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A Review of Color Blindness for Microscopists: Guidelines and Tools for Accommodating and Coping with Color Vision Deficiency

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  • Shriners Hospitals for Children in Portland Oregon

Abstract and Figures

"Color blindness" is a variable trait, including individuals with just slight color vision deficiency to those rare individuals with a complete lack of color perception. Approximately 75% of those with color impairment are green diminished; most of those remaining are red diminished. Red-Green color impairment is sex linked with the vast majority being male. The deficiency results in reds and greens being perceived as shades of yellow; therefore red-green images presented to the public will not illustrate regions of distinction to these individuals. Tools are available to authors wishing to accommodate those with color vision deficiency; most notable are components in FIJI (an extension of ImageJ) and Adobe Photoshop. Using these tools, hues of magenta may be substituted for red in red-green images resulting in striking definition for both the color sighted and color impaired. Web-based tools may be used (importantly) by color challenged individuals to convert red-green images archived in web-accessible journal articles into two-color images, which they may then discern.
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Cambridge University Press
Microsc. Microanal. 00, 111, 2015
1doi:10.1017/S1431927615000173
2
© MICROSCOPY SOCIETY OF AMERICA 2015
3A Review of Color Blindness for Microscopists:
4Guidelines and Tools for Accommodating and Coping
5with Color Vision Deficiency
6Douglas R. Keene
Q1 *
7Shriners Hospital for Children, Micro-Imaging Center, 3101 SW Sam Jackson Park Road, Portland, OR 97239, USA
8Abstract: Color blindnessis a variable trait, including individuals with just slight color vision deciency to
9those rare individuals with a complete lack of color perception. Approximately 75% of those with color
10 impairment are green diminished; most of those remaining are red diminished. Red-Green color impairment is
11 sex linked with the vast majority being male. The deciency results in reds and greens being perceived as shades of
12 yellow; therefore red-green images presented to the public will not illustrate regions of distinction to these
13 individuals. Tools are available to authors wishing to accommodate those with color vision deciency; most
14 notable are components in FIJI (an extension of ImageJ) and Adobe Photoshop. Using these tools, hues
15 of magenta may be substituted for red in red-green images resulting in striking denition for both the color
16 sighted and color impaired. Web-based tools may be used (importantly) by color challenged individuals to
17 convert red-green images archived in web-accessible journal articles into two-color images, which they may then
18 discern.
19 Key words:
Q2 accommodating color blindness, illustration, gure, simulate vision deciency, Photoshop, Image J
20 FIJI, journal archive, daltonize, protanopia, deuteranopia
21 INTRODUCTION
22 With the prevalence of diverse colors in histological stains,
23 uorescent labels, and multicolored illustrations presented in
24 the life sciences, consideration of the viewers ability to dis-
25 criminate different colors is appropriate. Color blindness
26 affects up to 8% of males and 0.4% of females. This article
27 alerts the microscopy community to the prevalence of color
28 vision deciency within our audience and suggests the use of
29 readily available tools to simulate how a multicolored image
30 is perceived by affected individuals. With these tools the
31 author may prepare data using a color scheme that allows
32 striking denition to both color sighted and color challenged
33 individuals. With the realization that many images within
34 published archives are intangible to color decient individuals,
35 real timetools that convert an image to one perceptible to
36 virtually all individuals are presented.
37 The term Color blindnessis unquestionably a mis-
38 nomer. The term leads one to believe that color blind
39 individuals perceive their surroundings only in grayscale, but
40 in fact the disorder has many nuances and degrees. To
41 understand these nuances, a basic understanding of the
42 anatomy of the human retina is helpful. Among the photo-
43 receptors of the retina, there are approximately seven million
44 cone cells and 120 million rod cells (Fig. 1). Cones are found
45 mainly in the central area of the retina (fovea), while rods are
46 found in the peripheral retina. These photoreceptors are
47composed of an inner segment and an outer segment, as well
48as a cell body and synaptic terminal. The photo pigment in
49rods is contained within attened, internalized discs within
50the outer segment, whereas in cones the photo pigments are
51contained within membrane infoldings of a much shorter
52outer segment. Cone cells are responsible for color vision and
53function best in high levels of illumination. Rod cells func-
54tion in low levels of illumination, triggered by just a few
55photons. Since cones are not stimulated by low light levels,
56night vision is primarily a function of rods and is mostly
57devoid of color; at higher light levels rods sense intensity, an
58important secondary role in color vision.
