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](https://apcacontrast.com)
151 |
152 | Myndex and Inclusive Reading Technologies are the only authoritative reference for APCA and related contrast guidelines.
17 |If you came here via the link from the xi repository, please be aware that repository is not authorized, and includes a substantial amount of misleading, incorrect, and or simply bizarre material that has little relationship to the reality of human perception of contrast.
18 |We were concerned regarding the potential confusion and furtherance of misunderstandings in a field that's already difficult to grasp, we analyzed and provided a corrected version, as well as rebuttals, to that very poorly conceived collection.
19 |If you are interested in seeing how math was being used to mislead, please see our fork
20 | 21 |
78 |
79 | ## APPENDIX: _Additional Reading_
80 | - [**Linktree of Selected Resources**](https://linktr.ee/Myndex) A good place to start.
81 | - [**Main Catalog of APCA Resources and Links**](https://git.myndex.com) For the much deeper divers.
82 |
83 | ### APCA Readability Criterion
84 | _Maintained by Inclusive Reading Technologies Inc., a California Non-Profit_.
85 | - [**Draft ARC Guidelines**](https://readtech.org/ARC/) for implementing APCA and related technologies.
86 | - [**Bronze Simple Mode**](https://readtech.org/ARC/tests/bronze-simple-mode/?tn=intro) is designed as an introductory mode that does not require look-up tables or matching to a reference font. Instead it's designed as a simple set of threshold levels, similar to how WCAG 2 works but using perceptually uniform math.
87 |
88 | ### Links To APCA and Related Tools
89 | - [**APCA Calculator**](https://apcacontrast.com), the official technology demonstrator for APCA, includes explainers.
90 | - Listing of [**Third Party Tools and Systems**](https://git.apcacontrast.com/documentation/thirdpartytools) that have adopted APCA.
91 | - An [**Accurate Colorblind Simulator**](https://myndex.com/CVD/) based on the well respected, peer-reviewed, Brettel et alia model.
92 |
93 | ### Discussion Forum
94 | - [**Readability Forum**](https://github.com/Myndex/SAPC-APCA/discussions/) questions and comments welcome.
95 | - [**DISCUSS: Using APCA with other fonts** ](https://github.com/Myndex/SAPC-APCA/discussions/28#discussioncomment-1610289) Draft method for font weight conformance.
96 | - [**DISCUSS: Inline text links theory and practice** ](https://github.com/Myndex/SAPC-APCA/discussions/65) Draft guidance regarding link identification.
97 | - [**DISCUSS: Draft Dark Mode Guidance**](https://github.com/Myndex/SAPC-APCA/discussions/74#discussioncomment-6646215) Draft guidance regarding darkmode from light mode, and more.
98 | - [**DISCUSS: Legal Issues of WCAG2 vs APCA**](https://github.com/Myndex/SAPC-APCA/discussions/68#discussion-3980510) Discussion of current and future legal status and incorporation into legislation.
99 |
100 | ### Peer Review & Third Party Discussion of APCA
101 | A listing of [**third party and peer reviews**](https://git.myndex.com/#apca-peer-review--third-party-discussion) of APCA and related technologies. This directory includes journal-published peer-reviews, trade-published evaluations, and less formal comparative analysis, covering the usage, math, efficacy, implementation/integration, workflows, and more.
102 |
103 | ### Published Articles on Color & Contrast by A.Somers
104 | - [**The Realities And Myths Of Contrast And Color**](https://www.smashingmagazine.com/2022/09/realities-myths-contrast-color/) Published by _Smashing Magazine_. A brief but comprehensive primer to vision, color, and contrast for design, with an emphasis on typography, readability, and visual accessibility needs.
105 | - [**Better Reading on the Web**](https://uxdesign.cc/better-reading-on-the-web-c943c4cfc91a) Published by _UX Collective_, this article discusses and demonstrates issues with automated testing and WCAG 2 contrast math, methods, and guidelines.
106 |
107 | - **The _Tangled Web_ tech blog** (TangledWeb.xyz):
108 | - [**Please Stop Using Grey Text**](https://tangledweb.xyz/please-stop-using-grey-text-3d3e71acfca8) This popular article debunks one of the worst myths regarding design contrast.
109 | - [**What’s Red & Black & Also Not Read?**](https://tangledweb.xyz/whats-red-black-also-not-read-573b9c0a97ed) examines the nature of color insensitivity and readability.
110 | - [**Busy Background Breaks Bulletin**](https://tangledweb.xyz/busy-background-breaks-bulletin-f4ff4bf67e5a) Examples of how to destroy readability by choosing the wrong image as a background. And also, how to fix it.
111 | - [**Hats off to ALL CAPS**](https://tangledweb.xyz/hats-off-to-all-caps-c0a43a2c30d4) myth-busting misunderstandings regarding dyslexia, are special dyslexia fonts even useful, and the shift from using ALL UPPERCASE LETTERS for various text elements.
112 | - [**A Contrast of Errors**](https://atangledwebweweave.com/a-contrast-of-errors-373c2665d42a) looks at the history and the current international readability crisis.
113 | - [**Contrasting Theories**](https://tangledweb.xyz/hi-roger-f51bde490a56) Background on the first two years of R&D.
114 |
115 |
116 |
117 |
118 |
35 |
36 | ### _Use Cases_
37 | Spot-reading-contrast has a lower requirement than fluent readability contrast. Non-text object contrast such as for a solid icon may also have a lower lightness contrast requirement. And there are some differences in terms of the importance of color (hue or saturation) for things such as information coding.
