//Decodes a byte array containing a compressed APIF image to a C# Bitmap image
public Bitmap Decode(byte[] bytes)
{
//Check if the file version matches the version of the this decoder
if (bytes[0] != version)
{
throw new Exception("Version not matching");
}
//Start timer for decoding time
encodingStart = DateTime.Now.TimeOfDay;
//Read the header info to the correct variables
int pixelBytes = bytes[1]; //The amount of color channels
int width = bytes[2] * 256 + bytes[3]; //The image width
int height = bytes[4] * 256 + bytes[5]; //The image heigth
compressionType = bytes[6]; //The compression type
//Store the image data apart from the header
byte[] image = new byte[bytes.Length - 7];
Array.Copy(bytes, 7, image, 0, image.Length);
//Initialize
AccessibleBitmap outputBitmap = null; //The final AccessibleBitmap object
//Choose the right decoding type from the header info
switch (compressionType)
{
//Uncompressed bitmap
case 0:
outputBitmap = UncompressedBitmapCompressor.Decompress(image, width, height, pixelBytes);
break;
//Individual compressed color channels merged together
case 1:
outputBitmap = ByteLayerVaryingCompression.Decompress(image, width, height, pixelBytes);
break;
//Run length encoding
case 2:
outputBitmap = RunLengthEncodingCompressor.Decompress(image, width, height, pixelBytes);
break;
//Run length encoding vertical
case 3:
outputBitmap = RunLengthEncodingCompressorVertical.Decompress(image, width, height, pixelBytes);
break;
//LZW compression
case 4:
outputBitmap = LZWCompressor.Decompress(image, width, height, pixelBytes);
break;
//To add a decompression type add a new case like the existing ones
//Unknown compression type: error
default:
throw new Exception("Unexisting compression type");
}
//Stop timer
encodingStop = DateTime.Now.TimeOfDay;
SetStatus("Finished");
//Calculate compression rate in bytes per pixel
compressionRate = (double)bytes.Length / (outputBitmap.width * outputBitmap.height);
//Return the output image as bitmap format
return(outputBitmap.GetBitmap());
}
//Encodes a C# Bitmap image to a byte array containing this image compressed as APIF image
public byte[] Encode(Bitmap bitmap)
{
//Start timer for compression time
encodingStart = DateTime.Now.TimeOfDay;
//Creates a AccessibleBitmap class for the input bitmap: this class makes reading pixels easier and faster
AccessibleBitmap aBitmap = new AccessibleBitmap(bitmap);
//Compress image using all different compression techniques, where possible at the same time
byte[][] compressionTechniques = new byte[4][];
Parallel.For(0, compressionTechniques.Length, (i, state) =>
{
switch (i)
{
//Uncompressed (only used if no compression technique is smaller)
case 0:
compressionTechniques[i] = UncompressedBitmapCompressor.Compress(aBitmap);
break;
//Split colors in their channels and apply compression over them
case 1:
compressionTechniques[i] = ByteLayerVaryingCompression.Compress(aBitmap);
break;
//Run length compression: save the length of a sequence of pixels with the same color instead of saving them seperately
case 2:
compressionTechniques[i] = RunLengthEncodingCompressor.Compress(aBitmap);
break;
//Run length compression vertical: run length compression, but scan the pixels horizontally, becouse with some images this yields better results
case 3:
compressionTechniques[i] = RunLengthEncodingCompressorVertical.Compress(aBitmap);
break;
//LZW compression: save sequences of pixels as a single value, without the need of adding a dictionary\
// REMOVED BECAUSE VERY SLOW AND NOT PROPERLY WORKING
//case 4:
//compressionTechniques[i] = LZWCompressor.Compress(aBitmap);
//break;
//To add a compression technique, add a new case like the existing ones and increase the length of new byte[??][]
}
});
//Choose the smallest compression type
//Initialize
int smallestID = 0;
int smallestSize = int.MaxValue;
//Loop trough all saved compression techniques
for (int i = 0; i < compressionTechniques.Length; i++)
{
//If the current technique is smaller than the smallest technique which has been checked
if (compressionTechniques[i].Length < smallestSize)
{
//Mark this technique as smallest
smallestSize = compressionTechniques[i].Length;
smallestID = i;
}
}
//Set the output byte array to the output of the smallest compression technique
byte[] image = compressionTechniques[smallestID];
compressionType = smallestID;
//Build the file header containing information for the decoder
byte[] header = new byte[7];
header[0] = (byte)version; //This byte indicates the version of the compressor, to handle possible changes in the future
header[1] = (byte)aBitmap.pixelBytes; //This byte indicates the amount of color channels in the image
header[2] = (byte)(aBitmap.width >> 8); //These 2 bytes together indicate the width of the image
header[3] = (byte)aBitmap.width; //The reason for using 2 bytes instead of 1, is that 1 byte can store a width of 0-255, while 2 bytes can store 0-65535
header[4] = (byte)(aBitmap.height >> 8); //These 2 bytes together indicate the heigth of the image
header[5] = (byte)aBitmap.height; //The reason for using 2 bytes instead of 1, is that 1 byte can store a width of 0-255, while 2 bytes can store 0-65535
header[6] = (byte)compressionType; //This contains the number of the compression technique used
//Merge the header with the image data to form the fimal file data
byte[] fileBytes = new byte[header.Length + image.Length];
Array.Copy(header, fileBytes, header.Length);
Array.Copy(image, 0, fileBytes, header.Length, image.Length);
//Stop timer
encodingStop = DateTime.Now.TimeOfDay;
compressionRate = (double)fileBytes.Length / (aBitmap.width * aBitmap.height);
//Return final file as byte array
return(fileBytes);
}
