写在前面

从浏览器的Html文本中获取图片链接并保存到本地，同时对图片的分辨率和品质进行处理，以满足某些平台的规格需求；可以放到多线程中调用以提高下载效率。

代码实现

    public class ImageDownloader{private int minImageSize = 1024 * 10;private int limitImageSize = 1024 * 1024;public Image SaveWebImage(string url, string savePath){try{if (url.EndsWith("gif"))return null;using (var c = new WebClient()){string imgUrl = url;if (imgUrl.StartsWith("//")){imgUrl = "http:" + imgUrl;}var img = Image.FromStream(new MemoryStream(c.DownloadData(imgUrl)));// 小图直接略过if (img.Width < 200 || img.Height < 200)return null;var r = Resize(img, 640, 640, true);r.Save(savePath);var fileInfo = new FileInfo(savePath);if (fileInfo.Length < minImageSize) // 如果小于10kb那就是无效图片return r;if (fileInfo.Length > limitImageSize) // 品质可以通过参数来控制{EncoderParameters encoderParams = new EncoderParameters();long[] quality = new long[1];quality[0] = 85; // 品质参数，最大为100EncoderParameter encoderParam = new EncoderParameter(Encoder.Quality, quality);encoderParams.Param[0] = encoderParam;ImageCodecInfo codecInfo = GetEncoder(ImageFormat.Jpeg);r.Save(savePath, codecInfo, encoderParams);encoderParam.Dispose();encoderParams.Dispose();}img.Dispose();return r;}}catch (Exception ex){LogHelper.Error(ex);LogHelper.Error("error url:" + url);return null;}}public Image Resize(Image image, int newWidth, int maxHeight, bool onlyResizeIfWider){if (onlyResizeIfWider && image.Width <= newWidth) newWidth = image.Width;var newHeight = image.Height * newWidth / image.Width;var res = new Bitmap(newWidth, newHeight);using (var graphic = Graphics.FromImage(res)){graphic.InterpolationMode = InterpolationMode.HighQualityBicubic;graphic.SmoothingMode = SmoothingMode.HighQuality;graphic.PixelOffsetMode = PixelOffsetMode.HighQuality;graphic.CompositingQuality = CompositingQuality.HighQuality;graphic.DrawImage(image, 0, 0, newWidth, newHeight);}return res;}#region Private Methodsprivate ImageCodecInfo GetEncoder(ImageFormat format){ImageCodecInfo[] codecs = ImageCodecInfo.GetImageDecoders();foreach (ImageCodecInfo codec in codecs){if (codec.FormatID == format.Guid){return codec;}}return null;}#endregion}