Filter

Overview

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.

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Features

• 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.

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Prerequisites

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:

Installing Clang and Make

Ubuntu/Linux

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

macOS

1. Install Xcode Command Line Tools:

   xcode-select --install

2. Verify installation:

   clang --version
   make --version

Windows

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

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Usage

Step 1: Compile the Program

Use the provided Makefile to compile the program:

make filter

This will generate an executable file named filter.

Step 2: Run the Program

Run the program using the following syntax:

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

Filters

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

Parameters

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

Examples

Apply Grayscale

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

Apply Sepia

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

Apply Reflection

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

Apply Blur

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

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Project Structure

├── 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.

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Filters in Detail

1. Grayscale

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.

2. Sepia

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.

3. Reflection

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

4. Blur

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.

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Development Notes

• 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

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Testing

Test Files

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

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

Running Tests

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.

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Authors

Developed by Shahir Ahmed.

License

This project is licensed under the MIT License.