C# Image 图片的缩放

将图片缩小或放大至目标宽高

public Image pictureProcess(Image sourceImage,int targetWidth,int targetHeight) {
            int width;//图片最终的宽
            int height;//图片最终的高
            try
            {
                System.Drawing.Imaging.ImageFormat format = sourceImage.RawFormat;
                Bitmap targetPicture = new Bitmap(targetWidth, targetHeight);
                Graphics g = Graphics.FromImage(targetPicture);
                g.Clear(Color.White);

                //计算缩放图片的大小
                if (sourceImage.Width > targetWidth && sourceImage.Height <= targetHeight) 
                {
                    width = targetWidth;
                    height = (width * sourceImage.Height) / sourceImage.Width;
                }
                else if(sourceImage.Width <= targetWidth && sourceImage.Height > targetHeight)
                {
                    height = targetHeight;
                    width = (height * sourceImage.Width) / sourceImage.Height;
                }
                else if (sourceImage.Width <= targetWidth && sourceImage.Height <= targetHeight)
                {
                    width = sourceImage.Width;
                    height = sourceImage.Height;
                }
                else 
                {
                    width = targetWidth;
                    height = (width * sourceImage.Height) / sourceImage.Width;
                    if(height>targetHeight)
                    {
                        height = targetHeight;
                        width = (height * sourceImage.Width) / sourceImage.Height;
                    }
                }
                g.DrawImage(sourceImage,(targetWidth-width)/2,(targetHeight-height)/2,width,height);
                sourceImage.Dispose();

                return targetPicture;
            }catch(Exception ex){

            }
            return null;
        }