如何获取图像文件的尺寸？

Question

I have a file called FPN = "c:\ggs\ggs Access\images\members\1.jpg "

I'm trying to get the dimension of image 1.jpg , and I'd like to check whether image dimension is valid or not before loading.

Answer 1

System.Drawing.Image img = System.Drawing.Image.FromFile(@"c:\ggs\ggs Access\images\members\1.jpg");
MessageBox.Show("Width: " + img.Width + ", Height: " + img.Height);

Answer 2

Wpf class System.Windows.Media.Imaging.BitmapDecoder doesn't read whole file, just metadata.

using(var imageStream = File.OpenRead("file"))
{
    var decoder = BitmapDecoder.Create(imageStream, BitmapCreateOptions.IgnoreColorProfile,
        BitmapCacheOption.Default);
    var height = decoder.Frames[0].PixelHeight;
    var width = decoder.Frames[0].PixelWidth;
}

Update 2019-07-07 Dealing with exif 'ed images is a little bit more complicated. For some reasons iphones save a rotated image and to compensate they also set "rotate this image before displaying" exif flag as such.

Gif is also a pretty complicated format. It is possible that no frame has full gif size, you have to aggregate it from offsets and frames sizes.

So I used ImageProcessor instead, which deals with all the problems for me. Never checked if it reads the whole file though, because some browsers have no exif support and I had to save a rotated version anyway.

using (var imageFactory = new ImageFactory())
{
    imageFactory
        .Load(stream)
        .AutoRotate(); //takes care of ex-if
    var height = imageFactory.Image.Height,
    var width = imageFactory.Image.Width
}

Answer 3

Unfortunately, System.Drawing and ImageProcessor are supported only on the Windows platform because they are a thin wrapper over GDI (Graphics Device Interface) which is very old Win32 (Windows) unmanaged drawing APIs.

Instead, just install the SixLabors/ImageSharp library from NuGet. And here is how you can get size with it:

using (var image = SixLabors.ImageSharp.Image.Load("image-path."))
{
    var width = image.Width;
    var height = image.Height;
}

Answer 4

For .NET Core users and anyone who don't want to use 3rd parity libraries (and like me read the specifications and keep things simple), here is solution for JPEG dimensions:

public class JPEGPicture
{
  private byte[] data;
  private ushort m_width;
  private ushort m_height;

  public byte[] Data { get => data; set => data = value; }
  public ushort Width { get => m_width; set => m_width = value; }
  public ushort Height { get => m_height; set => m_height = value; }
    
  public void GetJPEGSize()
  {
    ushort height = 0;
    ushort width = 0;
    for (int nIndex = 0; nIndex < Data.Length; nIndex++)
    {
      if (Data[nIndex] == 0xFF)
      {
        nIndex++;
        if (nIndex < Data.Length)
        {
          /*
              0xFF, 0xC0,             // SOF0 segement
              0x00, 0x11,             // length of segment depends on the number of components
              0x08,                   // bits per pixel
              0x00, 0x95,             // image height
              0x00, 0xE3,             // image width
              0x03,                   // number of components (should be 1 or 3)
              0x01, 0x22, 0x00,       // 0x01=Y component, 0x22=sampling factor, quantization table number
              0x02, 0x11, 0x01,       // 0x02=Cb component, ...
              0x03, 0x11, 0x01        // 0x03=Cr component, ...
          */
          if (Data[nIndex] == 0xC0)
          {
            Console.WriteLine("0xC0 information:"); // Start Of Frame (baseline DCT)
            nIndex+=4;
            if (nIndex < Data.Length-1)
            {
              // 2 bytes for height
              height = BitConverter.ToUInt16(new byte[2] { Data[++nIndex], Data[nIndex-1] }, 0);
              Console.WriteLine("height = " + height);
            }
            nIndex++;
            if (nIndex < Data.Length - 1)
            {
              // 2 bytes for width
              width = BitConverter.ToUInt16(new byte[2] { Data[++nIndex], Data[nIndex-1] }, 0);
              Console.WriteLine("width = " + width);
            }
          }
        }
      }
    }
    if (height != 0)
      Height = height;
    if (width != 0)
      Width = width;
  }

  public byte[] ImageToByteArray(string ImageName)
  {
    FileStream fs = new FileStream(ImageName, FileMode.Open, FileAccess.Read);
    byte[] ba = new byte[fs.Length];
    fs.Read(ba, 0, Convert.ToInt32(fs.Length));
    fs.Close();

    return ba;
   }
 }

class Program
{
  static void Main(string[] args)
  {
    JPEGPicture pic = new JPEGPicture();
    pic.Data = pic.imageToByteArray("C:\\Test.jpg");
    pic.GetJPEGSize();
  }
}
    

I leave a space for anyone who wants to improve the code for progressive DCT:

if (Data[nIndex] == 0xC2)