C Display PPM image as Text [duplicate] - c

Question

This question already has answers here:
read PPM file and store it in an array; coded with C
(2 answers)
Closed 6 years ago.
I am new to programming C and i am experimenting with file manipulation, i am trying to output a PPM file with its comments and rgb data values like so:
P3
# The same image with width 3 and height 2,
# using 0 or 1 per color (red, green, blue)
3 2 1
1 0 0 0 1 0 0 0 1
1 1 0 1 1 1 0 0 0
In this program i have been able to check that it has the correct format and read in to a struct but where i am stuck is how to collect the rgb data and then printing it out. Here is what i have so far. The method to display this information is the showPPM struct which i have started but do not know how to read the image struct and collect its rgb values and display it, any help would be great.
#include<stdio.h>
#include<stdlib.h>
typedef struct {
unsigned char red,green,blue;
} PPMPixel;
typedef struct {
int x, y;
PPMPixel *data;
} PPMImage;
static PPMImage *readPPM(const char *filename)
{
char buff[16];
PPMImage *img;
FILE *fp;
int c, rgb_comp_color;
//open PPM file for reading
fp = fopen(filename, "rb");
if (!fp) {
fprintf(stderr, "Unable to open file '%s'\n", filename);
exit(1);
}
//read image format
if (!fgets(buff, sizeof(buff), fp)) {
perror(filename);
exit(1);
}
//check the image format
if (buff[0] != 'P' || buff[1] != '3') {
fprintf(stderr, "Invalid image format (must be 'P6')\n");
exit(1);
}
//alloc memory form image
img = (PPMImage *)malloc(sizeof(PPMImage));
if (!img) {
fprintf(stderr, "Unable to allocate memory\n");
exit(1);
}
//check for comments
c = getc(fp);
while (c == '#') {
while (getc(fp) != '\n') ;
c = getc(fp);
}
ungetc(c, fp);
//read image size information
if (fscanf(fp, "%d %d", &img->x, &img->y) != 2) {
fprintf(stderr, "Invalid image size (error loading '%s')\n", filename);
exit(1);
}
while (fgetc(fp) != '\n') ;
//memory allocation for pixel data
img->data = (PPMPixel*)malloc(img->x * img->y * sizeof(PPMPixel));
if (!img) {
fprintf(stderr, "Unable to allocate memory\n");
exit(1);
}
//read pixel data from file
if (fread(img->data, 3 * img->x, img->y, fp) != img->y) {
fprintf(stderr, "Error loading image '%s'\n", filename);
exit(1);
}
fclose(fp);
return img;
}
void showPPM(struct * image){
int rgb_array[600][400];
int i;
int j;
for(i = 0; i<600; i++)
{
for(j = 0; j<400; j++)
{
printf("%d", rgb_array[i][j]);
}
}
}
int main(){
PPMImage *image;
image = readPPM("aab.ppm");
showPPM(image);
}

Answer 1

Your code looks suspiciously like:
read PPM file and store it in an array; coded with C
There were some really good comments and help on that as well.
So, I leave the other stuff below as further help:
Starting off somewhat vague here, to let you have chance to work through it yourself...
First, you need to read in the entire ppm file into a buffer. fread() is probably the function of choice for this. You can use ftell() to get the size of the file. Next, you can typecast your PPMImage structure on top of the buffer used by fread(), and from there, you should be able to access the data via the data field, maybe even using array notation if you wished. (I think this is the step you are missing right now...)
Once you can access the data, you should be able to iterate over the data and printf() or whatever you need to the console based on the input data.