I have to write a program where I take user input for a PPM image and then mirror the image from left to right (basically flipping it over the y-axis). So if the image was <, the new image would now be >. This should not be a 180 degree rotation, as that would make the image upside down. It should still be the same, just reflected.
I have the code here that I used to input and output the PPM, but I don't know how to mirror it. I made a function that would theoretically be used for the mirror code, but I'm not sure if that's the best way to do it either. If you know a better place to put the code, be my guest.
I have researched this topic quite a bit, but was only able to find issues where people needed to rotate the image.
Here is what I have so far:
#include<stdio.h>
#include<stdlib.h> //for fopen()
typedef struct {
unsigned char red,green,blue;
} pixel_t; //struct for pixels
typedef struct {
int x, y;
pixel_t *data;
} PPMImage; //struct for creating the image
#define RGB_COMPONENT_COLOR 255
static PPMImage *readPPM(const char *filename)
{
char buff[16];
PPMImage *img;
FILE *fp;
int c, rgb_comp_color;
fp = fopen(filename, "rb");
if (!fp) {
fprintf(stderr, "Unable to open file '%s'\n", filename);
exit(1);} //opens the ppm and checks to make sure it can be opened
if (!fgets(buff, sizeof(buff), fp)) {
perror(filename);
exit(1);} //read the format of the image
if (buff[0] != 'P' || buff[1] != '6') {
fprintf(stderr, "Invalid image format (must be 'P6')\n");
exit(1);} //checks to see if the format is ppm
img = (PPMImage *)malloc(sizeof(PPMImage));
if (!img) {
fprintf(stderr, "Unable to allocate memory\n");
exit(1);} //allocates the memory needed to form the input image
c = getc(fp);
while (c == '#') {
while (getc(fp) != '\n') ;
c = getc(fp);
}//checks for comments
ungetc(c, fp);
if (fscanf(fp, "%d %d", &img->x, &img->y) != 2) {
fprintf(stderr, "Invalid image size (error loading '%s')\n", filename);
exit(1);} //reads the size of the image, height becomes img->y, and width becomes img->x
if (fscanf(fp, "%d", &rgb_comp_color) != 1) {
fprintf(stderr, "Invalid rgb component (error loading '%s')\n", filename);
exit(1);} //reads how much of each color there is
if (rgb_comp_color!= RGB_COMPONENT_COLOR) {
fprintf(stderr, "'%s' does not have 8-bits components\n", filename);
exit(1);} //makes sure the the component is 8 bits
while (fgetc(fp) != '\n') ;
img->data = (pixel_t*)malloc(img->x * img->y * sizeof(pixel_t));
if (!img) {
fprintf(stderr, "Unable to allocate memory\n");
exit(1);} //allocates the memory need for the pixel data
if (fread(img->data, 3 * img->x, img->y, fp) != img->y) {
fprintf(stderr, "Error loading image '%s'\n", filename);
exit(1);} //reads the pixel data
fclose(fp);
return img;
}
void writePPM(const char *filename, PPMImage *img)
{
FILE *fp;
fp = fopen(filename, "wb");
if (!fp) {
fprintf(stderr, "Unable to open file '%s'\n", filename);
exit(1);} //opens the file for output
//write the header file
//image format
fprintf(fp, "P6\n");
//image size
fprintf(fp, "%d %d\n",img->x,img->y);
// rgb component depth
fprintf(fp, "%d\n",RGB_COMPONENT_COLOR);
// pixel data
fwrite(img->data, 3 * img->x, img->y, fp);
fclose(fp);
}
void mirror(PPMImage *img)
{
//this is where I want to insert the code for mirroring the image
}
int main(int argc, char* argv[]){ //takes command line parameters
PPMImage *image;
char* filename = argv[1];
image = readPPM(filename);
mirror(image);
writePPM("OutputFile.ppm",image); //creates the output file
printf("Press Enter");
getchar();
}