A Level Computer Science OCR Practice Exam

Lossy encoding is the method that does not relate to lossless compression. In lossless compression, the original data can be perfectly reconstructed from the compressed data, meaning no information is lost during the compression process. Examples of lossless compression techniques include run-length encoding and dictionary encoding, both of which retain all original data. Run-length encoding works by replacing sequences of the same data value that occur in a row with a single value and a count, maintaining complete fidelity to the original data. Dictionary encoding, on the other hand, replaces frequently occurring patterns or strings in the data with shorter, predefined codes, which also allows for perfect reconstruction of the original data. In contrast, lossy encoding involves some loss of data, which means that the original data cannot be fully reconstructed after compression. This method is often used in audio, video, and image compression where a perfect replication of the original quality is not necessary, thus trading off some detail for reduced file sizes. Bit rate reduction, while related more generally to controlling the amount of data transmitted or stored, is typically used in conjunction with lossy methods, leading to a loss of fidelity. Thus, lossy encoding stands apart from lossless methods due to its inherent nature of sacrificing some data for smaller file sizes