Recipe 9.25. Using the RGB, HSB (HSV), and HSL Color Schemes


Problem

You want to provide the user with options for color selection: RGB (red-green-blue), HSB (hue-saturation-brightness, also known as HSV for hue-saturation-value), and HSL (hue-saturation-luminosity).

Solution

Sample code folder: Chapter 09\RGBandHSV

The easiest way to provide user-based color selection is to use the ColorDialog control to prompt the user to choose a color. This standard Windows dialog includes fields for RGB numeric entry and for HSL entry. Each of the HSL scales ranges from 0 to 240 (239 for hue), and changes to those fields automatically update the displayed RBG values (see Figure 9-35).

The ColorDialog control is described in Recipe 9.3.

In addition to the ColorDialog control, the new .NET System.Drawing.Color structure provides access to many predefined colors, plus methods to specify and obtain color values. Three of its methods let you convert an instance's RBG value to distinct HSB values:

  • The GetHue() method returns a value from 0 to 360 that indicates the hue of the Color object's current color.

  • The GetSaturation() method returns a value from 0.0 to 1.0 for the active color, in which 0.0 indicates the neutral grayscale value, and 1.0 is the most saturated value.

  • The GetBrightness() method returns a value from 0.0 (black) to 1.0 (white).

Figure 9-35. Using the ColorDialog control with separate HSL and RBG fields


This recipe's sample code lets the user select a color using either the RBG method or the HSB (a.k.a. HSV) method.

Discussion

Create a new Windows Forms application, and add the following controls to Form1:

  • Three HScrollBar controls with the names ValueRed, ValueGreen, and ValueBlue. Set their Maximum properties to 255.

  • One HScrollBar control named ValueHue. Set its Maximum property to 360.

  • Two HScrollBar controls with the names ValueSaturation and ValueBrightness. Set their Maximum properties to 100.

  • A PictureBox control named ShowColor.

  • Six Label controls with the names NumberRed, NumberGreen, NumberBlue, NumberHue, NumberSaturation, and NumberBrightness. Set their Text properties to 0.

Add descriptive labels if desired. The form should look like Figure 9-36.

Now add the following source code to the form's class template:

 Private Sub RBG_Scroll(ByVal sender As System.Object, _       ByVal e As System.Windows.Forms.ScrollEventArgs) _       Handles ValueRed.Scroll, ValueGreen.Scroll, _       ValueBlue.Scroll    ' ----- Update the HSV values based on RBG.    Dim   rgbColor As Color 

Figure 9-36. The controls on the color model sample


    ' ----- The   color structure already has the formulas    ' built in.      rgbColor = Color.FromArgb(0, ValueRed.Value, _       ValueGreen.Value, ValueBlue.Value)    ValueHue.Value = CInt(rgbColor.GetHue())    ValueSaturation.Value = _       CInt(rgbColor.GetSaturation() * 100.0F)    ValueBrightness.Value = _       CInt(rgbColor.GetBrightness() * 100.0F)    ' ------ Refresh everything else.    RefreshDisplay() End Sub Private Sub ValueHue_Scroll(ByVal sender As Object, _       ByVal e As System.Windows.Forms.ScrollEventArgs) _       Handles ValueHue.Scroll, ValueSaturation.Scroll, _       ValueBrightness.Scroll    ' ----- Update the RBG values based on HSV.    Dim useRed As Integer    Dim useGreen As Integer    Dim useBlue As Integer    Dim useHue As Single    Dim useSaturation As Single    Dim useBrightness As Single    Dim hueSector As Integer    Dim factor As Single    Dim target1 As Single    Dim target2 As Single    Dim target3 As Single    ' ----- Convert to relative 0.0 to 1.0 values.    useHue = CSng(ValueHue.Value)    useSaturation = CSng(ValueSaturation.Value) / 100.0F    useBrightness = CSng(ValueBrightness.Value) / 100.0F    If (useSaturation = 0.0F) Then       ' ----- Pure grayscale.       useRed = CInt(useBrightness * 255)       useGreen = useRed       useBlue = useRed    Else       hueSector = CInt(useHue / 60.0F)       factor = Math.Abs((useHue / 60.0F) - CSng(hueSector))       target1 = useBrightness * (1 - useSaturation)       target2 = useBrightness * (1 - (factor * useSaturation))       target3 = useBrightness * (1 - ((1 - factor) * _          useSaturation))       Select Case hueSector          Case 0, 6             useRed = CInt(useBrightness * 255.0F)             useGreen = CInt(target3 * 255.0F)             useBlue = CInt(target1 * 255.0F)          Case 1             useRed = CInt(target2 * 255.0F)             useGreen = CInt(useBrightness * 255.0F)             useBlue = CInt(target1 * 255.0F)          Case 2             useRed = CInt(target1 * 255.0F)             useGreen = CInt(useBrightness * 255.0F)             useBlue = CInt(target3 * 255.0F)          Case 3             useRed = CInt(target1 * 255.0F)             useGreen = CInt(target2 * 255.0F)             useBlue = CInt(useBrightness * 255.0F)          Case 4             useRed = CInt(target3 * 255.0F)             useGreen = CInt(target1 * 255.0F)             useBlue = CInt(useBrightness * 255.0F)          Case 5             useRed = CInt(useBrightness * 255.0F)             useGreen = CInt(target1 * 255.0F)             useBlue = CInt(target2 * 255.0F)       End Select    End If    ' ----- Update the   RGB values.    ValueRed.Value = useRed    ValueGreen.Value = useGreen    ValueBlue.Value = useBlue    ' ------ Refresh everything else.    RefreshDisplay() End Sub Private Sub RefreshDisplay()    ' ----- Update the numeric display.    NumberRed.Text = CStr(ValueRed.Value)    NumberGreen.Text = CStr(ValueGreen.Value)    NumberBlue.Text = CStr(ValueBlue.Value)    NumberHue.Text = CStr(ValueHue.Value)    NumberSaturation.Text = _       Format(CDec(ValueSaturation.Value) / 100@, "0.00")    NumberBrightness.Text = _       Format(CDec(ValueBrightness.Value) / 100@, "0.00")    ' ----- Update the   color sample.    ShowColor.BackColor = Color.FromArgb(255, _       ValueRed.Value, ValueGreen.Value, ValueBlue.Value) End Sub Private Sub Form1_Load(ByVal sender As System.Object, _       ByVal e As System.EventArgs) Handles MyBase.Load    ' ----- Set the initial color.    RBG_Scroll(ValueRed, _       New Windows.Forms.ScrollEventArgs( _       ScrollEventType.EndScroll, 0)) End Sub 

Run the program, and use the six scrollbars to adjust the color selection.

The RGB model for describing colors numerically has become common for use in Microsoft Windows, but it is not always the most convenient method for certain applications or for output to devices other than computer monitors. The HSB/HSV system is more useful in selecting colors for computer-based artwork.

The System.Drawing.Color structure includes methods that let you extract the HSB components of an RGB color, but it doesn't work in the other direction. Therefore, the sample code includes the calculation for HSB-to-RGB conversions.

See Also

A useful web site that discusses color models is EasyRGB, found at http://www.easyrgb.com.

See Recipe 9.3 for details on using the ColorDialog control.




Visual Basic 2005 Cookbook(c) Solutions for VB 2005 Programmers
Visual Basic 2005 Cookbook: Solutions for VB 2005 Programmers (Cookbooks (OReilly))
ISBN: 0596101775
EAN: 2147483647
Year: 2006
Pages: 400

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