38 |
39 | No single figure such as 4.5:1 or 3:1 can be used as a blanket target for contrast between two colors, without considering the use case, size, thickness, etc. On this point, it has been demonstrated that WCAG 2 contrast can pass colors that should fail as not readable, and sometimes the WCAG 2 math fails a color pair that _should pass_ as very readable. Some articles with visual comparisons and examples of this are:
40 |
41 | ### _Contrasting Concerns_
42 |
43 | The problems of 4.5:1 as a target for a guideline not only impact accessibility, but impacts standard vision. The inherent problems with the WCAG 2 contrast math have been known for some time and [widely criticized](https://macwright.com/2019/03/30/color-contrast-is-a-problem.html). Including studies [by others showing that color insensitive types](https://www.bounteous.com/insights/2019/03/22/orange-you-accessible-mini-case-study-color-ratio/) are not well served. The WCAG 2 contrast specs often cause enough problems for designers [that it is ignored](https://uxmovement.com/buttons/the-myths-of-color-contrast-accessibility/) and today, some 86% of websites are failing WCAG\_2 contrast—though some failures are not due to actually poor accessibility, but due to the incorrect math of WCAG\_2 contrast.
44 |
45 | -----
46 | ## The Solution: APCA
47 | The Accessible Perceptual Contrast Algorithm (APCA) is a new method for calculating and predicting readability contrast. APCA is a part of the larger S-Luv Accessible Color Appearance Model known as SACAM (formerly SAPC). These models are specifically related to color appearance on self-illuminated RGB computer displays & devices, and also for modeling accessible user needs, with a focus on readability.
48 |
49 | ### _Lightness contrast (Lc)_
50 | The APCA generates a lightness/darkness contrast value based on a minimum font weight/size and color pair, and this value is perceptually based: that is, regardless of how light or dark the two colors are, a contrast value of Lc 60 represents the same _perceived_ readability contrast, across the available range of colors.
51 |
52 | This is absolutely not the case with WCAG 2.x, which far overstates contrast for dark colors to the point that 4.5:1 can be functionally unreadable when a color is near black. As a result, WCAG 2.x contrast cannot be used for guidance designing "dark mode". This also creates problems for color vision deficiency (sometimes called colorblind).
53 |
54 | The APCA contrast value is perceptually uniform, and pivots near the point where the CS curve flattens due to contrast constancy. Halving or doubling the APCA value relates to a halving or doubling of the perceived contrast. There is a subtle weighting for higher contrasts to smaller, thinner fonts.
55 |
56 | ### _Different Uses, Different Contrasts_
57 | The APCA has a set of levels related to use cases — for instance, Lc 90 is _preferred_ and Lc 75 is the _minimum_ for body text. This makes for an easy way to use ACPA, very similar to 1.4.3 in terms of ease of use.
58 |
59 | The APCA also has an **optional** lookup table to associate font size and weight to the readability contrast (Lc value). The lookup tables allow for even greater accuracy and therefore greater flexibility in design.
60 |
61 | ### _Failing Pass/Fail_
62 | A key takeaway is that a strict pass/fail with a blanket contrast ratio is not instructive as a guideline, and does not necessarily solve a given user need. In fact, user needs when it comes to contrast are conflicting—what is good for one can be harmful to another. This is even true of font size.
63 |
64 | This points to the importance of real user personalization, an area where the technology is literally missing (and a work in progress). For the guidelines though, we can set ranges for targets and expectations toward making the web readable for all.
65 |
66 | ## Visual Comparisons
67 | In the following chart, we're showing minimum passing contrasts for APCA and for WCAG 2. Notice WCAG 2 examples become unreadable with dark colors.
68 |
69 | 
70 |
71 | #### _And the problem is particularly severe for "dark mode":_
72 |
73 | 
74 |
75 |
76 | ## Use-Case Ranges
77 | These general levels are appropriate for use by themselves, without the need to reference a lookup table. APCA reports contrast as an Lc value (lightness contrast) from **Lc 0** to **Lc 105+**. For accessibility, consider Lc 15 the point of invisibility for many users, particularly for thin lines, and Lc 90 is preferred for body text.
78 |
79 | See [this on ranges](./APCA_in_a_Nutshell#use-case--size-ranges) for a more in-depth look.
80 |
81 | * **Lc 90** • Preferred level for fluent text and columns of body text with a font no smaller than 14px/weight 400 (normal).
82 | * **Lc 75** • The _minimum_ level for columns of body text with a font no smaller than 18px/400. Lc 75 should be considered a minimum for text where readability is important.
83 | * **Lc 60** • The _minimum_ level recommended for content text that is not body, column, or block text. In other words, text you want people to read. The minimums: 24px normal weight (400) or 16px/700 (bold). These values based on the reference font Helvetica.
84 | * **Lc 45** • The _minimum_ for larger, heavier text (36px normal weight or 24px bold) such as headlines. This is also the minimum for pictograms with fine details.
85 | * **Lc 30** • The _absolute minimum_ for any text not listed above. This includes placeholder text and disabled element text. This is also the minimum for large/solid semantic & understandable non-text elements.
86 | * **Lc 15** • The _absolute minimum_ for any non-text that needs to be _discernible_ and differentiable, and is no less than 5px in its smallest dimension. This may include disabled large buttons. **Designers should treat anything below this level as invisible**, as it will not be visible for many users. This minimum level should be avoided for any items important to the use, understanding, or interaction of the site.
87 |
88 | These define the basic minimum levels, what you might think of as A/AA in the old WCAG 2. For the equivalent to AAA, simply increase the contrast values by Lc 15. Maximum: for **large** fonts in dark mode, keep contrast less than Lc 90.
89 |
90 | ### _Range-Based Scoring_
91 | While the candidate for WCAG 3 is still in development, it includes a range-based conformance system. While it considers multiple factors, it is simple enough to be fully automated, and does not rely on an arbitrary pass/fail binary scoring.
92 |
93 | The overall approach improves design flexibility and readability at the same time. Readability is improved by increasing contrast in blocks of body text where it is most needed, and design flexibility is achieved by relaxing contrast for large non-text elements which do not need brute-force contrast levels due to their larger size (resulting in a lower spatial frequency).
