Cs50 pset4 edges - c

Question

Here is the check50 output:
:) edges correctly filters middle pixel
:( edges correctly filters pixel on edge expected "213 228 255\n", not "213 228 140\n"
:( edges correctly filters pixel in corner expected "76 117 255\n", not "76 117 66\n"
:( edges correctly filters 3x3 image expected "76 117 255\n21...", not "76 117 66\n213..."
:( edges correctly filters 4x4 image expected "76 117 255\n21...", not "76 117 66
Helpers.c (My problem is here, the rest of the code was provided by cs50, I include to to make a minimal reproducible example, and just in case you want to check any of the structs)
void edges(int height, int width, RGBTRIPLE image[height][width])
{
int sobel[3][3] =
{
{-1, 0, 1},
{-2, 0, 2},
{-1, 0, 1}
};
RGBTRIPLE edged[height][width];
for (int i = 0; i<height; i++){
for (int j = 0; j<width; j++){
double GxRed = 0 , GxGreen = 0 , GxBlue = 0 , GyRed = 0 , GyGreen = 0 , GyBlue = 0;
int boxRow[3][3] = {{i-1, i-1, i-1}, {i, i, i}, {i+1, i+1, i+1}}, boxCol[3][3] = {{j-1, j, j+1}, {j-1, j, j+1}, {j-1, j, j+1}};
for (int x = 0; x<3; x++){
for (int y = 0; y<3; y++){
if (boxRow[x][y] >= 0 && boxRow[x][y] < height && boxCol[x][y] >= 0 && boxCol[x][y] < width){
GxRed += image[boxRow[x][y]][boxCol[x][y]].rgbtRed * sobel[x][y];
GxGreen += image[boxRow[x][y]][boxCol[x][y]].rgbtGreen * sobel[x][y];
GxBlue += image[boxRow[x][y]][boxCol[x][y]].rgbtBlue * sobel[x][y];
GyRed += image[boxRow[x][y]][boxCol[x][y]].rgbtRed * sobel[y][x];
GyGreen += image[boxRow[x][y]][boxCol[x][y]].rgbtGreen * sobel[y][x];
GyBlue += image[boxRow[x][y]][boxCol[x][y]].rgbtBlue * sobel[y][x];
}
}
}
edged[i][j].rgbtRed = round(sqrt(pow(GxRed, 2) + pow(GyRed, 2)));
if (edged[i][j].rgbtRed > 255) {edged[i][j].rgbtRed = 255;}
if (edged[i][j].rgbtRed < 0) {edged[i][j].rgbtRed = 0;}
edged[i][j].rgbtGreen = round(sqrt(pow(GxGreen, 2) + pow(GyGreen, 2)));
if (edged[i][j].rgbtGreen > 255) {edged[i][j].rgbtGreen = 255;}
if (edged[i][j].rgbtGreen < 0) {edged[i][j].rgbtGreen = 0;}
edged[i][j].rgbtBlue = round(sqrt(pow(GxBlue, 2) + pow(GyBlue, 2)));
if (edged[i][j].rgbtBlue > 255) {edged[i][j].rgbtBlue = 255;}
if (edged[i][j].rgbtBlue < 0) {edged[i][j].rgbtBlue = 0;}
}
}
for (int i = 0; i<height; i++){
for (int j = 0; j<width; j++){
image[i][j] = edged[i][j];
}
}
return;
}
This is helpers.h
// Convert image to grayscale
void grayscale(int height, int width, RGBTRIPLE image[height][width]);
// Reflect image horizontally
void reflect(int height, int width, RGBTRIPLE image[height][width]);
// Detect edges
void edges(int height, int width, RGBTRIPLE image[height][width]);
// Blur image
void blur(int height, int width, RGBTRIPLE image[height][width]);
This is bmp.h
#include <stdint.h>
/**
* Common Data Types
*
* The data types in this section are essentially aliases for C/C++
* primitive data types.
*
* Adapted from http://msdn.microsoft.com/en-us/library/cc230309.aspx.
* See http://en.wikipedia.org/wiki/Stdint.h for more on stdint.h.
*/
typedef uint8_t BYTE;
typedef uint32_t DWORD;
typedef int32_t LONG;
typedef uint16_t WORD;
/**
* BITMAPFILEHEADER
*
* The BITMAPFILEHEADER structure contains information about the type, size,
* and layout of a file that contains a DIB [device-independent bitmap].
*
* Adapted from http://msdn.microsoft.com/en-us/library/dd183374(VS.85).aspx.
*/
typedef struct
{
WORD bfType;
DWORD bfSize;
WORD bfReserved1;
WORD bfReserved2;
DWORD bfOffBits;
} __attribute__((__packed__))
BITMAPFILEHEADER;
/**
* BITMAPINFOHEADER
*
* The BITMAPINFOHEADER structure contains information about the
* dimensions and color format of a DIB [device-independent bitmap].
*
* Adapted from http://msdn.microsoft.com/en-us/library/dd183376(VS.85).aspx.
*/
typedef struct
{
DWORD biSize;
LONG biWidth;
LONG biHeight;
WORD biPlanes;
WORD biBitCount;
DWORD biCompression;
DWORD biSizeImage;
LONG biXPelsPerMeter;
LONG biYPelsPerMeter;
DWORD biClrUsed;
DWORD biClrImportant;
} __attribute__((__packed__))
BITMAPINFOHEADER;
/**
* RGBTRIPLE
*
* This structure describes a color consisting of relative intensities of
* red, green, and blue.
*
