vb.net 教程 5-13 图像处理之像素处理 6

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vb.net 教程 5-13 图像处理之像素处理 6

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)

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

Dim threshold As Integer

Dim allSum, allCount As Integer

For k As Integer = 0 To 255

allCount += HistGram(k)

allSum += k * HistGram(k)

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)

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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原文链接：https://blog.csdn.net/uruseibest/article/details/70215449

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