图像中感兴趣区域(ROI)绘制的优化

Question

我通过将矩形区域外的区域变暗来绘制矩形区域，如此图像http://www.codeproject.com/script/Membership/Uploads/4613314/roi.jpg所示

但是image.MakeTransparent花费了太多的时间。提高绘图速度的最好方法是什么？

void DrawRoi(Bitmap Image, RectangleF rect)
{
        Rectangle roi = new Rectangle();

        roi.X = (int)((float)Image.Width * rect.X);
        roi.Y = (int)((float)Image.Height * rect.Y);
        roi.Width = (int)((float)Image.Width * rect.Width);
        roi.Height = (int)((float)Image.Height * rect.Height);

        Stopwatch timer = new Stopwatch();
        timer.Start();
        // graphics manipulation takes about 240ms on 1080p image
        using (Bitmap roiMaskImage = CreateRoiMaskImage(ImageWithRoi.Width, ImageWithRoi.Height, roi))
        {
                using (Graphics g = Graphics.FromImage(ImageWithRoi))
                {                                
                        g.DrawImage(Image, 0, 0);
                        g.DrawImage(roiMaskImage, 0, 0);
                        Pen borderPen = CreateRoiBorderPen(ImageWithRoi);
                        g.DrawRectangle(borderPen, roi);
                }
        }
        Debug.WriteLine("roi graphics: {0}ms", timer.ElapsedMilliseconds);
        this.imagePictureBox.Image = ImageWithRoi;
}

Bitmap CreateRoiMaskImage(int width, int height, Rectangle roi)
{
        Bitmap image = new Bitmap(width, height, PixelFormat.Format32bppArgb);
        using (Graphics g = Graphics.FromImage(image))
        {
                SolidBrush dimBrush = new SolidBrush(Color.FromArgb(64, 0, 0, 0));
                g.FillRectangle(dimBrush, 0, 0, width, height);
                SolidBrush roiBrush = new SolidBrush(Color.Red);
                g.FillRectangle(roiBrush, roi);
                image.MakeTransparent(Color.Red);
                return image;
        }                
}

Pen CreateRoiBorderPen(Bitmap image)
{
        float width = ((float)(image.Width + image.Height) * 2.5f) / (float)(640 + 480);
        if (width < 1.0f)
                width = 1.0f;
        Pen pen = new Pen(Color.FromArgb(255, 0, 255, 0), width);
        return pen;
}

Answer 1

根本不要操控图像。只需在您的图像顶部绘制“调光”即可。您可以实现相同的效果，例如，通过

1)在整个图像上绘制一个大的半透明区域，并将剪辑区域设置为您的ROI

// Assume for simplicity the image is size w*h, and the graphics is the same size. 
// The ROI is a rectangle named roiRect.
g.DrawImageUnscaled(image, 0, 0 , w, h);
g.SetClip(roiRect);
g.FillRectangle(new SolidBrush(Color.FromArgb(128, Color.Black)), 0, 0, w, h);
g.ResetClip();    

2)绘制图像，然后绘制调光矩形，然后在其上绘制图像的roi部分。

3)绘制4个独立的矩形顶部/右侧/左侧/底部，以省略您的ROI。

Answer 2

我完全看不出调用.MakeTransparent有什么意义。当您创建蒙版图像时

Bitmap image = new Bitmap(width, height, PixelFormat.Format32bppArgb);

它已经是透明的了。最好将dimBrush绘制为四个独立的矩形(ROI上方/下方/左侧/右侧)，避免在已经透明的区域中绘制！

Answer 3

看一下WriteableBitmap类。在WritePixels方法中，你可以用一个Int32Rect定义一个感兴趣区域。