Although not known widely, steganography is an art of concealing vital information that has been practiced since 1499. The term was first coined by Johannes Trithemius. This is a Greek term which is made of two words ‘steganos’ which means covered or protected and ‘graphein’ which means writing. The secret information may be concealed within a file, message, image, or video. In this article we will discuss about image steganography.
Images are the most popularly used medium or objects used in the field of digital steganography. The images may exist in different types of file formats and most of these have specific applications. There are different types of steganographic algorithms that exist for the different image file formats,
In the case of a computer, an image is basically an assortment of numbers which make up different types of light intensities. The numeric representation of the numbers form a grid and these individual points are known as pixels.
Most of the image steganography examples you will see in the Internet are mainly composed of rectangular map containing the image’s pixels, which are represented as bits. Each image pixel is located with its specific color scheme. These pixels are usually displayed in the horizontal form, row by row. The number of bits that you find in a color scheme is known as bit depth and they usually refer to the bits that are used for forming as pixel.
For example, if a number for bit in the color schemes 8 then it means that 8 bits are used to form that pixel. The greyscale and monochrome images are usually composed of 8 bits, and they are used to display the 256 various shades of grey. Typically, the digital color images are kept in the 24-bit files and they are used in the RGB format.
The different color variations for pixels used in the 24-bit images are usually derived from the primary colors that comprise red, green and blue. Each of the primary colors are characterized by 8 bits which form one pixel and there may be 256 diverse magnitudes of RGB.
What is Image Compression
Image compression is a commonly used terminology in image steganography and it mainly used when the image files become too large to be sent through Internet connection. So, this technique is used to shorten the image size and it uses mathematical formulas. It condenses the bigger image files into smaller size.
There are basically two different styles of compression and they are lossless and lossy. Both these methods are known to save the storage space for large images. The lossy compression type condenses the image files by removing the extra image data. The lossless compression style on the other hand does not remove any data from the original image instead it uses mathematical formulas to represent the data. The widely used format for the lossless compression type is GIF or Graphical Interchange Format and the other format is 8-bit BMP.
We hope the above information gives you a brief idea about the concept of image steganography.
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