94 |
95 | For demonstration purposes, the example tool provides real-time updates of minimum font size and weight vs contrast: [apcacontrast.com](https://apcacontrast.com) click on the color patches to bring up a color-picker.
96 |
97 | We hope this clarifies the useful differences of a perceptually accurate range-based model as the guideline for a future of best readability.
98 |
99 |
100 | Thank you for reading,
101 |
102 | **_Andrew Somers_**
103 | _Director of Research_
104 | _Myndex Technologies_
105 | _W3C Invited Expert_
106 | _APCA Research Lead_
107 |
108 | ----
109 | ## _THE WORLD IS READING_™
110 |
111 | ### Definitions of Terms Used In This Document
112 | - **Spatial or spatially:** relating to size, weight, or thickness.
113 | - **Hue:** the uniqueness of a given color vs other colors, i.e. blue vs red.
114 | - **Chroma/saturation:** the intensity or purity of a color vs no color.
115 | - **Luminance:** a physical measure of light, disregarding hue.
116 | - **Lightness:** the human perception of a given luminance. Also darkness and brightness.
117 |
118 | _This document was written in basic plain language using the [Hemingway app](https://hemingwayapp.com)._
119 |
120 | ### Study Volunteers Needed
121 | Would you like to help create a more readable world for all? Please let us know! We have several studies planned for 2023, and it requires minimal time on your part to participate. Please send an email to perceptex@myndex.com with "volunteer" in the subject line.
122 |
123 | **_NOTICE: Personal opinions expressed are the author's and may or may not reflect those of the W3 or AGWG._**
124 |
125 |
126 |
127 | ## APPENDIX: _Additional Reading_
128 | - [**Linktree of Selected Resources**](https://linktr.ee/Myndex) A good place to start.
129 | - [**Main Catalog of APCA Resources and Links**](https://git.myndex.com) For the much deeper divers.
130 |
131 | ### APCA Readability Criterion
132 | _Maintained by Inclusive Reading Technologies Inc., a California Non-Profit_.
133 | - [**Draft ARC Guidelines**](https://readtech.org/ARC/) for implementing APCA and related technologies.
134 | - [**Bronze Simple Mode**](https://readtech.org/ARC/tests/bronze-simple-mode/?tn=intro) is designed as an introductory mode that does not require look-up tables or matching to a reference font. Instead it's designed as a simple set of threshold levels, similar to how WCAG 2 works but using perceptually uniform math.
135 |
136 | ### Links To APCA and Related Tools
137 | - [**APCA Calculator**](https://apcacontrast.com), the official technology demonstrator for APCA, includes explainers.
138 | - Listing of [**Third Party Tools and Systems**](https://git.apcacontrast.com/documentation/thirdpartytools) that have adopted APCA.
139 | - An [**Accurate Colorblind Simulator**](https://myndex.com/CVD/) based on the well respected, peer-reviewed, Brettel et alia model.
140 |
141 | ### Discussion Forum
142 | - [**Readability Forum**](https://github.com/Myndex/SAPC-APCA/discussions/) questions and comments welcome.
143 | - [**DISCUSS: Using APCA with other fonts** ](https://github.com/Myndex/SAPC-APCA/discussions/28#discussioncomment-1610289) Draft method for font weight conformance.
144 | - [**DISCUSS: Inline text links theory and practice** ](https://github.com/Myndex/SAPC-APCA/discussions/65) Draft guidance regarding link identification.
145 | - [**DISCUSS: Draft Dark Mode Guidance**](https://github.com/Myndex/SAPC-APCA/discussions/74#discussioncomment-6646215) Draft guidance regarding darkmode from light mode, and more.
146 | - [**DISCUSS: Legal Issues of WCAG2 vs APCA**](https://github.com/Myndex/SAPC-APCA/discussions/68#discussion-3980510) Discussion of current and future legal status and incorporation into legislation.
147 |
148 | ### Peer Review & Third Party Discussion of APCA
149 | A listing of [**third party and peer reviews**](https://git.myndex.com/#apca-peer-review--third-party-discussion) of APCA and related technologies. This directory includes journal-published peer-reviews, trade-published evaluations, and less formal comparative analysis, covering the usage, math, efficacy, implementation/integration, workflows, and more.
150 |
151 | ### Published Articles on Color & Contrast by A.Somers
152 | - [**The Realities And Myths Of Contrast And Color**](https://www.smashingmagazine.com/2022/09/realities-myths-contrast-color/) Published by _Smashing Magazine_. A brief but comprehensive primer to vision, color, and contrast for design, with an emphasis on typography, readability, and visual accessibility needs.
153 | - [**Better Reading on the Web**](https://uxdesign.cc/better-reading-on-the-web-c943c4cfc91a) Published by _UX Collective_, this article discusses and demonstrates issues with automated testing and WCAG 2 contrast math, methods, and guidelines.
154 |
155 | - **The _Tangled Web_ tech blog** (TangledWeb.xyz):
156 | - [**Please Stop Using Grey Text**](https://tangledweb.xyz/please-stop-using-grey-text-3d3e71acfca8) This popular article debunks one of the worst myths regarding design contrast.
157 | - [**What’s Red & Black & Also Not Read?**](https://tangledweb.xyz/whats-red-black-also-not-read-573b9c0a97ed) examines the nature of color insensitivity and readability.
158 | - [**Busy Background Breaks Bulletin**](https://tangledweb.xyz/busy-background-breaks-bulletin-f4ff4bf67e5a) Examples of how to destroy readability by choosing the wrong image as a background. And also, how to fix it.
159 | - [**Hats off to ALL CAPS**](https://tangledweb.xyz/hats-off-to-all-caps-c0a43a2c30d4) myth-busting misunderstandings regarding dyslexia, are special dyslexia fonts even useful, and the shift from using ALL UPPERCASE LETTERS for various text elements.
