What is Dictionary Based Coding & How Does it’s Works

Dictionary-based coding is a data compression technique that uses a dictionary to represent repetitive patterns in data. It works by replacing frequently occurring phrases or strings in the data with a shorter code or symbol, resulting in a compressed version of the original data. This technique is widely used in various applications that require efficient storage and transmission of large amounts of data.

In this article, we will discuss the working of dictionary-based coding, its advantages and disadvantages, and examples of its use in various applications.

How Dictionary-Based Coding Works

Dictionary-based coding is a lossless compression technique, which means that the compressed data can be restored to its original form without any loss of information. This technique works by identifying repetitive patterns in the data and creating a dictionary of these patterns. The dictionary is a collection of phrases or strings that occur frequently in the data.

The dictionary can be created using various methods such as statistical analysis, machine learning algorithms, or manual construction. Once the dictionary is created, the compression process begins by scanning the data for occurrences of phrases in the dictionary. When a match is found, the phrase is replaced with a shorter code or symbol from the dictionary.

The compressed data is typically represented as a sequence of codes or symbols that correspond to the phrases in the dictionary. The decoder uses the same dictionary to restore the original data by replacing the codes or symbols with the corresponding phrases.

Advantages of Dictionary-Based Coding

1. Efficient Compression: Dictionary-based coding can achieve high compression ratios by identifying and replacing repetitive patterns in the data. This technique is especially effective for compressing text data, such as documents, where words and phrases are often repeated.

2. Fast Decompression: Since the dictionary is shared between the encoder and decoder, decompression can be performed quickly and efficiently. This makes dictionary-based coding well-suited for applications that require real-time data compression and decompression, such as video and audio streaming.

3. Flexibility: Dictionary-based coding can be adapted to different types of data and applications by using different dictionaries and compression algorithms. This flexibility allows it to be used in a wide range of applications, from text compression to image and video compression.

Disadvantages of Dictionary-Based Coding

1. Dictionary Overhead: The size of the dictionary can have a significant impact on the compression ratio and the compression speed. A larger dictionary can capture more patterns in the data, but it also requires more memory and processing power. A smaller dictionary, on the other hand, may not capture all the patterns in the data, resulting in lower compression ratios.

2. Compression Speed: The time required to create the dictionary and perform the compression can be a significant bottleneck in some applications. This can be particularly problematic for applications that require real-time compression, such as video and audio streaming.

3. Limited Compression for Random Data: Dictionary-based coding is most effective for compressing data that contains repetitive patterns. If the data is random or contains few repeating patterns, the compression ratio may be low.

Examples of Dictionary-Based Coding

1. ZIP Compression: ZIP is a popular compression format that uses dictionary-based coding to compress files. The ZIP format uses a dictionary of up to 32KB to compress the file data. This format is widely used for compressing and archiving files for storage and transmission.

2. JPEG Compression: The JPEG image compression format uses dictionary-based coding to compress the image data. The format uses a dictionary of Huffman codes to represent the frequency of occurrence of different color values in the image. This technique allows JPEG to achieve high compression ratios while maintaining high image quality.

3. LZW Compression: LZW is a dictionary-based compression algorithm that is widely used for compressing text data. The LZW algorithm uses a dynamic dictionary to capture repeating patterns in the text data. This technique allows LZW to achieve high compression ratios for text data.


Dictionary-based coding is a powerful data compression technique that is widely used in various applications. This technique is effective for compressing data that contains repetitive patterns, such as text, images, and videos. Dictionary-based coding offers many advantages, including efficient compression, fast decompression, and flexibility.

However, this technique also has some disadvantages, such as the overhead of maintaining the dictionary, the time required for compression, and the limited compression of random data. It is important to consider these factors when deciding whether to use dictionary-based coding for a particular application.

Overall, dictionary-based coding is a valuable tool for efficient data storage and transmission. Its effectiveness in various applications makes it an essential technique for modern computing systems.