59Within photoreceptors, the photosensitive pigments are
60the opsins, a group of light-sensitive 3555 kDa membrane-
61bound G protein-coupled receptors of the retinylidene
62protein family. Rod cells contain only rhodopsin. Cone cells
63contain various ratios of three opsins, distinguished by
64differences in their amino acid sequences, which result in
65differing light-absorption curves. Long-wave sensitive opsins
66(OPN1LW; MIM*300822) have a maximum absorbance
67at 561 nm, medium-wave sensitive opsins (OPN1MW;
68MIM*300821) at 531 nm and short-wave sensitive opsins
69(OPN1SW; MIM*613522) at 430 nm (Bowmaker & Dartnall,
701980; Baylor et al., 1987; McIntyre, 2002). These maximal
71sensitivities are very close to the primary colors red, green,
72and blue (RGB), respectively, and are therefore often referred
73to by those colors. Interestingly, red-green color deciency
74is a sex-linked recessive trait, with the OPN1LW (red)
75and OPN1MW (green) genes mapped to the distal part of
76chromosome X. Women may carry a defective X chromosome
*Corresponding author. drk@shcc.org
Received November 11, 2014; accepted January 27, 2015
77 but do not show any sign of deciency as the normal
78 X chromosome acts dominantly. Although rare, color de-
79 ciency resulting from mutations in the gene for OPN1SW
80 result in blue color insensitivities. The gene for OPN1SW is
81 mapped to chromosome 7 and is therefore not a sex-linked
82 trait (Nathans et al., 1986).
83 OPN1SW, OPN1MW, and OPN1LW are all normally
84 present in each of the three types of cones;which of the
85 opsins predominates dictates the cones sensitivity to a dif-
86 ferent part of the color spectrum, dening the cone as red,
87 green, or blue. An object whose color falls anywhere in the
88 visible spectrum will therefore excite all three types of cones
89 to a varying extent (Hurvich & Jameson, 1957; Shevell,
90 2003). Variation in perceived color among normal and color
91 decient individuals is most often caused by differences in
92 amino acids involved in tuning the spectra of the red and
93 green cone pigments. A non-null mutation in any one of the
94 opsins may result in a slight shift of the maximal sensitivity
95 of one of those three types of cones. This will result in less
96 possible color mixtures and therefore a reduction in some
97 portion of the perceived color spectrum (Rushton, 1966; Deeb,
98 2005). The disorder is referred to as anomalous trichromacy.
99 Among the variations, protanomaly, deuteranomaly, and tri-
100 tanomaly come from Greek and literally mean deviation
101 from the common(anomaly)withtherst (prot-), second
102 (deuter-), or third (trit-) [cone], respectively (Fig. 2).
103 Protanomaly results from a mutated form of the
104 long-wavelength (red) pigment OPNILW, leading to less
105 sensitivity to red light. The red portion of the spectrum is
106 darkened, causing reds to reduce in intensity to the point
107 where they can be mistaken for black. Although protanomaly
108
109
110
111
is a fairly rare form of color deciency (1% of males and 0.1%
112of females), for the benet of these individuals it is important
113to avoid dark red images in presentations; also red laser
114pointers will not be as visible green laser pointers.
115Deuteranomaly affects 6% of males and 0.4% of females
116(Nathans et al., 1986) and is the most common form of color
117deciency. Deuteranomaly results from a mutated form of
118the medium-wavelength (green) pigment OPN1MW. The
119peak sensitivity is shifted from the green region toward the
120red region of the spectrum. Similar to protanomaly, deuter-
121anomaly results in reduced discrimination within the red,
122orange, yellow, and green regions of the spectrum. In order
123to match a given hue of yellow light, deuteranomalous
124observers need more green in a red/green mixture than a
125normal observer. From a practical standpoint though, many
126protanomalous and deuteranomalous individuals have little
127difculty carrying out everyday tasks that require normal
128color vision, and may not even be aware that their color
129discrimination differs from normal. As an aside, my friend
130(pictured with the green sail, to the right in the windsurng
131picture, Fig. 3a) and I unfailingly disagree about the color of
132his sail. I insist that the color is green, and he insists that it is
133yellow. I showed him Figure 3, and to both our surprise he
134could not distinguish the normalfrom the deuteranopia
135image. As it turns out, the color blindtests discussed below
136suggest his vision deciency as moderate deuteranomaly.
