Free Color Blindness Simulator
This free color blindness simulator shows an uploaded image next to how it looks to people with protanopia, deuteranopia or tritanopia, the three main kinds of colour vision deficiency. Use it to check charts, buttons, logos and web designs for colour contrast and meaning. Uploads up to 8 MB are processed in memory and never stored.
Color Blindness Simulator
Images
About this tool
Many people have some form of colour vision deficiency, and the most common kinds make reds and greens hard to tell apart. A chart that separates two lines only by red and green, or a form that marks errors in red alone, can be unreadable for them. Seeing your own design through a simulator is the quickest way to find those problems before your visitors do.
Upload a screenshot, a chart, a logo or a photo and the tool shows it next to a simulation. Protanopia and deuteranopia are the red and green types, and tritanopia is the rarer blue and yellow type. The simulation applies a published colour transformation matrix at full severity to every pixel. Real vision varies from mild to complete, so the result is a useful guide rather than an exact picture of any one person's sight.
Fix the problems you find by adding more than colour to carry meaning: labels, patterns, icons, underlines and different lightness values. Check text contrast too, with a ratio of at least 4.5 to 1 for body text. For speed, pictures larger than 900 pixels on the long side are scaled down before the simulation. This is a design aid, not a medical test, and it cannot diagnose anyone. A qualified eye care professional can test colour vision.
Frequently asked questions
What are protanopia, deuteranopia and tritanopia?
They are types of colour blindness where one kind of cone cell in the eye does not work. Protanopia lacks red sensitivity and deuteranopia lacks green, and both make reds and greens look alike. Tritanopia lacks blue sensitivity and confuses blues with greens and yellows with pinks. The first two are far more common.
How accurate is the simulation?
It uses a well known published matrix model at full severity, which is good for checking design problems. Real colour vision ranges from mild to complete, and screens and settings affect what you see. Treat the result as a guide, and test critical designs with real users where you can.
How can I make my design colour-blind friendly?
Never use colour as the only signal. Add text labels, icons, patterns or underlines, and make sure the important elements differ in lightness as well as colour. Avoid red against green and blue against purple pairs. Check that text contrast is at least 4.5 to 1.
Can this tool tell me if I am colour blind?
No. It simulates how a picture may look to someone with the condition, but it does not test your own vision. Screens differ and an online picture cannot replace a proper test. If you think you may have a colour vision deficiency, an optician or eye doctor can test you.
Is my picture stored on your server?
No. The image is held in memory while it is processed and discarded when the page finishes loading. It is not saved to disk or shared. The simulated pictures in the result exist only on that page, so download any you need before you leave.