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If you are interested in color, explore my other color tools, Brewer palettes resources, color blindness palettes and math and an exhausting list of 10,000 color names for all those times you couldn't distinguish between tan hide, sea buckthorn, orange peel, west side, sunshade, california and pizzaz.

Designing for Color blindness

Color choices and transformations for deuteranopia and other afflictions

Here, I help you understand color blindness and describe a process by which you can make good color choices when designing for accessibility.

The opposite of color blindness is seeing all the colors and I can help you find 1,000 (or more) maximally distinct colors.

You can also delve into the mathematics behind the color blindness simulations and learn about copunctal points (the invisible color!) and lines of confusion.

Color blindness R code

R code for converting an RGB color for color blindness. For details see the math tab and the resources section for background reading.

---
title: 'RGB color correction for color blindess: protanopia, deuteranopia, tritanopia'
author: 'Martin Krzywinski'
web: http://mkweb.bcgsc.ca/colorblind
---

```{r}
gamma = 2.4
###############################################
# Linear RGB to XYZ
# https://en.wikipedia.org/wiki/SRGB
XYZ = matrix(c(0.4124564, 0.3575761, 0.1804375,
               0.2126729, 0.7151522, 0.0721750,
               0.0193339, 0.1191920, 0.9503041),
               byrow=TRUE,nrow=3)

SA = matrix(c(0.2126,0.7152,0.0722,
              0.2126,0.7152,0.0722,
              0.2126,0.7152,0.0722),byrow=TRUE,nrow=3)

###############################################
# XYZ to LMS, normalized to D65
# https://en.wikipedia.org/wiki/LMS_color_space
# Hunt, Normalized to D65
LMSD65 = matrix(c( 0.4002, 0.7076, -0.0808,
                   -0.2263, 1.1653,  0.0457,
                    0     , 0     ,  0.9182),
                   byrow=TRUE,nrow=3)
# Hunt, equal-energy illuminants
LMSEQ = matrix(c( 0.38971, 0.68898,-0.07868,
                 -0.22981, 1.18340, 0.04641,
                  0      , 0      , 1      ),
                byrow=TRUE,nrow=3)
# CIECAM97
SMSCAM97 = matrix(c(  0.8951,  0.2664, -0.1614,
                     -0.7502,  1.7135,  0.0367,
                      0.0389, -0.0685,  1.0296),
                  byrow=TRUE,nrow=3)
# CIECAM02
LMSCAM02 = matrix(c( 0.7328, 0.4296, -0.1624,
                    -0.7036, 1.6975,  0.0061,
                     0.0030, 0.0136,  0.9834),
                  byrow=TRUE,nrow=3)

###############################################
# Determine the color blindness correction in LMS space
# under the condition that the correction does not
# alter the appearance of white as well as 
# blue (for protanopia/deuteranopia) or red (for tritanopia).
# For achromatopsia, greyscale conversion is applied
# to the linear RGB values.
getcorrection = function(LMS,type="p",g=gamma) {
  red = matrix(c(255,0,0),nrow=3)
  blue = matrix(c(0,0,255),nrow=3)
  white = matrix(c(255,255,255),nrow=3)
  LMSr = LMS %*% XYZ %*% apply(red,1:2,linearize,g)
  LMSb = LMS %*% XYZ %*% apply(blue,1:2,linearize,g)
  LMSw = LMS %*% XYZ %*% apply(white,1:2,linearize,g)
  if(type == "p") {
    x = matrix(c(LMSb[2,1],LMSb[3,1],
                  LMSw[2,1],LMSw[3,1]),byrow=T,nrow=2)
    y = matrix(c(LMSb[1,1],LMSw[1,1]),nrow=2)
    ab = solve(x) %*% y
    C = matrix(c(0,ab[1,1],ab[2,1],0,1,0,0,0,1),byrow=T,nrow=3)
  } else if (type == "d") {
    x = matrix(c(LMSb[1,1],LMSb[3,1],
                  LMSw[1,1],LMSw[3,1]),byrow=T,nrow=2)
    y = matrix(c(LMSb[2,1],LMSw[2,1]),nrow=2)
    ab = solve(x) %*% y
