File deletion/ compression

Question 1

what happens when a file is deleted?

Answer 1

it is flagged by the operating system as free space to be overwritten, the file remains there in fragments or as a whole until it is overwritten

Question 2

what is a write blocker?

Answer 2

allows you to read information but not write to it –> a one way data transfer

Question 3

lossless / non lossy compression

Answer 3

reduces file size by removing unneccessary meta data. can be reversed
eg. PNG

Question 4

lossy compression

Answer 4

reduced file size by permanently removing some origional data
eg JPEG

Question 5

Coding redundancy

Answer 5

when there’s more code words than necessary, so can get rid of some

Question 6

Interpixel redundancy

Answer 6

apply a DCT to structure the image in a more efficient way

Question 7

Psychovisual redundancy

Answer 7

gaps in the pixel image because it is not needed for human visual processing

Question 8

compression ratio

Answer 8

no of bits for storage of uncompressed image / no of bits for storage of compressed image

Question 9

conversions:
1byte
1KB

Answer 9

1 byte = 8 bits
1 KB = 1024 bytes