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SAPC/APCA BAS ALGORITHM CURRENT VERSION: 0.0.98G-4g-lut3 Constants: 4g

May 28 2022

Font lookup table revised, still for 0.98G 4g constants. General (all use case) lookup table.

January 11 2022

Font lookup table revised, still for 4G constants. Now available as arrays in the DATA folder.

January 2 2022

Font lookup table revised, still for 4G constants.

December 1, 2021

All W3 licensed files moved to their own repository, AND A new npm package has been released (of the W3 version) to ease integration!!

November 23, 2021

Updated font LUT, and adding a 0. for semantic versioning (0.0.98G)

October 1, 2021:

0.0.98G-4g is the current version. A minimal APCA version is in the JS folder.

As of October 1, 2021 01:00 GMT

CURRENT VERSION: Beta 0.0.98G_g4

IMPORTANT: If you are making a tool to predict contrast for the new W3 standards for Visual Contrast, use only the files named APCA.

Change Notice October 1, 2021 01:00 GMT (February 15th constants)

The new version of the basic APCA javascript file is uploaded, and the main directory readme.md has been updated with the latest maths and code examples. Variable names and values have changed. The key constants have not changed since February 15, 2021, and they are:

Exponents:      mainTRC: 2.4    normBG: 0.56     normTXT: 0.57      revTXT: 0.62     revBG: 0.65
Scalers:        Scale: 1.14     loBoWthresh: 0.035991     loBoWoffset: 0.027         loBoWfactor: 27.7847239587675	
Clamps:         blkThrs: 0.022  blkClmp: 1.414   loClip: 0.001      deltaYmin: 0.0005

The sRGB coefficients are:
    Rco = 0.2126729;
    Gco = 0.7151522;
    Bco = 0.0721750;

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Change Notice January 28, 2021 02:00 GMT

The new version of the basic APCA javascript file is uploaded, and the main directory readme.md has been updated with the latest maths and code examples. Variable names and values have changed. The key constants are now:

Exponents:	mainTRC: 2.4	normBG: 0.55	normTXT: 0.58	revTXT: 0.57	revBG: 0.62
Scalers:	Scale: 1.25	loConThresh: 0.078	loConOffset: 0.06	loConFactor: 12.82051282051282
Clamps:  	blkThrs: 0.03	blkClmp: 1.45	loClip: 0.001	deltaYmin: 0.0005 Also changed the R,G,B coefficients to the less rounded matrix versions for better future compatibility.

Rco = 0.2126729;
Gco = 0.7151522;
Bco = 0.0721750;

Change Notice January 2021 General

Substantial code changes, including math and scaling. Literally all constants have changed. Typically the “equivalent colors” will be indicated 20 lower (more or less). The main takeaway here though is what was 100 is now 80, what was 80 is now 60 and what was 60 is now 40.

80: The general target for columns of body text.

60: The general target for most content text.

Change Notice November 18, 2020 08:00 GMT

IMPORTANT: Major reworking of the input objects, adding new methods including a complete CIE suite, piecewise sRGB processing, and much more. This file is INCOMPATIBLE WITH ALL PREVIOUS VERSIONS due to new features, naming, and organizing of properties and methods.

Change Notice October 22, 2020 0.0.97h2

Only applies to the JS files with the input parsing. Fixed the “Zero Hex Bug” thanks to Mitch @mfishma issue #5 for pointing it out!

Change Notice October 21, 2020 0.0.97h

Changes in the .JS files mainly centered around adding new methods and also adding new parsing, including for alpha channels.

New input feature: you only need to enter 2 hex digits to get a color, and it auto updates as you add more - 3,4,6,8 - if wen you enter two, such as e9, you are returned #e9e9e9. helpful for quickly toggling through grays.

New color object data returns include L* and methods for returning alpha data.

Changes in the .HTML files

Remember there’s a lot of useful JS in the HTML documents as well, and the latest in terms of the new multi-level scoring model. The font samples section is substantially cleaned up and revised to reflect the latest guidelines.

Change Notice October 12, 2020 0.0.97g

Fixed constant for Green coefficient — should be: const Gco = 0.7152; and not 0.7156 (lingering typo does not materially affect results but was nevertheless wrong.)

ALSO: Changed all power functions from the shorthand ** to the more standard Math.pow() for better compatibility.

Change Notice October 11, 2020

Added “APCAsRGBonly.js — this is the APCA algorithm only, suitable if you already have color parsing and just want to add the ACPA function. This version takes sRGB encoded 8 bit integers from 0-255.

Code cleanup in the JS files. The loConRamp moved to a separate function. HTML files have an improved UX for the manual color entry fields.

Change Notice October 10, 2020

Split the “APCA” version from the “SAPC” version. The APCA is intended for the forthcoming W3 accessibility standards (Silver/WCAG 3). The SAPC is the research version, which may not be in conformance due to experimental variations.

October 07, 2020

To any “early adopting” developers:

IMPORTANT: const VALUE CHANGE

Priority: HIGH — Affects Results If you are not interested in the low-contrast extension, then there is just one change that is important:

Change the const blkClmp from 1.75 to 1.33

This affects the results whenever the darker color is less than #2c2c28.

`const blkClmp = 1.75;	// OLD Exponent for the soft black clamp curve`
`const blkClmp = 1.33;	// NEW Exponent for the soft black clamp curve`

SAPC -> APCA

Also just FYI, SAPC is the research name and SAPC is licensed under AGPL v3. APCA is the release name in the new Working Draft of Silver/WCAG 3, and licensed to the W3 per their collaborative agreements.

Please feel free post issues or comments.

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