Filter is a program that applies various filters to 24-bit BMP (Bitmap) images. It supports grayscale, sepia, reflection, and blur filters. The program processes the image pixel by pixel and generates a new image file with the applied effect.

By modifying the RGB values in the pixels of a BMP file, Filter demonstrates image manipulation through low-level programming in C.

• Grayscale: Converts an image to black-and-white shades.
• Sepia: Applies an old-timey, reddish-brown filter.
• Reflection: Mirrors the image horizontally.
• Blur: Applies a box blur to smooth the image.

Before using Filter, ensure you have the following:

1. A C compiler (clang or gcc).
2. make build tool.

Follow these steps to install them based on your operating system:

1. Update your package list:

   sudo apt update

2. Install Clang and Make:

   sudo apt install clang make

3. Verify installation:

   clang --version
   make --version

1. Install Xcode Command Line Tools:

   xcode-select --install

2. Verify installation:

   clang --version
   make --version

1. Download the LLVM installer from the official LLVM website.
2. Run the installer and follow the setup instructions.
3. Add the LLVM bin directory (e.g., C:\Program Files\LLVM\bin) to your system's PATH environment variable:
   • Open "Environment Variables" in Windows settings.
   • Edit the Path variable and add the directory.
4. Install Make via Chocolatey or MinGW.
5. Verify installation:

   clang --version
   make --version

Use the provided Makefile to compile the program:

make filter

This will generate an executable file named filter.

Run the program using the following syntax:

./filter [FILTER_OPTION] infile.bmp outfile.bmp

• -g: Apply grayscale filter.
• -s: Apply sepia filter.
• -r: Apply reflection filter.
• -b: Apply blur filter.

• infile.bmp: Path to the input BMP file.
• outfile.bmp: Path where the filtered image will be saved.

./filter -g images/yard.bmp out.bmp

./filter -s images/yard.bmp out.bmp

./filter -r images/yard.bmp out.bmp

./filter -b images/yard.bmp out.bmp

├── filter/
│   ├── helpers.h
│   ├── helpers.c
│   ├── Makefile
│   ├── images/
│   │   ├── courtyard.bmp
│   │   ├── stadium.bmp
│   │   ├── yard.bmp
│   │   └── tower.bmp
│   ├── filter.c
│   ├── bmp.h
└── README.md

• helpers.h: Function prototypes for the filters.
• helpers.c: Implements the grayscale, sepia, reflection, and blur filters.
• filter.c: Main program logic for applying filters and handling BMP files.
• bmp.h: Defines data structures and types for BMP file handling.
• Makefile: Automates the build process.
• images/: Sample BMP files for testing.

Converts an image to black-and-white shades by averaging the red, green, and blue values for each pixel. The resulting value is applied to all three color channels.

Applies a reddish-brown filter using the following formula:

sepiaRed = .393 * red + .769 * green + .189 * blue
sepiaGreen = .349 * red + .686 * green + .168 * blue
sepiaBlue = .272 * red + .534 * green + .131 * blue

Values exceeding 255 are capped at 255.

Reflects the image horizontally by swapping pixels on the left side with those on the right side for each row.

Applies a box blur by averaging the RGB values of a pixel and its neighbors in a 3x3 grid. Edge pixels use only available neighbors.

• Dependencies: Standard C libraries (stdio.h, stdlib.h, math.h).
• Compatibility: Works on Unix-like systems (Linux, macOS) and Windows (with MinGW or WSL).
• Manual Compilation: If make is unavailable:

  clang -std=c11 -Wall -Werror -o filter filter.c helpers.c -lm

The images/ directory contains sample BMP files for testing, such as:

• yard.bmp
• courtyard.bmp
• stadium.bmp

To test the program, use:

./filter -g images/yard.bmp out.bmp

Inspect the output image (out.bmp) to confirm the filter was applied correctly.

Developed by Shahir Ahmed.

This project is licensed under the MIT License.