137There is a continuous gradation within color blindindi-
138viduals; deuteranomaly can be everything between near-
139normal color vision and deuteranopia, where OPN1MW is
140missing completely.
Figure 2. Two colored images are often presented in red-green,
with overlapping regions in yellow. The normal sighted would
perceive the colors red, yellow, green, and blue as in column N.
Column Psimulates the same colors as perceived by a person
with protanopia, column Ddeuteranopia, and column Ttrita-
nopia. Only Tritanopes would be able to distinguish all these color
dots as separate, albeit in different hues.
Figure 1. Scanning electron micrograph of human rod (gray) and
cone cells (magenta) adjacent to the outer nuclear layer (orange).
This colorized image is viewable to those with red, green, or blue
color deciencies [Image courtesy of Stephen Gschmeissner
(www.theworldcloseup.com)].
2Douglas R. Keene
141 Tritanomaly is the rarest form of color deciency, with
142 an incidence of just 0.01% in both males and females
143 (Nathans et al., 1986). Tritanomaly results from a mutated
144 form of the short-wavelength (blue) pigment resulting in
145 color perception that is shifted toward the green region of the
146 spectrum.
147 If one opsin is missing completely, there will be an
148 inability to see(anopia) red (prot-), green (deuter-), or
149 blue (trit-). These individuals have dichromatic vision,
150 meaning that they must match any color they see with a
151 mixture of just two primary colors.
152 Protanopia and deuteroanopia each occur in about 1%
153 of the male population (Nathans et al., 1986). For these
154 forms of color deciencies, both red and green are perceived
155 as yellow and therefore cannot be distinguished (Fig. 2).
156 Protanopes also perceive a reduced brightness that deuter-
157 anopes do not share, most pronounced in hues of red, which
158 may be so severe that dimmer reds blend into black. They
159 may confuse an active red lightwithin a trafc signal as
160 extinguished. These nuances are best appreciated by com-
161 paring a full spectrum color chart with one simulated for
162 color blindness(Fig. 4).
163 Monochromacy, resulting from a lack in all three opsins,
164 is the only true color blindness as only shades of gray are
165 seen. These individuals also have a severe light sensitivity, as
166 there are only rods available to retrieve visual information.
167There are currently no cures offered for human color
168blindness. However, studies in color blind monkeys that
169have provided the missing photo pigment by viral mediated
170gene transfer have successfully resulted in perception of the
171full color spectrum (Mancuso et al., 2009).
172
COLOR MODELING
173As a caveat, there is continual variability in the population
174resulting in different sensitivities of the color spectrum.
175Colors will also appear differently to the same individual in
176the context of lighting, shadows, luminosity, and intensities
177(Shevell & Kingdom, 2009). The perception of a paint-chip
178color chart is different under incandescent light as compared
179with natural sunlight; it also appears altered in bright light
180compared with dim; on a glossy surface compared with
181matte. Color modeling seeks to standardize, catalog, and
182reproduce color from one medium to another, but in the end
183there will always be variation in the individualistic percep-
184tion of those colors.
185
COLOR CODES
186The color of an object depends on both the physics of
187the object in its environment and the characteristics of the
Figure 3. Normal individuals perceive red-green images as in the left column (a,c), whereas deuteranopes (simulated
in the right column, b,d) and also protanopes perceive the same images only in shades of yellow.
Composing and Viewing Colored Illustrations 3
188 perceiving eye and brain. In its purest sense, color results
189 from spectral illumination which is reected, emitted, or
190 transmitted through an object; the remaining portion of the
191 spectrum is absorbed by that object. Absolute color refers to a
192 color space in which colors are explicit; the documentation
193 of color in this space is colorimetrically dened without
194 reference to external factors (Knudson, 1999). However, the
195 mathematical relationship that denes absolute color must
196 also factor the average human perception of color. These
197 data also need to be translated into a quantiable form that
198 can be understood by imaging software, monitors, printers,
199 and ultimately those who will view the image. CIELab and
200 sRGB are examples of absolute color spaces. The numeric
201 values in CIELab color models describe all the colors that a
202 person with normal vision sees, based on one channel for
203 luminance (L; values range from 0 to 100) and two color
204 channels (a,thegreenred axis and b,theblueyellow axis).
205 For example, the values L=72, a=59, and b=40 describe
206 the magenta color circled in the micrograph in Figure 5.
