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pset 4

filter

Implement a program that applies filters to BMPs, per the below.

Terminal window
$ ./filter -r image.bmp reflected.bmp

Filtering options:

  • -g = grayscale
  • -r = reflect
  • -b = blur
  • -e = edges
  • Directoryimages
    • courtyard.bmp
    • stadium.bmp
    • tower.bmp
    • yard.bmp
  • bmp.h
  • filter
  • filter.c
  • helpers.c
  • helpers.h
  • Makefile
  • out.bmp
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
#include <getopt.h>
#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 == '?')
    {
        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;


        // 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 infile
    fclose(inptr);


    // Close outfile
    fclose(outptr);


    return 0;
}
helpers.c
#include "helpers.h"
#include <math.h>
#include <stdio.h>
#include <stdlib.h>


// Convert image to grayscale
void grayscale(int height, int width, RGBTRIPLE image[height][width])
{
    float avg;
    int val;
    for (int i = 0; i < height; i++)
    {
        for (int j = 0; j < width; j++)
        {
            avg = (float)(image[i][j].rgbtBlue + image[i][j].rgbtGreen + image[i][j].rgbtRed) / 3.0;
            val = round(avg);
            image[i][j].rgbtBlue = image[i][j].rgbtGreen = image[i][j].rgbtRed = val;
        }
    }


    return;
}


// Reflect image horizontally
void reflect(int height, int width, RGBTRIPLE image[height][width])
{
    RGBTRIPLE temp;
    for (int i = 0; i < height; i++)
    {
        for (int j = 0, k = width - 1; j < width / 2; j++, k--)
        {
            temp = image[i][j];
            image[i][j] = image[i][k];
            image[i][k] = temp;
        }
    }


    return;
}


// Blur image
void blur(int height, int width, RGBTRIPLE image[height][width])
{
    RGBTRIPLE blurred[height][width];
    for (int i = 0; i < height; i++)
    {
        for (int j = 0; j < width; j++)
        {
            int cnt = 0;
            int sumRed = 0;
            int sumBlue = 0;
            int sumGreen = 0;
            for (int k = i - 1; k <= i + 1; k++)
            {
                for (int l = j - 1; l <= j + 1; l++)
                {
                    if ((k >= 0) && (k < height) && (l >= 0) && (l < width))
                    {
                        sumBlue += image[k][l].rgbtBlue;
                        sumGreen += image[k][l].rgbtGreen;
                        sumRed += image[k][l].rgbtRed;
                        cnt++;
                    }
                }
            }


            float avgBlue = sumBlue / (float) cnt;
            float avgGreen = sumGreen / (float) cnt;
            float avgRed = sumRed / (float) cnt;


            blurred[i][j].rgbtBlue = round(avgBlue);
            blurred[i][j].rgbtGreen = round(avgGreen);
            blurred[i][j].rgbtRed = round(avgRed);
        }
    }


    //copy blurred image to the original
    for (int i = 0; i < height; i++)
    {
        for (int j = 0; j < width; j++)
        {
            image[i][j] = blurred[i][j];
        }
    }


    return;
}


// Detect edges
void edges(int height, int width, RGBTRIPLE image[height][width])
{
    int Gxk[3][3] = {{-1, 0, 1}, {-2, 0, 2}, {-1, 0, 1}};
    int Gyk[3][3] = {{-1, -2, -1}, {0, 0, 0}, {1, 2, 1}};
    RGBTRIPLE(*edged)[width] = calloc(height, width * sizeof(RGBTRIPLE));


    for (int i = 0; i < height; i++)
    {
        for (int j = 0; j < width; j++)
        {
            int GxRed = 0, GyRed = 0, GxGreen = 0, GyGreen = 0, GxBlue = 0, GyBlue = 0;


            for (int k = i - 1; k <= i + 1; k++)
            {
                for (int l = j - 1; l <= j + 1; l++)
                {
                    if ((k >= 0) && (k < height) && (l >= 0) && (l < width))
                    {
                        GxRed += (image[k][l].rgbtRed * Gxk[k - i + 1][l - j + 1]);
                        GyRed += (image[k][l].rgbtRed * Gyk[k - i + 1][l - j + 1]);
                        GxGreen += (image[k][l].rgbtGreen * Gxk[k - i + 1][l - j + 1]);
                        GyGreen += (image[k][l].rgbtGreen * Gyk[k - i + 1][l - j + 1]);
                        GxBlue += (image[k][l].rgbtBlue * Gxk[k - i + 1][l - j + 1]);
                        GyBlue += (image[k][l].rgbtBlue * Gyk[k - i + 1][l - j + 1]);
                    }
                }
            }


            // combine the directional values
            double Red = sqrt((double)(GxRed * GxRed + GyRed * GyRed));
            double Blue = sqrt((double)(GxBlue * GxBlue + GyBlue * GyBlue));
            double Green = sqrt((double)(GxGreen * GxGreen + GyGreen * GyGreen));


            // cap the values at 255
            Red = (Red > 255) ? 255 : Red;
            Green = (Green > 255) ? 255 : Green;
            Blue = (Blue > 255) ? 255 : Blue;


            // round the values and save it
            edged[i][j].rgbtRed = round(Red);
            edged[i][j].rgbtGreen = round(Green);
            edged[i][j].rgbtBlue = round(Blue);
        }
    }


    // copy edged image to the original
    for (int i = 0; i < height; i++)
    {
        for (int j = 0; j < width; j++)
        {
            image[i][j] = edged[i][j];
        }
    }


    free(edged);


    return;
}
helpers.h
#include "bmp.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]);
// 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

recover

Implement a program that recovers JPEGs from a forensic image, per the below.

Terminal window
$ ./recover card.raw
  • card.raw
  • recovered-images
  • recover.c
recover.c
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <stdbool.h>


typedef uint8_t BYTE;


int main(int argc, char *argv[])
{
    // Ensure proper use
    if (argc != 2)
    {
        printf("Usage: ./recover image\n");
        return 1;
    }


    // Save the filename
    char *infile = argv[1];


    // Open input file
    FILE *inptr = fopen(infile, "r");
    if (inptr == NULL)
    {
        fclose(inptr);
        fprintf(stderr, "Could not open %s\n", infile);
        return 1;
    }


    // Recovery
    BYTE *buffer = malloc(512 * sizeof(BYTE));
    char *imgname = malloc(10 * sizeof(char));
    bool firstFound = false, running = false;


    int imgnameCnt = 0;
    sprintf(imgname, "%03i.jpg", imgnameCnt);
    FILE *img = fopen(imgname, "w");


    while (fread(buffer, 512 * sizeof(BYTE), 1, inptr) == 1)
    {
        if (buffer[0] == 0xff && buffer[1] == 0xd8 && buffer[2] == 0xff && (buffer[3] & 0xf0) == 0xe0)
        {
            if (firstFound == false)
            {
                firstFound = true;
                fwrite(buffer, 512 * sizeof(BYTE), 1, img);
                running = true;
            }
            else
            {
                fclose(img);
                running = false;
                sprintf(imgname, "%03i.jpg", ++imgnameCnt);
                img = fopen(imgname, "w");
                fwrite(buffer, 512 * sizeof(BYTE), 1, img);
                running = true;
            }
        }
        else
        {
            if (running == true)
            {
                fwrite(buffer, 512 * sizeof(BYTE), 1, img);
            }
        }
    }


    fclose(img);
    fclose(inptr);
    free(buffer);
    free(imgname);


}


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