Finding the Nearest Known Color

Jeremy Cowles — Mon, 21 Jan 2008 05:49:38 +0000

I recently ran across an interesting question in a usenet post; How do you convert an arbitrary color to a known / system color?

After some thought, I reasoned: in order to find the nearest known color, you must get the difference for each known color based on your sampled color. You could do this by looping through each known color in the enumeration Drawing.KnownColor.

Next, you could compare the R, G, and B values (or H, S, V values if that is more appropriate) for the known to the sample. To get the distance, you could either do a simple sum of the absolute differences, or if you are a Man or Woman of science, you would use the RMS (Root Mean Square) value. Finally, you keep the value with the smallest difference and return it.

In my sample code below, I also created a structure for returning the Name, Color and the Distance – this is just a little sugar to help the medicine go down, not really necessary.
Private R As New Random


Private Sub Button1_Click(ByVal sender As System.Object, _

              ByVal e As System.EventArgs) _

                      Handles Button1.Click
    Dim randColor As Color = _

                      Color.FromArgb(R.Next(0, 255), _

                                     R.Next(0, 255), _

                                     R.Next(0, 255))
    Me.RandomColorBox.BackColor = randColor

    Me.RandomColorLabel.Text = randColor.ToString
    '// now match to nearest known color

    Dim nearest As ColorName = FindNearestKnown(randColor)

    Me.KnownColorLabel.Text = nearest.Name

    Me.NearestColorBox.BackColor = nearest.Color
End Sub
Structure ColorName

    Public Color As Color

    Public Name As String

    Public Distance As Integer

End Structure
Public Function FindNearestKnown(ByVal c As Color) _

                                        As ColorName

    Dim best As ColorName
    best.Name = Nothing
    For Each colorName As String In _

                    [Enum].GetNames(GetType(KnownColor))

        Dim known As Color = Color.FromName(colorName)

        Dim dist As Integer
        dist = Math.Abs(CInt(c.R) - known.R) _

                + Math.Abs(CInt(c.G) - known.G) _

                + Math.Abs(CInt(c.B) - known.B)
        If best.Name Is Nothing _

                 OrElse dist < best.Distance Then

            best.Color = known

            best.Name = colorName

            best.Distance = dist

        End If

    Next

Return best End Function

Visual Core » Windows

Finding the Nearest Known Color