在Mac上使用System.Drawing.Common将BMP转换为TIFF

Question

我试图使用System.Drawing.Common将BMP图像转换为tiff映像，在Mac上使用以下C#代码(.NET核心3.1)：

        public void SaveBitmapAsTiff(string location, Bitmap image)
        {

            var imageCodecInfo = GetEncoderInfo("image/tiff");
            var encoder = Encoder.Compression;
            var encoderParameters = new EncoderParameters(1);
            
            var encoderParameter = new EncoderParameter(
                encoder,
                (long)EncoderValue.CompressionLZW);
            encoderParameters.Param[0] = encoderParameter;
            location = location.Replace(".bmp", "");
            image.Save(location + ".tiff", imageCodecInfo, encoderParameters);
            // image.Save(location + ".tiff", ImageFormat.Tiff); Also tried this method overload
        }
        
        private static ImageCodecInfo GetEncoderInfo(string mimeType)
        {
            int j;
            ImageCodecInfo[] encoders;
            encoders = ImageCodecInfo.GetImageEncoders();
            for(j = 0; j < encoders.Length; ++j)
            {
                if(encoders[j].MimeType == mimeType)
                    return encoders[j];
            }
            return null;
        }

location参数包含要写入的文件路径，image参数包含从磁盘加载的位图。

当我试图运行这段代码时，我会得到以下异常：

Unhandled exception. System.NotImplementedException: Not implemented.
   at System.Drawing.SafeNativeMethods.Gdip.CheckStatus(Int32 status)
   at System.Drawing.Image.Save(String filename, ImageCodecInfo encoder, EncoderParameters encoderParams)
   at System.Drawing.Image.Save(String filename, ImageFormat format)
   at BmpTiffConverter.Services.FileService.SaveBitmapAsTiff(String location, Bitmap image) in /Users/tomcoldenhoff/Documents/ReSoftware/Repositories/BmpTiffConverter/BmpTiffConverter/Services/FileService.cs:line 54
   at BmpTiffConverter.Services.ConverterService.ConvertBmpToTiff(String inputPath, String outputPath) in /Users/tomcoldenhoff/Documents/ReSoftware/Repositories/BmpTiffConverter/BmpTiffConverter/Services/ConverterService.cs:line 20

我的谷歌搜索表明，我必须安装libgdiplus，而我已经安装了brew install mono-libgdiplus和brew upgrade mono-libgdiplus。

我还通过安装runtime.osx.10.10-x64.CoreCompat.System.Drawing包尝试了@Andy的建议答案，不幸的是，这是行不通的。

有人有别的建议吗？

Answer 1

问题是mono-libgdiplus没有实现EncoderValue.CompressionLZW编码器参数。我建议不要使用这个库，而是安装这个nuget包：

​

​

runtime.osx.10.10-x64.CoreCompat.System.Drawing

一旦我添加了那个包，您的代码就完美地工作了。

Answer 2

不幸的是，我没有Mac需要测试。我用DotNet Core3.1在Windows和Ubuntu 20上测试了您的代码，您的代码看起来很好用。我只能猜测这与您如何创建或修改您的Bitmap有关。

下面是我如何在Linux下创建这个项目的。dotnet add package是我如何添加System.Drawing.Common NuGet包的。我不知道它是如何在Mono上工作的，或者你是否在使用Mono。

> dotnet new console
> dotnet add package System.Drawing.Common
> dotnet restore

我编辑了program.cs

> dotnet build
> dotnet run

一切都很好。我现在可以在任何图像查看器中打开tiff图像。

从代码风格的角度来看，我建议进行相当多的更改。我知道您遵循了MSDN的代码示例，但就目前情况而言，它们的示例在这个实例中并不十分清楚。我刚刚复制和粘贴了我的整个.cs文件，并在各种修改中添加了注释。编写清晰的代码和编写工作代码一样重要。

using System.Drawing;
using System.Drawing.Imaging;
using System.Linq;

class Program
{
    // made the function more generic Bitmap inherits from Image and Image contains
    // the save feature so it might as well be made more general
    public static void SaveImageAsTiff(string location, Image image)
    {
        // fetch tiffCodec
        var tiffCodec = ImageCodecInfo
            .GetImageEncoders()
            .Where(info => info.MimeType == "image/tiff")
            .First();

        // create encoderParameters
        // this structure is much clearer IMO
        // (Can you see that there is now a color depth parameter?)
        var encoderParameters = new EncoderParameters(2) 
        {
            Param = new EncoderParameter[]{
                new EncoderParameter(Encoder.Compression, (long)EncoderValue.CompressionLZW),
                new EncoderParameter(Encoder.ColorDepth, 24L)
            }
        };

        // save image using codec and encoder parameters
        // it is common behavior to just save the file with the given location parameter 
        // and not to try do some extension conversion
        image.Save(location, tiffCodec, encoderParameters);
    }

    static void Main(string[] args)
    {
        // original bitmap location
        // (Yes forward slashes work on Windows so relative file paths are simple to handle)
        string bmpLocation = @"C:/Images/test.bmp";
        //string bmpLocation = @"~/Images/test.bmp"; // test on Linux

        // tidy way to convert file extensions of a path in C#
        string tiffLocation = System.IO.Path.ChangeExtension(bmpLocation, "tiff");

        // open image and force it to be a bitmap for examples sakes
        Bitmap bmpImage = new Bitmap(Image.FromFile(bmpLocation));

        // save image as tiff
        SaveImageAsTiff(tiffLocation, bmpImage);
    }
}