Thread: Reading a PPM image into an array so it can be stored, accessed and manipulated

I'm trying to use malloc so that a PPM can be read into an array and then for that array to be saved into a file using a switch case statement. So far nothing really seems to happen. Any help is much appreciated. Thanks.

Code:

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


#define height 1080
#define width 1920
#define RGB_COMPONENT_COLOUR 255


typedef struct
{
    unsigned char red, green, blue;
} PPMPixel;


typedef struct
{
    int x, y;
    PPMPixel *data;
} PPMImage;


void clear_to_end(FILE *fp)
{
    int c;
    while ((c = fgetc(fp)) != EOF && c != '\n');
}


PPMImage* load_file()
{
    FILE *fp;
    PPMImage *img = malloc(sizeof(*img));
    int d, rgb_comp_colour;
    char buff[80];
    char fname[100];
    printf("Enter file name: ");
    scanf("%s", fname);
    fseek(stdin,0,SEEK_END);
    fp = fopen(fname, "r");
    if (fp == NULL)
    {   
        printf("\tError while opening the file\n");
        return NULL;
    }                        
    else    
    {
        printf("\tReading in %s\n", fname);
    }


    //Checking for comments
    //Skip whitespace and comments
    d = getc(fp);
    while (d=='#')
    {
        while(getc(fp)!='\n')
        d=getc(fp);
    }
    ungetc(d,fp);


    //Checking header
    if (!fgets(buff,sizeof(buff),fp))
    {
        perror(fname);
        exit(1);
    }


    if (buff[0] =='P' && (buff[1] == '2' || buff[1] == '3'))
    {
        printf("\tReading PGM/PPM image in...\n");
    }
    else
    {
        printf("\tIncorrect image format\n");
        return NULL;
    }


    //Read image size information
    if (fscanf(fp, "%u %u", &img->y, &img->x) !=2)
    {
        printf("\tInvalid image size\n");
        printf("\tImage size is: %u x %u\n", img->y, img->x);
    }
    else
    {
        printf("\tImage size is valid\n");
        printf("\tImage size is: %u x %u\n", img->y, img->x);
    }


    if (fscanf(fp, "%d", &rgb_comp_colour) !=1)
    {
        printf("Invalid RGB component for %s\n", fname);
    }
    else
    {
        printf("\tRGB component is valid\n");
        printf("%d", rgb_comp_colour);
    }
    fscanf(fp, "%c ", &d);


    //Check RGB component depth
    if (rgb_comp_colour!=RGB_COMPONENT_COLOUR)
    {
        printf("\t'%s' is not 8 bit\n", fname);
    }
    else
    {
    printf("\t'%s' is 8 bit\n", fname);
    }
    int i, j;
    int array[i][j];
    **array = malloc (width*height*sizeof(array[i][j]));
    for (i=0; i<width; i++)
    {
        *array[i] = malloc(width * sizeof(int));
        for(j=0; j<height; j++)
        {
            fseek(fp, 0, SEEK_SET);
            fscanf(fp, "%d ", &array[i][j]);
        }  
    }


    for (i=0; i<width; i++)
    {
        for(j=0; j<height; j++)
        {
            printf("%d ", array[i][j]);
        }
        printf("\n");
    }
    fclose(fp);
    return img;
}




void save_file(PPMImage *img)
{
    //Save PPM Array Into New PPM File
}




int main()
{
    char key = 0;
    PPMImage* img = NULL;
    do {
        puts("\tPress r to read in an image in ppm format");
        puts("\tPress s to save image in ppm format");
        puts("\tPress q to quit");
        
        scanf(" %c", &key);
        clear_to_end(stdin);
        switch (key) {
            case 'r':
            {
                PPMImage *img = load_file("fname");
                free(img);
            }
                break;
            case 's':
            {
                save_file(img);
            }
                break;
            case 'q':
            {
                puts("\tTerminating program...");
            }
                break;
            default:
            {
                puts("\tInvalid Input");
            }
                break;
        }
    } while (key != 'q');
    return 0;
}

Originally Posted by Salem

Code:

    int i, j;
    int array[i][j];
    **array = malloc (width*height*sizeof(array[i][j]));

This makes no sense.
i and j are uninitialised values, then you go and make an array out of them.

What you should be allocating is
img->data = malloc(width*height*sizeof(*img->data));


But as your pixel array is a 1D thing, not a 2D thing, you need to manually flatten the image.

Code:

int p = 0;
    for (i=0; i<width; i++)
    {
        for(j=0; j<height; j++)
        {
            int r,g,b;
            fscanf(fp, "%d %d %d", &r, &g, &b);
            img->data[p].red = r;
            img->data[p].green = g;
            img->data[p].blue = b;
            p++;
        }  
    }

Thanks again for the tips! The only issue is none of the array code can be seen in the terminal when I run the code, even my error checking (though this may be a problem with my software rather than the code itself). I am also wondering why omit array[i] malloc, what is p used for, and can this be made to work for greyscale (PGMs) as well?