Lossy compression and Lossless compression are the two terms broadly classified under data compression methods. The major difference between Lossy compression and Lossless compression is that lossy compression produces near match of the data after decompression whereas lossless produces exact original data. Data Compression is a technique of reducing the size of the data without significant loss of information.
Content: Lossy Compression Vs Lossless Compression
|Basis for comparison||Lossy Compression||Lossless Compression
|Basic||Lossy compression is the class of data encoding method that uses imprecise estimates to represent the content.||Lossless compression is a class of data compression algorithms that allow the original data to be accurately reconstructed from the compressed data.
|Algorithm||Transform coding, DCT, DWT, fractal compression, RSSMS.||RLW, LZW, Arithmetic encoding, Huffman encoding, Shannon Fano coding.
|Used in||Images, audio and video.||Text or program, images and sound.
|Application||JPEG, GUI, MP3, MP4, OGG, H-264, MKV, etc.||RAW, BMP, PNG, WAV, FLAC, ALAC etc.|
|Data-holding capacity of the channel||More||Less as compared to lossy method|
Definition of Lossy Compression
The Lossy compression method eliminates some amount of data that is not noticeable. This technique does not allow a file to restore in its original form but significantly reduces the size. The lossy compression technique is beneficial if the quality of the data is not your priority. It slightly degrades the quality of the file or data but is convenient when one wants to send or store the data. This type of data compression is used for natural data like audio signals and images.
Lossy Compression Technique
- Transform coding– This method transforms the pixels which are correlated in a representation into disassociated pixels. The new size is usually smaller than the original size and reduces the redundancy of the representation.
- Discrete Cosine Transform (DCT)– This is the most widely used image compression technique. JPEG process centres around DCT. DCT process separates the images into different parts of frequencies. In the quantization step, where compression actually occurs less important frequencies are discarded. And the critical frequencies are retained to retrieve the image in the decompression process. The reconstructed image could contain some distortion.
- Discrete Wavelet Transform (DWT)– It provides location of time and frequencies simultaneously and can be utilized in decomposing a signal into component wavelets.
Definition of Lossless Compression
The Lossless compression method is capable of reconstructing the original form of the data. The quality of the data is not compromised. This technique allows a file to restore its original form. Lossless compression can be applied to any file format can improve the performance of the compression ratio.
Lossless Compression Technique
- Run Length Encoding (RLE)– This technique reduces the frequency of repeating symbols in a string by using a special marker in the begining of the symbol.
- Lempel-Ziv-Welch (LZW)– This technique also works similar to RLE technique and searches for the repeating strings or words and stores them in variables. It then uses a pointer at the place of the string, and the pointer points the variable in which string is stored.
- Huffman Coding– This technique deals with data compression of ASCII characters. It built a full binary tree for different symbols after calculating the probability of each symbol and place it in descending order.
Key Differences Between Lossy Compression and Lossless Compression
- Lossy compression removes non-useful part of the data, that is undetectable while lossless compression reconstructs the exact data.
- Lossless compression can reduce the size of data at low extent. On the other hand, lossy compression can reduce the size to a greater extent.
- The quality of the data degrades in case of lossy compression whereas lossless doesn’t degrade the quality of the data.
- In the lossy technique, the channel accommodates more data. Conversely, channel holds a smaller amount of data in case of lossless technique.
Lossy compression can achieve a high level of data compression as compared to lossless compression. Lossless compression doesn’t degrade the quality of data, in contrast, lossy degrades the quality of the data. The lossy technique cannot be implemented in all types of the file because it works by removing some part of data (redundant) which is not possible in case of text.