C#更改上传图像的dpi

Question

我必须遵循被调用来改变图像分辨率的函数.我想这样做,所以上传的图像例如300dpi将被修改为72dpi(对于web).这个问题与我在哪里工作的另一个问题有关.

我创建了一个扩展方法,可以在我的应用程序中的更多位置使用此功能,而不是仅在上载新文件时.(见上述问题)

public static byte[] SetDpiTo72(this byte[] imageToFit, string mimeType, Size newSize)
{    
    using (MemoryStream memoryStream = new MemoryStream(), newMemoryStream = new MemoryStream())
    {
        memoryStream.Write(imageToFit, 0, imageToFit.Length);
        var originalImage = new Bitmap(memoryStream);

        using (var canvas = Graphics.FromImage(originalImage))
        {
            canvas.SmoothingMode = SmoothingMode.AntiAlias;
            canvas.InterpolationMode = InterpolationMode.HighQualityBicubic;
            canvas.PixelOffsetMode = PixelOffsetMode.HighQuality;
            canvas.DrawImage((Image)originalImage,0,0, newSize.Width, newSize.Height);

            newBitmap.SetResolution(72, 72);
            newBitmap.Save(newMemoryStream, ImageFunctions.GetEncoderInfo(mimeType), null);
        }
        return newMemoryStream.ToArray();
    }
}

提到的扩展方法在类似于下面情况的函数中被调用;

if (newSize.Width > originalImage.Width && newSize.Height > originalImage.Height)
{
     newSize.Width = originalImage.Width;
     newSize.Height = originalImage.Height;

     uploadedFileBuffer = uploadedFileBuffer.SetDpiTo72(uploadedFile.ContentType, newSize);

     return CreateFile(newSize, uploadedFile, uploadedFileBuffer);
}

进入的bytearray是一个bytearray文件.它已经具有正确的大小,但我想将分辨率更改为72dpi.但是在执行完并保存图像后,分辨率仍然是原始输入的分辨率,即300dpi.我怎样才能做到这一点？

几个答案后的更新:

public static byte[] SetDpiTo72(this byte[] imageToFit, string mimeType, Size newSize)
        {
            using (MemoryStream memoryStream = new MemoryStream(), newMemoryStream = new MemoryStream())
            {
                memoryStream.Write(imageToFit, 0, imageToFit.Length);
                var originalImage = new Bitmap(memoryStream);

                using (var canvas = Graphics.FromImage(originalImage))
                {
                    canvas.SmoothingMode = SmoothingMode.AntiAlias;
                    canvas.InterpolationMode = InterpolationMode.HighQualityBicubic;
                    canvas.PixelOffsetMode = PixelOffsetMode.HighQuality;
                    canvas.DrawImage((Image)originalImage,0,0, newSize.Width, newSize.Height);

                    originalImage.SetResolution(72, 72);

                    var epQuality = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, 75);
                    var epParameters = new EncoderParameters(1);
                    epParameters.Param[0] = epQuality;

                    Image newimg = Image.FromStream(memoryStream);

                    //Getting an GDI+ exception after the execution of this line.
                    newimg.Save("C:\\test1234.jpg", ImageFunctions.GetEncoderInfo(mimeType), epParameters);

                    originalImage.Save("test.jpg", ImageFormat.Jpeg);

                    //This line give me an Argumentexception - Parameter is not valid.
                    //originalImage.Save(newMemoryStream, ImageFunctions.GetEncoderInfo(mimeType), epParameters);
                    //newMemoryStream.Close();
                }
                return newMemoryStream.ToArray();
            }
        }

