---
myst:
  substitutions:
    image1: |-
      ```{image} 28369550088_617db0d6f2_m.jpg
      :alt: Colorful image of a cat's face, without modification```
    image2: |-
      ```{image} colorcat_protanopia.png
      :alt: Colorful image of a cat's face, with protanopia simulation```
    image3: |-
      ```{image} colorcat_deuteranopia.png
      :alt: Colorful image of a cat's face, with deuteranopia simulation```
    image4: |-
      ```{image} colorcat_tritanopia.png
      :alt: Colorful image of a cat's face, with tritanopia simulation```
    image5: |-
      ```{image} colorcat_achromatopsia.png
      :alt: Colorful image of a cat's face, with achromatopsia simulation```
    image6: |-
      ```{image} colorcat_contrastloss.png
      :alt: Colorful image of a cat's face, with contrast loss simulation```
---

# Color vision simulation

The simulator in the {doc}`Accessibility Inspector <../index>` in Firefox Developer Tools lets you see what a web page would look like to users with various forms of *color vision deficiency* (better known as "color blindness"), as well as *contrast sensitivity loss*.

"Color blindness" is a bit of a misnomer, since most people with these disorders can see colors, but do not see all of the distinctions that people with normal color vision can see; color vision deficiencies affect perception across the color spectrum, not only of specific colors like red or green. Color vision deficiencies affect about 8% of men, and 0.5% of women. The most common forms of color blindness (commonly lumped together as "red-green color blindness") affect more men than women, because they are due to a mutation in a gene in the X chromosome, which men usually have only one copy of.

Contrast sensitivity loss can be caused by cataracts, glaucoma, diabetic retinopathy, and other disorders of the retina; it can be age-related, congenital, or due to an injury.

:::{note}
This feature depends on webrender, an experimental featurethat is not enabled by default on all platforms. You can force-enablewebrender by settingthe preference `gfx.webrender.all` to `true` using the [Firefox Configuration Editor](https://support.mozilla.org/en-US/kb/about-config-editor-firefox) (note that if webrender is enabled by default on your platform, the setting has no effect.
:::

The current color simulation option may be selected from the **Simulate** menu as shown.

```{image} accessibily_color_simulation_menu.jpg
:alt: 'Simulate menu in Accessibility panel. Used for selecting the simulation mode:
:  None, Protanopia (no red), Deuteranopia (no green), Tritanopia (no blue), Achromatopsia
:  (no color), Contrast loss'
:class: center
```

The following table shows a colorful image of a cat's face, and what it looks like in the each of the simulations.

```{eval-rst}
.. list-table::
  :widths: 50 50
  :header-rows: 1

  * - Simulation
    - Image displayed

  * - None (Choose this to return to normal display)
    - .. image:: 28369550088_617db0d6f2_m.jpg

  * - Protanopia (no red)
    - .. image:: colorcat_protanopia.png

  * - Deuteranopia (no green)
    - .. image:: colorcat_deuteranopia.png

  * - Tritanopia (no blue)
    - .. image:: colorcat_tritanopia.png

  * - Achromatopsia (no color)
    - .. image:: colorcat_achromatopsia.png

  * - Contrast loss
    - .. image:: colorcat_contrastloss.png

```

:::{note}
The simulation transformation matrices are based on the paper: [A Physiologically-based Model for Simulation of Color Vision Deficiency](https://www.inf.ufrgs.br/~oliveira/pubs_files/CVD_Simulation/CVD_Simulation.html), Gustavo M. Machado, Manuel M. OliveiraLeandro A. F. Fernandes, IEEE Transactions on Visualization and Computer Graphics, Volume 15 (2009).
:::

## See also

- [Types of color blindness](https://www.color-blindness.com/types-of-color-blindness/)
- [Color blindness simulator](https://www.color-blindness.com/coblis-color-blindness-simulator/)
- [Contrast sensitivity](http://www.vision-and-eye-health.com/contrast-sensitivity.html)
- [Color palettes for color blindness](http://mkweb.bcgsc.ca/colorblind/)
- [Color universal design](https://jfly.uni-koeln.de/color/)
- [WCAG success criterion 1.4.1: Use of color](https://www.w3.org/TR/WCAG21/#use-of-color)
- [WCAG success criterion 1.4.11: Non-text contrast](https://www.w3.org/TR/WCAG21/#non-text-contrast)
