Compare two images online: see exactly where two photos differ
Pick a before photo and an after photo and see, with a slider and a difference map, where they changed. The tool also gives the share of changed pixels. The photos never leave your browser.
Opens without an account 3 times a day. A free account removes the limit.
- 2 imagesbefore and after
- 2 viewsslider and difference map
- Closer to the eyea difference in delta E, not in RGB
- Threshold 0.5 to 10in steps of 0.5
What it means to compare two images online
The image comparison from EduFacturing is a free online tool that shows where two photos of the same object differ. It compares them pixel by pixel by colour and gives the share of changed pixels, the mean difference, the largest difference above the threshold, the size of the changed patch, a before and after slider and a difference map.
The typical case is a part photographed before and after a change to a slicer setting (the slicer is the program that prepares a print). Everything is calculated in the browser: nothing is sent over the network and the photos do not leave your device.
Image difference checker: what the tool shows
Measures the colour difference closer to the eye
For every pixel it calculates delta E in CIELAB between the two photos. This is closer to perception than a difference in RGB, but the CIE76 formula is an approximation.
Shows what share of the photo differs
The share of pixels above the threshold, the mean difference, the largest difference above the threshold and the size of the patch that encloses every changed pixel, plus a plain-words summary.
Gives a before and after slider and a difference map
The slider reveals “before” and “after” on one canvas, and the map colours only the pixels above the threshold, in five bands.
Compares images of different sizes
You choose “Crop to common area” or “Stretch the second one”, and stretching warns when the aspect ratios differ.
When to compare two images for differences
A difference is easiest to find where the photos are the same in everything else.
A print before and after a setting
Photograph the part before and after changing a slicer setting, and the map shows where the surface changed.
A defect between two batches
Two parts from different batches, shot from one spot: the map shows where the differences are, and the size of the patch sums them up.
Screenshots and renders
Two versions of a page or a render have no sensor noise, so the threshold can be 0.5 to 1.
How two images are compared, pixel by pixel
The photos are brought to one size, every pixel becomes a colour in CIELAB and the distance between the two colours is measured.
A common size
“Crop to common area” takes the top left corner with the smallest width and height of the two photos; “Stretch the second one” scales the second to the size of the first.
Colour in CIELAB
Each pixel goes from sRGB through XYZ at the D65 white point to CIELAB, and the difference is the Euclidean distance delta E between the two colours.
Threshold and share
A pixel counts as different when delta E is equal to or above the threshold. The threshold is 2 by default, from 0.5 to 10.
| Applies to | Formula | Meaning |
|---|---|---|
| Difference between two pixels | ΔE = √[(ΔL)² + (Δa)² + (Δb)²] | Euclidean distance in CIELAB between the colours of the pixels at the same place in both photos |
| ΔE scale | under 1; 1 to 2; 2 to 5; 5 to 10; over 10 | no difference; trained eye only; noticeable; clearly visible; different colours |
| Changed pixel | ΔE ≥ threshold | the threshold is 2 by default |
| Share changed | pixels above threshold / all pixels · 100% | under 0.5% is a small patch, over 60% most likely means unaligned photos |
Image diff online that is closer to the eye than RGB
Closer to the eye than RGB
CIELAB is built so that distance matches perceived difference. CIE76 stays approximate: the number shows where there is a change, not exactly how much of it is seen.
The map does not cover the photo
Pixels below the threshold are fully transparent, and above it the opacity grows with the difference but never falls below a floor.
It says when the comparison is meaningless
With “Stretch the second one” and different aspect ratios it warns of deformation. Over 60% different pixels, it says the photos are probably not aligned.
The tool does not align the photos and does not recognise objects: it compares colours at the same places. A rotated or shifted photo gives a large share of changed pixels with nothing changed, so shoot from one spot and under one light.
It does not look for the cause of a difference and uses the simple CIE76 formula. The largest difference shown is only among the pixels above the threshold. For an exact colour match there is a separate tool, Color Code Converter.
Questions about comparing two images
How to compare two images for differences?
Pick a before photo and an after photo, then use the slider and the difference map. The tool gives the share of changed pixels, the mean and largest difference and the size of the changed patch.
How do I find the difference between two pictures?
Use the difference map: it colours only the pixels above the threshold, in five bands, and the larger the difference the more solid the colour. Shoot from one spot and under one light.
What does a delta E under 1 mean?
Practically no difference. From 1 to 2 only a trained eye catches it, from 2 to 5 it is noticeable, from 5 to 10 clearly visible, and over 10 the colours are different.
What threshold should I choose?
For real photos 2 to 3 is a sensible start. A threshold of 0.5 to 1 shows sensor noise and suits screenshots and renders, and above 5 only the large differences remain.
Are the images uploaded anywhere?
No. Both photos are read in the browser and the comparison sends nothing over the network.
Is the image comparison free?
Yes. Without an account the tool opens 3 times a day, and with a free account there is no limit. Pro is not needed.
The image comparison tool is free. Pro opens the rest
Pro costs 15 EUR a month and opens 45 Pro tools.
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Compare your two photos
Opens without an account 3 times a day. A free account removes the limit.