private void ReadChunkCrc(PngChunk chunk, byte[] typeBuffer)
        {
            byte[] crcBuffer = new byte[4];
            int    numBytes  = currentStream.Read(crcBuffer, 0, 4);

            if (numBytes >= 1 && numBytes <= 3)
            {
                throw new Exception("Image stream is not valid!");
            }
            Array.Reverse(crcBuffer);
            chunk.Crc = BitConverter.ToUInt32(crcBuffer, 0);
            Crc32 crc = new Crc32();

            crc.Update(typeBuffer);
            crc.Update(chunk.Data);
            if (crc.Value != chunk.Crc)
            {
                throw new Exception("CRC Error. Png Image chunk is corrupt!");
            }
        }
 private void ReadChunkData(PngChunk chunk)
 {
     chunk.Data = new byte[chunk.Length];
     currentStream.Read(chunk.Data, 0, chunk.Length);
 }