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How can I manipulate images to add a semi-transparent 1x1 checked overlay like the second image in C#?

enter image description here enter image description here

Roman
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  • depends. for example, do you want to load the image, mod it, and resave it, or save a whole new image, or only do something for your UI. we really need more information. – Muad'Dib Oct 26 '11 at 03:30
  • I want to create a new image and upload it to Amazon S3. What is the difference? – Roman Oct 26 '11 at 03:46
  • This [answer](http://stackoverflow.com/questions/4113900/c-sharp-add-watermark-to-the-photo-by-special-way/4114473#4114473) might help - use a 2x2 overlay for the texture brush. – Jeff Ogata Oct 26 '11 at 04:05
  • if you only want some effect on the image, your answer depends on what your platform is (asp.net, silverlight, etc). it sounds like you might want to look into GDI+ – Muad'Dib Oct 26 '11 at 04:27

2 Answers2

2

Load your original image in to a system.Drawing.Image, then create a graphics object from it. Load your 2nd image of the checker pattern you want to draw, and use the graphics object you created to repeatedly draw the checker image over the original image.

Untested Example

    Image Original;
    Image Overlay;

    Original = new Bitmap(100, 100, System.Drawing.Imaging.PixelFormat.Format32bppArgb); //Load your real image here.
    Overlay = new Bitmap(2, 2 ,System.Drawing.Imaging.PixelFormat.Format32bppArgb);//Load your 2x2 (or whatever size you want) overlay image here.

    Graphics gr = Graphics.FromImage(Original);
    for (int y = 0; y < Original.Height + Overlay.Height; y = y + Overlay.Height)
    {
        for (int x = 0; x < Original.Width + OverlayWidth; x = x + Overlay.Width)
        {
            gr.DrawImage(Overlay, x, y);
        }  
    }
    gr.Dispose();

After the code executes, Original will now contain the Original image with the overlay applied to it.

Bradley Uffner
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  • the way it's written it may not cover a few pixels of the left and bottom edge. I'm going to add the Overlay size to the loop bounds to correct for that. I also got one of my variables switched around, which is fixed now also. – Bradley Uffner Oct 27 '11 at 01:12
2

I was able to modify an answer I posted a while ago and create the overlay in code. After the overlay image is created, I use a TextureBrush to fill the area of the original image. The settings in the code below created the following image; you can change the size and colors to suit your needs.

enter image description here enter image description here

// set the light and dark overlay colors
Color c1 = Color.FromArgb(80, Color.Silver);
Color c2 = Color.FromArgb(80, Color.DarkGray);

// set up the tile size - this will be 8x8 pixels, with each light/dark square being 4x4 pixels
int length = 8;
int halfLength = length / 2;

using (Bitmap overlay = new Bitmap(length, length, PixelFormat.Format32bppArgb))
{
    // draw the overlay - this will be a 2 x 2 grid of squares,
    // alternating between colors c1 and c2
    for (int x = 0; x < length; x++)
    {
        for (int y = 0; y < length; y++)
        {
            if ((x < halfLength && y < halfLength) || (x >= halfLength && y >= halfLength)) 
                overlay.SetPixel(x, y, c1);
            else 
                overlay.SetPixel(x, y, c2);
        }
    }

    // open the source image
    using (Image image = Image.FromFile(@"C:\Users\Public\Pictures\Sample Pictures\homers_brain.jpg"))
    using (Graphics graphics = Graphics.FromImage(image))
    {
        // create a brush from the overlay image, draw over the source image and save to a new image
        using (Brush overlayBrush = new TextureBrush(overlay))
        {
            graphics.FillRectangle(overlayBrush, new Rectangle(new Point(0, 0), image.Size));
            image.Save(@"C:\Users\Public\Pictures\Sample Pictures\homers_brain_overlay.jpg");
        }
    }
}
Jeff Ogata
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