Applying Filters by Manipulating Pixel Values!

bmp.h

// BMP-related data types based on Microsoft's own

#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;

filter.c

// This program enables you to apply some filters to your .bmp images
// greyscale, blur, and sepia filters work. 

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

#include "helpers.h"

int main(int argc, char *argv[])
{

    // Define allowable filters
    char *filters = "bgrs";

    // Get filter flag and check validity
    char filter = getopt(argc, argv, filters);
    if (filter == '?')
    {
        fprintf(stderr, "Invalid filter.\n");
        return 1;
    }

    // Ensure only one filter
    if (getopt(argc, argv, filters) != -1)
    {
        fprintf(stderr, "Only one filter allowed.\n");
        return 2;
    }

    // Ensure proper usage
    if (argc != optind + 2)
    {
        fprintf(stderr, "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)
    {
        fprintf(stderr, "Could not open %s.\n", infile);
        return 4;
    }

    // Open output file
    FILE *outptr = fopen(outfile, "w");
    if (outptr == NULL)
    {
        fclose(inptr);
        fprintf(stderr, "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);
        fprintf(stderr, "Unsupported file format.\n");
        return 6;
    }

    int height = abs(bi.biHeight);
    int width = bi.biWidth;

    // Allocate memory for image
    RGBTRIPLE(*image)[width] = calloc(height, width * sizeof(RGBTRIPLE));
    if (image == NULL)
    {
        fprintf(stderr, "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;

        // Grayscale
        case 'g':
            grayscale(height, width, image);
            break;

        // Reflection
        case 'r':
            reflect(height, width, image);
            break;

        // Sepia
        case 's':
            sepia(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 infile
    fclose(inptr);

    // Close outfile
    fclose(outptr);

    return 0;
}

helpers.c

#include "helpers.h"
#include <math.h>
#include <stdio.h>
#include <string.h>

// Convert image to grayscale
void grayscale(int height, int width, RGBTRIPLE image[height][width])
{

    for (int i = 0; i < height; i++)
    {

        for (int j = 0; j < width; j++)
        {
            // Get average RGB values!
            int average = round((float)(image[i][j].rgbtBlue + image[i][j].rgbtRed + image[i][j].rgbtGreen) / 3);

            image[i][j].rgbtBlue = average;
            image[i][j].rgbtRed = average;
            image[i][j].rgbtGreen = average;

        }
    }

    return;
}

// Convert image to sepia
void sepia(int height, int width, RGBTRIPLE image[height][width])
{

    for (int i = 0; i < height; i++)
    {

        for (int j = 0; j < width; j++)
        {
            // use the Sepia conversion
            int sepiaRed = round(.393 * image[i][j].rgbtRed + .769 * image[i][j].rgbtGreen + .189 * image[i][j].rgbtBlue);
            int sepiaGreen = round(.349 * image[i][j].rgbtRed + .686 * image[i][j].rgbtGreen + .168 * image[i][j].rgbtBlue);
            int sepiaBlue = round(.272 * image[i][j].rgbtRed + .534 * image[i][j].rgbtGreen + .131 * image[i][j].rgbtBlue);

            if (sepiaBlue > 255)
            {
                sepiaBlue = 255;
            }

            if (sepiaRed > 255)
            {
                sepiaRed = 255;
            }

            if (sepiaGreen > 255)
            {
                sepiaGreen = 255;
            }
            // store the result in the image pixel.
            image[i][j].rgbtBlue = sepiaBlue;
            image[i][j].rgbtRed = sepiaRed;
            image[i][j].rgbtGreen = sepiaGreen;

        }
    }

    return;
}

// Reflect image horizontally
void reflect(int height, int width, RGBTRIPLE image[height][width])
{
    int half = round(width / 2);

    for (int i = 0; i < height; i++)
    {

        for (int j = 0; j < half; j++)
        {
            // initialize a temp struct to hold an RGB value
            RGBTRIPLE tempRGB;

            // put the select pixel in temp slot
            tempRGB.rgbtBlue = image[i][j].rgbtBlue;
            tempRGB.rgbtRed = image[i][j].rgbtRed;
            tempRGB.rgbtGreen = image[i][j].rgbtGreen;

            // switch the selected pixel with its opposite.
            image[i][j].rgbtBlue = image[i][width - 1 - j].rgbtBlue;
            image[i][j].rgbtRed = image[i][width - 1 - j].rgbtRed;
            image[i][j].rgbtGreen = image[i][width - 1 - j].rgbtGreen;

