-- Split Difference

function init()
    --create an empty image for the LUT
    img_lut = image8.new()
    --load the LUT
    img_lut:load_png(get_resource_path("lut/cal/abi_split_difference.png"), false)
    --return 3 channels, RGB
    return 3
end

function process()
    for x = 0, rgb_output:width() - 1, 1 do
        for y = 0, rgb_output:height() - 1, 1 do

            --get channels from satdump.json
            get_channel_values(x, y)
            local cch13 = get_channel_value(0)
            local cch15 = get_channel_value(1)

            --perform Difference, scaling -10 - 10 to 0-1
            local difference = (cch13-cch15+0.07299270072)/0.14598540146

            --range convert from 0-1 to 0-255
            local lutval = difference*255

            --sanity checks
            if lutval < 0 then
                lutval = 0
            end

            if lutval > 255 then
                lutval = 255
            end

            --don't forget to create a table!
            local lut_result = {}

            --send the lutval to the LUT, retrieve it back in the table as 3 R,G,B channels
            lut_result[0] = img_lut:get(0 * img_lut:height() * img_lut:width() + lutval) / 255.0
            lut_result[1] = img_lut:get(1 * img_lut:height() * img_lut:width() + lutval) / 255.0
            lut_result[2] = img_lut:get(2 * img_lut:height() * img_lut:width() + lutval) / 255.0

            --return RGB 0=R 1=G 2=B
            set_img_out(0, x, y, lut_result[0])
            set_img_out(1, x, y, lut_result[1])
            set_img_out(2, x, y, lut_result[2])

        end
        --set the progress bar accordingly
        set_progress(x, rgb_output:width())
    end
end