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Methods of information hiding in color images (Part 1)

Abstract: This paper introduces a method of how to use BMP color images to realize information hiding, namely bit map method. This method has high information hiding rate, good concealment, and is easy to implement

Keywords: information hiding; Color image; BMP file; Bitmap

0 introduction

information hiding is to hide the information that needs to be kept confidential or important into another media that can publicly store test data in arbitrary hard disk partitions. Specifically, it is to hide the specified information in digital images, sounds or texts, and make full use of people's psychology of "what you see is what you get from oil spills and other exits" to confuse malicious attackers. Usually, we call this media cover media, and the hidden action is called embedding. After embedding information, the cover media becomes a stego mcdia. In recent years, with the rapid development of computer and Internet, the problem of information hiding has attracted more and more attention. Information hiding is different from information encryption. Information encryption is the content of hidden information, while information hiding is the existence of hidden information and the room should have enough space. Information hiding is more secure than information encryption, because it is not easy to attract the attention of attackers

image information hiding is a new research topic in information hiding technology in recent years. It takes digital images as the cover media, embeds the information that needs to be kept secret into digital images according to some algorithm, and requires: ① there is no difference in human vision between the embedded image and the original image; ② Data hiding does not change the data volume of the cover media, that is, it directly modifies some parts of the media data without increasing the data of the cover media. This paper introduces a method of information hiding using BMP color image

1 early color image information hiding method

for a color image, in order to save storage space, people select the most representative color group in the image, use three bytes to record the RG value of each color respectively, and store it in the head of the file, which is the palette. If the total number of colors in the palette is 256, you need to use 1 byte to record the arrangement number of each color in the palette, and then, according to the RG color value of each pixel in the image, find the closest color in the palette and record its index number

in the early stage, the information was hidden in the palette of color images, and the order of color arrangement in the palette was used to represent the embedded information. Because this method did not change the color value of each pixel, but only the arrangement number of colors in the palette, the camouflaged image after embedding the information was exactly the same as the original image. However, the amount of information embedded in this method is very small. No matter how large the aluminum of the cover image is due to its light weight, the maximum amount of information available for embedding is the total number of palette colors

for this reason, this paper introduces another method to directly change the pixel RG value bitmap method

2 BMP file format of color image

bmp image file is a bitmap file, which indicates that an image is divided into grids. Each point of the grid is called a pixel, and each pixel has its own RG value, that is, an image is a lattice composed of a series of pixel points

bmp image file format is the standard image format set by Microsoft for its Windows environment, and contains a set of API functions for image processing. With the popularity of windows in the world, BMP file format is increasingly supported by various application software. The structural characteristics of 24 bit BMP image files are as follows: ① each file can only store one color image uncompressed; ② The file header is composed of 54 byte data segments, including the type, size, image size and print format of the bitmap file; ③ Starting from the 55th byte, it is the image data part of the file. The arrangement order of the data starts from the lower left corner of the image. Every three consecutive bytes describe the color information of a pixel of the image. These three bytes represent the brightness of the blue, green and red primary colors in this pixel respectively. If a certain three consecutive bytes are: 00h, 00h, FFH, it means that the color of this pixel is pure red