SkiaSharp Tiff支持

2 回答

• 4

  @DougS

  您的实现大多是正确的，但由于多个内存分配和副本，它的性能不是很高 .

  我注意到你创建了3个内存块，每个块的总大小为（w * h * 4字节）：

  // the int[]
  raster = new int[width * height];
  
  // the SKColor[]
  pixels = new SKColor[width * height];
  
  // the bitmap
  bitmap = new SKBitmap(width, height)
  

  您还要多次复制内存之间的像素：

  // decode the TIFF (first copy)
  tifImg.ReadRGBAImageOriented(width, height, raster, Orientation.TOPLEFT)
  
  // convert to SKColor (second copy)
  pixels[arrayOffset] = new SKColor(...);
  
  // set bitmap pixels (third copy)
  bitmap.Pixels = pixels;
  

  我想我设法创建了一个解码流的类似方法，只有一个副本和内存分配：

  public static SKBitmap OpenTiff(Stream tiffStream)
  {
      // open a TIFF stored in the stream
      using (var tifImg = Tiff.ClientOpen("in-memory", "r", tiffStream, new TiffStream()))
      {
          // read the dimensions
          var width = tifImg.GetField(TiffTag.IMAGEWIDTH)[0].ToInt();
          var height = tifImg.GetField(TiffTag.IMAGELENGTH)[0].ToInt();
  
          // create the bitmap
          var bitmap = new SKBitmap();
          var info = new SKImageInfo(width, height);
  
          // create the buffer that will hold the pixels
          var raster = new int[width * height];
  
          // get a pointer to the buffer, and give it to the bitmap
          var ptr = GCHandle.Alloc(raster, GCHandleType.Pinned);
          bitmap.InstallPixels(info, ptr.AddrOfPinnedObject(), info.RowBytes, null, (addr, ctx) => ptr.Free(), null);
  
          // read the image into the memory buffer
          if (!tifImg.ReadRGBAImageOriented(width, height, raster, Orientation.TOPLEFT))
          {
              // not a valid TIF image.
              return null;
          }
  
          // swap the red and blue because SkiaSharp may differ from the tiff
          if (SKImageInfo.PlatformColorType == SKColorType.Bgra8888)
          {
              SKSwizzle.SwapRedBlue(ptr.AddrOfPinnedObject(), raster.Length);
          }
  
          return bitmap;
      }
  }
  

  一个要点住在这里：https://gist.github.com/mattleibow/0a09babdf0dc9d2bc3deedf85f9b57d6

  让我解释一下代码......我基本上是在创建 int[] ，但是然后将其传递给 SKBitmap 并让它接管 . 我正在固定它，因为 SKBitmap 位于非托管内存中，GC可能会移动它，但我确定在处理位图时取消固定它 .

  这是一个更详细的步骤：

  // this does not actually allocate anything
  //  - the size is 0x0 / 0 bytes of pixels
  var bitmap = new SKBitmap();
  
  // I create the only buffer for pixel data
  var raster = new int[width * height];
  
  // pin the managed array so it can be passed to unmanaged memory
  var ptr = GCHandle.Alloc(raster, GCHandleType.Pinned);
  
  // pass the pointer of the array to the bitmap
  // making sure to free the pinned memory in the dispose delegate
  //  - this is also not an allocation, as the memory already exists
  bitmap.InstallPixels(info, ptr.AddrOfPinnedObject(), info.RowBytes, null, (addr, ctx) => ptr.Free(), null);
  
  // the first and only copy from the TIFF stream into memory
  tifImg.ReadRGBAImageOriented(width, height, raster, Orientation.TOPLEFT)
  
  // an unfortunate extra memory operation for some platforms
  //  - this is usually just for Windows as it uses a BGR color format
  //  - Linux, macOS, iOS, Android all are RGB, so no swizzle is needed
  SKSwizzle.SwapRedBlue(ptr.AddrOfPinnedObject(), raster.Length);
  

  对于调试会话中的一些原始统计数据，我的一个图像的代码大约需要500毫秒，但我的代码只需要20毫秒 .

  我希望我对你的代码听起来不太苛刻/消极，我不是以任何方式表达的 .

  回复于 2024-04-27T01:34:58+08:00
• 0

  我不是专家，所以我欢迎任何能够使这些代码更有效率的专家（或者有完全不同的想法来获取SKBitmap） .

  这使用LibTiff.Net

  using BitMiracle.LibTiff.Classic;
  
  . . . .
  
  public static void ConvertTiffToSKBitmap(MemoryStream tifImage)
  {
      SKColor[] pixels;
      int width, height;
      // open a Tiff stored in the memory stream, and grab its pixels
      using (Tiff tifImg = Tiff.ClientOpen("in-memory", "r", tifImage, new TiffStream()))
      {
          FieldValue[] value = tifImg.GetField(TiffTag.IMAGEWIDTH);
          width = value[0].ToInt();
  
          value = tifImg.GetField(TiffTag.IMAGELENGTH);
          height = value[0].ToInt();
  
          // Read the image into the memory buffer 
          int[] raster = new int[width * height];
          if (!tifImg.ReadRGBAImageOriented(width, height, raster, Orientation.TOPLEFT))
          {
              // Not a valid TIF image.
          }
          // store the pixels
          pixels = new SKColor[width * height];
          for (int y = 0; y < height; y++)
          {
              for (int x = 0; x < width; x++)
              {
                  int arrayOffset = y * width + x;
                  int rgba = raster[arrayOffset];
                  pixels[arrayOffset] = new SKColor((byte)Tiff.GetR(rgba), (byte)Tiff.GetG(rgba), (byte)Tiff.GetB(rgba), (byte)Tiff.GetA(rgba));
              }
          }
      }
      using (SKBitmap bitmap = new SKBitmap(width, height))
      {
          bitmap.Pixels = pixels;
  
          // do something with the SKBitmap
      }
  }
  

  回复于 2024-04-27T01:34:58+08:00