cropping image universal app c#

Question

i want to crop an image with x and y in universal app , i have searched alot and find nothing useful my idea is i have an image and i want to crop rectangle from it based on start x , y - end x and y

i have tried this

BitmapImage img = new BitmapImage(new Uri(file.Path));
WriteableBitmap topLeft = img.Crop(0, 0, halfWidth, halfHeight);

it say BitmapImage does not contain definition for crop

another thing : how can i convert BitmapImage to WriteableBitmap in universal app ?

Answer 1

  /// <summary>
        /// Gets the cropped bitmap asynchronously.
        /// </summary>
        /// <param name="originalImage">The original image.</param>
        /// <param name="startPoint">The start point.</param>
        /// <param name="cropSize">Size of the corp.</param>
        /// <param name="scale">The scale.</param>
        /// <returns>The cropped image.</returns>
        public static async Task<WriteableBitmap> GetCroppedBitmapAsync(IRandomAccessStream originalImage,
            Point startPoint, Size cropSize, double scale)
        {
            if (double.IsNaN(scale) || double.IsInfinity(scale))
            {
                scale = 1;
            }

            // Convert start point and size to integer.
            var startPointX = (uint)Math.Floor(startPoint.X * scale);
            var startPointY = (uint)Math.Floor(startPoint.Y * scale);
            var height = (uint)Math.Floor(cropSize.Height * scale);
            var width = (uint)Math.Floor(cropSize.Width * scale);

            // Create a decoder from the stream. With the decoder, we can get 
            // the properties of the image.
            var decoder = await BitmapDecoder.CreateAsync(originalImage);

            // The scaledSize of original image.
            var scaledWidth = (uint)Math.Floor(decoder.PixelWidth * scale);
            var scaledHeight = (uint)Math.Floor(decoder.PixelHeight * scale);

            // Refine the start point and the size. 
            if (startPointX + width > scaledWidth)
            {
                startPointX = scaledWidth - width;
            }

            if (startPointY + height > scaledHeight)
            {
                startPointY = scaledHeight - height;
            }

            // Get the cropped pixels.
            var pixels = await GetPixelData(decoder, startPointX, startPointY, width, height,
                scaledWidth, scaledHeight);

            // Stream the bytes into a WriteableBitmap
            var cropBmp = new WriteableBitmap((int)width, (int)height);
            var pixStream = cropBmp.PixelBuffer.AsStream();
            pixStream.Write(pixels, 0, (int)(width * height * 4));

            return cropBmp;
        }

Answer 2

Have you tried the BitmapEncoder/BitmapDecoder classes? Checkout the MSDN code sample.