今天研究了下.NET窗体应用程序生成透明底色的PNG图像。

我的.NET版本为.NET 4.5，VS版本为VS2012，操作系统版本为Win7旗舰版ServicePack1。

例程1：生成100%纯透明的PNG图片，这个例程生成的是一张没有任何杂质的透明PNG图片。

''' <summary>
''' 生成100%透明的PNG图片
''' </summary>
''' <param name="Width">横向长度</param>
''' <param name="Height">纵向长度</param>
''' <param name="OutputPath">图片输出地址</param>
''' <remarks></remarks>
Public Sub GenTransparentPNG(ByVal width As Integer,ByVal height As Integer,ByVal outputPath As String)Dim image As Bitmap = New Bitmap(width, height)Dim g As Graphics = Graphics.FromImage(image)g.Clear(Color.Transparent)image.Save(outputPath, System.Drawing.Imaging.ImageFormat.Png)
End Sub

例程2：生成100%透明的PNG图片+一个矩形。

''' <summary>
''' 生成100%透明的PNG图片+一个矩形
''' </summary>
''' <param name="Width">横向长度</param>
''' <param name="Height">纵向长度</param>
''' <param name="OutputPath">图片输出地址</param>
''' <remarks></remarks>
Public Sub GenTransparentPNGAndRect(ByVal width As Integer,ByVal height As Integer,ByVal outputPath As String)Dim image As Bitmap = New Bitmap(width, height)Dim g As Graphics = Graphics.FromImage(image)g.Clear(Color.Transparent)If width > 20 And height > 20 Theng.DrawRectangle(Pens.Black, New Rectangle(10, 10, width - 20, height - 20))End Ifimage.Save(outputPath, System.Drawing.Imaging.ImageFormat.Png)
End Sub

例程3：生成白色底色的PNG图片+一个矩形。

''' <summary>
''' 生成白色底色的PNG图片+一个矩形
''' </summary>
''' <param name="Width">横向长度</param>
''' <param name="Height">纵向长度</param>
''' <param name="OutputPath">图片输出地址</param>
''' <remarks></remarks>
Public Sub GenWhitePNGAndRect(ByVal width As Integer,ByVal height As Integer,ByVal outputPath As String)Dim image As Bitmap = New Bitmap(width, height)Dim g As Graphics = Graphics.FromImage(image)g.Clear(Color.White)If width > 20 And height > 20 Theng.DrawRectangle(Pens.Black, New Rectangle(10, 10, width - 20, height - 20))End Ifimage.Save(outputPath, System.Drawing.Imaging.ImageFormat.Png)
End Sub

例程4：将指定颜色替换为透明，如果有需要还可以将此例程进行改造，使得在一定范围内的颜色都被替换为透明。

''' <summary>
''' 将指定颜色替换为透明
''' </summary>
''' <param name="bitmapPath">被替换图像地址</param>
''' <param name="outputPath">新图像输出地址</param>
''' <param name="color">被替换颜色</param>
''' <remarks></remarks>
Public Sub ChangeBackgroundToTransparent(ByVal bitmapPath As String,ByVal outputPath As String,ByVal color As Color)Dim image As Bitmap = New Bitmap(bitmapPath)For i As Integer = 0 To image.Width - 1For j As Integer = 0 To image.Height - 1Dim colorTmp = image.GetPixel(i, j)If colorTmp.R = color.R And colorTmp.G = color.G And colorTmp.B = color.B Thenimage.SetPixel(i, j, Drawing.Color.Transparent)End IfNextNextimage.Save(outputPath, System.Drawing.Imaging.ImageFormat.Png)
End Sub

Main函数调用

Sub Main()'生成200*200的纯透明PNG图片GenTransparentPNG(200, 200, "C:\Users\Tsybius\Desktop\transparent.png")'生成200*200的透明PNG图片外加一个矩形GenTransparentPNGAndRect(200, 200, "C:\Users\Tsybius\Desktop\transparentRect.png")'生成200*200的白色背景PNG图像外加一个矩形GenWhitePNGAndRect(200, 200, "C:\Users\Tsybius\Desktop\whiteRect.png")'将200*200的白色背景PNG图像中白色抠去替换为透明GenWhitePNGAndRect(200, 200, "C:\Users\Tsybius\Desktop\whiteRect2.png")ChangeBackgroundToTransparent("C:\Users\Tsybius\Desktop\whiteRect2.png", "C:\Users\Tsybius\Desktop\transparentRect2.png", Color.White)'生成完毕Console.WriteLine("生成完毕")Console.ReadLine()
End Sub

运行结果如下：

附上另外两个实用的小技巧：

1、获取图像指定点的RGB值，用QQ截图工具，按下Ctrl+Alt+A进入截图模式后，鼠标右下角会自动显示出当前鼠标指针指向位置的颜色信息。

在截图模式下，按下Ctrl键，可以看到十六进制显示的RGB信息

2、判断图像的背景色是否为透明的，可以打开一个PowerPoint演示文稿，设置一个背景，然后将要判断的图像放入即可。

我使用的Office版本为：Microsoft Office Professional Plus 2010，PPT版本为：14.0.4760.1000（32位）。

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