About Vischeck What is it? Vischeck is a way of showing you what things look like to someone who is color blind. You can try Vischeck online- either run Vischeck on your own image files or run Vischeck on a web page. You can also download programs to let you run it on your own computer. What is it good for? Roughly 1 in 20 people have some sort of color vision deficiency. The world looks different to these people: they often find it hard to tell red and green things apart. This often means that they sometimes can't see things that 'color normal' people can see (examples). Many pictures, documents and web pages are hard for color blind people to read because the people who designed them didn't think about the problem. Vischeck lets them check their work for color blind visibility. It is also interesting to anyone who is just plain curious about what the world looks like if you're color blind. The technical stuff Vischeck is a computer simulation of the entire process of human vision. The model can be divided into three parts. The first stage includes the physical properties of the display devices (including various CRT and LCD monitors, and standard CYMK print on paper), the ambient lighting and the effects of physiological factors such as corneal haze, lens opacities and short or long-sightedness which might degrade the optical image. The second stage of the model describes the transformation of optical image on the retina into a neural representation of that image in the optic nerve. At this point, visual disabilities and anomalies such as color-blindness or retinal degeneration can be included in the model. The final stage in Vischeck is a model of human cortical vision. At this stage, we include information about the way in which color, spatial patterns and motion are combined and processed in the visual cortex, to form the observer's perception of the image