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WPF .png overlay using DrawingVisual

I'm using this example - I found around here - to overlay two .png images and then save the result as a third .png image.
The input images are:
The output image should (in my dreams) be:
And instead I get this:
Here is the code:
public static void Test()
{
// Loads the images to tile (no need to specify PngBitmapDecoder, the correct decoder is automatically selected)
BitmapFrame frame1 = BitmapDecoder.Create(new Uri(#"D:\_tmp_\MaxMara\Test\Monoscope.png"), BitmapCreateOptions.None, BitmapCacheOption.OnLoad).Frames.First();
BitmapFrame frame2 = BitmapDecoder.Create(new Uri(#"D:\_tmp_\MaxMara\Test\OverlayFrame.png"), BitmapCreateOptions.None, BitmapCacheOption.OnLoad).Frames.First();
// Gets the size of the images (I assume each image has the same size)
int imageWidth = 1920;
int imageHeight = 1080;
// Draws the images into a DrawingVisual component
DrawingVisual drawingVisual = new DrawingVisual();
using (DrawingContext drawingContext = drawingVisual.RenderOpen())
{
drawingContext.DrawImage(frame1, new Rect(0, 0, imageWidth, imageHeight));
drawingContext.DrawImage(frame2, new Rect(0, 0, imageWidth, imageHeight));
}
// Converts the Visual (DrawingVisual) into a BitmapSource
RenderTargetBitmap bmp = new RenderTargetBitmap(imageWidth, imageHeight, 300, 300, PixelFormats.Pbgra32);
bmp.Render(drawingVisual);
// Creates a PngBitmapEncoder and adds the BitmapSource to the frames of the encoder
PngBitmapEncoder encoder = new PngBitmapEncoder();
encoder.Frames.Add(BitmapFrame.Create(bmp));
// Saves the image into a file using the encoder
using (Stream stream = File.Create(#"D:\_tmp_\MaxMara\Test\Result.png"))
encoder.Save(stream);
}
Note: if i use 100 dpi as in:
RenderTargetBitmap bmp = new RenderTargetBitmap(imageWidth, imageHeight, 100, 100, PixelFormats.Pbgra32);
I get the correct result (meaning: the result I want).
I don't understand why. All images are 300 DPI
Can anyone shed some light on the topic please?
Thank you for your time
Orf

Do not use the PixelWidth and PixelHeight (i.e. your imageWidth and imageHeight values) of the bitmaps for drawing them into a DrawingContext.
Use their Width and Height values instead, because these give the bitmap size in device-independent units (1/96th inch per unit) as required for drawing.
using (var drawingContext = drawingVisual.RenderOpen())
{
drawingContext.DrawImage(frame1, new Rect(0, 0, frame1.Width, frame1.Height));
drawingContext.DrawImage(frame2, new Rect(0, 0, frame2.Width, frame2.Height));
}

How do I correctly transform an image in WPF?

I want to write program that functions something like PhotoShop.
1.upload image
2. Then I want to do skew transform, But when I do transform I have a problem, my picture goes beyond the edge of the workspace.
How do I transform without this problem(I think I should create a new Image every time I do a transform).
Then I crop, but crop makes the picture without transform. I think if I create a new image every time I do a transform, the problem will be fixed.
How do I do this correctly?
How do I correctly create this image in WPF? How to do transform and save an image? I am using(System.Drawing.Bitmap, System.Windows.Media.Imaging) Maybe, can someone show me experiences, code or useful material?

