[Multimedia] data compression type

There are two types of data compression:Lossless CompressionAndLossy Compression.

Lossless Compression

The so-called lossless compression format uses statistical redundancy to compress the data. It can completely restore the original data without causing any distortion. However, the compression rate is limited by the theory of statistical redundancy, generally from. this method is widely used for text data, program and image data (such as fingerprint images and medical images) compression in special applications. Due to the limited compression ratio, it is impossible to solve all the problems of storage and transmission of images and digital videos by using only lossless compression. the commonly used lossless compression methods include Shannon-Fano encoding, Huffman encoding, run-length encoding, Lempel-Ziv-Welch encoding, and arithmetic encoding.

The so-called lossless compression format, as its name implies, is the audio format that compresses audio signals without loss. Common formats such as MP3 and WMA are lossy compression formats, which have a considerable degree of signal loss compared to source wav files, this is also the root cause of their 10% compression rate. The lossless compression format is like compressing audio signals with compression software such as ZIP or RAR. The resulting compression format is restored to a WAV file, which is exactly the same as the source WAV file! However, if you use ZIP or RAR to compress wav files, you must decompress the package before playing the video. The lossless compression format can be directly played in real time through the playback software, which is identical to the lossy formats such as MP3. All in all, lossless compression can reduce the volume of wav files without sacrificing any audio signal.

Lossy Compression

Lossy compression is a feature that is not sensitive to certain frequency components in images or sound waves and allows loss of certain information during compression. Although it cannot completely recover original data, however, the effect of the loss on understanding the original image is reduced, but the compression ratio is greatly increased. Lossy compression is widely used to compress speech, image, and video data.

Common sound, image, and video compression operations are lossy.

In multimedia applications, common compression methods include: PCM (pulse coding modulation), predictive coding, transform coding, interpolation and push, statistical coding, vector quantization, and sub-band encoding, hybrid encoding is widely used in recent years.

MP3 DivX Xvid jpeg rm rmvb WMA wmv and so on are all lossy compression.

Lossy data compression is a compression method that is compressed and decompressed differently from the original data but very close to the original data. Lossy data compression, also known as destructive compression, compresses secondary information data at the cost of quality to reduce data volumes and increase the compression ratio. This method is often used on the Internet, especially in the streaming media and telephone fields.

Lossless compression format vs lossy compression format

What are the advantages and disadvantages of lossless compression compared with lossy compression formats? The following comparison should give you a clear understanding of lossless compression formats.

Advantages of lossless compression:

1. 100% storage, no signal loss
As mentioned earlier, lossless compression is equivalent to zip compression, which can save all data of wav files by 100%. This can be proved by the "WAV comparison" function of EAC. Save the beautifulday captured by U2 into WAV format as our original file. Compress this wav file into the APE format, and decompress it into the WAV format. Use the "WAV comparison" function of EAC to compare the data of these two wav files. The EAC does not report any inconsistency! If it is the wav file compressed into MP3 and decompressed, it is different from the original WAV file from start to end! Many friends hope to copy the cd "original" to the hard disk to the maximum extent and reduce space usage. In the past, it seems that only 320kbpscbrmp3 was a solution, but that is far from 100%! Now, the emergence of lossless compression formats provides an almost perfect solution.

2. High sound quality, not affected by the signal source
Since the original audio signal is saved in 100%, the sound quality of the lossless compression format is undoubtedly the same as that of the original CD! Can you see any difference between the WAV format and the FLAC compression format of beautifulday? Likewise, there cannot be any difference in actual listening! However, due to its inherent design (which requires a part of the signal to be lost), the lossy compression format can only be infinitely close to the sound source CD, so it is impossible to truly reach the CD level! In addition, due to the limitations of lossy compression formats, the sound quality of music with a large dynamic range, such as the compression of Symphony, is not satisfactory. The lossless compression format does not have such a problem. All types of music are correct!

3. Easy conversion
Lossless Compression formats can be easily restored to WAV, and can be directly converted to MP3, Ogg, and other lossy compression formats. They can even be converted between different lossless compression formats, without losing any data. This is much stronger than the lossy format! Because the secondary encoding in lossy compression format (converting from one lossy format to another, or changing the bit rate without changing the format) means losing more signals and causing greater distortion!

Disadvantages of lossless compression:

1. Large Space occupation and low compression ratio
Compared with lossy compression formats, lossless compression formats have much lower compression capabilities, generally around 60%. The lossy format of 14% kbps is only about of the original file, and the difference in compression ratio between the two is quite different. I used different formats to compress a U2 "beautifulday", including the ape in normal mode and La IN HIGH mode. However, we can see that the data is also saved in 100%, and the lossless compression capability is better than the RAR optimized for multimedia formats, while zip is almost impossible to compress the WAV format. In addition, the lossless format has real-time playback capabilities that are not available for both RAR and zip. We still admire the lossless format technology!

2. Lack of hardware support
Currently, only the FLAC format is supported by a small number of hardware devices, and karma is the only player that can play the lossless compression format. This is caused by many reasons. First, the current mainstream flash MP3 Flash Player capacity is only 256 MB or MB, it is obviously unrealistic to store lossless formats. Second, the decoding lossless compression format requires a greater amount of computing, which puts forward higher requirements on the processing speed of the decoding chip, and there are few such decoding chips. Thirdly, decoding lossless formats even consume more power than lossy formats, which is undoubtedly worse for MP3 players with poor battery performance!

Currently, the well-known lossless compression formats include ape, FLAC, LPAC, and wavpack.