    C = matrix(c(1,0,0,ab[1,1],0,ab[2,1],0,0,1),byrow=T,nrow=3)
  } else if (type == "t") {
    x = matrix(c(LMSr[1,1],LMSr[2,1],
                  LMSw[1,1],LMSw[2,1]),byrow=T,nrow=2)
    y = matrix(c(LMSr[3,1],LMSw[3,1]),nrow=2)
    ab = solve(x) %*% y
    C = matrix(c(1,0,0,0,1,0,ab[1,1],ab[2,1],0),byrow=T,nrow=3)
  } else if (type == "a" | type == "g") {
    C = matrix(c(0.2126,0.7152,0.0722,
                 0.2126,0.7152,0.0722,
                 0.2126,0.7152,0.0722),byrow=TRUE,nrow=3)
  }
  return(C)
}

# rgb is a column vector
convertcolor = function(rgb,LMS=LMSD65,type="d",g=gamma) {
  C = getcorrection(LMS,type)
  if(type == "a" | type == "g") {
    T = SA
  } else {
    M = LMS %*% XYZ
    Minv = solve(M)
    T = Minv %*% C %*% M
  }
  print(T)
  rgb_converted = T %*% apply(rgb,1:2,linearize,g)
  return(apply(rgb_converted,1:2,delinearize,g))
}

# This function implements the method by Vienot, Brettel, Mollon 1999.
# The approach is the same, just the values are different.
# http://vision.psychol.cam.ac.uk/jdmollon/papers/colourmaps.pdf
convertcolor2 = function(rgb,type="d",g=2.2) {
  xyz = matrix(c(40.9568, 35.5041, 17.9167,
                 21.3389, 70.6743, 7.98680,
                 1.86297, 11.4620, 91.2367),byrow=T,nrow=3)
  lms = matrix(c(0.15514, 0.54312, -0.03286,
                 -0.15514, 0.45684,0.03286,
                 0,0,0.01608),byrow=T,nrow=3)
  rgb = (rgb/255)**g
  if(type=="p") {
    S = matrix(c(0,2.02344,-2.52581,0,1,0,0,0,1),byrow=T,nrow=3)
    rgb = 0.992052*rgb+0.003974
  } else if(type=="d") {
    S = matrix(c(1,0,0,0.494207,0,1.24827,0,0,1),byrow=T,nrow=3)
    rgb = 0.957237*rgb+0.0213814
  } else {
    stop("Only type p,d defined for this function.")
  }
  M = lms %*% xyz
  T = solve(M) %*% S %*% M
  print(T)
  rgb = T %*% rgb
  rgb = 255*rgb**(1/g)
  return(rgb)
}

###############################################
# RGB to Lab
rgb2lab = function(rgb,g=gamma) {
  rgb = apply(rgb,1:2,linearize,g)
  xyz = XYZ %*% rgb
  delta = 6/29
  xyz = xyz / (c(95.0489,100,108.8840)/100)
  f = function(t) {
    if(t > delta**3) {
      return(t**(1/3))
    } else {
      return (t/(3*delta**2) + 4/29)
    }
  }
  L = 116*f(xyz[2]) - 16
  a = 500*(f(xyz[1]) - f(xyz[2]))
  b = 200*(f(xyz[2]) - f(xyz[3]))
  return(matrix(c(L,a,b),nrow=3))
}

# CIE76 (https://en.wikipedia.org/wiki/Color_difference)
deltaE = function(rgb1,rgb2) {
  lab1 = rgb2lab(rgb1)
  lab2 = rgb2lab(rgb2)
  return(sqrt(sum((lab1-lab2)**2)))
}

clip = function(v) {
  return(max(min(v,1),0))
}

###############################################
# RGB to/from linear RGB
#https://en.wikipedia.org/wiki/SRGB
linearize = function(v,g=gamma) {
  if(v <= 0.04045) {
    return(v/255/12.92)
  } else {
    return(((v/255 + 0.055)/1.055)**g)
  }
}

delinearize = function(v,g=gamma) {
  if(v <= 0.003130805) {
    return(255*12.92*clip(v))
  } else {
    return(255*clip(1.055*(clip(v)**(1/g))-0.055))
  }
}
pretty = function(x) {
  noquote(formatC(x,digits=10,format="f",width=9))
}

# a dark red
rgb1 = matrix(c(0,209,253),nrow=3)
# dark green
rgb2 = matrix(c(60,135,0),nrow=3)
# simulate deuteranopia
convertcolor(rgb1,type="d")
convertcolor(rgb2,type="d")
# get color distance before and after simulation
deltaE(rgb1,rgb2)
deltaE(convertcolor(rgb1,type="d"),convertcolor(rgb2,type="d"))
# transformation matrices for each color blindness type
M = LMSD65 %*% XYZ
pretty(solve(M) %*% getcorrection(LMSD65,"p") %*% M)
pretty(solve(M) %*% getcorrection(LMSD65,"d") %*% M)
pretty(solve(M) %*% getcorrection(LMSD65,"t") %*% M)
pretty(SA)
# method by Vienot, Brettel, Mollon, 1999
convertcolor2(rgb1,type="d",g=2.2)
convertcolor2(rgb2,type="d",g=2.2)
```