            // assign the selected pixel to its opposite.
            image[i][width - 1 - j].rgbtBlue = tempRGB.rgbtBlue;
            image[i][width - 1 - j].rgbtRed = tempRGB.rgbtRed;
            image[i][width - 1 - j].rgbtGreen = tempRGB.rgbtGreen;

        }
    }

    return;
}

// Blur image
void blur(int height, int width, RGBTRIPLE image[height][width])
{

    RGBTRIPLE tempIMG[height][width];

    for (int i = 0; i < height; i++)
    {

        for (int j = 0; j < width; j++)
        {
            int redAvg = 0;
            int blueAvg = 0;
            int greenAvg = 0;
            int blueSum = image[i][j].rgbtBlue;
            int redSum = image[i][j].rgbtRed;
            int greenSum = image[i][j].rgbtGreen;
            int count = 1;

            // check top left
            if ((i - 1) >= 0 && (j - 1) >= 0)
            {
                blueSum += image[i - 1][j - 1].rgbtBlue;
                redSum += image[i - 1][j - 1].rgbtRed;
                greenSum += image[i - 1][j - 1].rgbtGreen;
                count++;
            }
            // check top center
            if ((i - 1) >= 0)
            {
                blueSum += image[i - 1][j].rgbtBlue;
                redSum += image[i - 1][j].rgbtRed;
                greenSum += image[i - 1][j].rgbtGreen;
                count++;
            }
            // check top right
            if ((i - 1) >= 0 && (j + 1) < width)
            {
                blueSum += image[i - 1][j + 1].rgbtBlue;
                redSum += image[i - 1][j + 1].rgbtRed;
                greenSum += image[i - 1][j + 1].rgbtGreen;
                count++;
            }
            // check right
            if ((j + 1) < width)
            {
                blueSum += image[i][j + 1].rgbtBlue;
                redSum += image[i][j + 1].rgbtRed;
                greenSum += image[i][j + 1].rgbtGreen;
                count++;
            }
            // check bottom right
            if ((i + 1) < height && (j + 1) < width)
            {
                blueSum += image[i + 1][j + 1].rgbtBlue;
                redSum += image[i + 1][j + 1].rgbtRed;
                greenSum += image[i + 1][j + 1].rgbtGreen;
                count++;

            }
            // check bottom middle
            if ((i + 1) < height)
            {
                blueSum += image[i + 1][j].rgbtBlue;
                redSum += image[i + 1][j].rgbtRed;
                greenSum += image[i + 1][j].rgbtGreen;
                count++;
            }
            // check bottom left
            if ((i + 1) < height && (j - 1) >= 0)
            {
                blueSum += image[i + 1][j - 1].rgbtBlue;
                redSum += image[i + 1][j - 1].rgbtRed;
                greenSum += image[i + 1][j - 1].rgbtGreen;
                count++;
            }
            // check left
            if ((j - 1) >= 0)
            {
                blueSum += image[i][j - 1].rgbtBlue;
                redSum += image[i][j - 1].rgbtRed;
                greenSum += image[i][j - 1].rgbtGreen;
                count++;
            }

            // get RGB average of all surrounding pixels
            redAvg = round((float)redSum / count);
            blueAvg = round((float)blueSum / count);
            greenAvg = round((float)greenSum / count);

            // assign those to a slot in a temp array that mirrors our image[]
            tempIMG[i][j].rgbtBlue = blueAvg;
            tempIMG[i][j].rgbtRed = redAvg;
            tempIMG[i][j].rgbtGreen = greenAvg;

        }
    }

    for (int i = 0; i < height; i++)
    {

        for (int j = 0; j < width; j++)
        {
            // copy the temp array items to the image and overwrite their original values.
            image[i][j].rgbtBlue = tempIMG[i][j].rgbtBlue;
            image[i][j].rgbtRed = tempIMG[i][j].rgbtRed;
            image[i][j].rgbtGreen = tempIMG[i][j].rgbtGreen;

        }
    }

    return;
}

helpers.h

#include "bmp.h"

// Convert image to grayscale
void grayscale(int height, int width, RGBTRIPLE image[height][width]);

// Convert image to sepia
void sepia(int height, int width, RGBTRIPLE image[height][width]);

// Reflect image horizontally
void reflect(int height, int width, RGBTRIPLE image[height][width]);

// Blur image
void blur(int height, int width, RGBTRIPLE image[height][width]);

makefile

filter:
	clang -fsanitize=signed-integer-overflow -fsanitize=undefined -ggdb3 -O0 -Qunused-arguments -std=c11 -Wall -Werror -Wextra -Wno-sign-compare -Wno-unused-parameter -Wno-unused-variable -Wshadow -o filter filter.c helpers.c