bmp-image comparison library

This library is designed to compare two BMP images and returns an percentage of how similar they are to each other.

Info

This is a rather small project for me to learn more about C and image processing. As its a lot of fun to write C. But I think this gives and pretty good insight on how to read BMP files and do different things with them. If you are interested in more info I have an image in /info about BMP headers.

Installation

To install the library, simply run the following commands:

Make sure you have an c compiler installed and make (for Makefile).

1. Clone the repository

git clone https://github.com/Blize/bmp-image-compare.git

2. Build the project

make

3. Run the executable

./bmp_compare static/1.bmp static/1_lines.bmp

Usage / Current Features

This library has a few different ways of comparing the images. For example comparing every RGB to each other or comparing if there is an brightness shift in the image. And I am also working on comparing shapes in the image using the sobel operator.

An example output could look like this (comparing static/1.bmp with static/1_lines.bmp):

-------------- BMP File Header --------------
File Path: static/1.bmp
File Type: 4d42
File Size: 818058 bytes
Pixel Data Offset: 138 bytes
Image Width: 640 pixels
Image Height: 426 pixels
Bit Count: 24 (should be 24 for 24-bit)
Compression: 0 (should be 0 for no compression)
Image Size: 817920 bytes (biSizeImage)
---------------------------------------------

-------------- BMP File Header --------------
File Path: static/1_lines.bmp
File Type: 4d42
File Size: 818058 bytes
Pixel Data Offset: 138 bytes
Image Width: 640 pixels
Image Height: 426 pixels
Bit Count: 24 (should be 24 for 24-bit)
Compression: 0 (should be 0 for no compression)
Image Size: 817920 bytes (biSizeImage)
---------------------------------------------

---- Image Comparison Results: Every RGB -----
Average Red Similarity: 99.86%
Average Green Similarity: 99.88%
Average Blue Similarity: 99.87%
Average Overall Similarity: 99.87%

----------------------------------------------

---- Image Comparison Results: Color Shift ---
Average Red Brightness Shift: 99.86%
Average Green Brightness Shift: 99.88%
Average Blue Brightness Shift: 99.87%
Average Overall Brightness Shift: 99.87%
----------------------------------------------

------- Image Comparison Results: Shape ------
Number of differing pixels: 1022
Similarity: 99%
----------------------------------------------

Explanation

1. Every RGB compares every pixel in the image to each other and calculates the similarity using the compare_values function found in util.c.
2. Color Shift calculates the average difference of the R/G/B values and checks if they are increasing or decreasing all by the same amount.
3. Shape compares the shapes in the image using the sobel operator. This is still a work in progress and is not fully implemented yet. Currently we just count if the pixels that are edges are the same amount in both images. Note though that we also generate a new image with the edges found in the image (Find examples in examples directory).

Future Features

I want to add some more features in the future if I have time and motivation for this. The main two are following:

• Add different Bitmap file types support -> currently only supports 24-bit BMP files.
• Recognize patterns in binary edges