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Data Compression Methods

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In this article, I will present some basically developed data-compression algorithms. Amid them are:

  • RLE (Runtime-Length Encoding) methods
  • Grayscale bitmaps compression class
  1. Including rle.cpp, there are two methods: CompressRLE and DecompressRLE. As parameters, these methods need input/output file names. The bit-length can't get over 127 bytes. The input file can be presented in any binary format.
  2. Quad.cpp—this file contains the grayscale matrix class; the grayscale method is commonly used in a fine matrix compression, and can be used for any purpose.
  3. quad.in—is a sample of input file and has its own format: %C%C..%C - n times, where n is the first byte in sequence.
/*************************************************/
/* 2003 (C) Hannibal Lecturer */
/* Grayscale compression methods demo */
/*************************************************/
/* Format of input file (cycle allowed): */
/* typedef struct { */
/* int intSize; */
/* char* szData; */
/* } tagInputGrayScaleMatrix; */
/*************************************************/



#include <stdio.h>
#include <string.h>
#include <math.h>


#define MAX_DIMENSION 16



class GrayScaleMatrix
{
public:
int Dimension;
int intTotalBlocksCompressed;
unsigned char Matrix [MAX_DIMENSION][MAX_DIMENSION];
unsigned char szCompressedData [MAX_DIMENSION*MAX_DIMENSION];

GrayScaleMatrix (int Dimension);
~GrayScaleMatrix ();
void DisplayMatrix (FILE* display);
int GetMatrixBit (int y, int x);
int GetQuadType (int y, int x, int intSize);
int CompressMatrix (FILE* fout, int y, int x, int intSize, int
intType);
int SetMatrixBit (int y, int x, int intValue);
int DecompressMatrix (FILE* fin, int intType);

private:
char szPathString [MAX_DIMENSION*8];
int intPathLen;
}

GrayScaleMatrix::GrayScaleMatrix (int Dimension)
{
int i,j;
this->Dimension = Dimension;
for (i=0;i<sizeof(szPathString);i++) szPathString[i] = 0;
intPathLen = 0;
intTotalBlocksCompressed = 0;

for (i=0;i<Dimension;i++)
for (j=0;j<(Dimension/8);j++) Matrix[i][j] = 0;
}

GrayScaleMatrix::~GrayScaleMatrix ()
{
int i,j;
for (i=0;i<MAX_DIMENSION;i++)
for (j=0;j<MAX_DIMENSION;j++) Matrix[i][j] = 0;
}


void GrayScaleMatrix::DisplayMatrix (FILE* display)
{
if (display==0) return;

int i,j;
for (i=1;i<=Dimension;i++)
{
for (j=1;j<=Dimension;j++) fprintf
(display,"%d",GetMatrixBit(i,j));
fprintf (display,"\r\n");
};
}


int GrayScaleMatrix::GetQuadType (int y, int x, int intSize)
{
int i,j;
int blRes = 0;

for (i=0;i<intSize;i++)
for (j=0;j<intSize;j++) if (GetMatrixBit (y+i,x+j)!=0) blRes =
1;

if (blRes)
{
for (i=0;i<intSize;i++)
for (j=0;j<intSize;j++) if (GetMatrixBit(y+i,x+j)!=1) return
(2);
return (1);
}
else return (0);

return (2);
}


int GrayScaleMatrix::SetMatrixBit (int y, int x, int intValue)
{
if (GetMatrixBit(y,x)==intValue) return (0);
switch (intValue)
{
case 0: { Matrix[y-1][(x-1)/8] ^= (unsigned char)pow(2,(x-1)%8);
return(1); }
case 1: { Matrix[y-1][(x-1)/8] |= (unsigned char)pow(2,(x-1)%8);
return(1); }
default: return(0);
}
return(0);
}

int GrayScaleMatrix::GetMatrixBit (int y, int x)
{
return ( (unsigned char) (Matrix[y-1][(x-1)/8] << (8-x))
>> 7 );
}

int GrayScaleMatrix::DecompressMatrix (FILE* fin, int intType)
{
int i,j;
int intChar;

if (fin!=0)
{
intTotalBlocksCompressed = 0;
while ((intChar = getc(fin))!=EOF)
for (i=0;i<intChar;i++)
szCompressedData [intTotalBlocksCompressed++] = getc(fin);
}