160 | - [**A Contrast of Errors**](https://atangledwebweweave.com/a-contrast-of-errors-373c2665d42a) looks at the history and the current international readability crisis.
161 | - [**Contrasting Theories**](https://tangledweb.xyz/hi-roger-f51bde490a56) Background on the first two years of R&D.
162 |
163 |
164 |
165 |
166 |
72 |
73 | In this case 100px Helvetica would measure an x-height of about 52px. Determine the reference ratio by dividing the reference size by the font being tested. If the test font is 45px, such as this Times New Roman, then:
74 | ### 52/45 = 1.156
75 | _(round to at least two significant digits, three is shown here)_
76 |
77 | So for example, an APCA value of LC 75 specifies and 18px reference font. To use the example of Times New Roman, multiply 18px by 1.156 to arrive at a minimum font size of 20.8px, or 21px rounded.
78 |
79 | ### Why List Cursive?
80 | Make the fallback font-family after the test and reference fonts something very different, such as "cursive". This way if the browser does not load the font properly, it is immediately obvious, as in this example:
81 |
82 | 
83 |
84 | -----
85 | ## II - Weight
86 | While size per x-height is fairly straight forward, weight requires some visual judgment. There is active research into possible automated tools, but for the time being a visual reference is needed.
87 |
88 | In this case, set up several lines of test text, with the test and reference fonts near the eventual size, as in the above example that's a reference size of 18px. The test font needs to be adjusted so that it has the same excite as the reference font as render to the screen.
89 |
90 | In the example below, were using the common reference font Arial, at the standard normal and bold weights of 400 and 700. Arial is a clone of Helvetica, and either have very similar characteristics.
91 |
92 | We'll make a few lines to compare different weights, and one with high contrast, and another set with very low contrast to help exacerbate the differences.
93 |
94 | The test text is `Il 400 & IcyATOMsizedgap`, using an uppercase I & lowercase l as these make it easy to compare the vertical stroke widths. The sample text "&IcyATOMsizedgap" is short yet demonstrates most of the common design differences in a font.
95 |
96 |
97 | ### Part II.a - Setup
98 | 1. Setup a 400 normal weight, and 700 bold weight reference font as the comparison sample.
99 | - suitable reference fonts are Helvetica or Arial.
100 | 2. Make a test webpage with several lines comparing several weight examples of the test font to the 400 and 700 weight reference.
101 | - The test font's size must be normalized so that the test and reference x Heights are equivalent.
102 | 3. Create one test area for high contrast around LC 90 and a second test area for low contrast around LC 30.
103 | 4. Use a consistent line of sample text for each line, and include the weight that is being tested for each line.
104 | - An example is "&IcyATOMsizedgap".
105 | - Include the weight that is being tested in each line.
106 | - start and or end each line with a capital I and a lowercase l, to help make find comparisons of vertical stroke width.
107 | ### Part II.b - Evaluate
108 | 1. Evaluate each sample pair, and determine which test-font weight most closely resembles the reference font's weight.
109 | - If thr test-font is in between two weights of the reference font, it is best to round up.
110 | - If the test font is a variable font, as in the example below, find the variable weight that matches the reference.
111 | ### Part I.c - Determine Offset
112 | 1. Subtract the reference weight from the matching test font weight.
113 | 2. This value is the reference weight offset.
114 | 3. If there is a different reference weight offset among different reference weights, in-between weights may be interpolated.
115 | ### _Using the Reference Weight Offset_
116 | For a given indicated weight, add the reference weight offset to find the actual needed weight for the design font which was tested.
117 |
118 | ### Weight Example
119 | Below, a test setup for the "RALEWAY" Google font. Raleway has the same ex height as Ariel or Helvetica, so we can use the same size for both samples.
120 |
121 | ```html
122 |
123 |
124 |
125 |
126 |
127 | Il 400 & IcyATOMsizedgap Arial
209 |Il 300 & IcyATOMsizedgap Raleway
210 | 211 |Il 400 & IcyATOMsizedgap Arial
212 |Il 400 & IcyATOMsizedgap Raleway
213 | 214 |Il 400 & IcyATOMsizedgap Arial
215 |Il 500 & IcyATOMsizedgap Raleway
216 | 217 |Il 400 & IcyATOMsizedgap Arial
218 |Il 520 & IcyATOMsizedgap Raleway
219 | 220 |Il 400 & IcyATOMsizedgap Arial
221 |Il 600 & IcyATOMsizedgap Raleway
222 |Il 700 & IcyATOMsizedgap Arial
224 |Il 600 & IcyATOMsizedgap Raleway
225 | 226 |Il 700 & IcyATOMsizedgap Arial
227 |Il 700 & IcyATOMsizedgap Raleway
228 | 229 |Il 700 & IcyATOMsizedgap Arial
230 |Il 730 & IcyATOMsizedgap Raleway
231 | 232 |Il 700 & IcyATOMsizedgap Arial
233 |Il 800 & IcyATOMsizedgap Raleway
234 | 235 |400 & IcyATOMsizedgap Arial lI
242 |300 & IcyATOMsizedgap Raleway lI
243 | 244 |400 & IcyATOMsizedgap Arial lI
245 |400 & IcyATOMsizedgap Raleway lI
246 | 247 |400 & IcyATOMsizedgap Arial lI
248 |500 & IcyATOMsizedgap Raleway lI
249 | 250 |400 & IcyATOMsizedgap Arial lI
251 |520 & IcyATOMsizedgap Raleway lI
252 | 253 |400 & IcyATOMsizedgap Arial lI
254 |600 & IcyATOMsizedgap Raleway lI
255 |700 & IcyATOMsizedgap Arial lI
257 |600 & IcyATOMsizedgap Raleway lI
258 | 259 |700 & IcyATOMsizedgap Arial lI
260 |700 & IcyATOMsizedgap Raleway lI
261 | 262 |700 & IcyATOMsizedgap Arial lI
263 |730 & IcyATOMsizedgap Raleway lI
264 | 265 |700 & IcyATOMsizedgap Arial lI
266 |800 & IcyATOMsizedgap Raleway lI
267 | 268 |
281 |
282 | We see that Raleway is clearly lighter than Arial 400. Absent a variable font, we would say that Raleway 500 is close to Arial 400. As Raleway is available as a variable font, we can find tune and find that Raleway 520 is a close match to aerial 400. Therefore, the offset for a 400 weight font for Raleway is +120.
