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    Help with Color Coordinates please

    MoKaLuxMoKaLux Member
    edited September 2019 in General questions
    I need your help please:
    -I have an RGB image size (306 * 48)
    -I have an image (can be any size)

    I have a color picker, when I pick a color on the image I would like to get its x position on the RGB image.
    I have been trying everything that came to my mind but did not succeed.

    Do you know a formula to do it?

    Thank you in advance for your help.
    function SlideColorPicker:setHue(xhexcolor)
	--self.colors = {0xFF0000, 0xFFFF00, 0x00FF00, 0x00FFFF, 0x0000FF, 0xFF00FF, 0xFF0000}
	self.e = Event.new("COLOR_CHANGED")
	local r, g, b = self:hex2rgb(xhexcolor)
	self.currColor = r*65536 + g*256 + b
	local hpr = (1 - (r / 255)) * 51 -- 51 is image width 306 / 6 (#self.colors{} - 1)
	local hpg = (1 - (g / 255)) * 51
	local hpb = (1 - (b / 255)) * 51
	local hueposition = hpr + hpg + hpb
	self.hueArrows:setX(hueposition)
	self.e.color = self.currColor
	self:dispatchEvent(self.e)
end
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    Comments

    • olegoleg Member
      edited September 2019 Accepted Answer 
      function rgb(r, g, b) return ((r*256)+g)*256+b end
      function Util:hex2rgb(hex)
    hex = hex:gsub("#","")
    return tonumber("0x"..hex:sub(1,2)), tonumber("0x"..hex:sub(3,4)), tonumber("0x"..hex:sub(5,6))
end

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    • keszeghkeszegh Member
      Accepted Answer
      it seems your color slider goes linearly from H0 S50 L50 to H359 S50 L50
      see
      https://developer.mozilla.org/en-US/docs/Web/CSS/CSS_Colors/Color_picker_tool
      so you need only to convert the rgb of the pixel to hsl first
      e.g.
      https://www.rapidtables.com/convert/color/rgb-to-hsl.html
      and then you can easily get the right place on the color slider. of course only if the color is present there, i.e., has S50 and L50. otherwise you can get the closest color by caring only about the H value.

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    • MoKaLuxMoKaLux Member
      edited September 2019
      Thank you for your kind help. I am getting close:
      	local r, g, b = self:hex2rgb(xhexcolor)
	local h, s, l = self:rgb2hsl(r, g, b)
      I now have the h value (between 0 and 360).
      One problem is left I cannot figure out how to transform this h value to translate to my image (306 pixel wide).

      edit: I think I get it: local hueposition = h * (306 / 360)

      Wonderful thank you very much guys.
      my growING GIDEROS github repositories: https://github.com/mokalux?tab=repositories
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    • keszeghkeszegh Member
      Accepted Answer
      yes, although probably
      local hueposition = h * (305 / 359)
      is even more correct (assuming your colorslider has width 306)

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    • MoKaLuxMoKaLux Member
      @keszegh thank you our gfx specialist o:) thank you @oleg really appreciated!

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    • rrraptorrrraptor Member
      edited September 2019 Accepted Answer
      I prefer to use this:
      function rgbToHex(r, g, b) 
    return (r << 16) + (g << 8) + b
end
 
function hexToRGB(hex)
    local r = hex >> 16
    local g = hex >> 8 & 0xFF
    local b = hex & 0xFF
    return r,g,b
end
      And if you want to print/display hex number, just use
      string.format("0x%06x", hex)

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