xy to RGB

[sticilface]

I've just spent several hours on this particular problem and have not solved it, its a bit out of my area.
For the iOS Hue app to work, I require xy colour space numbers.

your equation for rgb to xy works.

I cannot derive one that converts RGB back to xy!

can you help?

[probonopd]

Afaik, @me-no-dev has been working on this topic. Pull requests welcome!

[Schischu]

I wrote this code mode than a year ago. If I remember right it is not an 1:1 mapping but its pretty close.

`

def rgbToXY(self):
    red = self.lw12.red / 255.0
    green = self.lw12.green / 255.0
    blue = self.lw12.blue / 255.0

    if red == 0 and green == 0 and blue == 0:
        red = 52
        blue = 23
        green = 15

    print red, green, blue

    if red > 0.04045:
        r = math.pow((red   + 0.055) / (1.0 + 0.055), 2.4)
    else:
        r = red  / 12.92

    if green   > 0.04045:
        g = math.pow((green   + 0.055) / (1.0 + 0.055), 2.4)
    else:
        g = green  / 12.92

    if blue   > 0.04045:
        b = math.pow((blue   + 0.055) / (1.0 + 0.055), 2.4)
    else:
        b = blue  / 12.92

    X = r * 0.649926 + g * 0.103455 + b * 0.197109
    Y = r * 0.234327 + g * 0.743075 + b * 0.022598
    Z = r * 0.0000000 + g * 0.053077 + b * 1.035763

    try:
        cx = X / (X + Y + Z)
    except:
        cx = 0.0

    try:
        cy = Y / (X + Y + Z)
    except:
        cy = 0.0

    print cx, cy

    if math.isnan(cx):
        cx = 0.0
    if math.isnan(cy):
        cy = 0.0

    self.state.xy[0] = cx
    self.state.xy[1] = cy`

[probonopd]

@Schischu thanks for this code, would you mind sending a pull request?

[probonopd]

@Schischu still around?