283 |
284 | Raleway bold is also lighter than Arial 700, but here the difference is not as great. Using the variable, Raleway 730 matches Ariel 700, so the offset for Raleway is +30.
285 |
286 | ### Here it is closeup:
287 | _Click for larger_
288 |
289 | 
290 |
291 | A look to the lo-con version on the left helps to accentuate the weight differences.
292 |
293 | ## Summary
294 | Following a simple procedure, compare a desired design font to a reference font, and determine the Size and weight offsets needed for equivalence.
295 |
--------------------------------------------------------------------------------
/documentation/regardingexponents.md:
--------------------------------------------------------------------------------
1 | ---
2 | layout: simple
3 | ---
4 | # Regarding APCA Exponents
5 | #### The TLDR is "For non-HDR displays, the colorspace is simply selected by the three coefficients, and the pre-processing exponent."
6 |
7 | ## Input Stage Notes
8 |
9 | Technically, the input modules do not convert to a traditional calculated CIEXYZ luminance, and it is not intended to. They calculate a unique value "estimated screen luminance" denoted **Ys**. The first stage is a conversion to model of typical monitors in typical environmental settings. Included is consideration of surveys and case studies of monitors in real-world environments, and our own measurements and studies of various devices and displays.
10 |
11 | It is useful to point out that the defined peak output in the circa-1998 IEC sRGB spec is 80 cd/m², and today's devices are capable of exceeding 1200 cd/m². The needed gamma setting for a display depends on the ambient lighting, which drives global adaptation, and the screen luminance which drives field and local adaptation. There is a user preference component in here too, resulting in a fairly wide range of gamma settings in use. For example, some calibration software can calibrate to L* which is about 2.35 to 2.4. Higher gammas can be useful, depending on many factors, including the peak white level and the ambient illumination.
12 |
13 | This pre-processing stage also includes a soft clamp at black for initial monitor modeling. As an interesting side note, the need for the soft clamp makes using the piecewise _redundant_, as that section near black is completely reshaped by the soft clamp to account for ambient flare and other psychophysical factors.
14 |
15 | The contrast calculation stage then applies a different exponent to the background, which drives local adaptation, and another to the stimuli (text).
16 |
17 | The piecewise sRGB TRC is not an emulation of actual monitor behavior, having been created to prevent infinite slope at 0 to facilitate digital processing, back in the days before math coprocessors were standard and computers relied on integer math, and RAM and other resources were precious. I.e. the dark ages. But the APCA is not about processing images and lossless round trips, where using the piecewise curve is of benefit. The object is emulating real world monitor behavior. It is useful to note that many ICC profiles (including those that ship with Adobe products) do not use the piecewise, and instead use the simple 2.2 gamma, which the piecewise was intended to emulate, and the IEC standard indicates the physical display EOTF being the simple gamma in four separate places in that document.
18 |
19 | The only thing in the APCA input stage that is really different is the exponent set to 2.4. This slightly higher exponent is added as part of pre-processing to relax the exponents in the contrast determination stage, and the aforementioned modeling of real-world monitors and devices. The "extra" could be added separately before the contrast stage, but is combined for simplicity in the current implementation.
20 |
21 | That said, APCA is intended only to predict a display, and the perceived supra-threshold contrast for best readability, and to be perceptually uniform when doing so. Any alternate colorspaces therefore must be the destination display colorspace.
22 |
23 | For AdobeRGB, Apple Display P3, and sRGB, changing destination colorspace is a matter of swapping out the coefficients.
24 |
25 | For Rec2020, there may need to be an additional pre-processing adjustment to the exponent. I have yet to evaluate Rec2020 as I do not have a Rec2020 monitor at my disposal. Rec2020 does have some additional accessibility issues which will entail some separate discussion, largely that the red primary is out of range of someone with protanopia (invisible).
26 |
27 | For Rec2100 and other HDR types, a different set of constants and exponents is expected, and probably other modifications.
28 |
29 | But for non-HDR displays, the colorspace is simply selected by the three coefficients, and the pre-processing exponent.
30 |
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1 | ---
2 | layout: simple
3 | ---
4 |
5 | # Myndex and APCA Repositories
6 |
7 | - Myndex on GitHub: https://git.myndex.com/
8 |
9 | ## GitHub
10 |
11 | - Main (This): https://github.com/Myndex/SAPC-APCA
12 | - Canonical repository for discussion, documentation, issues, etc.
13 | - W3 licensed APCA: https://github.com/Myndex/apca-w3
14 | - The specific iteration designed for supporting WCAG 3.0
15 | - Bridge-PCA: https://github.com/Myndex/bridge-pca
16 | - A version that is backwards compatible to WCAG 2
17 | - ColorParsley: https://github.com/Myndex/colorparsley
18 | - A lightweight but versatile color string parsing function
19 | - SeeStars: https://github.com/Myndex/seestars
20 | - A very lightweight luminance and L\* converter.
21 | - DeltaPhiStar: https://github.com/Myndex/deltaphistar
22 | - A simplified perceptually uniform contrast metric.
23 | - SACAM: ---
24 | - A full color model using the technology that is the foundation for APCA.
