A simple tool for online image comparison

This website allows you to quickly and easily compare the difference between two images - pixel by pixel.

Simply drop the first image you wish to compare into the left box, and the other image in the right box. (You can also click on the boxes to get a upload dialog)

Drop image A in this area

Drop image B in this area

Highlight Color allows you to choose in which colour the differences should be highlighted.

The Fuzz option decides how big the difference between the pixels that are being compared has to be. A high value means that only large differences are shown. A low value means that even tiny differences are shown.

About this website

Comparing two images can be quite a pain. Large differences are usually obvious on first sight, but small differences in images can be very hard to find – especially in busy pictures where a lot is going on. When you look at the two example images below, you will find it almost impossible to discern where they differ. Making absolutely sure that you have found all differences will take quite a bit of time and effort.

Unmodified Image for Comparison

Unmodified image
(click to see full size)

Modified Image for Comparison

Modified image
(click to see full size)

However, for a computer finding the difference is quite easy – it can compare the color of every pixel and check if there is any difference between them. It can even calculate how much of a difference there is between the pixel colors. This allows it to create an image that contains only the differences between the two images. The differences between the two images above can be seen in the following image:

Result Image of Comparison

Result Image
(click to see full size)

As you can see the differences are nearly invisible for the naked eye, but easily recognizable for a machine.

Why did you make this image diff tool?

There are numerous software-libraries out there that allow you to calculate such diffs of images, but most of them are just intended for use from the command line or inside some software. That can be quite frustrating when you just want to find out what the difference between two images – you have to install the software, work out what parameters to use on the command-line etc. etc.
That's why we built this little site – it's intended to allow you to quickly compare some images without the hassle of manually using a library.

Which underlying software do you use to diff the images?

The image-processing library we use for this is the ImageMagick Library. It actually offers a an incredible amount of additional functionality for image comparison compared to what we use here, so if you need anything more we really recommend that you use the library directly.

What are the “Highlight Colour” and “Fuzz” options?

The two options we offer are “Highlight Colour” and “Fuzz”. The Highlight Color is the color in which, as the name suggests, the differences between the images will be highlighted. The Fuzz value describes how tolerant the comparison should be. A Fuzz of 0 means that any difference, no matter how small, will be shown. A higher value for the Fuzz means, that differences have to be bigger in order to be shown. This is useful when comparing images that are degraded, for example through a lossy change in size or image-format.

Can you diff images of different size or format?

Generally, yes. The images will automatically be resized and scaled to the same size before being compared. However there will most certainly be some additional inaccuracy.