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PIPELINED 2D DCT FOR JPEG IMAGE COMPRESSION

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Abstract

This project presents the architecture and the verilog design of a Two Dimensional Discrete Cosine Transform (2-D DCT) for JPEG image compression. Uncompressed multimedia (graphics, audio and video) data requires considerable storage capacity and transmission bandwidth despite rapid progress in mass-storage density, processor speeds and digital communication system performance, demand for data storage capacity and data transmission bandwidth continues to challenge the capabilities of available technologies. The recent growth of data intensive multimedia based web applications have not only sustained the need for more efficient ways to encode signals and images, but have made compression of such signals central to storage and communication technology. Discrete Cosine Transform, DCT, is a commonly used compression technique. DCT is similar to Discrete Fourier Transform, DFT, using only real numbers. It is equivalent to DFT of roughly twice the length, operating on real data with even symmetry, since the Fourier Transform of a real and even function is real and even. DCT helps separate the image into parts of differing importance with respect to the image’s visual quality. DCT separates the image from spatial domain to frequency domain, high frequency and low frequency components. Thus, transmission media can be used more efficiently to reach application goals, as, compact representation, fast transmission, memory savings etc.

INTRODUCTION

A novel architecture for 2-D DCT is described. The 2-D DCT calculation exploits the separability property and allows row column decomposition by using 2 successive results are transposed with a parallel transposition memory high operating frequency can be reached and pipeline Technique is adopted by additional SIPO , PISO and register banks . Moreover , the 2-D DCT architecture can be modularized and suitably reused in many image and video codec systems. Multimedia applications, and in particular the encoding and decoding of standard image and video formats, are usually a typical target for Systems on- Chip (SoC). The bi-dimensional Discrete Cosine Transformation (2D-DCT) is a commonly used frequency transformation in graphic compression algorithms. Many hardware implementations, adopting disparate algorithms, have been proposed for Field Programmable Gate Arrays (FPGA). These designs focus either on performance or area, and often do not succeed in balancing the two aspects.

The design of a fast 2D DCT hardware accelerator for a FPGA-based SoC is presented . This accelerator makes use of a single seven stages 1D-DCT pipeline able to alternate computation for the even and odd coefficients in every cycle. In addition, it uses special memories to perform the transpose operations. The hardware takes 80 clock cycles at 107MHz to generate a complete 8x8 2D DCT, from the writing of the first input sample to the reading of the last result (including the overhead of the interface logic). It is shown that this architecture provides optimal performance/ area ratio with respect to several alternative designs.

Compression (DCT & IDCT).

This step deals with techniques for reducing the storage required to save an image, or the bandwidth required to transmit it. Although storage technology has improved significantly over the past decade, the same cannot be said for transmission capability. This is true particularly in uses of the internet, which is characterized by significant pictorial content. Uses of DCT & IDCT techniques to reduce the storage space of an image. IDCT is used to retrieve the Image from compressed data.

Morphological processing.

Morphological processing deals with tools for extracting image components that are useful in representation and description.

Segmentation

Segmentation procedures partition an image into its constituent parts or objects. In general, autonomous segmentation is one of the most difficult tasks in digital image processing .

Representation & Description

This step always follows segmentation step and uses raw pixel data , constituting of either the boundary of a region .

Recognition

This step helps in description of image based on its descriptors and this procedure assign a label (e.g., “vehicle” ) to an object based on descriptors.[8]

BASICS OF DCT

Discrete cosine transform is a lossy compression scheme where N×N image block is transformed from the spatial domain to DCT domain. DCT decomposes the signal into spatial frequency components called DCT coefficients. The lower frequency DCT coefficients appear toward the upper left-hand corner of the DCT matrix ,and the higher frequency coefficients are in lower right hand corner of the DCT matrix.

Conclusion

DCT is a very useful transform in IMAGE compression . To save hardware resources Multiplication free row column Approach is adopted. It occupies less area and can operate at high speeds(when implemented in pipelined form).

DCT is very useful in many bio-medical & image processing applications.