ez_img_diff

A tool for doing quick percieved image difference analysis

What does ez_img_diff do?

ez_img_diff is a CLI and api for doing a simple form of percieved image difference analysis with SSIM. This allows for tons of features, but the main one is being able to compare some sort of "baseline" image of an application to a "current" itteration in visual regression testing.

Down the road I will write a selenium integration to tie this whole process together!

Why should I use ez_img_diff?

There are a ton of great and more robust tools out there for this analysis, or for visual regression testing, but I found each of them had their own problems, here's a list:

Package	Issue
needle	Requires a Nose test runner, and had out of date dependencies
pytest-needle	Works well, but cannot use webdiver_manager with it
dpxdt	Didn't test, but was 7 years old and mostly focused on CI/CD usage
Visual Regression Tracker	Works great, but for some of my use cases I need an API not a full application
hermione	Could not use javascript/nodeJS for my use case
specter	Could not use javascript/nodeJS for my use case
Cypress-image-screenshot	Could not use javascript/nodeJS for my use case

Quick-start

Installation

From source

Clone this repo: https://github.com/Descent098/ez-img-diff
Run pip install . or sudo pip3 install .in the root directory

From PyPi

Run pip install ez_img_diff

Examples

API Examples

Compare 2 images without saving difference files

from ez_img_diff.api import compare_images

img1 = "baseline.png"
img2 = "current.png"

compare_images(im1, img2) # 14.03

Compare 2 images with saving difference and threshold files

from ez_img_diff.api import compare_images

img1 = "baseline.png"
img2 = "current.png"

compare_images(im1, img2, "difference.png", "threshold.png") # 14.03

CLI Usage

ez img diff

A tool for doing quick perceptual image difference analysis

Usage: 
    img_diff [-h] [-v]
    img_diff (<img1> <img2>) [-o OUTPUT_FOLDER] 

Options:
    -h, --help            show this help message and exit
    -v, --version         show program's version number and exit
    -o OUTPUT_FOLDER, --output OUTPUT_FOLDER 
                        the folder to output difference files to

so for example to get the diff of two images use:

$> img_diff baseline.png current.png
14.03

You can then store the diff and threshold of the two images with:

$> img_diff baseline.png current.png -o results
14.03

$> cd results && ls
diff.png
thresh.png

Notes

Some things to keep in mind:

Output folder will have 2 files in it diff.png and thresh.png
- diff.png is the regular difference png, which shows where things differ
- thresh.png is the threshold png, which is much higher contrast and shows you where the biggest changes happened more clearly

How the system works

In the interest of promoting learning here is some detail on how the system works. It is largely adapted from this post, I would highly recommend reading and downloading their resource guide for even more details!

Primarily it works on computer vision, and a library called opencv-python, which is a python port of a computer vision toolkit called opencv. Without getting into the math too much it uses computer vision combined with SSIM. SSIM is a percieved quality analysis metric that tends to be used to benchmark how well compression systems retain the original image quality. We can use the same principle to help with regression testing by using it to compare the "quality differences" between two images (a baseline, and a current itteration), to be able to tell the percieved differences between them. This comparison is provided by scikit-image.

With opencv we also end up mostly dealing with arrays of numbers representing each pixel in an image. Working with these types is hard so we use imutils to work with these values more effectively!

Descent098/ez-img-diff