Patent ID: 7539355

Claim:
A data transform method for acquiring lossless Hadamard transform coefficients for 16 pieces of input image data in 4×4 matrix form and generating a reduced amount of coded data based on the acquired lossless Hadamard transform coefficients, comprising: one or more computers implementing the following steps of: a linear transform step of acquiring 16 linear Hadamard transform coefficients by multiplying said 16 pieces of input image data by an Hadamard transform matrix; an offset step of classifying said 16 linear Hadamard transform coefficients into four groups, each group containing an odd number of coefficients, and adding predetermined offset values to the linear Hadamard transform coefficients in every group; an integral step of acquiring said lossless Hadamard transform coefficients by truncating decimal fractions down from a decimal point from the linear Hadamard transform coefficients added with said predetermined offset values; and a coding step of coding said lossless Hadamard transform coefficients acquired in said integral step, wherein values below a decimal point of said 16 linear Hadamard transform coefficients are one of 0, 0.25, 0.5 and 0.75, wherein in said offset step, no addition is made to a first group of transform coefficients, 0.25 is added to a second group of transform coefficients, 0.5 is added to a third group of transform coefficients, and 0.75 is added to a fourth group of transform coefficients as the offset values, wherein among the four groups, into which said 16 linear Hadamard transform coefficients are classified, three groups contain three or five transform coefficients, and wherein in a 4×4 offset matrix containing values four times the number of offset values corresponding to said 16 linear Hadamard transform coefficients, sums of the values in a row direction are odd in all rows or even in all rows, and sums of the values in a column direction are odd in all columns or even in all columns.