图像上传不会降低质量

Question

我在网站上有一个用户图库,访问者可以上传一些图片.上传后,图像应调整为一些预定义的预设.另外原始图像也应该保存.所有工作正常png和bmp图像格式.但是,如果我上传gif格式或jpeg以一种颜色占优势上传的原始图像似乎被压缩.

例如:

原版的:

上传时间:

我在谷歌搜索过,并找到了一些如何正确上传图片的例子.最后我写了下一个方法:

void UploadImagePreset(Image image, ImageFormat imgFormat, string imgPath)
{
    using (var uploadStream = imageUploader.CreateUploadStream(imagePath))
    {
        var newWidth = image.Width;
        var newHeight = image.Height;
        using (var outBitmap = new Bitmap(newWidth, newHeight))
        {
            using (var outGraph = Graphics.FromImage(outBitmap))
            {
                outGraph.CompositingQuality = CompositingQuality.HighQuality;
                outGraph.SmoothingMode = SmoothingMode.HighQuality;
                outGraph.PixelOffsetMode = PixelOffsetMode.HighQuality;
                outGraph.InterpolationMode = InterpolationMode.HighQualityBicubic;

                var imageRect = new Rectangle(0, 0, newWidth, newHeight);
                outGraph.DrawImage(image, imageRect);

                outBitmap.Save(uploadStream, imgFormat);
            }
        }
    }
}

但它没有帮助.上载的图像与上述相同.我试图像这样指定结果图像的qaulity:

var encoderParameters = new EncoderParameters();
var encoderParameter = new EncoderParameter(Encoder.Quality, 100);
encoderParameters.Param[0] = encoderParameter;
var encoder = ImageCodecInfo.GetImageEncoders()
    .Where(e => e.FormatID == imgFormat.Guid)
    .FirstOrDefault();
outBitmap.Save(uploadStream, encoder, encoderParameters);

它也不起作用.另外当我上传jpeg图像时发生异常.

有没有办法上传图像而不压缩或调整大小？我花了几个小时试图解决这个问题并坚持下去.

Answer 1

您正在通过Image类传递上传的图像- 这是一个基于传入流的新图像.

然后使用一些默认参数保存它,这些参数将不再反映原始图像.

您只需将传入的流直接保存到磁盘 - 这将导致原始图像的精确副本.

像这样(.NET 4.0):

using (var uploadStream = imageUploader.CreateUploadStream(imagePath))
{
   using(var fileStream = new FileStream(imgPath, FileMode.Create))
   {
       uploadStream.CopyTo(fileStream);
   }
}

或者(.NET 4.0之前版本):

using (var uploadStream = imageUploader.CreateUploadStream(imagePath))
{
    using(var fileStream = new FileStream(imgPath, FileMode.Create))
    {
        byte[] buffer = new byte[32768];
        int read;
        while ((read = uploadStream.Read(buffer, 0, buffer.Length)) > 0)
        {
            fileStream.Write(buffer, 0, read);
        }
    }
}

改编自这个答案.