Accord.Imaging.Formats.PNMCodec.ReadP5Image C# (CSharp) Method

        private static unsafe Bitmap ReadP5Image(Stream stream, int width, int height, int maxValue)
        {
            double scalingFactor = (double)255 / maxValue;

            // create new bitmap and lock it
            Bitmap image = Tools.CreateGrayscaleImage(width, height);
            BitmapData imageData = image.LockBits(new Rectangle(0, 0, width, height),
                ImageLockMode.ReadWrite, PixelFormat.Format8bppIndexed);

            int stride = imageData.Stride;
            byte* ptr = (byte*)imageData.Scan0.ToPointer();

            // prepare a buffer for one line
            byte[] line = new byte[width];

            int totalBytesRead = 0, bytesRead = 0;

            // load all rows
            for (int y = 0; y < height; y++)
            {
                totalBytesRead = 0;
                bytesRead = 0;

                // load next line
                while (totalBytesRead != width)
                {
                    bytesRead = stream.Read(line, totalBytesRead, width - totalBytesRead);

                    if (bytesRead == 0)
                    {
                        // if we've reached the end before complete image is loaded, then there should
                        // be something wrong
                        throw new InvalidOperationException("Execution should not reach here.");
                    }

                    totalBytesRead += bytesRead;
                }

                // fill next image row
                byte* row = ptr + stride * y;

                for (int x = 0; x < width; x++, row++)
                {
                    *row = (byte)(scalingFactor * line[x]);
                }
            }

            // unlock image and return it
            image.UnlockBits(imageData);
            return image;
        }