CODEWITHSUNDEEP
c#performanceoptimizationgraphics
Chesnokov Yuriy
Chesnokov Yuriy

Reputation: 1838

Optimization of region of interest (ROI) drawing in the image

I draw rectangular ROI region by darkening the area outside of it as in this image http://www.codeproject.com/script/Membership/Uploads/4613314/roi.jpg

But image.MakeTransparent takes too much time. What is the best way to increase drawing speed?

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;
}

Upvotes: 0

Views: 3520

Answers (3)

Andreas
Andreas

Reputation: 4013

Take a look at the WriteableBitmap class. In the WritePixels Method u can define a ROI with a Int32Rect.

Upvotes: 0

Anders Forsgren
Anders Forsgren

Reputation: 11111

Don't manipulate the image at all. Just draw the "dimming" on top of your image. You can achieve the same effect for example by

1) Drawing a large semi-transparent region over the entire image, with the clip region set to your 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) Drawing the image, then the dimming rectangle, then the roi part of the image on top of that.

3) Drawing 4 separate rectangles top/right/left/bottom to leave out your ROI.

Upvotes: 2

Dan Bystr&#246;m
Dan Bystr&#246;m

Reputation: 9244

I can't see any point in calling .MakeTransparent at all. When you create your mask image

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

it is already transparent. It would be better to draw the dimBrush as four separate rectangles (areas above/below/left of/right of ROI) instead and avoid drawing in the area that already is transparent!

Upvotes: 1

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