a sample for image processing with look-up-table(before memorized)

luminor_gen.py

def get_luminorImpl(input, b_sigma, c_sigma, g_sigma, with_alpha):
    """
    input: a Buffer as an bitmap image on memory
    b_sigma: float value for brightness(default: 0.0, range: -255 to 255)
    c_sigma: float value for contrast(default: 1.0, range: 0.1 to 10.0)
    g_sigma: float value for gamma value(default: 1.0, range: 0.1 to 10.0)
    """

    assert type(input) == ImageParam
    assert input.dimensions() == 3

    x, y, c = Var("x"), Var("y"), Var("c")
    
    table = Buffer(uint8_t, 256)
    v = Var("v")

    px = cast(float_t, v)
    px = px * (1.0/255.0)

    # change brightness
    px = px + b_sigma * (1.0/255.0)

    # change contrast
    px = (px-0.5)*c_sigma+0.5

    # change gamma value
    px = pow(px, 1.0/g_sigma)

    px = max(px, 0.0)
    px = min(px, 1.0)

    px = cast(uint8_t, px*255)
        
    luminor_table = Func('luminor_table')
    luminor_table[v] = px
    luminor_table.trace_stores()
    luminor_table.compute_root().vectorize(v, 16)
    luminor_table.realize(table)

    luminor = Func('luminor')
    luminor[x, y, c] = table[input[x, y, c]]

    # for RGBA pixels, Alpha is not modified
    if with_alpha:
        luminor[x, y, 3] = input[x, y, 3]

    luminor.compute_root().parallel(y).vectorize(x, 16)

    return luminor

after memorized, to see https://gist.github.com/kanryu/d176b9480e2e15b2b68a16814588a6ba