高强度不失真在线压缩图片（jpg与png）

在线图片压缩，压缩Jpg与Png格式图片。

压缩PNG可使用类库：PNGCompressor

压缩jpg可使用类库：TJCompressor

以下为封装后的部分代码片段。

点我在线体验

 [HttpPost]
        public ApiResult ImageCompress(GeneralImageCompressViewModel vm)
        {
            if (!ModelState.IsValid) { return this.ModelErrorTextResult(); }


            int quality = 80;
            if (vm.QualityType == 1) { quality = 80; }
            else if (vm.QualityType == 2) { quality = 60; }
            else if (vm.QualityType == 3) { quality = 40; }
            else if (vm.QualityType == 4) { quality = 20; }
            string fileName = Path.GetFileNameWithoutExtension(vm.ImageUrl);
            string targetUrl = vm.ImageUrl.Replace(fileName, $"{fileName}_compress_{quality}");

            string extName = Path.GetExtension(vm.ImageUrl).Replace(".", "").ToLower();
            string sourceFullName = UrlOper.MapPath(vm.ImageUrl);
            string targetFullName = UrlOper.MapPath(targetUrl);

            bool isSuccess = true;
            Size newSize = new Size();
            try
            {
                using (Image img = Image.FromFile(sourceFullName))
                {
                    newSize = Commons.EqualRatioSize(img.Width, img.Height, vm.ImgWidth, vm.ImgHeight);
                    using (var bmp = new Bitmap(img, newSize.Width, newSize.Height))
                    {
                        //压缩PNG
                        if (extName == "png")
                        {
                            string tmpImg = UrlOper.MapPath(vm.ImageUrl.Replace(fileName, $"{fileName}_pngsitesize_{newSize.Width}_{newSize.Height}"));
                            bmp.Save(tmpImg);
                            bmp.Dispose();

                            var pngCompressor = new PNGCompression.PNGCompressor
                            {
                                PNGToolPath = UrlOper.MapPath("~/content/tools/pngquant"),
                                PNGExeName = "pngquant.exe"
                            };
                            pngCompressor.CompressImageLossy(tmpImg, targetFullName, new PNGCompression.LossyInputSettings
                            {
                                MinQuality = 0,
                                MaxQuality = (quality + 20)
                            });

                            System.IO.File.Delete(tmpImg);
                        }
                        //压缩JPG
                        else if (extName == "jpg" || extName == "jpeg")
                        {
                            var jpgCompressor = new MozJpegSharp.TJCompressor();
                            var compressed = jpgCompressor.Compress(bmp, MozJpegSharp.TJSubsamplingOption.Chrominance420, quality, MozJpegSharp.TJFlags.None);
                            System.IO.File.WriteAllBytes(targetFullName, compressed);
                        }
                    }
                }
                if (!System.IO.File.Exists(targetFullName))
                {
                    isSuccess = false;
                }
            }
            catch
            {
                isSuccess = false;
            }
            if (!isSuccess)
            {
                return this.Ok(new
                {
                    IsCompressOK = false
                });
            }

            long sourceLength = new System.IO.FileInfo(sourceFullName).Length;
            long targetLength = new System.IO.FileInfo(targetFullName).Length;
            //如果压缩后更大，则返回原图
            if (targetLength > sourceLength)
            {
                targetLength = sourceLength;
                targetUrl = vm.ImageUrl;
            }

            var compressRatio = 100 - (int)(((decimal)targetLength / (decimal)sourceLength) * 100m);
            if (compressRatio == 100) { compressRatio = 99; }
            string sourceSizeDesc = FileHelper.GetFileSizeDesc(sourceLength);
            string targetSizeDesc = FileHelper.GetFileSizeDesc(targetLength);
            object result = new
            {
                Source = UrlOper.ResolveClientUrl(vm.ImageUrl),
                Target = targetUrl,
                IsCompressOK = true,
                ImgWidth = newSize.Width,
                ImgHeight = newSize.Height,
                SourceSizeDesc = sourceSizeDesc,
                TargetSizeDesc = targetSizeDesc,
                CompressRatio = compressRatio
            };

            return this.Ok(result);
        }