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这篇文章谈谈图像的二值化，也就是将彩色图像转为黑白图像。
步骤是：
彩色图像的灰度化，根据灰度和阈值来确定颜色是黑色还是白色。
通常情况下将阈值设置为128：
'黑白1
Private Sub btn2Color_Click(sender As Object, e As EventArgs) Handles btn2Color1.Click
Dim pSourceColor As Color
Dim pDestColor As Color
Dim destImg As New Bitmap(sourceImg.Width, sourceImg.Height)
Dim R, G, B As Integer
Dim AvgColor As Integer
For i As Integer = 0 To sourceImg.Width - 1
For j As Integer = 0 To sourceImg.Height - 1
pSourceColor = sourceImg.GetPixel(i, j)
R = pSourceColor.R
G = pSourceColor.G
B = pSourceColor.B
AvgColor = (R + G + B) / 3
If AvgColor >= 128 Then AvgColor = 255 Else AvgColor = 0
pDestColor = Color.FromArgb(AvgColor, AvgColor, AvgColor)
destImg.SetPixel(i, j, pDestColor)
Next
Next
picDest.Image = destImg
End Sub
处理后的图像如下：
可以看出选择128作为阈值实际并不是很好，网上有大量的求阈值的方法，比如大律法等，下面我采用的是一种比较简单的算法：
Private Sub btn2Color2_Click(sender As Object, e As EventArgs) Handles btn2Color2.Click
Dim pSourceColor As Color
Dim pDestColor As Color
Dim destImg As New Bitmap(sourceImg.Width, sourceImg.Height)
Dim R, G, B As Integer
Dim HistGram(255) As Integer
For i As Integer = 0 To sourceImg.Width - 1
For j As Integer = 0 To sourceImg.Height - 1
pSourceColor = sourceImg.GetPixel(i, j)
HistGram(pSourceColor.R) += 1
Next
Next
Dim threshold As Integer
Dim allSum, allCount As Integer
For k As Integer = 0 To 255
allCount += HistGram(k)
allSum += k * HistGram(k)
Next
threshold = allSum / allCount
For i As Integer = 0 To sourceImg.Width - 1
For j As Integer = 0 To sourceImg.Height - 1
pSourceColor = sourceImg.GetPixel(i, j)
R = pSourceColor.R
If R >= threshold Then R = 255 Else R = 0
pDestColor = Color.FromArgb(R, R, R)
destImg.SetPixel(i, j, pDestColor)
Next
Next
picDest.Image = destImg
End Sub
运行如下：
由于本人数学不是很好，更多的算法以后有空研究后再发出来，大家也可以网上搜索一下相应的算法。
由于.net平台下C#和vb.NET很相似，本文也可以为C#爱好者提供参考。
学习更多vb.net知识，请参看 vb.net教程 目录
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版权声明：本文为CSDN博主「VB.Net」的原创文章，遵循CC 4.0 BY-SA版权协议，转载请附上原文出处链接及本声明。
