I've been given an assignment where we have to carry out some kind of image compression. What kind of compression is up to us but I will hopefully be using a mixture of huffman coding, arithmetic coding, run-length coding, quad trees, quantization and transform coding, just because they are the one's we have discussed in lectures.
To help he has given us test images (.ppm format) together with some source code that can save and load the images. Here is the code:
Header:
Source:
Now I havn't done any kind of compression before but I would have thought the main area we alter is how the images are saved and loaded?
However, he STRONGLY recommends that we use the code he's provided. This just writes integers between 0-255 to the file doesn't it? Surely we need to work at a lower level than this? Or am I mistaken?
Thanks.
To help he has given us test images (.ppm format) together with some source code that can save and load the images. Here is the code:
Header:
Code:
#include <stdio.h>
#include <string.h>
#define RED 0
#define GREEN 1
#define BLUE 2
class _ppm{
public:
_ppm();
~_ppm();
int load_ppm(const char* filename, int xx = 0, int yy = 0);
int save_ppm(const char* filename);
int get_image_height(){return height;};
int get_image_width(){return width;};
int get_image_depth(){return depth;};
int get_pixel(int x, int y, int channel);
int set_pixel(int x, int y, int channel, int value);
protected:
void clear();
int* data;
int width,height,depth;
private:
bool loaded;
};Source:
Code:
#include "PPM.h"
#include <iomanip>
_ppm::_ppm()
{
loaded = false;
}
_ppm::~_ppm()
{
if(loaded)
clear();
}
/* save_ppm - Saves the image as PPM format to the file stream.
* Arguments: filename to save into, x1, y1 to x2, y2 area to save.
* Returns: 0 on success, -1 on error
*/
int _ppm::save_ppm(const char* filename)
{
if(!loaded)
return -1;
FILE * fi;
int x, y, rgb;
int x1 = 0;
int y1 = 0;
int x2 = width;
int y2 = height;
if((fi = fopen(filename,"w+b"))==0)
return -2;
if (x1 < 0 || x1 > width || y1 < 0 || y1 > height ||
x2 < 0 || x2 > width || y2 < 0 || y2 > height)
return -1;
/* Dump PPM header: */
fprintf(fi, "P6\n %d %d\n%d\n", x2 - x1, y2 - y1, depth);
/* Dump data: */
for (y = y1; y < y2; y++)
for (x = x1; x < x2; x++)
for (rgb = 0; rgb < 3; rgb++)
fputc(data[((y*width+x)*3)+rgb], fi);
return 0;
}
/* load_ppm - Loads a PPM format image.
* Arguments: filename to load from,x and y locations to start
* loading into, and opacity with which to add the data to the
* existing image (default is 255 - full opacity).
* Returns: 0 on success, -1 on error
*/
int _ppm::load_ppm(const char* filename, int xx, int yy)
{
if(loaded)
clear();
FILE * fi;
char temp[10240];
int x, y, rgb, m;
if((fi=fopen(filename,"rb"))==0)
return -1;
/* Load PPM header: */
fscanf(fi, "%s %d %d %d", &temp, &width, &height, &m);
depth = m;
/* Create storage array for data */
data = new int[(width*height)*3];
/* Get some data from the ppm */
fgetc(fi);
/* Load real data: */
for (y = 0; y < height; y++)
{
for (x = 0; x < width; x++)
{
for (rgb = 0; rgb < 3; rgb++)
{
data[((y*width+x)*3)+rgb] = fgetc(fi);
}
}
}
loaded = true;
return 1;
}
int _ppm::set_pixel(int x, int y, int channel, int value)
{
if(!loaded)
return -1;
if (x < 0 || x > width || y < 0 || y > height)
return -1;
if(channel > 2 || channel < 0)
return -1;
if(value < 0 || value > 255)
return -1;
data[(((y*width)+x)*3)+channel] = value;
return 0;
}
int _ppm::get_pixel(int x, int y, int channel)
{
if(!loaded)
return -1;
if (x < 0 || x > width || y < 0 || y > height)
return -1;
return data[(((y*width)+x)*3)+channel];
}
void _ppm::clear()
{
delete[] data;
height = 0;
width = 0;
depth = 0;
loaded = false;
}Now I havn't done any kind of compression before but I would have thought the main area we alter is how the images are saved and loaded?
However, he STRONGLY recommends that we use the code he's provided. This just writes integers between 0-255 to the file doesn't it? Surely we need to work at a lower level than this? Or am I mistaken?
Thanks.
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