File input for histogram (programming)

Unregistered · 07-21-2002

Below is my program where I have been refine from some seniors ' advises from this board . I need to write a program to count the max ,min ,average and print the histogram for a image .(513row*513column ,263169pixel ).
However , when I check the result from the output is different from the given answer .

********************************************
#include <stdio.h>

int main ()

{
int histogram[256],i,ch,max,min,sum;
sum=0;max=0;min=256;

FILE *fp;
for ( i = 0 ; i < 256 ; i++ )
{histogram[i] = 0;}

fp = fopen( "a.img", "rb" ); /* input is image file */

while ( (ch=fgetc(fp)) != EOF )
{histogram[ch/32]++;}

fclose( fp );

for ( i = 0 ; i < 256 ; i++ )
{histogram[i] = 0;}

fp = fopen( "a.img", "rb" );

while ( (ch=fgetc(fp)) != EOF )
{ histogram[ch/32]++;
sum += ch;
if ( ch > max ) max = ch;
if ( ch < min ) min = ch; }
fclose( fp );

for ( i = 0 ; i < 256 ; i++ )
{printf( "%2d: %d * \n", i, histogram[2] );}

printf("\n\nTotal pixel values ===>%d" , sum);
printf("\n\nMaximum value of the pixel===>%d",max);
printf("\n\nMinimum value of the pixel===>%d",min);
printf("\n\nAverage====%d",sum/263169);
}
*******************************************

the output is like that .

0 :2*
1 :3*
2 :5* /* until 256 */
255:3*

Total pixel values =====>1782
Maximum value of the pixel===>255
Minimum value of the pixel===>0
Average====>0

=====================================

My problem :

1. The program can't count the frequency of pixel value correctly .
I think I should change my input file to other format . What format should I import or export from the image file (*.img) to ?

2. The result of sum and average value is uncorrected . Can I fix the problem by changing file input format or change some command in the program ?

3. Although I have put the command "histogram[ch/32]++;" , my output still show the frequency of each pixel value . How can I change to the form like this :

0-31 : 12
32-63 : 8
64-95 :88
/*utnil*/
223-255:15

4. How can I put the symbol * according to the repeatness ,like
0-31 : 12 ************
32-63 : 8 ******** and etc .

Thanks you for reading .

Unregistered · 07-22-2002

Still looking for solutions . Hope seniors can give some commands and advises . Thank you .

**Hammer** · 07-22-2002

>histogram[ch/32]++;
These are incorrect, I believe. If you are trying to count the occurences of each byte value within the file, do this instead:
>histogram[ch]++;

To determine the average value, you need to know the number of bytes in the file. You could do this various ways, here's one:

Code:

fp = fopen("a.img", "rb");
/* error check the fopen */
fseek( fp, 0L, SEEK_END );
size_of_file = ftell( fp );
fseek( fp, 0L, SEEK_SET );
/* perform loop using fgetc() */
......

printf("\n\nAverage====%d", sum / size_of_file);

I'd recommend using a long int for the sum variable, as a normal int might overflow.

Hope this helps....

And don't bump your threads!

Unregistered · 07-22-2002

Dear Hammer , below is my refined program according to you suggestion .

****************************************
#include <stdio.h>

int main ()
{
int histogram[256] , i , ch , max ,min ;
long int sum,size_of_file;
sum=0 ;
max=0;
min=256;

FILE *fp;

fp = fopen("subset2.img", "rb");
fseek( fp, 0L, SEEK_END );
size_of_file = ftell( fp );
fseek( fp, 0L, SEEK_SET );
fclose(fp);

for ( i = 0 ; i < 256 ; i++ )
{histogram[i] = 0;}
fp = fopen( "a.img", "rb" );
while ( (ch=fgetc(fp)) != EOF )
{histogram[ch]++;}
fclose( fp );

for ( i = 0 ; i < 256 ; i++ )
{histogram[i] = 0;}
fp = fopen( "a.img", "rb" );
while ( (ch=fgetc(fp)) != EOF ) {
histogram[ch]++;
sum += ch;
if ( ch > max ) max = ch;
if ( ch < min ) min = ch;
}

fclose( fp );

for ( i = 0 ; i < 256 ; i++ )
{printf( "%2d: %d * \n", i, histogram[i] , histogram[i] );}

printf("\n\nTotal pixel values ===>%d" , sum);
printf("\n\nMaximum value of the pixel===>%d",max);
printf("\n\nMinimum value of the pixel===>%d",min);
printf("\n\nAverage====%d", sum/size_of_file);

}

***************************************

problems :

1. My program still didn't show a oputput correctly . For example , there are not pixel value is 0 , but it show there are some frequency for that particular pixel value . And plus , this influence my max and min answer . All the value in output is uncorrect . Show I export my image input to other format ? What format is it ?

2. How can I show the frequency in the range of 0-31 , 32-63 and etc .

3. How can I use symbol * to represent the repeatness of the particular pixel value ?

Thank again .

**Hammer** · 07-22-2002

Here, have a look at this version, and see if it does what you want.

Code:

#include <stdio.h>

int main(void)
{
    int         histogram[256], i, ch, max, min, tempsum;
    long int    size_of_file, sum;
    FILE        *fp;
    sum = 0;
    max = -1;
    min = 257;

    for (i = 0; i < 256; i++)
    {
        histogram[i] = 0;
    }

    fp = fopen("a.img", "rb");

    if (fp == NULL)
    {
        perror("a.img");
        return 1;
    }

    fseek(fp, 0L, SEEK_END);
    size_of_file = ftell(fp);
    fseek(fp, 0L, SEEK_SET);

    if (size_of_file == 0)
    {
        printf("Empty file\n");
        fclose(fp);
        return 1;
    }

    while ((ch = fgetc(fp)) != EOF)
    {
        histogram[ch]++;
        sum += ch;
        if (ch > max) max = ch;
        if (ch < min) min = ch;
    }

    fclose(fp);

    for (i = 0, tempsum = 0; i < 256; i++)
    {
        tempsum += histogram[i];
        if ((i + 1) % 32 == 0)
        {
            int j;
            printf("%03d:%03d %5d ", i - 31, i, tempsum);
            for (j = 0; j < tempsum; j++) putchar('*');
            putchar('\n');
            tempsum = 0;
        }
    }

    printf("\n\nTotal pixel values ===>%d", sum);
    printf("\n\nMaximum value of the pixel===>%d", max);
    printf("\n\nMinimum value of the pixel===>%d", min);
    printf("\n\nAverage====%d", sum / size_of_file);

    return 0;
}

Unregistered · 07-22-2002

Thank you for your advise . I will try at home later . Now I'm in campus . Have a nice day .

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File input for histogram (programming)

Anybody can give advises ?

file input problem ?

Thank Hammer .

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