This is a small script that leverages Nathaniel Smith's
colorspacious library to check for or simulate colorblindess
given an input image.
Colorblindness or color vision deficiency (CVD) affects roughly 8% of men and 0.05% of women. Almost all vertebrates express a type photoreceptor called rhodopsin (rods) in the retina which is responsible for our baseline and low-light vision. In addition to rod cells, humans (unlike many mammals) are trichromats meaning that there are 3 additional photosensitive receptors (called opsins) grant us our colorvision[1][1]; these are cone cells and each type of cone responds most strongly to a different portion of the light spectrum. The L-cone (or long-wave cone, OPN1LW) gives us red perception, the M-cone (or medium-wave cone, OPN1MW) gives us green perception, and the S-cone (or short-wave cone, OPN1SW) gives us blue perception.
The major forms of color vision deficiency stem from problems with individual cone types, resulting in 3 types of dichromatism:
- protanopia (protanomoly): problematic L-cone
- deuteranopia (deuteranomoly): problematic M-cone
- tritanopia (tritanomoly): problematic S-cone
These problems can be genetic or trauma related and their severity can range from mild (*-anomolous) to complete absence (*-opia). Problems with red or green cones is substantially more common than problems with the blue cone. This is a consequence of the fact that our green cone is actually a genetic duplicate of our red cone that happened sometime within the last 80 million years[2][2]! Because of this gene duplication, both the red and green opsin genes are encoded on the X chromosome (whereas blue is encoded on chromosome 6). Thus mutations on the X chromosome may interfer with the normal expression of the opsin proteins, leading to color deficient vision. Because men only have one copy of the X chromosome, a defective X chromosome necessarily leads to colorblindness whereas women can be carriers of colorblindness assuming they have not inherited two defective X chromosomes[3][3].
Blue CVD ("tritan"s) is substantially rarer because the gene is encoded on chromosome 6. That said, it can (and so can red and green CVD) occur due to trauma, aging, some diseases, or drugs. For example, through diabetes, shaken baby syndrome, macular degeneration, and the TB drug ethambutol.
[1]: Note that there are many opsins in the retina of which more than 4 are involved in light sensing and vision. [2]: True green opsins that can be found in birds, for example, have maximal sensitivity near 500nm with red cone sensitivity maximal at 560nm. Us humans have green and red maximal sensitivity around 530nm and 560nm respectively. [3]: Some women are carriers of colorblindness can actually be tetrachromats. In female mammals, one X chromosome is always inactivated in each cell, but this X-inactivation is random, resulting in both the normal and defective X chromosomes being expressed in different retinal cells. In rare cases, the defect opsin may be sensitive to other areas of the visual spectrum not covered by the traditional red, green, and blue opsins, meaning these females can effectively have 4 different active color photoreceptors.
Currently, this needs to be installed manually:
git clone https://github.com/wflynny/cbviz.git
cd cbviz
python setup.py install
then run
cbviz simulate --help
cbviz-fast --help
There are two main functions supplied, test and simulate.
Alternatively, simulate transforms the input image from a simulated colorvision
deficient sRGB space to the sRGB space, simulating how someone will colorvision
deficiency would perceive the image.
usage: cbviz simulate [-h] [-s SEVERITY] (-t TYPE | -a) [--individual-plots]
[--no-original]
infile outfile
positional arguments:
infile Input image path
outfile Path to save resulting image(s)
optional arguments:
-h, --help show this help message and exit
-s SEVERITY, --severity SEVERITY
[0-100]: severity of colorblindess, 0 being no
deficiency, 100 being completely *opic
-t TYPE, --type TYPE One or more of 'protan*', 'deuteran*', 'tritan*',
'mono*' in **comma** separated list.
-a, --all Include completely *opic versions as well as anomalous
versions with given severity.If severity is 100, then
show anomalous versions at severity=50 too.
--individual-plots Store each image as separate file
--no-original Don't show original for comparison
The parameters that control what type of CVD is plotted are the following:
-a, --all
-t, --type 'protan,deuteran,tritan,monochrome' ['p,d,t,m']
-s, --severity [0-100, default=100]
Note that --all and --type are mutually exclusive. If --all is specified,
simulate all types of color deficient vision at two severity levels. If a
specific --severity S is specified, then it will plot everything with severity
= S and 100. Otherwise, it will plot things with severity = 50 and 100.
When invoking the --individual-plots command, note that the plots will be
saved with prefixes outfile.{cvd-type}.png.
cbviz simulate -a test/demo4.png test/demo4.cb.png
cbviz simulate -t protan,deuteran,tritan -s 50 test/demo4.png test/demo4.cb50.png
cbviz simulate -a test/colorblindr.fig1.png test/colorblindr.fig1.cb.png
For the last image, see Claus Wilke's colorblindr R package, which allows one to simulate color deficient vision within ggplot2 before saving the output.
In theory, test will attempt to check whether a supplied input image is
'colorblind-friendly' and provide text-based output telling the user a.) the
image is indeed colorblind-friendly or b.) which types of colorblindness for
which the image is poorly suited.
However, this curerntly doesn't work. I've tried implementing two algorithms,
but both have downsides. One way I've tried is to compare the original image
and the colorblind images all in the CAM02-UCS colorspace (meaning they go from
sRGB+CVD to sRGB to JCh) and comparing the J/h channels. Images are judged
whether each pair of pixels (original and CVD) are close enough under some
relative threshold (controlled by the parameter -e, --epsilon Threshold).
This script just assumes some default options and makes it very easy to make a 2x2 grid consisting of the original and the 3 CVD types.
See the documentation of colorspacious.