207 Because CIELab describes how a color looks rather than
208 how much of a particular colorant is needed for reproduc-
209 tion (using a device such as a monitor, desktop printer, or
210 digital camera), CIELab is considered to be a device-
211 independent color model. Color management systems use
212 Labas a color reference to predictably transform a color
213 from one color space to a different color space, such as the
214 different codes used by a monitor and a printer. Lab images
215can be saved in Photoshop, Photoshop PDF, and Tiff, as well
216as other formats.
217
RGB COLOR MODEL
218The RGB color mode most closely mimics color vision in the
219human eye (using RGB cones to dene color) and is the
220default mode for displaying an image on monitors. Each of
221the color channels has an intensity level range between 0 and
222255 in an 8-bit image; combinations of these channels result
223in over 16 million possible colors. This mode assigns an
224intensity value to each pixel. In 8-bit images, the intensity
225values range from 0 (black) to 255 (white) for each of the
226RGB components of a color image. When the values of all
227three components are equal, the result is a shade of neutral
228gray. When the values of all components are 255, the result is
229pure white; when the values are 0, pure black. For example,
230the magenta color circled in Figure 5 has an R value of 253, a
231G value of 131, and a B value of 253. As in the eye, the RGB
232color model is also additive, meaning that colors become
233more brilliant as more light is added. RGB is the most vibrant
234of the color models and is supported by nearly all le for-
235mats. An unhappy analogy to color perception is that the
236range of colors displayed on different monitors will depend
237on variations among those monitors. However, if the RGB
238colors of the monitor are calibrated exactly (together with
Figure 4. Reprinted with permission from visibone.com, the left panel demonstrates the full spectrum of visible colors
as perceived by those with normal vision. The right panel simulates how a person with deuteranopia would perceive
the same spectrum. These charts are enormously useful for designing illustrations and web pages accessible to color
challenged individuals.
4Douglas R. Keene
239 other properties of the monitor) then RGB values on that
240 monitor can be considered absolute.
241 TESTING FOR COLOR DEFICIENCIES
242 The best known test for red-green color deciency was
243 developed by Dr. Shinobu Ishihara at Tokyo University in
244 1917. It consists of 38 pseudoisochromeric plates, each with a
245 pattern of differently shaded dots. Within each plate is a
246 number or shape composed of dots with contrasting hues
247 (Ishihara, 1972). To those with normal color vision, these
248 dots will be dissimilar enough from the background to form
249 agure or recognizable pattern on each plate, whereas those
250 with a red-green color vision defect will not detect a gure on
251 all plates. The success and failures of each plate are con-
252 sidered together, resulting in a diagnosis of normal to a
253 particular degree of color insensitivity. Dr. Ishihara was
254 concerned that if the plates were not exactly reproduced
255 misdiagnosis would ensue, to the extent that he controlled
256 the production of the plates for many years. Today there are
257 many online versions that will give some indication of the
258 type and degree of color vision deciencies (see Colblindor at
259www.color-blindness.com). The accuracy of these tests may
260be diminished since most computer monitors are not cali-
261brated; however, a general diagnosis is often made after
262viewing just a few plates (Fig. 6).
263Deemed among the more accurate of the tests, the
264Farnnsworth-Munsell 100 Hue Color test contains four dis-
265tinct rows of tiles arranged based on different color families.
266The left- and right-most tile in each is anchored, but all other
267tiles may be arranged so that the nearest neighbors are
268closest in hue. The test result is based on the number of
269instances that a hue cluster is misplaced, or the severity of a
270tile displacement. The test result seeks to specically classify
271individual color deciency in terms of deut-, prot-, and trit-
272severities (Supplementary Figure 1). Similarly, Anomalo-
273scope color blind tests allow the user to continuously vary the
274colors and hues on one panel to match the color presented
275on a second xed panel (Nagel, 1907; Cole & Vingrys, 1982).
277
278
279
Supplementary Figure 1
280Supplementary Figure 1 can be found online. Please visit
281journals.cambridge.org/jid_MAM.
Figure 5. Colors are assigned different numeric values that are unique to each color mode. A color table (b) showing
all the hues in an open image (a) may be accessed in Photoshop by rst converting the image to Indexed color mode
(Image/Mode/Indexed color); then: Image/Mode/Color table. A left clickon any color in the color table followed by
left clickon any color in the image will display the numeric color values (arrow, c). The circled color in the micro-
graph (arrow, a) is identied in HSB mode with hue, saturation, and brightness values of 300°, 48 and 99%, respec-
tively. HSB mode seeks to dene color as we see it, for example bright reddish-pink.In RGB mode the color circled
in the micrograph is identied as 253 parts red, 131 parts green, and 253 parts blue. In Lab mode the circled region has
a luminosity value of 72; it is at position 59 on the red-green scale and at position 40 on the blue-yellow scale. The
percentage of cyan, magenta, yellow, and black inks used to print the image would be 19, 54, 0, and 0, respectively.
