filter.c

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

// Convert image to grayscale
// Refer to the article below for more information:
// https://cs50.harvard.edu/x/2025/psets/4/filter/less/
// https://tannerhelland.com/2011/10/01/grayscale-image-algorithm-vb6.html

void grayscale(int height, int width, RGBTRIPLE image[height][width])
{
    for (int i = 0; i < height; i++)
    {
        for (int j = 0; j < width; j++)
        {
            int red = image[i][j].rgbtRed;
            int green = image[i][j].rgbtGreen;
            int blue = image[i][j].rgbtBlue;
            int gray = round((red + green + blue) / 3.0);

            image[i][j].rgbtRed = gray;
            image[i][j].rgbtGreen = gray;
            image[i][j].rgbtBlue = gray;
        }
    }

    return;
}

// Convert image to sepia
// Refer to these article:
// https://en.wikipedia.org/wiki/Sepia_tone#Sepia_tone_in_photography
// https://stackoverflow.com/questions/1061093/how-is-a-sepia-tone-created

void sepia(int height, int width, RGBTRIPLE image[height][width])
{
    for (int i = 0; i < height; i++)
    {
        for (int j = 0; j < width; j++)
        {
            int originalRed = image[i][j].rgbtRed;
            int originalGreen = image[i][j].rgbtGreen;
            int originalBlue = image[i][j].rgbtBlue;

            int sepiaRed = round(.393 * originalRed + .769 * originalGreen + .189 * originalBlue);
            int sepiaGreen = round(.349 * originalRed + .686 * originalGreen + .168 * originalBlue);
            int sepiaBlue = round(.272 * originalRed + .534 * originalGreen + .131 * originalBlue);

            image[i][j].rgbtRed = sepiaRed > 255 ? 255 : sepiaRed;
            image[i][j].rgbtGreen = sepiaGreen > 255 ? 255 : sepiaGreen;
            image[i][j].rgbtBlue = sepiaBlue > 255 ? 255 : sepiaBlue;
        }
    }

    return;
}

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

// Blur image
// This function averages the color values of each pixel with its neighbors

// Refer to the article below for more information:
// https://cs50.harvard.edu/x/2025/psets/4/filter/less/
// https://en.wikipedia.org/wiki/Box_blur
void blur(int height, int width, RGBTRIPLE image[height][width])
{
    RGBTRIPLE copy[height][width];
    for (int i = 0; i < height; i++)
    {
        for (int j = 0; j < width; j++)
        {
            copy[i][j] = image[i][j];
        }
    }

    for (int i = 0; i < height; i++)
    {
        for (int j = 0; j < width; j++)
        {
            int redSum = 0, greenSum = 0, blueSum = 0;
            int count = 0;

            for (int di = -1; di <= 1; di++)
            {
                for (int dj = -1; dj <= 1; dj++)
                {
                    int newI = i + di;
                    int newJ = j + dj;

                    if (newI >= 0 && newI < height && newJ >= 0 && newJ < width)
                    {
                        redSum += copy[newI][newJ].rgbtRed;
                        greenSum += copy[newI][newJ].rgbtGreen;
                        blueSum += copy[newI][newJ].rgbtBlue;
                        count++;
                    }
                }
            }

            image[i][j].rgbtRed = round(redSum / (float) count);
            image[i][j].rgbtGreen = round(greenSum / (float) count);
            image[i][j].rgbtBlue = round(blueSum / (float) count);
        }
    }

    return;
}

// Brighten image
// This function increases the brightness of each pixel by a fixed amount (50 in this case)

// Refer to the article below for more information:
// https://ie.nitk.ac.in/blog/2020/01/19/algorithms-for-adjusting-brightness-and-contrast-of-an-image/#:~:text=To%20change%20the%20brightness%20of,every%20pixel%20of%20the%20image.
void brighten(int height, int width, RGBTRIPLE image[height][width])
{
    for (int i = 0; i < height; i++)
    {
        for (int j = 0; j < width; j++)
        {
            int red = image[i][j].rgbtRed + 50;
            int green = image[i][j].rgbtGreen + 50;
            int blue = image[i][j].rgbtBlue + 50;

            image[i][j].rgbtRed = red > 255 ? 255 : red;
            image[i][j].rgbtGreen = green > 255 ? 255 : green;
            image[i][j].rgbtBlue = blue > 255 ? 255 : blue;
        }
    }
}