A Novel Method for Reducing Number of Computation in 2d-dct

The DCT performs very important role in the application of lossy compression for representing the pixel values of an image using lesser number of coefficients. Recently, many algorithms have been devised to compute DCT. In the initial stage of image compression, the image is generally subdivided into smaller sub-blocks and then these sub-blocks are applied to DCT. In this paper we have presented a novel method for DCT computation to reduce the number of computations based on the difference between the pixel values of adjacent rows. The DCT computations for second row are replaced by first row DCT computations when all the pixel values of second row are having very less difference from the first row pixels. In this way a larger number of computations are reduced. The method is verified with various high and less correlated images and the result shows that image quality is not much affected even though 4 bits per pixel are considered for row comparison. The correlation between the pixels of two rows is calculated by fixing a threshold value which depends on the elimination of number of bits used for row pixel comparison. The simulation results shows that the proposed DCT method reduces the Number of computations by 50.02 % for highly correlated images and reduces 23.63 % for less correlated images without much affecting the image quality.