Composing and Viewing Colored Illustrations 5
282
283 FIJI
284 It is likely that the keystrokes dened here will change with
285 newer versions of FIJI. The version of FIJI used for these
286 descriptions was updated in late December 2014.
287 Algorithms have been developed for normal sighted
288 individuals wishing to simulate color as perceived by color
289 decient individuals. Algorithms for color decient indivi-
290 duals to simulate normal color vision have also been devel-
291 oped (Brettel et al., 1997). Simulating how an image is
292 perceived by an individual with a color vision decit is par-
293 ticularly useful in determining the accessibility of an image
294 before presentation or publication. This can be easily facili-
295 tated using FIJI, which is an extension of ImageJ. FIJI is an
296 image processing package having an array of pluginsof
297 interest to the life scientist. It is available as a free download
298 (FIJI.sc), installs easily, and has an automatic update func-
299 tion. FIJI includes an algorithm that simulates the perception
300 of a color image by individuals affected with protanopia,
301 deuteroanopia, or tritanopia (FIJI/Image/Color/Simulate
302 Color Blindness). Alternatively, a plugin may be downloaded
303 (currently at Vischeck.com) and added to FIJI, allowing
304 continuous access to the simulation (Plugins/Vischeck
305 Panel). This plugin produced the deuteranopia simulation of
306 the full spectrum image in Figure 4. The comparison is
307 arresting and beautifully demonstrates the utility of the
308 protocol. This plugin was also applied to the images of
309 windsurfers and cultured cells (Fig. 3), demonstrating that a
310 person with deuteranopia would not be able to distinguish
311the sail colors or differences in cell component localization in
312these red/green images.
313Developed by Masataka Okabe (Jikei Medical School)
314and Kei Ito (U. Tokyo) and implemented by Johannes
315Schindelin (University of Wisconsin-Madison), a one-button
Figure 6. Take the Ishihara Test! Color sighted individuals will perceive the numbers 7 and 2 embedded in the dot
matrix (left). Protanopia (center) and deuteranopia (right) visions are simulated; these individuals will not perceive the
numbers.
Figure 7. Normal vision distinguishes the color dots as red,
yellow, green, and blue (column N). Those affected with prot-
and deuter-anopias cannot distinguish red and green from yellow.
If the entire column Nis opened as a single image in FIJI; then
Image/Color/Replace Red with Magenta/, the resultant is column
(R M). Columns P, D, and T simulate how persons with
protanopia, deuteranopia, and tritanopia would perceive column
(R M). Note that all color dots may now be distinguished by
color challenged individuals. Note also that yellows are perceived
as white; overlap in red-green images would be perceived as
shades of white.
6Douglas R. Keene
316 solution (FIJI/Image/Color/Convert Red to Magenta) to
317 altering a red/green image so that it is discernible by all is
318 offered in FIJI. Magenta is substituted for red. The resulting
319 image is striking for both the color sighted and color impaired
320 (Figs. 7, 8). This is a fantastic tool for illustrators in the life
321 sciences. When applied to a red/green confocal image, regions
322 of overlap can be distinguished as shades of white (Supple-
323 mentary Figure 2). An argument may be made to unilaterally
324 substitute magenta for red in all two-color images. We may
325 hope that manufacturers will include magenta as an option in
326assigning color to multicolored uorescent images and also
327apply it to systems producing multicolored graphs.
329
330
331
Supplementary Figure 2
332Supplementary Figure 2 can be found online. Please visit
333journals.cambridge.org/jid_MAM.
334335The conversion of red to magenta will not work for three
336color images showing co-localization (Supplementary Figure 3).
Figure 8. The red portion of the red-green image in Figure 3c is converted in FIJI to magenta, allowing striking
contrast for both the color sighted (a) and also Deuteroanopia individuals (simulated in b).
Figure 9. Replacement of one color with another selected for its specic hue may be accomplished in Photoshop (Image/
Adjustments/Replace Color). In this gure the red colored vesicles (arrow, a)wereselectedandaspecic hue of magenta
substituted for red (arrow, b). A livesimulation of deuteranopia or protanopia, as the hues are varied, may be toggled
on and off (see the text for keystrokes). Given its ease and versatility, this method for color substitution is favored.
