exercise14.c

// C Primer Plus
// Chapter 13 Exercise 14:

// Digital images, particularly those radioed back from spacecraft, may have
// glitches. Add a de-glitching function to programming exercise 12. It should
// compare each value to its immediate neighbors to the left and right, above
// and below. If the value differs by more than 1 from each of its neighbors,
// replace the value with the average of the neighboring values. You should
// round the average to the nearest integer value. Note that the points along
// the boundaries have fewer than four neighbors, so they require special
// handling.

// Note: use data.txt as input file to test this program.

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

#define ROWS 20
#define COLS 30

void deglitch(int data[ROWS][COLS]);

int main(int argc, char *argv[])
{
	FILE *fp;
	int data[ROWS][COLS];
	char img[ROWS][COLS + 1];
	char ch;

	if (argc != 3)
	{
		printf("Usage: %s <data file> <image file>\n", argv[0]);
		exit(EXIT_FAILURE);
	}

	// open data file
	if ((fp = fopen(argv[1], "r")) == NULL)
	{
		fprintf(stderr, "Could not open file %s.\n", argv[1]);
		exit(EXIT_FAILURE);
	}

	// read ints from file
	for (int i = 0; i < ROWS; i++)
		for (int j = 0; j < COLS; j++)
			if (fscanf(fp, "%d", *(data + i) + j) != 1)
			{
				fprintf(stderr, "Invalid or corrupted data file.\n");
				exit(EXIT_FAILURE);
			}
	fclose(fp); // done with fp for now

	// de-glitch the data
	deglitch(data);

	// convert ints to characters
	for (int i = 0; i < ROWS; i++)
	{	
		int j;
		for (j = 0; j < COLS; j++)
		{
			switch (data[i][j])
			{
				case(0):
					ch = ' ';
					break;
				case(1):
					ch = '.';
					break;
				case(2):
					ch = '\'';
					break;
				case(3):
					ch = ':';
					break;
				case(4):
					ch = '~';
					break;
				case(5):
					ch = '*';
					break;
				case(6):
					ch = '=';
					break;
				case(7):
					ch = '}';
					break;
				case(8):
					ch = '&';
					break;
				case(9):
					ch = '#';
					break;
				default:
					fprintf(stderr, "Error: int out of bounds.\n");
					exit(EXIT_FAILURE);
			}
			img[i][j] = ch;
		}
		img[i][j] = '\0'; // j = COLS here
	}

	// open image file
	if ((fp = fopen(argv[2], "w")) == NULL)
	{
		fprintf(stderr, "Could not open file %s.\n", argv[2]);
		exit(EXIT_FAILURE);
	}

	for (int i = 0; i < ROWS; i++)
	{
		// print to console and file
		puts(img[i]);
		fprintf(fp, "%s\n", img[i]);
	}
	fclose(fp);

	return 0;
}

void deglitch(int data[ROWS][COLS])
{
	float total;
	int count;

	for (int i = 0; i < ROWS; i++)
		for (int j = 0; j < COLS; j++)
		{
			total = 0;
			count = 0;
			if (i + 1 < ROWS)
			{
				if (abs(data[i][j] - data[i + 1][j]) < 2)
					continue;

				total += data[i + 1][j];
				count++;
			}
			if (j + 1 < COLS)
			{
				if (abs(data[i][j] - data[i][j + 1]) < 2)
					continue;
				
				total += data[i][j + 1];
				count++;
			}
			if (i > 0)
			{
				if (abs(data[i][j] - data[i - 1][j]) < 2)
					continue;
				
				total += data[i - 1][j];
				count++;
			}
			if (j > 0)
			{
				if (abs(data[i][j] - data[i][j - 1]) < 2)
					continue;
				
				total += data[i][j - 1];
				count++;
			}
			
			// if none of the continue statements have been triggered,
			// replace data[i][j] with the rounded average of its neighbors
			data[i][j] = (int) rintf(total / count);
		}
}