public void Read( 
   int topLeftCornerX,
   int topLeftCornerY,
   PixelBlock pixelBlock
)

await QueuedTask.Run(() =>
{
  // Create a full raster from the raster dataset.
  ArcGIS.Core.Data.Raster.Raster raster = rasterDataset.CreateFullRaster();

  // Calculate size of pixel block to create. Use 128 or height/width of the raster, whichever is smaller.
  var height = raster.GetHeight();
  var width = raster.GetWidth();
  int pixelBlockHeight = height > 128 ? 128 : height;
  int pixelBlockWidth = width > 128 ? 128 : width;

  // Create a new (blank) pixel block.
  PixelBlock currentPixelBlock = raster.CreatePixelBlock(pixelBlockWidth, pixelBlockHeight);

  // Read pixel values from the raster dataset into the pixel block starting from the given top left corner.
  raster.Read(0, 0, currentPixelBlock);

  // Do something with the pixel block...

  // Write the pixel block to the raster dataset starting from the given top left corner.
  raster.Write(0, 0, currentPixelBlock);
});

await QueuedTask.Run(() =>
{
  // Read pixel values from the raster dataset into the pixel block starting from the given top left corner.
  raster.Read(0, 0, currentPixelBlock);

  // For each plane (band) in the pixel block
  for (int plane = 0; plane < currentPixelBlock.GetPlaneCount(); plane++)
  {
    // Get a copy of the array of pixels from the pixel block corresponding to the current plane.
    Array sourcePixels = currentPixelBlock.GetPixelData(plane, true);
    // Get the height and width of the pixel block.
    int pBHeight = currentPixelBlock.GetHeight();
    int pBWidth = currentPixelBlock.GetWidth();

    // Iterate through the pixels in the array.
    for (int i = 0; i < pBHeight; i++)
    {
      for (int j = 0; j < pBWidth; j++)
      {
        // Get the NoData mask value to see if the pixel is a valid pixel.
        if (Convert.ToByte(currentPixelBlock.GetNoDataMaskValue(plane, j, i)) == 1)
        {
          // Get the pixel value from the array and process it (add 5 to the value).
          // Note: This is assuming the pixel type is Unisigned 8bit.
          int pixelValue = Convert.ToInt16(sourcePixels.GetValue(j, i)) + 5;
          // Make sure the pixel value does not go above the range of the pixel type.
          pixelValue = pixelValue > 254 ? 254 : pixelValue;
          // Set the new pixel value to the array.
          // Note: This is assuming the pixel type is Unisigned 8bit.
          sourcePixels.SetValue(Convert.ToByte(pixelValue), j, i);
        }
      }
    }
    // Set the modified array of pixels back to the pixel block.
    currentPixelBlock.SetPixelData(plane, sourcePixels);
  }
  // Write the pixel block to the raster dataset starting from the given top left corner.
  raster.Write(0, 0, currentPixelBlock);
});