Composing and Viewing Colored Illustrations 7
337 Here, the only solution is to represent two channels at a
338 time, or grayscale versions of the three separated channels,
339 which often benets all viewers as grayscale images will
340 demonstrate minor grades in intensity to best advantage
341 (Supplementary Figure 4).
343
344
345 Supplementary Figures 3 and 4
346 Supplementary Figures 3 and 4 can be found online.
347 Please visit journals.cambridge.org/jid_MAM.
348
349 ADOBE PHOTOSHOP
350 Keystrokes may change with upcoming versions of Adobe
351 Photoshop; the keystrokes dened here are available using
352 either CS5.1 or CS6.
353 When working in Photoshop, the analytical tools avail-
354 able are dependent on the chosen color mode [Image/Mode
355 (select Indexed, RGB, CMYK, Lab color, or Multichannel)]
356 one is working with. While editing an image, RGB is a good
357 choice since the color range is the broadest; however, if the
358image is to be printed it should be checked in CMYK mode,
359which is the code printers use to reproduce images.
360Adobe Photoshop allows the same adjustments and
361simulations available in FIJI. To simulate either protanopia
362or deuteranopia, open the image and then select (View/Proof
363Setup/Color Blindness/select either Deuteranopia or Prota-
364nopia). Then, selecting (View/Proof Colors) will toggle the
365image between the original and the simulation for deuter-
366anopia or protanopia (depending on which was selected).
367This is very convenient, as it allows a quick and seamless
368transition between the original and the simulation, which
369may be toggled as one manipulates the image.
370Adobe Photoshop does not share the one-button con-
371version of red to magentaoffered in FIJI. However, repla-
372cing one color with another is quite simple. To do this, open
373the image in RGB mode and then select (Image/Adjust-
374ments/Replace Color). This will open the Replace Color
375screen. Select the box for Localized Color Clusters,select
376the left eyedropper tool, set fuzzinessto 200, select
377Selection,then single click on the color to be changed
378(Fig. 9). Most often adjustment of the hueslider will result
379in a wanted color replacement. One may wish to adjust the
Figure 10. Color decient individuals are often signicantly challenged by multicolored graphs and charts. Red and
green lines cannot be distinguished by many individuals. Care should be taken not to rely on a color key;instead
arrows should designate the identity of each plot. Alternatively, Photoshop may be used, as in Figure 8, to choose and
adjust hues within the plots. In this gure, the red dashed line (arrow, a) was replaced with a magenta dashed line
(arrow, b) using the Replace Colortool in Photoshop (c). A simulation of deuteranopia and tritanopia demonstrates
that the colors black, yellow, green, magenta, and dark blue in the lower graph may be distinguished; however,
Protanopes will still have difculty with this color combination. The use of dotted, dashed (etc.) lines is highly
recommended.
8Douglas R. Keene
380 fuzzinessslider with selectionchecked, which will show
381 like-colored regions in the image where the color will be
382 replaced. If deuteranopia or protanopia have already been
383 selected via the View/Proof Setup keystrokes, the View/Proof
384 Colors option will allow live simulation of color blindness as
385 the Hue slider is adjusted. Depressing Ctlon the keyboard
386 will open a small image visualization of the original, non-
387 adjusted image. The control of image color is so thoroughly
388 interactive and adjustable that this has become a favorite
389 mechanism for color replacement.
390 Similarly, multicolored graphs and tables can also be
391 problematic for color challenged individuals. As shown in
392 Figure 10, good choices for colored lines include black, dark
393yellow, green, magenta ,and dark blue. It is very helpful to
394designate the identity of each line with a symbol and arrow,
395alas not with a color key. In addition, valuable is the inclusion
396of differing solid, dotted, and dashed lines, making color a
397useful (to the color sighted) but unnecessary (for the color
398decient) element in discerning one plot from another.
399
WEB-BASED TOOLS
400An extension to the Google Chromebrowser dubbed
401Chrome Daltonizeis invaluable to both color vision
402normal and impaired individuals. Once Google Chrome is
Figure 11. An image may be directed to Colorblinds.org either by opening the image directly in colorblinds.org or
using an extension to Mozilla Firefox (see text). The image may be Daltonized or displayed as the original. The original
image is shown in (b), with (c) simulating the deuteranopia vision of (b). a: Simulates that deuteranopes distinguish
two colors, with regions of co-localization, in the Daltonized image. Interactively, the cursor (arrow, a) may be posi-
tioned over any part of the image and the color (yellow) and hue (golden poppy) at that position within the original
image will be reported.
