RGB relative dimming from KNX

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To dim a color your need to convert RGB to HSV, change V up/down and then convert back to RGB.
Here are the functions that you can use.

Code:

function rgbtohsv(r, g, b)   local max, min, d, h, s, v   max = math.max(r, g, b)   min = math.min(r, g, b)   d = max - min   s = max == 0 and 0 or (d / max)   v = max / 255   if max == min then     h = 0   elseif max == r then     h = (g - b) + d * (g < b and 6 or 0)     h = h / (6 * d)   elseif max == g then     h = (b - r) + d * 2     h = h / (6 * d)   elseif max == b then     h = (r - g) + d * 4     h = h / (6 * d)   end   return h, s, v end function hsvtorgb(h, s, v)   local r, g, b, i, f, p, q, t, z   i = math.floor(h * 6)   f = h * 6 - i   p = v * (1 - s)   q = v * (1 - f * s)   t = v * (1 - (1 - f) * s)   z = i % 6   if z == 0 then     r = v     g = t     b = p   elseif z == 1 then     r = q     g = v     b = p   elseif z == 2 then     r = p     g = v     b = t   elseif z == 3 then     r = p     g = q     b = v   elseif z == 4 then     r = t     g = p     b = v   elseif z == 5 then     r = v     g = p     b = q   end   r = math.round(r * 255)   g = math.round(g * 255)   b = math.round(b * 255)   return r, g, b end function rgbstep(r, g, b, up, step)   local h, s, v = rgbtohsv(r, g, b)   local v2 = up and math.min(1, v + step) or math.max(0, v - step)     if v == v2 then     return   end   return hsvtorgb(h, s, v2) end

rgbstep(r, g, b, up, step) can perform up/down step of current RGB value.
arguments:

• r, g, b - color components in 0..255 range
  
• up - true = step up / false = step down
  
• step - step size, V range is 0..1 so the step should be something like 0.1 or 0.05 depending on how many total steps you want
  

rgbstep will return new RGB values but it might also return nil when further step is not possible.

Code:

-- values from split RGB value r = 127 g = 255 b = 10 -- step down up = false -- maximum 20 steps between min and max step = 0.05 r, g, b = rgbstep(r, g, b, up, step) if r then   -- write new values else   -- stop dimming end