[转][C#]ImageHelper

{
    internal static class ImageHelper
    {
        public static Bitmap CloneBitmap(Image source)
        {
            if (source == null)
                return null;

            Bitmap image = new Bitmap(source.Width, source.Height);
            image.SetResolution(source.HorizontalResolution, source.VerticalResolution);
            using (Graphics g = Graphics.FromImage(image))
            {
                g.DrawImageUnscaled(source, 0, 0);
            }
            return image;

            // this can throw OutOfMemory when creating a grayscale image from a cloned bitmap
            //      return source.Clone() as Bitmap;
        }

        public static void Save(Image image, Stream stream)
        {
            Save(image, stream, ImageFormat.Png);
        }

        public static void Save(Image image, string fileName, ImageFormat format)
        {
            using (FileStream stream = new FileStream(fileName, FileMode.Create))
            {
                Save(image, stream, format);
            }
        }

        public static void Save(Image image, Stream stream, ImageFormat format)
        {
            if (image == null)
                return;
            if (image is Bitmap)
                image.Save(stream, format);
            else if (image is Metafile)
            {
                Metafile emf = null;
                using (Bitmap bmp = new Bitmap(1, 1))
                using (Graphics g = Graphics.FromImage(bmp))
                {
                    IntPtr hdc = g.GetHdc();
                    emf = new Metafile(stream, hdc);
                    g.ReleaseHdc(hdc);
                }
                using (Graphics g = Graphics.FromImage(emf))
                {
                    g.DrawImage(image, 0, 0);
                }
            }
        }

        public static byte[] Load(string fileName)
        {
            if (!String.IsNullOrEmpty(fileName))
                return File.ReadAllBytes(fileName);
            return null;
        }

        public static Image Load(byte[] bytes)
        {
            if (bytes != null && bytes.Length > 0)
            {
                try
                {
                    return new ImageConverter().ConvertFrom(bytes) as Image;
                }
                catch
                {
                    Bitmap errorBmp = new Bitmap(10, 10);
                    using (Graphics g = Graphics.FromImage(errorBmp))
                    {
                        g.DrawLine(Pens.Red, 0, 0, 10, 10);
                        g.DrawLine(Pens.Red, 0, 10, 10, 0);
                    }
                    return errorBmp;
                }
            }
            return null;
        }

        public static byte[] LoadURL(string url)
        {
            if (!String.IsNullOrEmpty(url))
            {
                using (WebClient web = new WebClient())
                {
                    return web.DownloadData(url);
                }
            }
            return null;
        }

        public static Bitmap GetTransparentBitmap(Image source, float transparency)
        {
            if (source == null)
                return null;

            ColorMatrix colorMatrix = new ColorMatrix();
            colorMatrix.Matrix33 = 1 - transparency;
            ImageAttributes imageAttributes = new ImageAttributes();
            imageAttributes.SetColorMatrix(
               colorMatrix,
               ColorMatrixFlag.Default,
               ColorAdjustType.Bitmap);

            int width = source.Width;
            int height = source.Height;
            Bitmap image = new Bitmap(width, height);
            image.SetResolution(source.HorizontalResolution, source.VerticalResolution);

            using (Graphics g = Graphics.FromImage(image))
            {
                g.Clear(Color.Transparent);
                g.DrawImage(
                  source,
                  new Rectangle(0, 0, width, height),
                  0, 0, width, height,
                  GraphicsUnit.Pixel,
                  imageAttributes);
            }
            return image;
        }

        public static Bitmap GetGrayscaleBitmap(Image source)
        {
            Bitmap grayscaleBitmap = new Bitmap(source.Width, source.Height, source.PixelFormat);
            
            // Red should be converted to (R*.299)+(G*.587)+(B*.114)
            // Green should be converted to (R*.299)+(G*.587)+(B*.114)
            // Blue should be converted to (R*.299)+(G*.587)+(B*.114)
            // Alpha should stay the same.
            ColorMatrix grayscaleMatrix = new ColorMatrix(new float[][]{
                                                          new float[] {0.299f, 0.299f, 0.299f, 0, 0},
                                                          new float[] {0.587f, 0.587f, 0.587f, 0, 0},
                                                          new float[] {0.114f, 0.114f, 0.114f, 0, 0},
                                                          new float[] {     0,      0,      0, 1, 0},
                                                          new float[] {     0,      0,      0, 0, 1}});

            ImageAttributes attributes = new ImageAttributes();
            attributes.SetColorMatrix(grayscaleMatrix);
            
            // Use a Graphics object from the new image
            using (Graphics graphics = Graphics.FromImage(grayscaleBitmap))
            {
                // Draw the original image using the ImageAttributes we created
                graphics.DrawImage(source,
                    new Rectangle(0, 0, grayscaleBitmap.Width, grayscaleBitmap.Height),
                    0, 0, grayscaleBitmap.Width, grayscaleBitmap.Height,
                    GraphicsUnit.Pixel, attributes);
            }

            return grayscaleBitmap;
        }
    }
}

来自：https://github.com/FastReports/FastReport