25 |
26 |
27 | ## NPM
28 |
29 | ```JS
30 | npm i apca-w3
31 |
32 | npm i bridge-pca
33 |
34 | npm i colorparsley
35 |
36 | npm i seestars
37 |
38 | npm i deltaphistar
39 | ```
40 |
41 | ## Myndex Technologies
42 |
43 | - Live Demo: https://www.myndex.com/APCA/
44 | - Color Vision Simulator: https://www.myndex.com/CVD/
45 | - General Info: https://www.myndex.com/WEB/Perception
46 | - Research Tools: https://www.myndex.com/SAPC/
47 |
48 | ## W3 / AGWG
49 |
50 | - Contrast WIKI: https://www.w3.org/WAI/GL/task-forces/silver/wiki/Visual_Contrast_of_Text_Subgroup
51 |
52 |
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/documentation/thirdpartytools.md:
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1 | ---
2 | layout: simple
3 | ---
4 |
5 | # APCA Tools & Apps
6 | As APCA popularity increases, there is a rapidly growing list of tools. Please post a message in the [tools discussion](https://github.com/Myndex/SAPC-APCA/discussions/51) to have your tool added to this list, or send me a message—my DMs open on Twitter and Linkedin.
7 |
8 | Take note that some of these tools are works in progress, and not all of them have been fully analyzed for accuracy or conformance to APCA standards. We will be starting qualification testing in the near future. When in doubt, check values with the [canonical APCA tool](https://apcacontrast.com).
9 |
10 | For Bridge PCA, use the [canonical BPCA tool](https://bridgepca.com).
11 |
12 |
13 | ## _Third Party APCA Tools—Systems_
14 | **Design Systems or Pallette Generation tools**
15 |
16 |
17 | ### [Tailwind](https://uicolors.app/create)
18 | - It's a very cool tool, with a plugin for Figma, make sure to use the latest version as it is now updated to use the current APCA constants. This tool can show either WCAG2 or APCA.
19 |
20 |
21 | ### [Stark APCA Beta](https://www.getstark.co/blog/stark-APCA-beta)
22 | - Yes, Stark has added APCA to their toolset as an option! It's available across the product line, and included in the free versions. Make sure to use the latest version which is updated to use the current APCA constants. This tool can show either WCAG2 or APCA.
23 |
24 |
25 | ### [Accessible Palette](https://AccessiblePalette.com)
26 | - A very nice color selector by Eugene, see [his article as well](https://wildbit.com/blog/accessible-palette-stop-using-hsl-for-color-systems) This shows both WCAG 2 and APCA.
27 |
28 |
29 | ### [Huetone](https://huetone.ardov.me/?palette=N4IgdghgtgpiBcICiAPaAHANjABABQmwBci4AaEACwFcYBnBAbVElgRAHEAnGATxAoBjAPaZhXBvEYgAxADMAbIsUDZMAIwaNqmQCMAJgYM6I606Z0AOAEw2bOhdceOdAFgDsHjzusBOP3466pbBwSAAugC%2BZCzQcIh4AJZgANaqImISTLJyudZy7jq5%2Bu4wAMxFuhCuggAMRcoQFRTy1tYQlgCsOrq%2BmgquVnVyrr46nZ217u06ZZNlYVEx4HHsAEow%2Bumi4pLS8rmuMOQ5cvq%2Bgify%2BhDuvmMtue7uCluP6mX6ruo90%2BX1LUsfRg1gBsk6ZVqcnUYJkcymtXqS1ibEQAE0YJgxAB3baZPanOSdGCWBqGXSkx5lCAFZpqSyWJoKHSCXQKdy1H4tXy6Vz6Tk6dwfSy1QYtVxtRGw9rqGFI6Io%2BKcHgwMB43bZeRQ3wwB6yQRyXW6XQ6XwQVnuSmyBQ8splK4S3yuKE%2BAqIwotdRE0Gw9SuSGIoKc3SB5ErVEgAAqMEI6qyUjU%2BRpch6ChjcitMhegl8%2BiutU6IcEb1ktQUljkEGZLSmCkEpR0iNcRJLMk51nKHtLst0oIiCvDSoAQphaHGCfJm0oUy1DPpcjPZBAIFVclY-Lo1%2BKpgbM%2BpBJ19II918-GLS-4FMTGwp1AoyiaouEKERhGB6NlJqo5aofaoA6ozpgpMYIKIGFAcmCIrykAA)
30 | - Cool interface under development, lots of options. This tool can show either WCAG2 or APCA.
31 |
32 | ### [Ambient Color Generation Tool](https://ambient-rvx.web.app)
33 | - This tool is designed to generate contrast ready color pallets built specifically for UI/UX design. Unlike other palette generation tools, Ambient generates the colors based on the primary color.
34 |
35 |
36 | ### [Atmos](https://atmos.style/contrast-checker)
37 | - a contrast checker that is part of the Atmos design system.
38 |
39 |
40 |
41 | ### [Leonardo](https://leonardocolor.io/#)
42 | - The adaptive color theme function has an APCA option, however APCA has not yet been integrated into the color contrast tool or the dataviz tool. The Leonardo tool is pretty cool as it stands.
43 |
44 |
45 | ----
46 | ## _Third Party APCA Tools-Calculators_
47 | **Calculators and Technology Demos**
48 |
49 | ### [a11ycolor.tools](https://a11ycolor.tools)
50 | - Nice tool, compares WCAG2 and APCA Bronze Simple mode, and conveniently allows multiple color swatches.
51 |
52 | ### [Achecks APCA Contrast Checker](https://www.achecks.org/apca-wcag-3-accessible-colour-contrast-checker/)
53 | - Nice simple APCA checker. Has a dynamic lookup table that updates with new contrasts.