For the skew tranformation you may use MatrixTranform. Basic idea is described here
Below is the code that transforms an image located at "D:\input.png", attaches transformation result to the source of Image that defined in the .xaml file:
<Image Name="imgProcess" />
and writes result to the file "D:\skew.png"
double skewX = .0;
double skewY = Math.Tan(Math.PI / 18);
MatrixTransform transformation = new MatrixTransform(1, skewY, skewX, 1, 0, 0)
BitmapImage image = new BitmapImage(new Uri(#"D:\input.png"));
var boundingRect = new Rect(0, 0, image.Width + image.Height * skewX, image.Height + image.Width * skewY);
DrawingGroup dGroup = new DrawingGroup();
using (DrawingContext dc = dGroup.Open())
{
dc.PushTransform(transformation);
dc.DrawImage(image, boundingRect);
}
DrawingImage imageSource = new DrawingImage(dGroup);
imgProcess.Source = imageSource;
SaveDrawingToFile(ToBitmapSource(imageSource), #"D:\skew.png", (int)boundingRect.Width, (int)boundingRect.Height);
private BitmapSource ToBitmapSource(DrawingImage source)
{
DrawingVisual drawingVisual = new DrawingVisual();
DrawingContext drawingContext = drawingVisual.RenderOpen();
drawingContext.DrawImage(source, new Rect(new Point(0, 0), new Size(source.Width, source.Height)));
drawingContext.Close();
RenderTargetBitmap bmp = new RenderTargetBitmap((int)source.Width, (int)source.Height, 96, 96, PixelFormats.Pbgra32);
bmp.Render(drawingVisual);
return bmp;
}
private void SaveDrawingToFile(BitmapSource image, string fileName, int width, int height)
{
var encoder = new PngBitmapEncoder();
encoder.Frames.Add(BitmapFrame.Create(image));
using (var stream = new FileStream(fileName, FileMode.Create))
{
encoder.Save(stream);
}
}
Results

C# RenderTargetBitmap with grey borders

public RenderTargetBitmap GetSketchContentForExport()
{
Rect rectBounds = VisualTreeHelper.GetDescendantBounds(drawingCanvas);
RenderTargetBitmap renderTarget = new RenderTargetBitmap((int)rectBounds.Width, (int)rectBounds.Height, 96, 96, PixelFormats.Pbgra32);
DrawingVisual drawingVisual = new DrawingVisual();
using (DrawingContext drawingContext = drawingVisual.RenderOpen())
{
VisualBrush visualBrush = new VisualBrush(drawingCanvas);
drawingContext.DrawRectangle(visualBrush, null, new Rect(new Point(), rectBounds.Size));
}
renderTarget.Render(drawingVisual);
return renderTarget;
}
When rendering the canvas content into a bitmap, all the content is displayed but has also grey borders (exactly the parts that are not in the current view).
Editing the resulting image in an external tool (XnView) and using the option "True Colour" fixes that problem. Does anyone see how I can fix this problem in my code? I appreciate any help!

Resize bitmap image

I want to have smaller size at image saved.
How can I resize it?
I use this code for redering the image:
Size size = new Size(surface.Width, surface.Height);
surface.Measure(size);
surface.Arrange(new Rect(size));
// Create a render bitmap and push the surface to it
RenderTargetBitmap renderBitmap =
new RenderTargetBitmap(
(int)size.Width,
(int)size.Height, 96d, 96d,
PixelFormats.Default);
renderBitmap.Render(surface);
BmpBitmapEncoder encoder = new BmpBitmapEncoder();
// push the rendered bitmap to it
encoder.Frames.Add(BitmapFrame.Create(renderBitmap));
// save the data to the stream
encoder.Save(outStream);

public static Bitmap ResizeImage(Bitmap imgToResize, Size size)
{
try
{
Bitmap b = new Bitmap(size.Width, size.Height);
using (Graphics g = Graphics.FromImage((Image)b))
{
g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
g.DrawImage(imgToResize, 0, 0, size.Width, size.Height);
}
return b;
}
catch
{
Console.WriteLine("Bitmap could not be resized");
return imgToResize;
}
}

The shortest way to resize a Bitmap is to pass it to a Bitmap-constructor together with the desired size (or width and height):
bitmap = new Bitmap(bitmap, width, height);

Does your "surface" visual have scaling capability? You can wrap it in a Viewbox if not, then render the Viewbox at the size you want.
When you call Measure and Arrange on the surface, you should provide the size you want the bitmap to be.
To use the Viewbox, change your code to something like the following:
Viewbox viewbox = new Viewbox();
Size desiredSize = new Size(surface.Width / 2, surface.Height / 2);
viewbox.Child = surface;
viewbox.Measure(desiredSize);
viewbox.Arrange(new Rect(desiredSize));
RenderTargetBitmap renderBitmap =
new RenderTargetBitmap(
(int)desiredSize.Width,
(int)desiredSize.Height, 96d, 96d,
PixelFormats.Default);
renderBitmap.Render(viewbox);

