c＃watermark具有索引像素格式的图像

Question

我正在尝试升级此工具：http://www.codeproject.com/Articles/31538/Watermarker-Embedding-image-and-text-watermarks但我对带有索引像素格式的图片有问题。

我已经尝试了我在这里找到的所有解决方案以及其他解决方案，但我不能让它绘制水印。

以下是需要修复的代码部分：

    public void DrawImage(Bitmap watermark)
    {

        if (watermark == null)
            throw new ArgumentOutOfRangeException("Watermark");

        if (m_opacity < 0 || m_opacity > 1)
            throw new ArgumentOutOfRangeException("Opacity");

        if (m_scaleRatio <= 0)
            throw new ArgumentOutOfRangeException("ScaleRatio");

        // Creates a new watermark with margins (if margins are not specified returns the original watermark)
        m_watermark = GetWatermarkImage(watermark);

        // Rotates and/or flips the watermark
        m_watermark.RotateFlip(m_rotateFlip);

        // Calculate watermark position
        Point waterPos = GetWatermarkPosition();

        // Watermark destination rectangle
        Rectangle destRect = new Rectangle(waterPos.X, waterPos.Y, m_watermark.Width, m_watermark.Height);

        ColorMatrix colorMatrix = new ColorMatrix(
            new float[][] { 
                new float[] { 1, 0f, 0f, 0f, 0f},
                new float[] { 0f, 1, 0f, 0f, 0f},
                new float[] { 0f, 0f, 1, 0f, 0f},
                new float[] { 0f, 0f, 0f, m_opacity, 0f},
                new float[] { 0f, 0f, 0f, 0f, 1}                    
            });

        ImageAttributes attributes = new ImageAttributes();

        // Set the opacity of the watermark
        attributes.SetColorMatrix(colorMatrix);

        // Set the transparent color 
        if (m_transparentColor != Color.Empty)
        {
            attributes.SetColorKey(m_transparentColor, m_transparentColor);
        }

        // Draw the watermark
        using (Graphics gr = Graphics.FromImage(m_image)) <- Тhis is the place where A Graphics object cannot be created from an image that has an indexed pixel format error occurs.
        {
            gr.DrawImage(m_watermark, destRect, 0, 0, m_watermark.Width, m_watermark.Height, GraphicsUnit.Pixel, attributes);
        }
    }

我尝试使用正确的像素格式创建临时位图，但不会绘制水印。

Bitmap orig = new Bitmap(m_image);
Bitmap clone = new Bitmap(orig.Width, orig.Height, System.Drawing.Imaging.PixelFormat.Format32bppPArgb);
using (Graphics gr = Graphics.FromImage(clone)) {
    gr.DrawImage(orig, new Rectangle(0, 0, clone.Width, clone.Height));
}

任何帮助将不胜感激！