// This function is used to compress the image using the LZW algorithm
public static byte[] Compress(AccessibleBitmap source)
{
// Add first 255 standard values to LZWDictionary in LZWCompressor.cs
string[] LZWDictionary = new string[256];
for (int i = 0; i < 256; i++)
{
LZWDictionary[i] = ((char)i).ToString();
}
List <string> dictionary = new List <string>(LZWDictionary); // Clone dictionary of all bytes
Queue <byte> bytes = new Queue <byte>(source.GetRawPixelBytes()); // Get all bytes from the source image
BitStreamFIFO bs = new BitStreamFIFO(); // Create bitstream for output
int maxDictSize = (int)Math.Pow(2, maxBitCount); // Get maximum dictionary size
string encodingString = ((char)bytes.Dequeue()).ToString(); // Create string to add encoding to
while (bytes.Count > 0)
{
// Clear dict if full
if (dictionary.Count >= maxDictSize)
{
dictionary = new List <string>(LZWDictionary);
}
char b = (char)bytes.Dequeue();
if (dictionary.Contains(encodingString + b))
{
encodingString += b;
}
else
{
bs.Write(dictionary.FindIndex(x => x.StartsWith(encodingString)), maxBitCount);
dictionary.Add(encodingString + b);
encodingString = b.ToString();
}
}
// Write remaining byte to bitstream
bs.Write(dictionary.FindIndex(x => x.StartsWith(encodingString)), maxBitCount);
// Return the bitstream as byte array
return(bs.ToByteArray());
}
public static byte[] CompressVertical(AccessibleBitmap source)
{
byte[] lastpixel = null; // Create variable to store the last pixel
int colorCounter = 1; // Create counter for current color
BitStreamFIFO bs = new BitStreamFIFO(); // Create new bitstream for all the bits
int maxCount = 0; // Create variable to store the max bitcount
Queue<PixelArray> output = new Queue<PixelArray>(); // Create list to store all the pixelvalues in
// Write one bit to the bitstream, so the decompressor knows to decompress vertically
bs.Write(true);
// Iterate through every vertical row
for (int x = 0; x < source.width; x++)
{
// Iterate through every pixel in the vertical row
for (int y = 0; y < source.height; y++)
{
// Check if the variable lastpixel is empty
if (lastpixel == null)
{
// If lastpixel is empty, set last pixel to the first pixel
lastpixel = source.GetPixel(x, y);
}
else
{
// If lastpixel isn't empty, compare last pixel with new pixel
if (lastpixel.SequenceEqual(source.GetPixel(x, y)))
{
// Pixels matched, so increase the counter value
colorCounter++;
}
else
{
// If the pixels don't match, add the counter with the last pixel to the output queue
output.Enqueue(new PixelArray(colorCounter, lastpixel));
// Check if the new countervalue is higher then the last one, if so set maxBitCount to that
if (colorCounter > maxCount)
maxCount = colorCounter;
// Reset the colorCounter and set the last pixel to the new pixel
colorCounter = 1;
lastpixel = source.GetPixel(x, y);
}
}
}
}
// Add the remaining pixel(s) to the bitstream
output.Enqueue(new PixelArray(colorCounter, lastpixel));
// Check if the new countervalue is higher then the last one, if so set maxBitCount to that
if (colorCounter > maxCount)
maxCount = colorCounter;
// Write the maxCount to the bitstream
bs.Write((byte)Math.Ceiling(Math.Log(maxCount, 2)));
// Add all the pixels from the queue to the bitstream
while (output.Count > 0)
{
PixelArray pixel = output.Dequeue();
bs.Write(pixel.Count, (int)Math.Ceiling(Math.Log(maxCount, 2)));
bs.Write(pixel.Pixel);
}
// Return the bitsream as a byte[]
return bs.ToByteArray();
}
