C#:Bitmap类使用方法—第4讲

大家好，今天接着上一篇文章继续讲。

下面是今天的方法：

（1）Bitmap.MakeTransparent 方法：使此 Bitmap的默认透明颜色透明。

private void MakeTransparent_Example1(PaintEventArgs e)
{

    // Create a Bitmap object from an image file.
    Bitmap myBitmap = new Bitmap("Grapes.gif");

    // Draw myBitmap to the screen.
    e.Graphics.DrawImage(myBitmap, 0, 0, myBitmap.Width,
        myBitmap.Height);

    // Make the default transparent color transparent for myBitmap.
    myBitmap.MakeTransparent();

    // Draw the transparent bitmap to the screen.
    e.Graphics.DrawImage(myBitmap, myBitmap.Width, 0,
        myBitmap.Width, myBitmap.Height);
}

private void MakeTransparent_Example2(PaintEventArgs e)
{

    // Create a Bitmap object from an image file.
    Bitmap myBitmap = new Bitmap("Grapes.gif");

    // Draw myBitmap to the screen.
    e.Graphics.DrawImage(
        myBitmap, 0, 0, myBitmap.Width, myBitmap.Height);

    // Get the color of a background pixel.
    Color backColor = myBitmap.GetPixel(1, 1);

    // Make backColor transparent for myBitmap.
    myBitmap.MakeTransparent(backColor);

    // Draw the transparent bitmap to the screen.
    e.Graphics.DrawImage(
        myBitmap, myBitmap.Width, 0, myBitmap.Width, myBitmap.Height);
}

（2）Bitmap.SetPixel(Int32, Int32, Color) 方法：设置此 Bitmap中指定像素的颜色。

private void SetPixel_Example(PaintEventArgs e)
{

    // Create a Bitmap object from a file.
    Bitmap myBitmap = new Bitmap("Grapes.jpg");

    // Draw myBitmap to the screen.
    e.Graphics.DrawImage(myBitmap, 0, 0, myBitmap.Width,
        myBitmap.Height);

    // Set each pixel in myBitmap to black.
    for (int Xcount = 0; Xcount < myBitmap.Width; Xcount++)
    {
        for (int Ycount = 0; Ycount < myBitmap.Height; Ycount++)
        {
            myBitmap.SetPixel(Xcount, Ycount, Color.Black);
        }
    }

    // Draw myBitmap to the screen again.
    e.Graphics.DrawImage(myBitmap, myBitmap.Width, 0,
        myBitmap.Width, myBitmap.Height);
}

（3）Bitmap.SetResolution(Single, Single) 方法：设置此 Bitmap 的分辨率。

（4）Bitmap.UnlockBits(BitmapData) 方法：从系统内存解锁此 Bitmap。

private void LockUnlockBitsExample(PaintEventArgs e)
    {

        // Create a new bitmap.
        Bitmap bmp = new Bitmap("c:\\fakePhoto.jpg");

        // Lock the bitmap's bits.  
        Rectangle rect = new Rectangle(0, 0, bmp.Width, bmp.Height);
        System.Drawing.Imaging.BitmapData bmpData =
            bmp.LockBits(rect, System.Drawing.Imaging.ImageLockMode.ReadWrite,
            bmp.PixelFormat);

        // Get the address of the first line.
        IntPtr ptr = bmpData.Scan0;

        // Declare an array to hold the bytes of the bitmap.
        int bytes  = Math.Abs(bmpData.Stride) * bmp.Height;
        byte[] rgbValues = new byte[bytes];

        // Copy the RGB values into the array.
        System.Runtime.InteropServices.Marshal.Copy(ptr, rgbValues, 0, bytes);

        // Set every third value to 255. A 24bpp bitmap will look red.  
        for (int counter = 2; counter < rgbValues.Length; counter += 3)
            rgbValues[counter] = 255;

        // Copy the RGB values back to the bitmap
        System.Runtime.InteropServices.Marshal.Copy(rgbValues, 0, ptr, bytes);

        // Unlock the bits.
        bmp.UnlockBits(bmpData);

        // Draw the modified image.
        e.Graphics.DrawImage(bmp, 0, 150);
    }

今天要介绍的就是这么多，我们下篇文章再见。