Median of a 2d matrix

Hey,

I m doing a image processing project. I need to find the median in a 2d matrix.

What is the another way, instead of saving elements in 1d array, sort and then find median.

Quote:

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What is the another way, instead of saving elements in 1d array, sort and then find median.

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Why not just sort the 2d array, then find the median?


Jim

I think complexity can be reduced in that way..

The only optimisation Wikipedia mentions is the use of a selection sort, but only until the median value is found.

Since this is for an image processing project,
Are you referring to a median filter?

Median filter - Wikipedia, the free encyclopedia

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Yes, I am referring median filter

hey I am getting below error in my code.I am really fail to overcome this.
median22: malloc.c:2451: sYSMALLOc: Assertion `(old_top == (((mbinptr) (((char *) &((av)->bins[((1) - 1) * 2])) - __builtin_offsetof (struct malloc_chunk, fd)))) && old_size == 0) || ((unsigned long) (old_size) >= (unsigned long)((((__builtin_offsetof (struct malloc_chunk, fd_nextsize))+((2 * (sizeof(size_t))) - 1)) & ~((2 * (sizeof(size_t))) - 1))) && ((old_top)->size & 0x1) && ((unsigned long)old_end & pagemask) == 0)' failed.
Aborted (core dumped)


My code is:

#include <stdio.h>
#include <stdlib.h>
#define SIZE 50

typedef struct PGM
{
char name[100];
int width;
int height;
int max_value;
int **matrix;
} PGM;

int ** create_matrix(int height, int width)
{

int **matrix = malloc(height*sizeof(int*)) ;

if (matrix)
{
int i;
for (i = 0; i < height; i++)
{
matrix[i] =malloc(width * sizeof (int)) ;
}
}
return matrix;
}


//void display(PGM *p) {
// printf("displaying p matrix");
// printf("name %s\n", p->name);
// printf("height %d width %d max_value %d\n", p->height, p->width, p->max_value);
// int i,j;
// for (i = 0; i < p->height; i++) {
// for (j = 0; j < p->width; j++) {
// printf("%2d ", p->matrix[i][j]);
// }
// printf("\n");
// }
// }


void skip_comments(FILE* fp, char* line, int size)
{
do{
fgets(line, size, fp);
if (line[0] != '#')
{
return ;
}
} while(line!= NULL);
}

PGM* f2p(char *file_name) {

FILE * fp;
char c;
char name[100];
char line[SIZE];
int height, width, max_value;

fp = fopen(file_name, "r");

if (fp == NULL)
return NULL;

PGM *p = malloc(sizeof(PGM));


skip_comments(fp, line, SIZE);
sscanf(line, "%s", p->name);

skip_comments(fp, line, SIZE);
sscanf(line, "%d %d", &width, &height);

skip_comments(fp, line, SIZE);
sscanf(line, "%d", &max_value);

int **matrix = malloc(height*sizeof(int*)) ;
if (matrix){
int i,j;
for (i = 0; i < height; i++) {

matrix[i] = malloc(width * sizeof (int)) ;
for (j = 0; j < width; j++) {

c = fscanf(fp, "%d", &matrix[i][j]);
}
}

p->matrix = matrix;
p->height = height;
p->width = width;
p->max_value = max_value;
return p;
}

fclose(fp);
return NULL;
}

void p2f(PGM* p, char *file_name) {
FILE* fp = fopen(file_name, "w");
fprintf(fp, "%s\n", p->name);
fprintf(fp, "%d %d\n%d\n", p->width, p->height, p->max_value);
int i,j;
for (i = 0; i < p->height; i++)
{
for (j = 0; j < p->width; j++)
{
fprintf(fp, "%d ", p->matrix[i][j]);
}
fprintf(fp,"\n");
}
fclose(fp);
}

int sort(int *a,int filt)
{
int i,j,t;
for (i = 1 ; i <= filt; i++)
{
for (j = 1 ; j <= filt ; j++)
{
if (a[j] <= a[j+1])
{
t = a[j];
a[j] = a[j+1];
a[j+1] = t;
}
else continue ;
}
}
return a[(filt+1)/2];
}


void apply_median_filter(int** source, int** dest, int height, int width,int k,int filt) {
int i,j,m,l,median;
for (i = k; i < height; i++){
for (j = k; j < width ; j++){
int c=0;
int *temp=(int*)malloc(filt*filt*sizeof(int));
for(m=0;m<filt;m++){

for(l=0;l<filt;l++)
temp[c++]=source[i-k+m][j-k+l];
}

median=sort(temp,filt*filt);
dest[i-k][j-k]=median;
}
}

}



void apply_padding(PGM* p,int n)
{
int k;
k=n/2;
int new_height = p->height + k;
int new_width = p->width + k;


int **matrix = create_matrix(new_height, new_width);


if (matrix){
int i,j;


for (i = 0; i < new_height; i++){
for (j = 0; j < new_width; j++){

if((i<k) || (j<k) || i>(p->height) || j>(p->width))

matrix[i][j] = 0;
}
}


for (i = k; i < new_height-k; i++){
for (j = k; j < new_width-k; j++) {
matrix[i][j] = p->matrix[i-k][j-k];
}
}

apply_median_filter(matrix, p->matrix, p->height, p->width,k,n);


}
}
int main()
{
char file_name[50];
int n;
printf("Enter the file name you want to open\n");
scanf("%s",file_name);
PGM *p = f2p(file_name);

printf("Enter any odd number for the mask-size which you want to apply\n");
scanf("%d",&n);

apply_padding(p,n);
//display(p);

char file_name1[] = "output.pgm";
p2f(p, file_name1);
}

Argh! My eyes are bleeding!

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