METHOD OF COMPACTING IMAGE EXPRESSED BY BLOCK OF REAL NUMBER DIGITAL DATA XJ

摘要

PURPOSE: To speedily compress an image with a little calculation quantity by determining a discrete cosine transform(DCT) coefficient by adding/ subtracting the required real number digital data of an image block as required while including the multiplication due to a specified factor. CONSTITUTION: In the two-dimensional image expressed in the block of real number digital data Xi (i=4 or the like), the data X0 and X7 and data X1 and X6 among data X0-X7,..., are respectively added/subtracted. Concerning factors Ci=1/(2(Cosi±/8) (i=1...4), factors C1-C4 are respectively multiplied so that intermediate values can be calculated. These intermediate values are similarly added/subtracted and multiplied while using factors C2, C4, C6 and C4 in addition to C2 and C6 and further, the addition/subtraction of the multiplied results and the multiplication of the factor C4 or the like are performed. Thus, DCT coefficients F0-F7 are determined with a little calculation quantity in comparison with the case of using only the factors C1-C4, and image compression due to DCT is speedily performed.