Algorithm to Switch Between RGB and HSB Color Values

Question

I read the article Algorithm to Switch Between RGB and HSB Color Values

Type RGBColor
     Red As Byte
     Green As Byte
     Blue As Byte
End Type

Type HS         


        

Answer 1

Solution

You can calculate the Brightness component quite simply as it's the max of R, G, and B (reference: formula for RGB to HSV from the Rochester Institute of Technology). You can scale it however you like by dividing by 255 and multiplying by the scale. This is the same as done in your existing code:

maxRGB = Max(Max(rgb.Red, rgb.Green), rgb.Blue)
b = maxRGB    
...    
RGBToHSB.Brightness = b * 100 / 255

So, in the end you can use the built-in .Net functions and just calculate your brightness. Full code would be (excluding your types):

Function RGBToHSB(rgb As RGBColor) As HSBColor
  Dim maxRGB As Double
  maxRGB = Max(Max(rgb.Red, rgb.Green), rgb.Blue)

  Dim c As Color = Color.FromArgb(rgb.Red, rgb.Green, rgb.Blue)
  RGBToHSB.Hue = c.GetHue()
  RGBToHSB.Saturation = c.GetSaturation() * 100
  RGBToHSB.Brightness = maxRGB * 100 / 255
End Function

A bit about HSB (same as HSV)

From Darel Rex Finley:

In the HSV (also called HSB) system, the brightness of a color is its V component. That component is defined simply as the maximum value of any of the three RGB components of the color — the other two RGB components are ignored when determining V.

According the the Microsoft Documentation for Color.GetBrightness:

Gets the hue-saturation-brightness (HSB) brightness value for this Color structure.

I have found some references saying the MSDN uses HSB when it means HSL like this one from MSDN blogs (see the comments). A quick test proves this to be true (in C#):

// Define a color which gives different HSL and HSB value
Color c = Color.FromArgb(255, 0, 0);
// Get the brightness, scale it from 0.0 - 1.0 up to 0 - 255
int bright = (int)(c.GetBrightness() * 255.00);
// Output it
Console.WriteLine(bright.ToString());

This results in a value of 127, which is clearly HSL. If it was HSB the value should be the max of R G and B (i.e. 255).