* Adapted from http://msdn.microsoft.com/en-us/library/aa922590.aspx.
*/
typedef struct
{
BYTE rgbtBlue;
BYTE rgbtGreen;
BYTE rgbtRed;
} __attribute__((__packed__))
RGBTRIPLE;
This is filter.c
#include <stdio.h>
#include <stdlib.h>
#include "helpers.h"
int main(int argc, char *argv[])
{
// Define allowable filters
char *filters = "begr";
// Get filter flag and check validity
char filter = getopt(argc, argv, filters);
if (filter == '?')
{
printf("Invalid filter.\n");
return 1;
}
// Ensure only one filter
if (getopt(argc, argv, filters) != -1)
{
printf("Only one filter allowed.\n");
return 2;
}
// Ensure proper usage
if (argc != optind + 2)
{
printf("Usage: ./filter [flag] infile outfile\n");
return 3;
}
// Remember filenames
char *infile = argv[optind];
char *outfile = argv[optind + 1];
// Open input file
FILE *inptr = fopen(infile, "r");
if (inptr == NULL)
{
printf("Could not open %s.\n", infile);
return 4;
}
// Open output file
FILE *outptr = fopen(outfile, "w");
if (outptr == NULL)
{
fclose(inptr);
printf("Could not create %s.\n", outfile);
return 5;
}
// Read infile's BITMAPFILEHEADER
BITMAPFILEHEADER bf;
fread(&bf, sizeof(BITMAPFILEHEADER), 1, inptr);
// Read infile's BITMAPINFOHEADER
BITMAPINFOHEADER bi;
fread(&bi, sizeof(BITMAPINFOHEADER), 1, inptr);
// Ensure infile is (likely) a 24-bit uncompressed BMP 4.0
if (bf.bfType != 0x4d42 || bf.bfOffBits != 54 || bi.biSize != 40 ||
bi.biBitCount != 24 || bi.biCompression != 0)
{
fclose(outptr);
fclose(inptr);
printf("Unsupported file format.\n");
return 6;
}
// Get image's dimensions
int height = abs(bi.biHeight);
int width = bi.biWidth;
// Allocate memory for image
RGBTRIPLE(*image)[width] = calloc(height, width * sizeof(RGBTRIPLE));
if (image == NULL)
{
printf("Not enough memory to store image.\n");
fclose(outptr);
fclose(inptr);
return 7;
}
// Determine padding for scanlines
int padding = (4 - (width * sizeof(RGBTRIPLE)) % 4) % 4;
// Iterate over infile's scanlines
for (int i = 0; i < height; i++)
{
// Read row into pixel array
fread(image[i], sizeof(RGBTRIPLE), width, inptr);
// Skip over padding
fseek(inptr, padding, SEEK_CUR);
}
// Filter image
switch (filter)
{
// Blur
case 'b':
blur(height, width, image);
break;
// Edges
case 'e':
edges(height, width, image);
break;
// Grayscale
case 'g':
grayscale(height, width, image);
break;
// Reflect
case 'r':
reflect(height, width, image);
break;
}
// Write outfile's BITMAPFILEHEADER
fwrite(&bf, sizeof(BITMAPFILEHEADER), 1, outptr);
// Write outfile's BITMAPINFOHEADER
fwrite(&bi, sizeof(BITMAPINFOHEADER), 1, outptr);
// Write new pixels to outfile
for (int i = 0; i < height; i++)
{
// Write row to outfile
fwrite(image[i], sizeof(RGBTRIPLE), width, outptr);
// Write padding at end of row
for (int k = 0; k < padding; k++)
{
fputc(0x00, outptr);
}
}
// Free memory for image
free(image);
// Close files
fclose(inptr);
fclose(outptr);
return 0;
}
This is Makefile
filter:
clang -ggdb3 -gdwarf-4 -O0 -Qunused-arguments -std=c11 -Wall -Werror -Wextra -Wno-gnu-folding-constant -Wno-sign-compare -Wno-unused-parameter -Wno-unused-variable -Wshadow -lm -o filter filter.c helpers.c
To reproduce use any .bmp image. when you run the program, the command line arguments are -e INFILE.bmp OUTFILE.bmp
My code seems to be having problems with the blue values(I think...).
I've checked other posts, where they had a typo, I've checked and there doesn't seem to be any.
Others used rgbtriple so the values would sum until 255 and stop, but here I am using doubles.
I hope its not something stupid, but I've been checking and can't find the problem.
Hope someone can help me. Thank you
https://cs50.harvard.edu/x/2022/psets/4/filter/more/. (Here is the link to a description of the problem, you can skip to the edges part.)

Answer 1

I just had this problem too. You might have already fixed it, but I'll describe the problem anyways.
A byte can only store values up to 255. If you perform some math on values like that, then the resulting integer might be above 255, causing some overflow glitch. How might you store integers above 255 if a single byte can't?