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Draw transparent rectangles on image

I want to create an overlay on an image, similar to the one in the picture.
Creating the translucent cover is easy, I just create a rectangle the size of the image and give it a low alpha value.
How can I get the transparent "cut-outs" though? Drawing over the image again just increases its alpha value. I need to explicitly set it to zero.
var image = picOriginal.Image;
var graphics = Graphics.FromImage(image);
var color = Color.FromArgb(200, Color.Black);
var brush = new SolidBrush(color);
var transparentColor = Color.Transparent;
var transparentBrush = new SolidBrush(transparentColor);
var rectangle = new Rectangle(Point.Empty, image.Size);
graphics.FillRectangle(brush, rectangle);
graphics.FillEllipse(transparentBrush, 100, 100, 100, 150);
var bitmap = new Bitmap(image);
picGenerated.Image = bitmap;

Convert html string to image for xamarin Ios

I want to convert HTML string to image format for print receipt in Xamarin ios. Please any one convert below my code for xamarin ios. Thanks in advance.
private Bitmap CreateBitmapImage(string html)
{
Bitmap objBmpImage = new Bitmap(1, 1);
int intWidth = 0;
int intHeight = 0;
// Create the Font object for the image text drawing.
Font objFont = new Font("Arial", 20, System.Drawing.FontStyle.Bold, System.Drawing.GraphicsUnit.Pixel);
// Create a graphics object to measure the text's width and height.
Graphics objGraphics = Graphics.FromImage(objBmpImage);
// This is where the bitmap size is determined.
intWidth = (int)objGraphics.MeasureString(html, objFont).Width;
intHeight = (int)objGraphics.MeasureString(html, objFont).Height;
// Create the bmpImage again with the correct size for the text and font.
objBmpImage = new Bitmap(objBmpImage, new Size(intWidth, intHeight));
// Add the colors to the new bitmap.
objGraphics = Graphics.FromImage(objBmpImage);
// Set Background color
objGraphics.Clear(Color.White);
objGraphics.SmoothingMode = SmoothingMode.AntiAlias;
objGraphics.TextRenderingHint = TextRenderingHint.AntiAlias;
objGraphics.DrawString(html, objFont, new SolidBrush(Color.FromArgb(102, 102, 102)), 0, 0);
objGraphics.Flush();
return (objBmpImage);
}

Why is my Shapes.Line twice the size I want it to be on Canvas?

Using this method, I want to render a canvas to a bitmap.
When I add a Shape to the Canvas, it is rendered twice the specified size.
In the example below, I am drawing a line from (0;0) to (50;50) on a canvas of size 200 by 200.
public bool exportToBmp(string path, int dpi = 96)
{
if (path == null)
return false;
var canvas = new System.Windows.Controls.Canvas();
// This diagonal Line should span a quarter of the rendered Image
var myLine = new System.Windows.Shapes.Line();
myLine.Stroke = System.Windows.Media.Brushes.LightSteelBlue;
myLine.X1 = 0;
myLine.X2 = 50;
myLine.Y1 = 0;
myLine.Y2 = 50;
myLine.StrokeThickness = 2;
canvas.Children.Add(myLine);
canvas.Height = 200;
canvas.Width = 200;
Size size = new Size(canvas.Width, canvas.Height);
canvas.Measure(size);
canvas.Arrange(new Rect(size));
var width = (int)canvas.ActualWidth;
var height = (int)canvas.ActualHeight;
RenderTargetBitmap bmp = new RenderTargetBitmap(width, height, dpi, dpi, PixelFormats.Pbgra32);
bmp.Render(canvas);
PngBitmapEncoder image = new PngBitmapEncoder();
image.Frames.Add(BitmapFrame.Create(bmp));
using (Stream fs = File.Create(path))
{
image.Save(fs);
}
return false;
}
The rendered image I get is 200 by 200 px big, but the diagonal goes all the way to (100;100)
What am I doing wrong?