RenderTargetBitmap is blurry

Hi i'm creating an image in memory from a Canvas using a PngBitmapEncoder.
public void CaptureGraphic()
{
Canvas canvas = new Canvas();
canvas.SnapsToDevicePixels = true;
canvas.Height = IMAGEHEIGHT;
canvas.Width = IMAGEWIDTH;
Draw(canvas);
canvas.Arrange(new Rect(0, 0, IMAGEWIDTH, IMAGEHEIGHT));
member.MemberImage = GetPngFromUIElement(canvas);
}
public static System.Drawing.Image GetPngFromUIElement(Canvas source)
{
int width = (int)source.ActualWidth;
int height = (int)source.ActualHeight;
if (width == 0)
width = (int)source.Width;
if (height == 0)
height = (int)source.Height;
RenderTargetBitmap bitmap = new RenderTargetBitmap(width, height, 96d, 96d, PixelFormats.Pbgra32);
bitmap.Render(source);
PngBitmapEncoder enc = new PngBitmapEncoder();
enc.Interlace = PngInterlaceOption.Off;
enc.Frames.Add(BitmapFrame.Create(bitmap));
System.IO.MemoryStream ms = new System.IO.MemoryStream();
enc.Save(ms);
System.Drawing.Image image = System.Drawing.Image.FromStream(ms);
ms.Flush();
ms.Dispose();
return image;
}
Then i'm sending the image to the printer using the GDI+ DrawImage() method. However the printed result is blurry.
I've tried to match the original canvas size to the printed size to avoid any scaling, equally i've tried to make the original considerably bigger so the scaled image retains the quality however the final printed image is always blurred.
Can anyone offer any suggestions/alternatives. I have a considerable GDI+ print routine already setup and moving to wpf documents is not an option just yet.
Thanks

You're capturing the bitmap at 96 DPI. Instead of using 96 in the constructor of the RenderTargetBitmap, try to match the DPI of your printer output. Alternatively, you could do the math and calculate the difference in width/height and rescale the image on the report accordingly (the result is the image on the report will appear smaller).

I had the same blurry result and have come up with the following piece of code, which applies the same idea with the offset, but using the Offset property on the DrawingVisual (since I was using DrawDrawing, which doesn't have an overload with the offset argument):
public static Image ToBitmap(Image source)
{
var dv = new DrawingVisual();
// Blur workaround
dv.Offset = new Vector(0.5, 0.5);
using (var dc = dv.RenderOpen())
dc.DrawDrawing(((DrawingImage)source.Source).Drawing);
var bmp = new RenderTargetBitmap((int)source.Width, (int)source.Height, 96, 96, PixelFormats.Pbgra32);
bmp.Render(dv);
var bitMapImage = new Image();
bitMapImage.Source = bmp;
bitMapImage.Width = source.Width;
bitMapImage.Height = source.Height;
return bitMapImage;
}

Think i've found the answer.
http://www.charlespetzold.com/blog/2007/12/High-Resolution-Printing-of-WPF-3D-Visuals.html
I just needed to scale up the image size along with the dpi and voila, massively increased file size!

I had the same problem. To avoid blurry text and lines, I had to draw everything with an offset of 0.5 in X and Y direction. E.g, an horizontal line could be
drawingContext.DrawLine(pen, new Point(10.5,10.5), new Point(100.5,10.5));
In my case, I was rendering to a RenderTargetBitmap in a different thread to improve the UI performance. The rendered bitmap is then frozen and drawn onto the UI using
drawingContext.DrawImage(bitmap, new Rect(0.5, 0, bitmap.Width, bitmap.Height));
Here, I needed an additional offset of 0.5, but (strangely) only in X direction, so that the rendered image did not look Blurry any more.