54 |
55 | ### [Polypane Color Contrast](https://colorcontrast.app/#fg=%23107db5&bg=%23fff&level=aa&format=rgb&algo=APCA&filter=none)
56 | - Killian's Contrast app, can show either WCAG2 or APCA.
57 | - _(Also to mention, Killian was the key designer behind the updated APCA demo tool at Myndex.)_
58 |
59 | ### [Cliam's Contrast](https://cliambrown.com/contrast/)
60 | - A neat color checker that allows you to click to find a given contrast level.
61 |
62 | ### [contrast-suggester.com](https://contrast-suggester.com)
63 | Also a [GitHub repo too](https://github.com/Munawwar/apca-color-contrast)
64 | - Suggests a contrasting color for a given color, font size, and font weight.
65 |
66 |
67 | ### [Zebra for Figma](https://www.figma.com/community/plugin/806578669827234193)
68 | - Dan Hollick's Zebra contrast plug in for Figma.
69 |
70 |
71 | ### [Caravage for Figma](https://www.figma.com/community/plugin/1059851135811973410/Caravage)
72 | - A Figma plugin to check the contrast accessibility of the selected text. It is still in beta, the developer @simonbrtrnd mentions any feedback is appreciated.
73 |
74 |
75 | ### [RandomA11y APCA](https://randoma11y.com/apca?color=%23c91313)
76 | - this is an interesting take on a tool that gives you the opposite color for the color that you choose.
77 |
78 |
79 | ### [contrast-checker Vercel app](https://contrast-checker.vercel.app/000000e6/d40511/ffcc00/ffcc004d/ffffff/0000000d/0000001a/76BD22/007C39)
80 | - This WCAG 2 checker also shows APCA so you can see the relative differences.
81 |
82 |
83 | ### [Contrast Tools](https://contrast.tools)
84 | - Nice clean interface, easy to use. This tool can show either WCAG2 or APCA.
85 |
86 |
87 | ### [Contrast Checker](https://contrast-checker.bellette.com.au/)
88 | - A clever interface that demonstrates the key concepts as well.
89 |
90 |
91 | ### [APCA Flip Black/White](https://apca.digitallymarked.com)
92 | Also, [the GitHib repo](https://github.com/digitallymarked/apca-calculator)
93 |
94 | - This is a simple but informative interface, text is only black or white, and it's using APCA to determine when to flip between the two.
95 |
96 |
97 | ### [Japanese Experimental](https://develop.apca-calculator-ja.pages.dev)
98 | Also, [the GitHib repo](https://github.com/shunito/apca-calculator-ja)
99 |
100 | - This is a Japanese experimental version, it's part of the project for working on aligning Japanese writing systems.
101 |
102 | ----
103 | ### _BRIDGE PCS VARIANTS_
104 |
105 | ### [color-contrast.dev](https://www.color-contrast.dev)
106 | - this is the first third-party implementation I've seen of Bridge PCA, the drop in replacement that's backwards compatible with WCAG2. Nice simple input interface that also gives you suggested colors to improve contrast.
107 |
108 |
109 | ### [Color Contrast iOS app](https://apps.apple.com/app/color-contrast/id1095478187?platform=iphone)
110 | - This an iOS app to measure the contrast between two colours in a screenshot or mobile website. The APCA algorithm is available as an option, with the Bridge PCA being used to show the modified WCAG ratio.
111 |
112 |
113 | -----
114 | ## _Browsers_
115 |
116 | ### [Chrome Dev Tools](https://developer.chrome.com/blog/new-in-devtools-89/#apca)
117 | - Available as an experimental feature, note that some versions maybe using obsolete constants and therefore may give incorrect results.
118 |
119 | ### [Microsoft Edge Dev Tools](https://docs.microsoft.com/en-us/microsoft-edge/devtools-guide-chromium/whats-new/2021/01/devtools#new-color-contrast-calculation---advanced-perceptual-contrast-algorithm-apca)
120 | - Available as an experimental feature, note that some versions maybe using obsolete constants and therefore may give incorrect results.
121 |
122 |
123 | -----
124 | ## _Code Libraries & Systems with APCA_
125 |
126 | ### [Color.js](https://colorjs.io)
127 | - Comprehensive JS color library by Lea Verou and Chris Lilly.
128 | - See the [contrast demo page](https://colorjs.io/apps/blackwhite/)
129 |
130 | ### [SASS-APCA](https://github.com/gfellerph/sass-apca)
131 | - a sass library
132 |
133 | ### [A11y Color Contrast](https://deno.land/x/a11y_color_contrast)
134 | - a typescript library
135 |
136 | ### [Colorspace r-forge](http://colorspace.r-forge.r-project.org/reference/contrast_ratio.html)
137 | - an R library
138 |
139 | ### [OxyProps/BrickProps](https://docs.oxyprops.com/en/features/global-colors/)
140 | - this is the design system plug-in for WordPress, I'm not quite sure how they're integrating a PCA but they do mention in the docs.
141 |
142 | ### [Accessibility: Color-Contrast Models](https://observablehq.com/@ijlyttle/apca-w3-color-contrast)
143 | - Ian Lyttle's library on ObservableHQ
144 |
145 | ## _Works in Progress_
146 | These are some works in progress, functionality was not complete at the last time I checked, and or may have math or implementation errors. If your tool is on this portion of the list, please feel free to reach out, I'm more than happy to assist.
147 |
148 |
149 | ### [ROKING-A11Y APCA Evaluator](https://hrobertking.github.io/roking-a11y/apca.htm)
150 | - Has a visible look up table which changes based on the contrast. Has a pending pull request due to some errors in terms of the exponents and look up.
151 |
152 |
153 | ### [AdamSzakal APCA-contrast](https://acpa-contrast.netlify.app)
154 | - The repo is spelled wrong (oops!): https://github.com/AdamSzakal/ACPA-contrast
155 | Basically looks like a work in progress, does not show polarity in the results.