除了异常之外的stackstrace告诉我以下内容;

   at System.Drawing.Image.Save(String filename, ImageCodecInfo encoder, EncoderParameters encoderParams)
   at Extensions.ByteArrayExtensions.SetDpiTo72(Byte[] imageToFit, String mimeType, Size newSize) in C:\Website\Project\Extensions\ByteArrayExtensions.cs:line 356
   at CMS.Presentation.FileFunctions.CreateFullsizeImage(HttpPostedFileBase uploadedFile, Size newSize, Byte[] uploadedFileBuffer) in C:\Website\Project\CMS.Presentation\FileFunctions.cs:line 197
   at CMS.Presentation.FileFunctions.CreateFile(HttpPostedFileBase uploadedFile, INodeService nodeservice, Guid userId, Node parentNode) in C:\Website\Project\CMS.Presentation\FileFunctions.cs:line 53

与此同时,我还开发了另一个函数(见下文),仅调整位图大小.而这似乎工作正常.我不能在我当前的实现中使用此函数,因为它只返回一个Bitmap.或者我应该改变一切以使用位图？

private static Bitmap ResizeImage(Image image, int width, int height)
        {
            var frameCount = image.GetFrameCount(new FrameDimension(image.FrameDimensionsList[0]));
            var newDimensions = ImageFunctions.GenerateImageDimensions(image.Width, image.Height, width, height);
            Bitmap resizedImage;

            if (frameCount > 1)
            {
                //we have a animated GIF
                resizedImage = ResizeAnimatedGifImage(image, width, height);
            }
            else
            {
                resizedImage = (Bitmap)image.GetThumbnailImage(newDimensions.Width, newDimensions.Height, null, IntPtr.Zero);
            }

            resizedImage.SetResolution(72,72);

            return resizedImage;
        }

Answer 1

我花了一段时间，终于找到问题所在了！问题出在我使用的 ResizeImage 函数上。具体在“GetThumbnailImage”中。我遇到了另一个图像模糊的问题，这是可以解释的，因为 GetThumbnailImage 会将创建的 ThumbNail 拉伸到所需的大小。并且缩略图的分辨率永远不会改变。

private static Bitmap ResizeImage(Image image, int width, int height)
        {
            var frameCount = image.GetFrameCount(new FrameDimension(image.FrameDimensionsList[0]));
            var newDimensions = ImageFunctions.GenerateImageDimensions(image.Width, image.Height, width, height);
            Bitmap resizedImage;

            if (frameCount > 1)
            {
                //we have a animated GIF
                resizedImage = ResizeAnimatedGifImage(image, width, height);
            }
            else
            {
                resizedImage = (Bitmap)image.GetThumbnailImage(newDimensions.Width, newDimensions.Height, null, IntPtr.Zero);
            }

            resizedImage.SetResolution(72,72);

            return resizedImage;
        }

通过将上面的函数修改为下面的函数，我能够使用 Graphics.DrawImage 在渲染新图像之前重绘新图像来解决该问题。此外，GenerateImageDimensions 也进行了轻微修改。综上所述，问题就解决了。

private static Bitmap ResizeImage(Image image, int width, int height)
        {
            var frameCount = image.GetFrameCount(new FrameDimension(image.FrameDimensionsList[0]));
            var newDimensions = ImageFunctions.GenerateImageDimensions(image.Width, image.Height, width, height);

            var resizedImage = new Bitmap(newDimensions.Width, newDimensions.Height);
            if (frameCount > 1)
            {
                //we have a animated GIF
                resizedImage = ResizeAnimatedGifImage(image, width, height);
            }
            else
            {

                //we have a normal image
                using (var gfx = Graphics.FromImage(resizedImage))
                {
                    gfx.SmoothingMode = SmoothingMode.HighQuality;
                    gfx.InterpolationMode = InterpolationMode.HighQualityBicubic;
                    gfx.PixelOffsetMode = PixelOffsetMode.HighQuality;

                    var targRectangle = new Rectangle(0, 0, newDimensions.Width, newDimensions.Height);
                    var srcRectangle = new Rectangle(0, 0, image.Width, image.Height);

                    gfx.DrawImage(image, targRectangle, srcRectangle, GraphicsUnit.Pixel);
                }
            }

            return resizedImage;
        }