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### Mat per-element operation: vector-matrix multiplication

I is an mxn matrix and each element of I is a 1x3 vector (I is a 3-channel Mat image actually).

M is a 3x3 matrix.

J is an matrix having the same dimension as I and is computed as follows: each element of J is the vector-matrix product of the corresponding (i.e. having the same coordinates) element of I and M.

I.e. if v1(r1,g1,b1) is an element of I and v2(r2,g2,b2) is its corresponding element of J, then v2 = v1 * M (this is a vector-matrix product, not a per-element product).

Question: How to compute J efficiently (in terms of speed)?

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### Mat per-element operation: vector-matrix multiplication

I is an mxn matrix and each element of I is a 1x3 vector (I is a 3-channel Mat image actually).

M is a 3x3 matrix.

J is an matrix having the same dimension as I and is computed as follows: each element of J is the vector-matrix product of the corresponding (i.e. having the same coordinates) element of I and M.

I.e. if v1(r1,g1,b1) is an element of I and v2(r2,g2,b2) is its corresponding element of J, then v2 = v1 * M (this is a vector-matrix product, not a per-element product).

Question: How to compute J efficiently (in terms of speed)?