Data compression first time job

1-1: One of the basic questions about data compression is "what are we going to compress" and how do you understand that?

A: Data compression refers to the process of significantly reducing the amount of data required to represent a signal in the range of non-loss of information and distortion tolerance, using methods such as changing sampling rate, predictive coding, and transformation coding. In the transmission and storage, can reduce the storage space and communication media bandwidth, increase transmission speed, shorten the transmission time, improve confidentiality and reduce the cost of the process. Data compression technology has three main indicators, one is the compression of information required before and after the ratio of the data to be large, the second is to achieve the compression of the algorithm to be simple, compression, decompression speed, as far as possible to achieve real-time compression and decompression; The recovery effect is better, to restore the original data as completely as possible. To put it simply, I think data compression is mainly the process of reducing data size by using some techniques to reduce data redundancy.

1-2: Another problem with data compression is "Why compress", and how do you understand it?

A: With the advent of the big data age, mobile communications, shopping, social activities and so on have produced a lot of data, and these data are still showing exponential growth. But our hard disk storage capacity is limited. Guided by this trend, we have to find a way to reduce the capacity of data storage, but also produced a data compression technology, so it can be said that data compression has far-reaching significance, can be said to be a very important auxiliary tool in the era of big data, he is not only the product of big data is a trend.

1-6: How is data compression categorized?

Answer: Data compression is mainly divided into lossy compression and lossless compression

1: Lossless compression

The so-called lossless compression format, is the use of statistical redundancy of data compression, can completely restore the original data without causing any distortion, but the compression rate is subject to statistical redundancy of the theoretical limit, generally 2:1 to 5:1. Such methods are widely used in text data, programs and special applications such as image data, such as fingerprint images, Medical images, etc.) are compressed. Due to the limitation of compression ratio, only using lossless compression method is not possible to solve all the problems of image and digital video storage and transmission. The lossless compression method used often has Shannon-fano encoding, Huffman encoding, run (run-length) encoding, LZW ( Lempel-ziv-welch) encoding and arithmetic coding.

The so-called lossless compression format, as the name implies, is no loss of sound signal compression of the audio format. Common formats such as MP3, WMA, and so on are lossy compression formats, which have a significant loss of signal compared to WAV files as sources, which is the root cause of the 10% compression rate they can achieve. and lossless compression format, like ZIP or rar compression software to compress the audio signal, the resulting compression format to restore WAV files, and as the source of the WAV file is identical! However, if you compress wav files with zip or RAR, you must extract the compressed packets before they can be played. and lossless compression format can be directly through the playback software to achieve real-time playback, the use of MP3 and other lossy format is identical. All in all, lossless compression is a format that reduces the volume of WAV files without sacrificing any audio signal.

2: lossy compression

The so-called lossy compression is the use of human image or sound in some of the frequency components are not sensitive to the characteristics of the compression process to allow the loss of certain information, although the original data can not be completely restored, but the loss of the part of the understanding of the original image of the effect of narrowing, but in exchange for a much larger compression ratio. Lossy compression is widely used in the compression of voice, image and video data.

Common sound, image, video compression is basically lossy.

In multimedia applications, the common compression methods include PCM (pulse code modulation), Predictive coding, transformation coding, interpolation and extrapolation, statistical coding, vector quantization and sub-band coding, and hybrid coding is a widely used method in recent years.

MP3 DivX Xvid JPEG RM rmvb wma WMV, etc. are lossy compression.

lossy data compression is a compression method that compresses and extracts data that is different but very close to the original data. lossy data compression, also known as destructive compression, is about to compress the secondary information data, sacrificing some quality to reduce the amount of data, so that the compression ratio is improved. This method is often used in the Internet, especially in streaming media and telephony fields.

Data compression first time job