Data transforming apparatus and control method thereof

This invention implements a fast lossless transform almost free from a delay with a small calculation amount. The lossless transform can be used to perform lossless coding and lossy coding quickly. A first calculation means (111) multiplies data D0, D1, D2, and D3 input to the input terminals (101-104) by respective weighting coefficients {a0, al, a2, a3} of {1/2, -1/2, -1/2, -1/2}, and summates the products. A rounding means (113) in the first calculation means (111) rounds the sum into an integer and outputs the integer value E. A second calculation means (112) multiplies the value E by weighting coefficients {b0, b1, b2, b3} of {-1, 1, 1, 1} set for the respective input data, and adds the products to the respective input data. This invention sets, for the relationship between the first and second weighting coefficients, a condition that a0*b0 + a1*b1 + a2*b2 + a3*b3 = -2 or 0.