Design and Implementation of JPEG Image Compression and Decompression

Image compression is very important for efficient transmission and storage of images. Demand for communication of multimedia data through the telecommunications network and accessing the multimedia data through Internet is growing explosively. With the use of digital cameras, requirements for storage, manipulation, and transfer of digital images, has grown explosively. These image files can be very large and can occupy a lot of memory. A gray scale image that is 256 x 256 pixels have 65, 536 elements to store and a typical 640 x 480 color image have nearly a million. The basic objective of image compression is to find an image representation in which pixels are less correlated. Architecture and VHDL design of 2-D DCT, combined with quantization and zig-zag arrangement, is described in this paper. The output of DCT module needs to be multiplied with post-scalar value to get the real DCT coefficients. Post-scaling process is done together with quantization process. The decompression has to revert the transformations applied by the compression to the image data. The decoder therefore takes the compressed image data as its input. It then subsequently applies a Run length decoding [RLD], Inverse zigzag scan [ZZ], dequantization [DQ], inverse discrete cosine transform [IDCT], a color conversion and reordering to it. It then obtains the reconstructed image.