bjorn

Image comparison tool for Bjorn

bjorn allow the users (like Bjorn) to compare images that are provided as a list in a csv file

Table of Contents

• Installation
• Usage
• Development
  • Project Structure
  • Image Comparison Algorithm
  • Further Development
  • Running Tests

Installation

LATEST RELEASE

Download the appropriate release package as per you operating system. Supported operating systems are:

• MacOS (Darwin)
• Windows
• Linux

Unpack the downloaded archive in you local directory to install the bjorn cli tool.

Usage

Usage:
  bjorn [command]

Available Commands:
  diff        compare images listed in a csv file
  help        Help about any command

bjorn diff

compare images listed in a csv file.

bjorn diff [flags]

Options

  -f, --file string   CSV file to read image list
  -h, --help          help for diff
  -o, --out string    Output file location
      --alsologtostderr                  log to standard error as well as files
      --config string                    config file (default is $HOME/.bjorn.yaml)
  -h, --help                             help for bjorn
      --log_backtrace_at traceLocation   when logging hits line file:N, emit a stack trace (default :0)
      --log_dir string                   If non-empty, write log files in this directory
      --logtostderr                      log to standard error instead of files
      --stderrthreshold severity         logs at or above this threshold go to stderr (default 2)
  -v, --v Level                          log level for V logs
      --vmodule moduleSpec               comma-separated list of pattern=N settings for file-filtered logging

Development

Project structure

We are using Cobra (a library for creating CLI applications using Go) to build this project. This allows to quickly prototype the solution as a user friendly CLI application and makes future extension with more commands easier.

For release management we are using GoReleaser along with TravisCI when a new tag is pushed. It generates binaries for each of the supported operating systems (MacOs, Windows, Linux).

Image Comparison Algorithm

Bjorn uses a simple pixel based approach to image comparison. Each pixel of the 2 images being compared using the RGB values of each pixel. This is a relatively simple approach to image comparison, suitable for basic percentage difference comparison.

The Score is calculated by summing up the difference in RGB values for each pixel and using this value to get the ratio of different pixels to total pixels in the images. To calculate the time taken for each comparison we called a deferred function elapsed() at start of each Compare() call.

Limitations of current approach:

• It assumes the images are of the same size. Scaled versions of the same image will be considered different.
• Comparing same images in different formats (png, jpg, gif) can produce a score of ~0.01 to 0.02. The comparison algorithm uses a threshold of 0.01, below which images are considered similar.

Further Development

The comparison algorithm is defined as the Compare() function in the pair package. This function may be extended to improve the comparison algorithm. Possible improvements include:

• Improve comparison algorithm to consider scaled images.
• Add ability to define multiple comparison algorithm and flags to select each.
• Add command to compare 2 images separately (eg bjorn diff images img1 img2).

Tests

Run tests using go test ./..