uwp
Windowsのユニバーサルアプリで画像サイズを変換して画像ファイルをトリミングする

ビットマップツールを使用して画像を切り抜き、サイズを変更する

 public class BitmapTools
    {
        /// <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;
        }

        /// <summary>
        /// Gets the pixel data.
        /// </summary>
        /// <remarks>
        /// If you want to get the pixel data of a scaled image, set the scaledWidth and scaledHeight
        /// of the scaled image.
        /// </remarks>
        /// <param name="decoder">The bitmap decoder.</param>
        /// <param name="startPointX">The X coordinate of the start point.</param>
        /// <param name="startPointY">The Y coordinate of the start point.</param>
        /// <param name="width">The width of the source rect.</param>
        /// <param name="height">The height of the source rect.</param>
        /// <param name="scaledWidth">The desired width.</param>
        /// <param name="scaledHeight">The desired height.</param>
        /// <returns>The image data.</returns>
        private static async Task<byte[]> GetPixelData(BitmapDecoder decoder, uint startPointX, uint startPointY,
            uint width, uint height, uint scaledWidth, uint scaledHeight)
        {
            var transform = new BitmapTransform();
            var bounds = new BitmapBounds();
            bounds.X = startPointX;
            bounds.Y = startPointY;
            bounds.Height = height;
            bounds.Width = width;
            transform.Bounds = bounds;

            transform.ScaledWidth = scaledWidth;
            transform.ScaledHeight = scaledHeight;

            // Get the cropped pixels within the bounds of transform.
            var pix = await decoder.GetPixelDataAsync(
                BitmapPixelFormat.Bgra8,
                BitmapAlphaMode.Straight,
                transform,
                ExifOrientationMode.IgnoreExifOrientation,
                ColorManagementMode.ColorManageToSRgb);
            var pixels = pix.DetachPixelData();
            return pixels;
        }

        /// <summary>
        /// Resizes the specified stream.
        /// </summary>
        /// <param name="sourceStream">The source stream to resize.</param>
        /// <param name="newWidth">The width of the resized image.</param>
        /// <param name="newHeight">The height of the resized image.</param>
        /// <returns>The resized image stream.</returns>
        public static async Task<InMemoryRandomAccessStream> Resize(IRandomAccessStream sourceStream, uint requestedMinSide)
        {
            var decoder = await BitmapDecoder.CreateAsync(sourceStream);
            uint originalPixelWidth = decoder.OrientedPixelWidth;
            uint originalPixelHeight = decoder.OrientedPixelHeight;

            double widthRatio = (double)requestedMinSide / originalPixelWidth;
            double heightRatio = (double)requestedMinSide / originalPixelHeight;
            uint aspectHeight = (uint)requestedMinSide;
            uint aspectWidth = (uint)requestedMinSide;
            var scaledSize = (uint)requestedMinSide;
            if (originalPixelWidth < originalPixelHeight)
            {
                aspectWidth = (uint)(heightRatio * originalPixelWidth);
            }
            else
            {
                aspectHeight = (uint)(widthRatio * originalPixelHeight);
            }

            var destinationStream = new InMemoryRandomAccessStream();

     
            var transform = new BitmapTransform { ScaledWidth = aspectWidth, ScaledHeight = aspectHeight };

            var pixelData = await decoder.GetPixelDataAsync(
                BitmapPixelFormat.Bgra8,
                BitmapAlphaMode.Straight,
                transform,
                ExifOrientationMode.RespectExifOrientation,
                ColorManagementMode.DoNotColorManage);

            var encoder =
                await BitmapEncoder.CreateAsync(BitmapEncoder.JpegEncoderId, destinationStream);

            if(decoder.OrientedPixelHeight!=decoder.PixelHeight && decoder.OrientedPixelWidth!=decoder.PixelWidth)
            encoder.BitmapTransform.Rotation = BitmapRotation.Clockwise270Degrees;