Composing and Viewing Colored Illustrations 9
403 installed, the Chrome Daltonize extension may be added. A
404 small color wheel will appear next to the address window of
405 the Google Chrome browser (Supplementary Figure 5). A
406 right click on the color wheel will open an options menu.
407 From this menu one may choose to Simulate or Daltonize
408 prot, deuter- ,or trit-anopia subsequently opened websites.
409 Chrome Daltonize can be toggled on/off by selecting the
410 customize button at the farthest right side of the address
411 window (settings/extensions/Chrome Daltonize). Daltoni-
412 zation is a technique of modifying hues by enabling specic
413 algorithms designed to compensate for each color deciency.
414 When enacted, a red-green image that would not be dis-
415 cernible to one with red-green deciency is transformed to
416 an image that is discernible. It works much like the Fiji
417 plugin (Convert Red to Magenta) described above. This is an
418 enormously useful tool for those with color deciencies
419 wishing to discriminate two-color archived journal images,
420 which are most often red and green. These images are pre-
421 valent in our journals as evidenced by Allred et al. (2014),
422 reporting that among the papers published in Nature from
423 January to April 2014 with at least one gure requiring color
424 discrimination, 75% used red-green images. Even if red/
425 green images in future publications were eliminated, these
426 archived images will exist for eternity.
428
429
430 Supplementary Figure 5
431 Supplementary Figure 5 can be found online. Please visit
432 journals.cambridge.org/jid_MAM.
433434 An extension may be added to the Mozilla Firefox
435 browser so that a web image may be Daltonized with hues
436 specically modied for protanopia, deuteroanopia, or tri-
437 tanopia. The extension adds the menu item open image on
438 colorblinds.orgto the right-click menu as the mouse is
439 hovered over a web image. This redirects the image to col-
440 orblinds.org where it is daltonized. An added feature of this
441 site is the ability for color decient individuals to identify the
442 hues and specic colors in an image as it is visualized by
443normal sighted individuals. This can be very useful for the
444color challenged individual wishing to identify specic
445colored regions in a ber when directed by text (Fig. 11).
446Currently the extension may be downloaded from Color-
447blinds.org.
448Although somewhat more cumbersome for web-based
449image simulation, Chrometricwill simulate anopias and
450anomalies from images stored on your computer, making it a
451more versatile than FIJI or Photoshop for simulating a wider
452variety of color disorders. Images may be directly entered
453into the browser window, but since the browser does not
454include a search engine URLs must also be entered directly.
455Supplementary Figure 6 demonstrates the utility of the
456simulator. The free browser may be downloaded from
457vaadin.com.
459
460
461
Supplementary Figure 6
462Supplementary Figure 6 can be found online. Please visit
463journals.cambridge.org/jid_MAM.
464465There are also hardware items that will aid the color
466impaired to better discriminate red/green images. Oxy-Iso
467lenses were developed for use by the medical community to
468identify veins and bruising that are otherwise undetectable to
469the naked eye. The lenses enhance red hues to the extent that
470people with red-green color deciencies will likely pass the
471Ishihara test. However, the lenses are not a cure for color
472insensitivities as they lter out yellow and blues to the extent
473that a yellow light may appear extinguished. Another eye-
474wear alternative are EnChromalenses designed specically
475for correction of either protanopia or deuteranopia. These
476lenses have ~100 coatings of dielectric material, each just a
477few nanometers thick, for ltering or reecting specic
478portions of the spectrum between the primary colors to
479enhance reds and greens (Fig. 12).
480DanKam(Fig. 12) is an application available for
481smartphones that allows the user to display a scene through
482the camera and compensate for his or her color deciency by
Figure 12. Hardware tools for those with color blindness include oxy-isoand enchromalenses (left panel). Appli-
cations (apps) are available for smartphones that can be tuned for an individuals particular deciency (i.e., DanKam,
right panel). Both tools will likely allow a color decient individual to pass the Ishihara test and signicantly aid in red-
green denition.
10 Douglas R. Keene
483 using a continuously variable lter, allowing one to enhance
484 various spectral colors. With this inexpensive app, a person
485 with red-green color deciency can see patterns in an
486 Ishihara test (Fig. 7) that were previously not detectable.
487 Although somewhat sluggish in response, the application
488 allows “‘liveimage conversionwith
Q3 the portability of a
489 smartphone.