for (i=1;i<=Dimension;i++)
for (j=1;j<=Dimension;j++)
if (intTotalBlocksCompressed==0) SetMatrixBit(i,j,intType);
else SetMatrixBit (i,j,~intType);


for (i=0;i<intTotalBlocksCompressed;i++)
{
intChar = szCompressedData[i];
int intPos [8] = {0,0,0,0,0,0,0,0}, intTotal = 0;
int y = 1, x = 1, intSize = Dimension, k;

while (intChar>3)
{
intPos[intTotal] = intChar%4;
intChar /= 4;
intTotal++;
}
intPos [intTotal++] = intChar;

for (j=intTotal-1;j>=0;j--)
{
intSize /= 2;
y += (intPos[j]/2)*intSize;
x += (intPos[j]%2)*intSize;
}

for (k=y;k<y+intSize;k++)
for (j=x;j<x+intSize;j++)
{
SetMatrixBit (k,j,intType);
}
}
return (1);
}


int GrayScaleMatrix::CompressMatrix (FILE* fout, int y, int x,
int intSize, int intType)
{
int i,j;
int intSizeNew = intSize/2;

if (GetQuadType(y,x,intSize)==intType) return (0);

for (i=0;i<2;i++)
for (j=0;j<2;j++)
{
szPathString [intPathLen] = 2*i + j;
intPathLen++;
if (GetQuadType(y+i*intSizeNew,x+j*intSizeNew,intSizeNew)==2)
CompressMatrix
(fout,y+i*intSizeNew,x+j*intSizeNew,intSizeNew,intType);
else if
(GetQuadType(y+i*intSizeNew,x+j*intSizeNew,intSizeNew)==intType)
{
int k, intRes = 0;
for (k=intPathLen-1;k>=0;k--) intRes +=
szPathString[k]*pow(4,intPathLen-1-k);
szCompressedData [intTotalBlocksCompressed] = (unsigned
char)intRes;
intTotalBlocksCompressed++;
if (fout!=0) fprintf(fout,"%c",(unsigned char)intRes);
}
intPathLen--;
szPathString [intPathLen] = 0;
}

return (0);
}

int CompressQuadFile (char* strIn, char* strOut)
{
int chIn;
FILE* fin = fopen (strIn,"rb");
FILE* fout = fopen (strOut,"wb");

while ((chIn=getc(fin))!=EOF)
{
char chAdd;
int i, j;
GrayScaleMatrix* mtx1 = new GrayScaleMatrix (chIn);

for (i=0;i<chIn;i++)
for (j=0;j<chIn/8;j++) mtx1->Matrix[i][j] = getc(fin);
mtx1->DisplayMatrix(stdout);

mtx1->CompressMatrix (0,1,1,chIn,1);
fprintf (fout,"%c",(unsigned
char)mtx1->intTotalBlocksCompressed);
mtx1->CompressMatrix (fout,1,1,chIn,1);
}

fclose (fin);
fclose (fout);
return (1);
}

int main (int argc, char** argv)
{

if (argc!=4)
{
printf ("Grayscale matrix compression demo\n");
printf ("Usage: %s [-c|-d] <in>
<out>\n",argv[0]);
printf ("Options: -c - compress existing file\n");
printf (" -d - decompress existing file\n");
printf ("Essemple gratia: %s -c file1.bin
file1.out\n\n",argv[0]);
}
else if (!strcmp(argv[1],"-c")) CompressQuadFile
(argv[2],argv[3]);
else if (!strcmp(argv[1],"-d"))
{
FILE* fin = fopen (argv[2],"rb");
GrayScaleMatrix* mtx1 = new GrayScaleMatrix(MAX_DIMENSION);
mtx1->DecompressMatrix (fin,1);
printf ("\nDecomposed raw of data:\n");
mtx1->DisplayMatrix (stdout);
fclose (fin);
return (0);
}
else return (1);

return (0);
}

I hope these simple tools will be helpful for every data-compression methods researcher.

I appreciate your every improvement or note on any related topic—huanito@ok.kz.

Downloads

Download demo project - 4 Kb



This article was originally published on February 28th, 2003

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