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What is Delta E and will it help me choose a better monitor?

What is Delta E

Delta E is one of those terms that’s casually bandied about by monitor manufacturers and in online reviews. What’s less clear is exactly what it means, so here’s a basic explainer that could help you in your next purchase of a monitor, laptop, tablet or phone.

What is Delta E?

Delta E is a measurement of colour accuracy.

If the Delta E is less than 1, the theory goes that no human eye will be able to spot the difference. Between 1 and 2? Fine for the vast majority of people, but if you look closely (and you know what you’re looking for) then you’ll notice there’s a problem.

It’s less than ideal if a screen has a Delta E value between 2 and 3, but it’s only when you get to 4 or 5 that the average punter will start noticing that things don’t look quite right.

So, how do we calculate Delta E? I’m going to hugely simplify things here, but if you’re interested in the background then I recommend the excellent “A guide to understanding colour” by X-rite.

I’ll ease you in gently with a picture taken from that guide:

An image of two yellow roses to illustrate Delta E

These are two yellow roses, but the yellow is different at the centre of the target. It’s broken down into three values: L (lightness), a (the red/green value) and b (the yellow/blue value).

We then use an equation to merge those values into a single number – Delta E (or 𝜟E) – to express that difference. The actual equation isn’t really important in terms of understanding Delta E, but for completeness I’ll include it here:

𝜟E=√(𝜟L² + 𝜟a² + 𝜟b²)

So, you add all the squares of the differences between the values and then square root them. 

Feel free to work this out yourself, but the total colour difference between those two images of yellow roses, in the middle of the target area, is 13.31. That’s the Delta E.

What does Delta E mean in reviews and manufacturer claims?

When you see reviews of monitors, laptops, phones and tablets talk about Delta E, they’re referring to the average value across all measured colours. And so do manufacturers when they talk about average Delta E.

The reviewer will have used a colorimeter (such as this one by X-rite) and placed it in the centre of the screen. Software then flashes up a wide selection of colours for the spectrometer to analyse, and it then compares the differences in what it saw to what it expected.

The software generates an average Delta based on the differences it saw across all the measured colours. Here, for example, is the result from the truly excellent Eizo ColorEdge CG297X. Its average Delta E is 0.45.

Here’s a report from the Amazon Kindle Fire 8 HD tablet, currently £55, which has an average Delta E of 1.97:

And here’s one from a budget laptop aimed at businesses with an average Delta E of 3.89:

Does Delta E really matter?

Does Delta E matter? I can answer that with a resounding “yes!”.

In fact, as you can see from the tables above, it would be handy for reviews to publish the full Delta E details rather than just giving us an average. Take the Amazon Fire’s figures. An average Delta E of 1.97 sounds okay, but when you dive in to the detail you soon realise this is not a colour-accurate screen.

This is why an average Delta E of under 1 is still a great guide to quality; it means that the vast majority of the readings (that is, for each colour) are probably going to be under 1, or at least under 2. 

However, I will add a big caveat to this: I can’t think of a single desktop monitor I’ve reviewed over the past two years that has had a problem with Delta E. Admittedly, these tend to be good monitors, from companies such as Acer, AOC, Dell, Iiyama, LG, Philips, Samsung. I can’t vouch for the really cheap ones you might be tempted to buy in a Black Friday deal.

If you’re buying a laptop, tablet or phone, you should be much more aware of the average Delta E as their figures tend to vary. More expensive laptops (those costing over £800) tend to have high-quality panels, but once you get into the low-hundreds you run the risk of a low-quality panel with poor colour accuracy.

The other reason to pay attention to Delta E is that it acts as a great shorthand for quality. Chances are that a screen with an average Delta E of 2 or over will be a second-grade panel that also suffers from poor contrast, poor brightness and poor colour coverage.

Any questions? Please ask them in the comments field below.

READ NEXT: How do you make a monitor the primary display on a Mac?

About the author

Tim Danton

Tim Danton is editor-in-chief of PC Pro magazine and has written about technology since 1999. He enjoys playing with gadgets, playing with words and playing tennis. Email tim@bigtechquestion.com

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