490 In addition, there are some excellent websites that suggest
491 guidelines for the preparation of gures and presentations
492 accessible to color decient individuals. It is enormously use-
493 ful to consider the experience of color challenged individuals.
494 Most notableamong these sites is (M. Okabe and K. Ito. How
495 to make gures and presentations that are friendly to Color
496 blind people.Modied 2008: http://jy.iam.u-tokyo.ac.jp/
497 color/index.html#checker (see al
Q4 so Wong, 2010, 2011).
498 REFERENCES
499 ALLRED, S.C., SCHREINER, W.J. & SMITHIES, O. (2014). Color blindness:
500 Still too many red-green gures. Nature 510, 340.
501 BAYLOR, D.A., NUNN, B.J. & SCHNAPF, J.L. (1987). Spectral sensitivity
502 of cones of the monkey Macaca fascicularis. J Physiol 390,
503 145160.
504 BOWMAKER, J.K. & DARTNALL, H.J. (1980). Visual pigments of rods
505 and cones in human retina. J Physiol 298, 501511.
506 BRETTEL, H., VIENOT,F.&MOLLON, J.D. (1997). Computerized
507 simulation of color appearance for dichromats. J Opt Soc Am A
508 14, 26472655.
509COLE,B.L.&VINGRYS, A.J. (1982). A survey and evaluation of lantern
510tests of color vision. Am J Optom Physiol Opt 59,346374.
511DEEB, S.S. (2005). The molecular basis of variation in human
512color vision. Clin Genet 67, 369377.
513HURVICH, L.M. & JAMESON, D. (1957). An opponent-process theory
514of color vision. Psychol Rev 64, 384404.
515ISHIHARA, S. (1972). Tests for Colour-Blindness. Tokyo, Japan:
516Kanehara Shuppan Co., LTD.
517KNUDSEN, J.B. (1999). Java 2D Graphics. Sebastopol, CA: OReilly &
518Associates.
519MANCUSO, K., HAUSWIRTH, W.W., LI, Q., CONNOR, T.B.,
520KUCHENBECKER, J.A., MAUCK, M.C., NEITZ,J.&NEITZ, M. (2009).
521Gene therapy for red-green colour blindness in adult primates.
522Nature 461, 784787.
523MCINTYRE, D. (2002). Colour Blindness: Causes and Effects. Chester,
524UK: Dalton Publishing.
525NAGEL, W.A. (1907). Two cameras for Augenärzliche function test.
526Adaptometer and small spectrophotometer (Anomaloscope).
527J Ophthalmol 17, 201222.
528NATHANS, J., THOMAS,D.&HOGNESS, D.S. (1986). Molecular genetics
529of human color vision: Genes encoding blue, green, and red
530pigments. Science 232, 193202.
531RUSHTON, W.A. (1966). Densitometry of pigments in rods and cones
532of normal and color defective subjects. Invest Ophthalmol 5,
533233241.
534SHEVELL, S.K. (2003). The Science of Color. Oxford, UK: Elsevier.
535SHEVELL, S.K. & KINGDOM, A.A. (2009). Color in complex scenes.
536Annu Rev Psychol 59, 143166.
537WONG, B. (2010). Points of view: Color coding. Nat Met 7, 573.
538WONG, B. (2011). Color blindness. Nat Met 8, 441.
539
Composing and Viewing Colored Illustrations 11
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This paper reports a survey of the lantern tests that have been or are used to evaluate the color vision of people who wish to enter occupations that require the ability to recognize colored signal lights reliably. The origin of each lantern is traced and the principal features of each are described. The available data concerning failure rate of normals, the failure rate of people with defective color vision, and the extent to which scores on lantern tests correlate with field trials are summarized. Despite the fact that lantern tests have been used since the turn of the century and that some lanterns have been in use for more than 30 years and some for much longer periods, the available validation data are incomplete and sometimes conflicting. However, the data do indicate that some lanterns may fail a significant proportion of normals and that there is considerable variation between lanterns in the proportion of color vision defectives that will fail. It is noted that most lanterns will pass some protanomals despite their reduced sensitivity to red light and correspondingly short visual range for red signals. The view of Cameron is supported that a more rational approach would be to made a clinical diagnosis of the type of color vision defect, to reject protanopes, deuteranopes, and protanomals and to use a lantern test only to determine which deuteranomals should be accepted.