https://bugs.documentfoundation.org/show_bug.cgi?id=156182
Bug ID: 156182
Summary: FORMATTING Automatic text color can be unreadable
with darker cell colors
Product: LibreOffice
Version: Inherited From OOo
Hardware: All
OS: All
Status: UNCONFIRMED
Severity: normal
Priority: medium
Component: Calc
Assignee: [email protected]
Reporter: [email protected]
Description:
When the text color is set the automatic, the colors for text are frequently
illegible with darker cell backgrounds. At present, the text color flips from
black to white only when the cell is darker than about #3f3f3f.
For accessible contrast for readability, the central contrast point is much
higher, approximately #a4a4a4.
I have an example image showing the current LibreOffice flip point, and then
APCA, luminance at 36Y, and the old WCAG2:
https://www.myndex.com/PUB/IMG/libreofficetextproblem.png
Will attach here as well
As you can see on the image the current flip point is too dark. Either APCA or
a simple luminance flip point at 0.36Y brings the contrast to ~perceptual
center.
NOTE: WCAG 2 math also fails for dark colors, and is not fit for use here, as
can also be seen on the example.
Assuming sRGB, the following simple code will take eight bit RGB values and
convert to a relative luminance value, that then can be used to determine the
flip point.
```
// ANDY'S DOWN AND DIRTY LUMINANCE™
// Rs Gs Bs are 0-255 sRGB values. JS shown.
// FlipY is a value 0.0-1.0, and 0.36 is a good point to flip text
black or white.
// For purists: Yea this is NOT the IEC piecewise, but it's fast and
simple
let flipY =
(Rs/255.0)**2.2*0.2126+(Gs/255.0)**2.2*0.7152+(Bs/255.0)**2.2*0.0722;
```
Steps to Reproduce:
1. Set text color to automatic
2. Set the cell color to a very dark color but is lighter than about #3f3f3f
3. Some example cell backgrounds are #6d3400, #444, #005682
4. This is an accessibility fail but it is also a failure for all users as text
becomes essentially unreadable.
Actual Results:
Unreadable with insufficient contrast and too dark
Expected Results:
Ideally text should be readable in most cases. The simplest answer, the text
should flip from black to white or vice versa, when the luminance of the cell
color is approximately 0.36Y
There is a demonstrator repo with links to examples and discussion:
https://github.com/Myndex/fancyfontflipping
Reproducible: Always
User Profile Reset: Yes
Additional Info:
Version: 7.5.3.2 (X86_64) / LibreOffice Community
Build ID: 9f56dff12ba03b9acd7730a5a481eea045e468f3
CPU threads: 8; OS: Mac OS X 10.15.7; UI render: default; VCL: osx
Locale: en-US (en_US.UTF-8); UI: en-US
Calc: threaded
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