            encoder.SetPixelData(BitmapPixelFormat.Bgra8, BitmapAlphaMode.Premultiplied, aspectWidth, aspectHeight, 96, 96,
                pixelData.DetachPixelData());
            await encoder.FlushAsync();


            return destinationStream;
        }

        /// <summary>
        /// Rotates the given stream.
        /// </summary>
        /// <param name="randomAccessStream">The random access stream.</param>
        /// <param name="rotation">The rotation.</param>
        /// <returns>The stream.</returns>
        public static async Task<InMemoryRandomAccessStream> Rotate(IRandomAccessStream randomAccessStream,
            BitmapRotation rotation)
        {
            var decoder = await BitmapDecoder.CreateAsync(randomAccessStream);

            var rotatedStream = new InMemoryRandomAccessStream();

            var encoder = await BitmapEncoder.CreateForTranscodingAsync(rotatedStream, decoder);

            encoder.BitmapTransform.Rotation = rotation;
            encoder.BitmapTransform.InterpolationMode = BitmapInterpolationMode.Fant;

            await encoder.FlushAsync();

            return rotatedStream;
        }


        /// <summary>
        /// Resizes and crops source file image so that resized image width/height are not larger than <param name="requestedMinSide"></param>
        /// </summary>
        /// <param name="sourceFile">Source StorageFile</param>
        /// <param name="requestedMinSide">Width/Height of the output image</param>
        /// <param name="resizedImageFile">Target StorageFile</param>
        /// <returns></returns>
        public static async Task<IStorageFile> CreateThumbnaiImage(StorageFile sourceFile, int requestedMinSide, StorageFile resizedImageFile)
        {
            var imageStream = await sourceFile.OpenReadAsync();
            var decoder = await BitmapDecoder.CreateAsync(imageStream);
            var originalPixelWidth = decoder.PixelWidth;
            var originalPixelHeight = decoder.PixelHeight;
            using (imageStream)
            {
                //do resize only if needed
                if (originalPixelHeight > requestedMinSide && originalPixelWidth > requestedMinSide)
                {
                    using (var resizedStream = await resizedImageFile.OpenAsync(FileAccessMode.ReadWrite))
                    {
                        //create encoder based on decoder of the source file
                        var encoder = await BitmapEncoder.CreateForTranscodingAsync(resizedStream, decoder);
                        double widthRatio = (double)requestedMinSide / originalPixelWidth;
                        double heightRatio = (double)requestedMinSide / originalPixelHeight;
                        uint aspectHeight = (uint)requestedMinSide;
                        uint aspectWidth = (uint)requestedMinSide;
                        uint cropX = 0, cropY = 0;
                        var scaledSize = (uint)requestedMinSide;
                        if (originalPixelWidth > originalPixelHeight)
                        {
                            aspectWidth = (uint)(heightRatio * originalPixelWidth);
                            cropX = (aspectWidth - aspectHeight) / 2;
                        }
                        else
                        {
                            aspectHeight = (uint)(widthRatio * originalPixelHeight);
                            cropY = (aspectHeight - aspectWidth) / 2;
                        }
                        //you can adjust interpolation and other options here, so far linear is fine for thumbnails
                        encoder.BitmapTransform.InterpolationMode = BitmapInterpolationMode.Linear;
                        encoder.BitmapTransform.ScaledHeight = aspectHeight;
                        encoder.BitmapTransform.ScaledWidth = aspectWidth;
                        encoder.BitmapTransform.Bounds = new BitmapBounds()
                        {
                            Width = scaledSize,
                            Height = scaledSize,
                            X = cropX,
                            Y = cropY,
                        };
                        await encoder.FlushAsync();
                    }
                }
                else
                {
                    //otherwise just use source file as thumbnail
                    await sourceFile.CopyAndReplaceAsync(resizedImageFile);
                }
            }
            return resizedImageFile;
        }

    }