Max & Min value and refine histogram

This is a discussion on Max & Min value and refine histogram within the C Programming forums, part of the General Programming Boards category; Hi again . I need to write a program to calculate maximum , minimum , average pixel value for a ...

  1. #1
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    Talking Max & Min value and refine histogram

    Hi again . I need to write a program to calculate maximum , minimum , average pixel value for a image file ( 513 row X 513 columm , there are 263169 pixel ) . Besides , a histogram for the pixel distribution is needed to print . Below is my whole program .

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

    int histogram[256] , i , ch , max , min , sum ;
    FILE *fp;

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

    FILE *fp;

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

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

    {sum +=histogram[256];}

    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 as below :

    0: 2 * //0-255 is pixel value , 2*,100* is the frequency for that particular pixel value .//
    1: 100*
    3: 5*
    (0 until 255)
    255: 8*

    Total pixel value ===>1306
    Maximum value for the pixel ===>0
    Minimum value for the pixel ====>0
    Average =====>0

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

    1. How can I print histogram output like this (or similiar format ):

    *
    *...........*
    *...........*.....* .....................*
    *...........*.....*.....*...............*......... .* ..........................
    ( 202) (150) (98) . ( 48 ) ... ( 102 ) . ( 50) .. .( 10 ) .. ( 0 )
    -----------------------------------------------------------------------------------
    0-31 32-63 64-95 96-127 128-159 160-191 192--223 224-255

    where one * represent 50 repeatness . For example , there are 202 pixel value in the range of 0-31 and represented by **** .

    2. Besides , this program can't not show the correct total pixel value , max , min and average pixel value .
    For example , the correct total pixel value is 32895940 , but the program show 1306 . How to solve these problems ?

    3. Thank a lot to read this .

    Have a nice day :P

  2. #2
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    Exclamation Any solution ?

    I still try to get it work .......

  3. #3
    and the hat of wrongness Salem's Avatar
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    > int histogram[256] , i , ch , max , min , sum ;
    > FILE *fp;
    These global variables are redundant, since you also declare them inside main

    Well except for max and min, which you should also move to main as well

    Before you read the file, set the max and min values like so
    min = 256;
    max = 0;

    Then make your while loop like this
    Code:
    while ( (ch=fgetc(fp)) != EOF ) {
        histogram[ch]++;
        sum += ch;
        if ( ch > max ) max = ch;
        if ( ch < min ) min = ch;
    }
    > {sum +=histogram[256];}
    Remove this, it does nothing but pick up an illegal array element.

    > 1. How can I print histogram output like this (or similiar format ):
    Well rather than having an histogram of all values, create a histogram for ranges of values, which you would do like so

    histogram[ch/32]++;

    This would make histogram[0] the sum of all the pixel values in the range 0..31, histogram[1] the sum of all the pixel values in the range 32..63 etc

  4. #4
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    Talking Thank Salem !

    Thanks you Salem . You are very friendly and kindly . I try to put your solution into my program . Thank you . :P

  5. #5
    Registered User red_baron's Avatar
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    i made a program a little similar to that once for an assignment for school, its not very well coded but i was very new to programming at the time, basically its got a nice histogram (well at least i think so )
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