156 |
157 |
158 | ### [Visual Contrast Figma Plugin](https://www.figma.com/community/plugin/1090308131937420683)
159 | - Does not seem to work correctly??
160 |
161 |
162 | ### [jolly-feynman-28ea37.netlify.app](https://jolly-feynman-28ea37.netlify.app)
163 | - https://github.com/tomreinert/contrast-calculator-2
164 |
165 | -----
166 | ## _Official Myndex Tools_
167 |
168 | ### [APCA W3 Tool](https://www.myndex.com/APCA/)
169 | - The main canonical demonstration tool. Public beta. The is the candidate for the future WCAG 3 contrast method.
170 | - Note that this is not fully backwards compatible with WCAG 2 contrast math due to the non-perceptual nature of WCAG 2.
171 | - Legacy version available on [a backup link](https://myndex.github.io/SAPC-APCA/WEBTOOLS/APCA/) at this repo.
172 | - The dedicated domain name is [apcacontrast.com](https://apcacontrast.com)
173 |
174 | ### [Color Vision Deficiency (ColorBlind) Simulator](https://www.myndex.com/CVD/)
175 | - The CVD sim, a clinically accurate simulation of various forms of color insensitive vision (aka color blind), most of the sims are derived from or based directly on the clinically accurate Brettel model. Allows you to process a screenshot of your page design and view several CVD types at once..
176 |
177 | ### [Bridge-PCA](https://www.myndex.com/BPCA/)
178 | - Bridge PCA is a modified tool that is backwards compatible with WCAG 2 contrast, but using APCA technology.
179 | - In order to be backwards compatible, some design flexibility is given up, but accessibility is substantially improved over WCAG 2.
180 | - The dedicated domain name is [bridgepca.com](https://bridgepca.com)
181 |
182 | ### [SAPC Development Site](https://www.myndex.com/SAPC/)
183 | - The SAPC research demonstration tool, more detailed results than the APCA tool above, and a clickable "research mode" with technology demonstrators, interactive experiments, and much data about the colors in use.
184 | - NOTE: This tool may not always match the main tool depending on current experimental protocols.
185 |
186 | -----
187 |
188 | ## _Official Repositories_
189 |
190 | ### [APCA W3](https://github.com/Myndex/apca-w3)
191 | And the npm install is ` npm i apca-w3 `
192 |
193 | ### [Bridge-PCA](https://github.com/Myndex/bridge-pca)
194 | And the npm install is ` npm i bridge-pca `
195 |
196 | ### [The Main SAPC APCA SARCAM](https://github.com/Myndex/SAPC-APCA)
197 | This repo right here...
198 |
199 | ### [Guidelines for Accessible Readable Design](https://github.com/A11yReadTech/GARD)
200 | In development at Accessible Reading Technologies: GARD is a developing set of readability design guidelines.
201 |
202 | ### [deltaPhiStar](https://github.com/Myndex/deltaphistar)
203 | An alternate and highly simplified contrast algorithm. Still fairly perceptually uniform though less accurate for very high and very low contrast, and it's not polarity aware.
204 |
205 | ### [See Stars](https://github.com/Myndex/seestars)
206 | Myndex microlibrary for CIE Lstar, for use with deltaPhiStar
207 |
208 | ### [Fancy Font Flipping](https://github.com/Myndex/fancyfontflipping)
209 | Related to APCA methods, but separate—this is a demonstrator for when to flip a text color from black to white, based on the luminance of the background. CodePen also available, and also read [this Gist article.](https://gist.github.com/Myndex/e1025706436736166561d339fd667493#lets-flip-for-color)
210 |
211 | ### [Color Parsley](https://github.com/Myndex/colorparsley)
212 | A lightweight but versatile color parsing utility with no dependencies
213 | _NPM Install:_ ` npm i colorparsley `
214 |
215 | ----
216 | ## Other Resources
217 |
218 | ### [linktr.ee/Myndex](https://linktr.ee/Myndex)
219 | This is a linktree of articles and information regarding APCA.
220 |
221 | ### [Easy Intro to APCA](https://git.apcacontrast.com/documentation/APCAeasyIntro)
222 | A brief overview of APCA. This is a good place to start if you are new to perceptually uniform contrast.
223 |
224 | ### [APCA Readability Criterion](https://readtech.org/ARC/)
225 | Publisck Workging Draft of the developing guidelines for using APCA and related systems and technologies.
226 |
227 | ### [Myndex Color & Contrast Resources](https://git.myndex.com/)
228 | A large catalog of contrast and color resources.
229 |
230 |
231 | ----
232 | ## Accessibility Statement for Beta Testers
233 | **Beta testers may wish to include the following statement in their sites boilerplate:**
234 |
235 | There are additional versions in the [Accessibility Statements file](https://github.com/Myndex/SAPC-APCA/blob/master/documentation/accessibilitystatement.md)
236 |
237 | -----
238 | ### This website is using the [APCA](https://git.apcacontrast.com/documentation/APCAeasyIntro)™ readability guidelines for determining visual contrast of text and non-text elements.
239 |
240 | This site's visually-readable primary content is designed to meet or exceed the ***Bronze Simple*** conformance level, as defined in version: (Public Beta Working Draft 2023), of the [APCA Readability Criteria (ARC)](https://readtech.org/ARC/), which provides improved visual readability, enhancing the actual accessibility for users of this website. If you have questions, concerns, or problems, please contact the accessibility manager or webmaster of this site. The APCA Readability Criteria is designed to substantially exceed WCAG 2.1, SC 1.4.3 and 1.4.11 guidelines for actual accessibility. If you find you are experiencing a functional problem with text contrast on this site, please forward to the URL to _bugreport_ at _readtech.org_
241 |
242 | -----
243 |
244 | Copyright © 2021-2023 by Andrew Somers. All Rights Reserved. Patent(s) Pending.
245 |
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