Patent ID: 7430330

Claim:
A method of JPEG compression of an image frame divided up into a plurality of non-overlapping, tiled 8×8 pixel blocks X i comprising: (a) forming a discrete cosine transform (DCT) of each block X i of the image frame to produce a matrix of blocks of transform coefficients Y i ; (b) calculating a visual importance, I i , for each block of the image, based upon assigning zeros for flat features and values approaching unity for sharply varying features; (c) forming a global quantization matrix Q by one of (i) selecting a standard JPEG quantization table and (ii) selecting a quantization table such that the magnitude of each quantization matrix coefficient Q[m,n] is inversely proportional to the aggregate visual importance in the image of a corresponding DCT basis vector; and (d) calculating linear scaling factors S i defining bounds over which the image is to be variably quantized; (e) approximating variable quantization of the transform coefficients, Y i [m,n], using the local quantization table S i Q while actually producing coefficients T i [m,n] that have been quantized using global quantization table S min Q where S min is a scaling value used in compressing the image that defines the quality bounds over which the image will be variably quantized; and (f) entropy encoding quantized coefficients T i [m,n] and global quantization table S min Q to create a JPEG Part 1 image file.