How to save a non-blurry, high quality image of a control in WPF?

Question

I am using a DrawingContext to draw images. I then render the result to a RenderTargetBitmap. The image is crisp & sharp on the screen, but becomes blurred when saved. Even on 100% scaling the issue persists. Interesting part is that if the image width is less than 2000px it exports fine. But as the width increases, exported image keeps getting more and more blur.

Here is my code ( Sample project )

        private void Window_Loaded(object sender, RoutedEventArgs e)
        {
            BitmapImage bitmap = new BitmapImage();
            bitmap.BeginInit();
            bitmap.UriSource = new Uri(@"image-full-hd.png");
            bitmap.EndInit();
            img1.Source = bitmap;

            img1.Width = bitmap.Width;
            img1.Height= bitmap.Height;
        }

        private void btnExport_Click(object sender, RoutedEventArgs e)
        {
            var result = CaptureSnapshot(img1);
            Clipboard.SetImage(result);
        }

        public BitmapSource CaptureSnapshot(UIElement source)
        {
            var dpi = VisualTreeHelper.GetDpi(source);
            double dpiX = dpi.DpiScaleX, dpiY = dpi.DpiScaleY;

            double newImageWidth = source.RenderSize.Width * dpiX;
            double newImageHeight = source.RenderSize.Height * dpiY;

            RenderTargetBitmap renderTarget = new RenderTargetBitmap((int)newImageWidth, (int)newImageHeight, 96, 96, PixelFormats.Pbgra32);

            DrawingVisual visual = new DrawingVisual();

            using (DrawingContext context = visual.RenderOpen())
            {
                VisualBrush sourceBrush1 = new VisualBrush(source)
                {
                    Stretch = Stretch.None
                };

                context.DrawRectangle(sourceBrush1, null, new Rect(source.RenderSize));
            }

            System.Windows.Size s1size = new System.Windows.Size(newImageWidth, newImageHeight);
            source.Measure(s1size); 
            source.Arrange(new Rect(s1size));

            RenderOptions.SetEdgeMode(renderTarget, EdgeMode.Unspecified);
            RenderOptions.SetBitmapScalingMode(renderTarget, BitmapScalingMode.HighQuality);
            renderTarget.Render(visual);

            return renderTarget;
        }

Application Window

Clip from an Exported Image which was 3400px wide