使用 LockBits 确定像素颜色（慢）答案

【问题标题】：Using LockBits to determine pixel colors (slow)使用 LockBits 确定像素颜色（慢）
【发布时间】：2015-01-31 22:26:53
【问题描述】：

我正在尝试使用 Lockbits 来确定图像中每个像素的颜色。特别是黑色与白色与其他。我最初是用 GetPixel 写的，但它太慢了；但是，使用 Lockbits 也同样慢。它在几秒钟内飞过前 200 个像素，然后减速得非常厉害（大约 1 个像素/秒）。是否存在实施错误、疏忽或更好的解决方案？

    Dim bmp As Bitmap = New Bitmap("path") 
    Dim rect As New Rectangle(0, 0, bmp.Width, bmp.Height)
    Dim bmpData As System.Drawing.Imaging.BitmapData = bmp.LockBits _
            (rect, Drawing.Imaging.ImageLockMode.ReadWrite, _
            Imaging.PixelFormat.Format24bppRgb)
    Dim ptr As IntPtr = bmpData.Scan0
    Dim bytes As Integer = Math.Abs(bmpData.Stride) * bmp.Height
    Dim rgbValues(bytes - 1) As Byte
    System.Runtime.InteropServices.Marshal.Copy(ptr, rgbValues, 0, bytes)
    pbStatus.Maximum = bmp.Width * bmp.Height
    ' Retrieve RGB values
    Dim RedValue As Int32
    Dim GreenValue As Int32
    Dim BlueValue As Int32
    Dim l As Integer = 0        
    Dim progress As Integer = 0          
    For x = 0 To bmp.Width - 1 
        For y = 0 To bmp.Height - 1
            Application.DoEvents()
            l = ((bmp.Width * 3 * y) + (x * 3))
            RedValue = rgbValues(l)
            GreenValue = rgbValues(l + 1)
            BlueValue = rgbValues(l + 2)
            If RedValue & GreenValue & BlueValue = "000" Then
                txtTX.Text = txtTX.Text + "Black, "
            ElseIf RedValue & GreenValue & BlueValue = "255255255" Then
                txtTX.Text = txtTX.Text + "White, "
            Else
                txtTX.Text = txtTX.Text + "Neither, "
            End If
            progress = progress + 1
            lblProgress.text = progress
        Next
    Next
    bmp.UnlockBits(bmpData)

【问题讨论】：

删除代码的日志部分（If-Statement）后，速度明显加快。寻找更快的方法来记录数据。
1) 使用 StringBuilder 来表示文本，2) 只做 DoEvents/lblProgress.text = 偶尔一次，说每扫描线一次。

标签： vb.net performance image-processing

【解决方案1】：

您过于频繁地调用 Application.DoEvents，如果您需要更新 UI 线程上的控件，请执行以下操作：

Dim bmp As Bitmap = New Bitmap("path") 
Dim rect As New Rectangle(0, 0, bmp.Width, bmp.Height)
Dim bmpData As System.Drawing.Imaging.BitmapData = bmp.LockBits _
        (rect, Drawing.Imaging.ImageLockMode.ReadWrite, _
        Imaging.PixelFormat.Format24bppRgb)
Dim ptr As IntPtr = bmpData.Scan0
Dim bytes As Integer = Math.Abs(bmpData.Stride) * bmp.Height
Dim rgbValues(bytes - 1) As Byte
System.Runtime.InteropServices.Marshal.Copy(ptr, rgbValues, 0, bytes)
pbStatus.Maximum = bmp.Width * bmp.Height
' Retrieve RGB values
Dim RedValue As Int32
Dim GreenValue As Int32
Dim BlueValue As Int32
Dim l As Integer = 0        
Dim progress As Integer = 0          
DIM BreatheUI as integer = 0

For x = 0 To bmp.Width - 1 
    For y = 0 To bmp.Height - 1

        ' Update the UI every 500 cycles
        BreatheUI += 1 
        IF BreatheUI = 500 Then Application.DoEvents(): BreatheUI = 0

        l = ((bmp.Width * 3 * y) + (x * 3))
        RedValue = rgbValues(l)
        GreenValue = rgbValues(l + 1)
        BlueValue = rgbValues(l + 2)
        If RedValue & GreenValue & BlueValue = "000" Then
            txtTX.Text = txtTX.Text + "Black, "
        ElseIf RedValue & GreenValue & BlueValue = "255255255" Then
            txtTX.Text = txtTX.Text + "White, "
        Else
            txtTX.Text = txtTX.Text + "Neither, "
        End If
        progress = progress + 1
        lblProgress.text = progress
    Next
Next
bmp.UnlockBits(bmpData)

【讨论】：