Each color channel is going through 4 stages that each look like this: (I+A)*E+O

I = input (25bit unsigned) A = adjustment (30bit signed) E = matrix coefficient (18bit signed) O = offset (48bit signed)

The four stages are connected together that the offset of stage N is the output of stage N-1. The offset of stage 1 is set in registers (32-35). The output of stage 4 is the final result.

For each channel that results in the following fomular:

Ri = SUMj ((Ij + Aij) * Eij) + Oi

Which in other words mean the result of matrix (Eij) multiplied with an input vector (Ij + Aij) plus an offset vector (Oi).

Currently all registers (beside input/output) are shortened to 16bit signed (this could be changed easily) values so the matrix is currently limited to 1/256 of the possible accuracy (due to a 8bit shift of the output).

All input /output register are tested for over/underflow and clipped to 12 bit (this can also be disabled).

Setting/Getting Registers:

. ./hdmi.func # load functions

mat_reg 0 # Read value of register 0 = A0 mat_reg 0 1 # Sett value of register 0 (A0) to 1

4x4 matrix coefficients (A0, A1, A2, A3, B0, B1, B2, B3, B4, C0, C1, C2, C3, D0, D1, D2, D3) are mapped to addresses 0 - 15. In registers 16 - 31 there are adjustment values and from 32 - 35 there are 4 offset values.

Input format per default is (R, G1, G2, B).

All values of the 4x4 matrix can be set conveniently with this script:

Syntax:

./mat4_conf.sh A0 A1 A2 A3 B0 B1 B2 B3 B4 C0 C1 C2 C3 D0 D1 D2 D3 O1 O2 O3 O4

Where the last quadruple is optional, it defaults to 0.

An RGB 3x3 matrix can easily be extended to a 4x4 matrix by using the coefficient for green and offsets twice or better to half both of the green coefficients and use the same value for both greens twice.

AXIOM Beta is a professional digital cinema camera built around FOSS and open hardware licenses.

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