Image Search Using Hash Code

This paper introduced an effective method for query adaptive image retrieval using low level feature extraction and hashing method. Low level features mainly constitute color, shape, and texture functions. For the color feature extraction color moment, the color histogram method and the color correlation graph method are executed, and the wavelet moment method is used for texture feature extraction. The hash method is used to embed high dimensional image features in the Hamming space, and the search can be performed in real time based on the Hamming distance of the compact hash code.

An encrypted hash function is a "one-way" mapping from variable length input (password) to fixed length output (called a hash code or hash value). Hash codes with specific values ​​do not provide enough information to reconstruct the input values. In addition, the input value should (ideally) map to a unique output value. In other words, you can not generate the same hash code with two different passwords. Because the output length is fixed, it is theoretically impossible to guarantee this property of the hash function. For example, if the length of the hash code is only 8 bits, there are only 256 unique hash codes, so irrespective of how the hash code is calculated, as long as 257 unique passwords have been hashed, contradiction recent The encrypted hash algorithm produces longer hash codes; values ​​between 512 and 2048 bits are common.

A hash function is any function you can use to map data of arbitrary size to fixed size data. The value returned by the hash function is called a hash value, a hash code, a digest, or a simple hash. ... Hash function speeds searching of tables and databases by detecting duplicate records of large files

To insert a value into the hash table, send the key of the data to the hash function. The hash function returns an integer (hash code). This is used as the modulo of the size of the array as the storage index of the values ​​in the array. If you want to retrieve the value from the hash table, simply recalculate the hash code from the key and then retrieve the data from that location in the array. This place is the physical address of our data. For libraries that use the Dewey Decimal system, "key" is a set of categories to which the book belongs, and "value" is the book itself. "Hash code" is a value created using Dewey decimal method. For example, books on analytical geometry got a "hash code" of 516.3. Natural science is 500, mathematics 510, geometry 516, analysis geometry is 516.3.