如何在C#中正确显示被误判为黑白的灰度TIFF图像

我有一张灰度TIFF图像，使用ImageMagick、ImageSharp、System.Drawing等库处理时，均被识别为黑白图像，但在ImageJ、Photoshop、Incarta等软件中可清晰显示为灰度图。尝试了以下代码仍未解决问题：

TiffEncoder encoder = new TiffEncoder();
encoder.PhotometricInterpretation = SixLabors.ImageSharp.Formats.Tiff.Constants.TiffPhotometricInterpretation.BlackIsZero;

SixLabors.ImageSharp.Image image = SixLabors.ImageSharp.Image.Load(mysteryTiff);

PixelTypeInfo pixType = image.PixelType;
// Stretches the image to fit the pictureBox.
Stream stream = new MemoryStream();

image.SaveAsTiff(stream, encoder);
stream.Position = 0;
MagickImage magickImage = new MagickImage(stream);

pictureBox1.SizeMode = PictureBoxSizeMode.StretchImage;
pictureBox1.ClientSize = new System.Drawing.Size(1200, 1200);
pictureBox1.Image = magickImage.ToBitmap();

问题原因 #

这类现象通常源于TIFF文件的光度解释元数据标记与实际像素数据不匹配，或是图像采用了带灰度调色板的索引色格式，但.NET类库严格遵循元数据解析，未像专业图像软件那样自动校正格式偏差。

解决方案 #

方案1：ImageMagick强制转灰度

直接加载后转换为8位灰度格式，跳过元数据干扰：

using (MagickImage magickImage = new MagickImage(mysteryTiff))
{
    magickImage.Format = MagickFormat.Gray;
    magickImage.Depth = 8;
    
    pictureBox1.SizeMode = PictureBoxSizeMode.StretchImage;
    pictureBox1.ClientSize = new System.Drawing.Size(1200, 1200);
    pictureBox1.Image = magickImage.ToBitmap();
}

方案2：ImageSharp校正像素格式

先判断是否为索引色格式，再转换为8位灰度：

using SixLabors.ImageSharp;
using SixLabors.ImageSharp.PixelFormats;

using (Image image = Image.Load(mysteryTiff))
{
    if (image.PixelType.Indexed)
    {
        using (var grayImage = image.CloneAs<Gray8>())
        {
            using (MemoryStream stream = new MemoryStream())
            {
                grayImage.SaveAsTiff(stream);
                stream.Position = 0;
                pictureBox1.Image = System.Drawing.Image.FromStream(stream);
            }
        }
    }
    else
    {
        TiffEncoder encoder = new TiffEncoder();
        encoder.PhotometricInterpretation = SixLabors.ImageSharp.Formats.Tiff.Constants.TiffPhotometricInterpretation.BlackIsZero;
        using (MemoryStream stream = new MemoryStream())
        {
            image.SaveAsTiff(stream, encoder);
            stream.Position = 0;
            pictureBox1.Image = System.Drawing.Image.FromStream(stream);
        }
    }
    
    pictureBox1.SizeMode = PictureBoxSizeMode.StretchImage;
    pictureBox1.ClientSize = new System.Drawing.Size(1200, 1200);
}

方案3：System.Drawing手动生成灰度图

通过克隆图像并替换调色板实现灰度转换：

using (System.Drawing.Image sourceImage = System.Drawing.Image.FromFile(mysteryTiff))
{
    System.Drawing.Bitmap grayBitmap = new System.Drawing.Bitmap(sourceImage.Width, sourceImage.Height, System.Drawing.Imaging.PixelFormat.Format8bppIndexed);
    
    // 生成灰度调色板
    System.Drawing.Imaging.ColorPalette palette = grayBitmap.Palette;
    for (int i = 0; i < 256; i++)
    {
        palette.Entries[i] = System.Drawing.Color.FromArgb(i, i, i);
    }
    grayBitmap.Palette = palette;
    
    // 绘制原图像到灰度画布
    using (System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(grayBitmap))
    {
        g.DrawImage(sourceImage, new System.Drawing.Rectangle(0, 0, sourceImage.Width, sourceImage.Height));
    }
    
    pictureBox1.SizeMode = PictureBoxSizeMode.StretchImage;
    pictureBox1.ClientSize = new System.Drawing.Size(1200, 1200);
    pictureBox1.Image = grayBitmap;
}

内容的提问来源于stack exchange，提问作者jdmneon