handl_ /lab/vision-simulator
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Vision simulator

See your design through the eyes of people with colour blindness or impaired vision. Upload a screenshot, or try the sample.

1 · Image A sample page is shown for now.

Then choose a condition, even one you have yourself. Side by side you will see how the same image looks to a person with typical vision and to a person with this condition.

2 · Colour vision
impaired eyesight
Side by side: typical vision and deuteranomaly
Typical vision
Room booking Office Prague · 14 March
Room AFree
Room BBooked
Room CFree
Email for confirmation jan.novak@
Book
Deuteranomaly · as you see it
Room booking Office Prague · 14 March
Room AFree
Room BBooked
Room CFree
Email for confirmation jan.novak@
Book

If you have this deficiency yourself, both sides may look almost the same to you. That is exactly where the difference lies that people with typical vision see and you do not: mainly the Free and Booked labels, the bars in the chart and the red frame on the email. Below in Colour adjustment you will see how to recalculate colours so the difference is visible to you too.

Deuteranomaly

Weakened perception of green. Green, yellow and red hues are more alike and less saturated.

How many people

About 5% of men. The most common colour vision deficiency of all.

What to watch out for

Traffic lights made of green and red are unreliable for these people. Add text or an icon.

The simulation is approximate and serves to uncover problems, not for exact diagnosis.

The other way round: adjusting colours for people with a deficiency

Choose a condition and the tool recalculates the colours of the image so that differences the person cannot see are moved into colours they can perceive. It works on the sample chart and on your uploaded screenshot above.

Try the colour vision test →
Condition
Sample chart. Upload your own screenshot above.
Original
OriginalThis is how most people see the image.
How a person with the deficiency sees it
How a person with the deficiency sees itSimulace: deuteranopia (green). Some colours blend.
Adjusted colours
Adjusted coloursDifferences moved into colours the person can tell apart.
Adjusted, seen by a person with the deficiency
Adjusted, seen by a person with the deficiencyThe colours can be told apart again.

What the adjustment can and cannot do

Typical vision cannot be restored; a missing type of cone cannot be replaced. The adjustment only “moves” the differences: for example red and green are told apart through blue and lightness. Colours then do not look natural, but a chart, a map or a traffic light make sense again. Filters in phones and computers use the same principle.

Turn it on right on your device

  • iPhone and iPad: Settings → Accessibility → Display & Text Size → Colour Filters
  • Android: Settings → Accessibility → Colour correction (the name varies by manufacturer)
  • Windows 11: Settings → Accessibility → Colour filters
  • macOS: System Settings → Accessibility → Display → Colour Filters

A better way for designers

Do not rely on colour alone. Add labels, icons, patterns or a difference in lightness to colours. Then no adjustment is needed at all and the design works for everyone, even in black-and-white print.

How many people see colours differently

8 % of men have a red–green perception deficiency. Roughly one in twelve.
0,5 % of women, roughly one in two hundred. The genes for red and green perception lie on the X chromosome. A man has one X, so one faulty gene is enough. A woman has two and the deficiency shows only when both are faulty. Many more women are carriers.
5 % of men have deuteranomaly, a weakened perception of green. It is by far the most common type.

-anopia = a cone is missing

The eye has three types of cones for red, green and blue. When one type is missing completely, a person cannot tell two colours apart at all.

-anomaly = a cone is weakened

The cone works but perceives the colour shifted. Colours are less saturated and similar hues blend, especially in low light.

Proto-, deutero-, trito-

They indicate which cone is affected: the first (red), the second (green), the third (blue). Blue deficiencies are not inherited through the X chromosome, so they affect men and women equally, but they are very rare.

Colour vision data: Colour Blind Awareness. For impaired eyesight we give only a description; frequency varies with age and cause.