# a dark red
rgb1 = matrix(c(225,0,30),nrow=3)

# dark green
rgb2 = matrix(c(60,135,0),nrow=3)

# simulate deuteranopia
convertcolor(rgb1,type="d")
         [,1]
[1,] 136.7002
[2,] 136.7002
[3,]   0.0000
convertcolor(rgb2,type="d")
          [,1]
[1,] 116.76071
[2,] 116.76071
[3,]  16.73263
# get color distance before and after simulation
deltaE(rgb1,rgb2)
[1] 116.9496
deltaE(convertcolor(rgb1,type="d"),convertcolor(rgb2,type="d"))
[1] 12.72204
# transformation matrices for each color blindness type
M = LMSD65 %*% XYZ

pretty(solve(M) %*% getcorrection(LMSD65,"p") %*% M)
     [,1]          [,2]         [,3]         
[1,] 0.1705569911  0.8294430089 0.0000000000 
[2,] 0.1705569911  0.8294430089 -0.0000000000
[3,] -0.0045171442 0.0045171442 1.0000000000 

pretty(solve(M) %*% getcorrection(LMSD65,"d") %*% M)
     [,1]          [,2]         [,3]         
[1,] 0.3306600735  0.6693399265 -0.0000000000
[2,] 0.3306600735  0.6693399265 0.0000000000 
[3,] -0.0278553826 0.0278553826 1.0000000000 

pretty(solve(M) %*% getcorrection(LMSD65,"t") %*% M)
     [,1]          [,2]         [,3]         
[1,] 1.0000000000  0.1273988634 -0.1273988634
[2,] -0.0000000000 0.8739092990 0.1260907010 
[3,] 0.0000000000  0.8739092990 0.1260907010 

pretty(SA)
     [,1]         [,2]         [,3]        
[1,] 0.2126000000 0.7152000000 0.0722000000
[2,] 0.2126000000 0.7152000000 0.0722000000
[3,] 0.2126000000 0.7152000000 0.0722000000
# method by Vienot, Brettel, Mollon, 1999
convertcolor2(rgb1,type="d",g=2.2)
            [,1]       [,2]          [,3]
[1,]  0.29275003 0.70724967 -2.978356e-08
[2,]  0.29275015 0.70724997  1.232823e-08
[3,] -0.02233659 0.02233658  1.000000e+00
          [,1]
[1,] 131.81223
[2,] 131.81226
[3,]  36.37274
convertcolor2(rgb2,type="d",g=2.2)
            [,1]       [,2]          [,3]
[1,]  0.29275003 0.70724967 -2.978356e-08
[2,]  0.29275015 0.70724997  1.232823e-08
[3,] -0.02233659 0.02233658  1.000000e+00
          [,1]
[1,] 122.71798
[2,] 122.71801
[3,]  48.34316
news + thoughts

Nasa to send our human genome discs to the Moon

Sat 23-03-2024

We'd like to say a ‘cosmic hello’: mathematics, culture, palaeontology, art and science, and ... human genomes.

Martin Krzywinski @MKrzywinski mkweb.bcgsc.ca
SANCTUARY PROJECT | A cosmic hello of art, science, and genomes. (details)
Martin Krzywinski @MKrzywinski mkweb.bcgsc.ca
SANCTUARY PROJECT | Benoit Faiveley, founder of the Sanctuary project gives the Sanctuary disc a visual check at CEA LeQ Grenoble (image: Vincent Thomas). (details)
Martin Krzywinski @MKrzywinski mkweb.bcgsc.ca
SANCTUARY PROJECT | Sanctuary team examines the Life disc at INRIA Paris Saclay (image: Benedict Redgrove) (details)

Comparing classifier performance with baselines

Sat 23-03-2024

All animals are equal, but some animals are more equal than others. —George Orwell

This month, we will illustrate the importance of establishing a baseline performance level.

Baselines are typically generated independently for each dataset using very simple models. Their role is to set the minimum level of acceptable performance and help with comparing relative improvements in performance of other models.

