Methodology to convert RGB to Wavelength

Question

I want to convert the RGB image matrix to corresponding Wavelenth matrix. If there any methodology or alogorithm just mention here.

Wavelength as in the size of the lightwave in nanometers? You can't do this, only a very small set of values correspond to a wavelength. You don't have a wavelength for brown or pink for example. — D.J. Klomp, Aug 11 '19 at 16:26

score 3 · Answer 1 · edited May 23 '17 at 12:31

Looking at other answers you could do two-step process:

Convert RGB to HSV colour model (see How to get the wavelength of a pixel using RGB?)
Convert Hue value to wavelength (see Hue to wavelength mapping)

Converting from RGB to HSV

function [h,s,v] = rgb2hsv(r, g, b)

    MAX_PIXEL_VALUE = 255.0;

    assert_checktrue ( r <= MAX_PIXEL_VALUE )
    assert_checktrue ( g <= MAX_PIXEL_VALUE )
    assert_checktrue ( b <= MAX_PIXEL_VALUE )

    r = r / MAX_PIXEL_VALUE;
    g = g / MAX_PIXEL_VALUE;
    b = b / MAX_PIXEL_VALUE;

    max_val = max(r, g, b);
    min_val = min(r, g, b);

    v = max_val;

    if max_val == 0.0 then
        s = 0;
        h = 0;
    elseif (max_val - min_val) == 0.0 then
        s = 0;
        h = 0;
    else
        s = (max_val - min_val) / max_val;

        if max_val == r then
            h = 60 * ((g - b) / (max_val - min_val)) + 0;
        elseif max_val == g then
            h = 60 * ((b - r) / (max_val - min_val)) + 120;
        else
            h = 60 * ((r - g) / (max_val - min_val)) + 240;
        end
    end

    if h < 0 then
        h = h + 360.0;
    end

    h = h / 2;
    s = s * MAX_PIXEL_VALUE;
    v = v * MAX_PIXEL_VALUE;

    return [h, s, v]
endfunction

Converting from Hue to wavelength

function wavelength = hue2wavelength(hue)

    // There is nothing corresponding to magenta in the light spectrum, 
    // So let's assume that we only use hue values between 0 and 270.
    assert_checktrue(hue >= 0);
    assert_checktrue(hue <= 270);

    // Estimating that the usable part of the visible spectrum is 450-620nm, 
    // with wavelength (in nm) and hue value (in degrees), you can improvise this:
    wavelength = 620 - 170 / 270 * hue;

endfunction

Putting it together

function wavelength = rgb2wavelength(r,g,b)
    [h,s,v] = rgb2hsv(r,g,b);
    wavelength = hue2wavelength(h);
endfunction

Methodology to convert RGB to Wavelength

1 Answers1