C# 控件上绘制可调透明度的图片(PictureBox为例)

    添加PictureBox控件的事件 - Paint，在控件重新绘制时发生的事件。

private void pictureBox1_Paint(object sender, PaintEventArgs e)
       {
           Bitmap bitmap = new Bitmap(@"C:\Documents and Settings\Administrator\桌面\images\1234.jpg");

           ChangePictureAlpha(e,bitmap,0.5f);
       }

写一个方法，参数

                        PaintEventArgs e 绘制事件

                        Bitmap bitmap  覆盖的可变透明度的图片

                        float colorAlpha  透明度

 方法可以根据不同的需要改变。

private void ChangePictureAlpha(PaintEventArgs e, Bitmap bitmap,float colorAlpha)
        {
            // Create the Bitmap object and load it with the texture image.
            //Bitmap bitmap = new Bitmap("..\\..\\test.jpg");C:\Documents and Settings\Administrator\桌面\images
            // Initialize the color matrix.
            // Note the value 0.8 in row 4, column 4.
            float[][] matrixItems ={
            new float[] {1, 0, 0, 0, 0},
            new float[] {0, 1, 0,0 , 0},
            new float[] {0, 0, 1, 0, 0},
            new float[] {0, 0, 0, colorAlpha, 0},
            new float[] {0, 0, 0, 0, 1}};
            ColorMatrix colorMatrix = new ColorMatrix(matrixItems);

            // Create an ImageAttributes object and set its color matrix.  设置色调整矩阵
            ImageAttributes imageAtt = new ImageAttributes();
            imageAtt.SetColorMatrix(
                colorMatrix,
                ColorMatrixFlag.Default,
                ColorAdjustType.Bitmap);

            // Now draw the semitransparent bitmap image.
            int iWidth = bitmap.Width;
            int iHeight = bitmap.Height;
            e.Graphics.DrawImage(
                bitmap,
                new Rectangle(0, 0, iWidth, iHeight),  // destination rectangle  图片位置
                0.0f,                          // source rectangle x
                0.0f,                          // source rectangle y
                iWidth,                        // source rectangle width
                iHeight,                       // source rectangle height
                GraphicsUnit.Pixel,
                imageAtt);  
        }