Martin Krzywinski @MKrzywinski mkweb.bcgsc.ca
Nature Methods Points of Significance column: Comparing classifier performance with baselines. (read)

Unfortunately, baselines are often overlooked and, in the presence of a class imbalance5, must be established with care.

Megahed, F.M, Chen, Y-J., Jones-Farmer, A., Rigdon, S.E., Krzywinski, M. & Altman, N. (2024) Points of significance: Comparing classifier performance with baselines. Nat. Methods 20.

Happy 2024 π Day—
sunflowers ho!

Sat 09-03-2024

Celebrate π Day (March 14th) and dig into the digit garden. Let's grow something.

Martin Krzywinski @MKrzywinski mkweb.bcgsc.ca
2024 π DAY | A garden of 1,000 digits of π. (details)

How Analyzing Cosmic Nothing Might Explain Everything

Thu 18-01-2024

Huge empty areas of the universe called voids could help solve the greatest mysteries in the cosmos.

My graphic accompanying How Analyzing Cosmic Nothing Might Explain Everything in the January 2024 issue of Scientific American depicts the entire Universe in a two-page spread — full of nothing.

Martin Krzywinski @MKrzywinski mkweb.bcgsc.ca
How Analyzing Cosmic Nothing Might Explain Everything. Text by Michael Lemonick (editor), art direction by Jen Christiansen (Senior Graphics Editor), source: SDSS

The graphic uses the latest data from SDSS 12 and is an update to my Superclusters and Voids poster.

Michael Lemonick (editor) explains on the graphic:

“Regions of relatively empty space called cosmic voids are everywhere in the universe, and scientists believe studying their size, shape and spread across the cosmos could help them understand dark matter, dark energy and other big mysteries.

To use voids in this way, astronomers must map these regions in detail—a project that is just beginning.

Shown here are voids discovered by the Sloan Digital Sky Survey (SDSS), along with a selection of 16 previously named voids. Scientists expect voids to be evenly distributed throughout space—the lack of voids in some regions on the globe simply reflects SDSS’s sky coverage.”

voids

Sofia Contarini, Alice Pisani, Nico Hamaus, Federico Marulli Lauro Moscardini & Marco Baldi (2023) Cosmological Constraints from the BOSS DR12 Void Size Function Astrophysical Journal 953:46.

Nico Hamaus, Alice Pisani, Jin-Ah Choi, Guilhem Lavaux, Benjamin D. Wandelt & Jochen Weller (2020) Journal of Cosmology and Astroparticle Physics 2020:023.

Sloan Digital Sky Survey Data Release 12

constellation figures

Alan MacRobert (Sky & Telescope), Paulina Rowicka/Martin Krzywinski (revisions & Microscopium)

stars

Hoffleit & Warren Jr. (1991) The Bright Star Catalog, 5th Revised Edition (Preliminary Version).

cosmology

H0 = 67.4 km/(Mpc·s), Ωm = 0.315, Ωv = 0.685. Planck collaboration Planck 2018 results. VI. Cosmological parameters (2018).

Error in predictor variables

Tue 02-01-2024

It is the mark of an educated mind to rest satisfied with the degree of precision that the nature of the subject admits and not to seek exactness where only an approximation is possible. —Aristotle

In regression, the predictors are (typically) assumed to have known values that are measured without error.

Practically, however, predictors are often measured with error. This has a profound (but predictable) effect on the estimates of relationships among variables – the so-called “error in variables” problem.

Martin Krzywinski @MKrzywinski mkweb.bcgsc.ca
Nature Methods Points of Significance column: Error in predictor variables. (read)

Error in measuring the predictors is often ignored. In this column, we discuss when ignoring this error is harmless and when it can lead to large bias that can leads us to miss important effects.

Altman, N. & Krzywinski, M. (2024) Points of significance: Error in predictor variables. Nat. Methods 20.

Background reading

Altman, N. & Krzywinski, M. (2015) Points of significance: Simple linear regression. Nat. Methods 12:999–1000.

Lever, J., Krzywinski, M. & Altman, N. (2016) Points of significance: Logistic regression. Nat. Methods 13:541–542 (2016).

Das, K., Krzywinski, M. & Altman, N. (2019) Points of significance: Quantile regression. Nat. Methods 16:451–452.

Martin Krzywinski | contact | Canada's Michael Smith Genome Sciences CentreBC Cancer Research CenterBC CancerPHSA
Google whack “vicissitudinal corporealization”
{ 10.9.234.151 }