------------------------------
• 2 8
• You do (16 x 2) + (8x1) = 32 + 8= 40

lossy verses lossless

• Lossless --> reduces file size without losing detail
• Lossy --> Reduces file size with losing detail,