在互联网上，有许多自定义的颜色选择器，包括在MSDN和Code Project上。虽然有很多类似的文章讨论自定义颜色选择器，但还没有看到有文章讨论如何将图像/位图转换为颜色选择器，所以决定尝试实现它，希望对CodeProject的成员有所帮助。
要从图像/位图中获取像素颜色，可以使用Bitmap类的GetPixel方法。首先需要定义一个Image对象，然后将像素的x和y坐标传递给GetPixel方法，这样就可以得到像素的颜色。以下是VB.NET的代码示例：
Dim bmp As New Bitmap("Grapes.jpg")
Dim x As Integer = 20
Dim y As Integer = 20
Dim pixelColor As Color = bmp.GetPixel(x, y)
这段代码首先创建了一个Bitmap对象，然后定义了要检索的像素的x和y坐标，最后通过GetPixel方法获取了像素的颜色。
图像颜色选择器的核心思想是将MouseDown和MouseMove事件的引用传递给一个私有方法，以获取鼠标位置，然后使用该点获取该点的颜色。
ImageColorPicker.vb：扩展了Windows.Forms.Control类。
Image：用于设置用户选择的图像/位图。
Public Property Image As Bitmap
Get
Return Me.originalBitmap
End Get
Set(ByVal value As Bitmap)
Me.originalBitmap = value
Me.DrawImage()
Me.Invalidate()
End Set
End Property
Color：获取选定的颜色。
Public Property Color As Color
Get
Return Me.selectedColor
End Get
Set(ByVal value As Color)
Me.selectedColor = value
Me.PixelColorToPoint()
Me.DrawImage()
MyBase.Invalidate()
End Set
End Property
ColorChanged：当图像像素颜色变化时发生，它也代表控件的DefaultEvent。
Public Custom Event ColorChanged As EventHandler
AddHandler(ByVal value As EventHandler)
Me.Events.AddHandler("ColorChangedEvent", value)
End AddHandler
RemoveHandler(ByVal value As EventHandler)
Me.Events.RemoveHandler("ColorChangedEvent", value)
End RemoveHandler
RaiseEvent(ByVal sender As Object, ByVal e As System.EventArgs)
CType(Me.Events("ColorChangedEvent"), EventHandler).Invoke(sender, e)
End RaiseEvent
End Event
以下是一些关键的方法，包括绘制图像、获取像素颜色点、检查像素颜色点是否在指定的边界内等。
Private Sub DrawImage()
If MyBase.Width > 0 AndAlso Me.originalBitmap IsNot Nothing Then
Me.pickerBitmap = New Bitmap(MyBase.ClientRectangle.Width - _
(Me.controlBorder * 2), MyBase.ClientRectangle.Height - _
(Me.controlBorder * 2))
Dim g As Graphics = Graphics.FromImage(Me.pickerBitmap)
Dim mode As SmoothingMode = g.SmoothingMode
Dim rect As New Rectangle(0, 0, Me.pickerBitmap.Width, _
Me.pickerBitmap.Height)
g.DrawImage(Me.originalBitmap, rect)
g.SmoothingMode = mode
g.Dispose()
End If
End Sub
使用控件：
Public Class Form1
Private selectedColor As Color
Private Sub ImagColorPicker1_ColorChanged(ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles ImagColorPicker1.ColorChanged
selectedColor = Me.ImagColorPicker1.Color
Me.Invalidate()
End Sub
Protected Overrides Sub OnPaint(ByVal e As System.Windows.Forms.PaintEventArgs)
MyBase.OnPaint(e)
e.Graphics.FillRectangle(New SolidBrush(Me.selectedColor), _
New Rectangle(0, 0, 30, 30))
End Sub
End Class