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mpdph09 0 Newbie Poster

I am working with C# windows application. I am using split container to display image in picture box in the first panel(with scroll bar(50% of the the picture can be seen only by scrolling down)) and data entry fields in the second panel. One field will always be at the bottom of the page which cannot be seen without scrolling down. I am trying for something that will display zoom in part of that area every time picture is loaded(on basis of co-ordinates). I will appreciate if I can get some suggestions. I appreciate all the help.

I have tried with another picture box to magnify that part on image selection(combobox index changed). It works fine for the coordinates till size of panel 1 in splitcontainer, if I try with higher co-ordinates instead of showing bottom part of the image it displays top part of panel2 or the partition depending on the coordinates. I need help with displaying bottom part of the image.

pictureBox3.Refresh();
                   pictureBox3.BorderStyle = BorderStyle.FixedSingle;
                   Point startpoint = pictureBox2.PointToScreen(new Point(0, 420));
                   Graphics G = this.CreateGraphics();
                   Bitmap screenGrab = new Bitmap(pictureBox2.Image.Width, pictureBox2.Image.Height, System.Drawing.Imaging.PixelFormat.Format32bppArgb);
                   G = Graphics.FromImage(screenGrab);
                   G.CopyFromScreen(startpoint, new Point(0, 0), pictureBox2.Size, CopyPixelOperation.SourceCopy);
                   pictureBox3.Image = screenGrab;
                   pictureBox3.BringToFront();
                   pictureBox3.Visible = true;

pictureBox3.Refresh();
                   Graphics G1 = Graphics.FromImage(pictureBox3.Image);
                   //pictureBox3.CreateGraphics
                   GraphicsPath path = new GraphicsPath();
                   int L = 0;
                   int T = 0;
                   //int X = 1000;
                   //int Y = 1000;
                   L = pictureBox3.Width / 2 + (pictureBox2.Image.Width) / pictureBox2.Width;
                   T = pictureBox3.Height / 2 + pictureBox2.Height - (pictureBox2.Image.Height) / pictureBox2.Height;
                   path.AddRectangle(R1);
                   G1.DrawPath(cpen, path);
                   G1.SetClip(path, CombineMode.Replace);
                  // Clip Magnifying area to screen capture
                   pictureBox3.Refresh();
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Dani AI

Generated

— the main issue is mixing screen/Control coordinates with image pixel coordinates and relying on CopyFromScreen. CopyFromScreen grabs pixels from the window surface (and will be wrong when the image is larger than the control, scaled, or scrolled). A robust approach is to work directly on the image Bitmap: compute the source rectangle in image pixels (taking SizeMode and any scroll offset into account), crop that rectangle from the original image, then scale it to the magnifier picture box. That avoids screen capture, is deterministic, and handles any coordinates (including the bottom of the image).

Example helpers (map client → image, crop+scale, safe usage):

// get the rectangle on the PictureBox where the image is actually drawn (handles Zoom/Stretch/Normal)
RectangleF GetImageDisplayRect(PictureBox pb)
{
    var img = pb.Image;
    if (img == null) return RectangleF.Empty;
    if (pb.SizeMode == PictureBoxSizeMode.Normal || pb.SizeMode == PictureBoxSizeMode.AutoSize)
        return new RectangleF(0, 0, img.Width, img.Height);
    if (pb.SizeMode == PictureBoxSizeMode.StretchImage)
        return new RectangleF(0, 0, pb.ClientSize.Width, pb.ClientSize.Height);

    float imgRatio = (float)img.Width / img.Height;
    float boxRatio = (float)pb.ClientSize.Width / pb.ClientSize.Height;
    if (imgRatio > boxRatio)
    {
        float scale = (float)pb.ClientSize.Width / img.Width;
        float dispH = img.Height * scale;
        return new RectangleF(0, (pb.ClientSize.Height - dispH) / 2f, pb.ClientSize.Width, dispH);
    }
    else
    {
        float scale = (float)pb.ClientSize.Height / img.Height;
        float dispW = img.Width * scale;
        return new RectangleF((pb.ClientSize.Width - dispW) / 2f, 0, dispW, pb.ClientSize.Height);
    }
}

PointF ClientToImage(PictureBox pb, Point clientPt)
{
    var img = pb.Image;
    var r = GetImageDisplayRect(pb);
    float x = (clientPt.X - r.X) * img.Width / r.Width;
    float y = (clientPt.Y - r.Y) * img.Height / r.Height;
    x = Math.Max(0, Math.Min(img.Width - 1, x));
    y = Math.Max(0, Math.Min(img.Height - 1, y));
    return new PointF(x, y);
}

Bitmap CropAndScale(Bitmap src, Rectangle srcRect, Size destSize)
{
    srcRect.Intersect(new Rectangle(0, 0, src.Width, src.Height));
    var dest = new Bitmap(destSize.Width, destSize.Height);
    using (var g = Graphics.FromImage(dest))
    {
        g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
        g.DrawImage(src, new Rectangle(0, 0, destSize.Width, destSize.Height), srcRect, GraphicsUnit.Pixel);
    }
    return dest;
}

Usage notes and quick checklist:

  • If you want the bottom of the image, compute srcRect using image pixel coordinates (e.g., x=0, y=image.Height - height, width=..., height=...); clamp to image bounds.
  • If your PictureBox is inside a scrolling Panel and you're after the currently visible portion, use the Panel.AutoScrollPosition (visibleTopLeft = new Point(-panel.AutoScrollPosition.X, -panel.AutoScrollPosition.Y)) and map that client point into image coordinates with ClientToImage.
  • Dispose old Images before replacing pictureBox3.Image to avoid memory leaks, and perform heavy work off the UI thread if needed.
  • Avoid CreateGraphics/CopyFromScreen for this task — they’re fragile and depend on window z-order and screen scaling.

This method gives precise, repeatable magnification for any coordinates (including the bottom of a tall image).

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