When I run your code, I see the following image (border added for clarity):
Are you passing a DPI other than 96?
What DPI settings are in use on your computer?

how to draw a part of a png image c#

I'm trying to draw a part of a .png image but the code i found is not working. this is my code
//define canvas
canvas = pb.CreateGraphics();
sPicture = new Bitmap(pb.Width, pb.Height);
sCanvas = Graphics.FromImage(sPicture);
// Create a Bitmap object from a file.
Image image = Image.FromFile(#"");
// Clone a portion of the Bitmap object.
Rectangle cloneRect = new Rectangle(0, 0, 11, 6);
System.Drawing.Imaging.PixelFormat format =
image.PixelFormat;
Image cloneBitmap = image.Clone(cloneRect, format); //Error: No overload for method 'Clone' takes2 arguments
// Draw the cloned portion of the Bitmap object.
canvas.DrawImage(cloneBitmap, 0, 0);
This is for a sprite sheet and thanks.

You don't need to use Clone(), you can do this directly with Graphics.DrawImage(). It looks like you are trying to do this in WinForms. If, so handle OnPaint for the control you want to draw on. In the example below I'm drawing directly on the form.
private void Form1_Paint(object sender, PaintEventArgs e)
{
Graphics graphics = e.Graphics;
int width = 60;
int height = 60;
// Create a Bitmap object from a file.
Image sourceImage = Image.FromFile(#"C:\Users\Mike\Downloads\logo.png");
// Draw a portion of the source image.
Rectangle sourceRect = new Rectangle(0, 0, width, height);
graphics.DrawImage(sourceImage, 0, 0, sourceRect, GraphicsUnit.Pixel);
}
If you want to do this without WinForms, there is the extra step of creating the target Graphics instance.
int width = 60;
int height = 60;
// Create a Bitmap object from a file.
Image sourceImage = Image.FromFile(#"C:\Users\Mike\Downloads\logo.png");
// Create a drawing target
Bitmap bitmap = new Bitmap(width, height, sourceImage.PixelFormat);
Graphics graphics = Graphics.FromImage(bitmap);
// Draw a portion of the source image.
Rectangle sourceRect = new Rectangle(0, 0, width, height);
graphics.DrawImage(sourceImage, 0, 0, sourceRect, GraphicsUnit.Pixel);
// Save
bitmap.Save(#"C:\Users\Mike\Downloads\out.png");

C# images cropping,splitting,saving

as stated in subject, i have an image:
private Image testing;
testing = new Bitmap(#"sampleimg.jpg");
I would like to split it into 3 x 3 matrix meaning 9 images in total and save it.Any tips or tricks to do this simple? I'm using visual studios 2008 and working on smart devices. Tried some ways but i can't get it. This is what i tried:
int x = 0;
int y = 0;
int width = 3;
int height = 3;
int count = testing.Width / width;
Bitmap bmp = new Bitmap(width, height);
Graphics g = Graphics.FromImage(bmp);
for (int i = 0; i < count; i++)
{
g.Clear(Color.Transparent);
g.DrawImage(testing, new Rectangle(0, 0, width, height), new Rectangle(x, y, width, height), GraphicsUnit.Pixel);
bmp.Save(Path.ChangeExtension(#"C\AndrewPictures\", String.Format(".{0}.bmp",i)));
x += width;
}

Depending on the .NET version, you could do one of the following to crop:
.NET 2.0
private static Image cropImage(Image img, Rectangle cropArea)
{
Bitmap bmpImage = new Bitmap(img);
Bitmap bmpCrop = bmpImage.Clone(cropArea,
bmpImage.PixelFormat);
return (Image)(bmpCrop);
}
Or .NET 3.5+
// Create an Image element.
Image croppedImage = new Image();
croppedImage.Width = 200;
croppedImage.Margin = new Thickness(5);
// Create a CroppedBitmap based off of a xaml defined resource.
CroppedBitmap cb = new CroppedBitmap(
(BitmapSource)this.Resources["masterImage"],
new Int32Rect(30, 20, 105, 50)); //select region rect
croppedImage.Source = cb; //set image source to cropped
As you can see, it's a bit more simple than what you're doing. The first example clones the current image and takes a subset of it; the second example uses CroppedBitmap, which supports taking a section of the image right from the constructor.
The splitting part is simple maths, just splitting the image into 9 sets of coordinates and passing them into the constructor.