https://issues.apache.org/ooo/show_bug.cgi?id=121870
Bug ID: 121870
Issue Type: DEFECT
Summary: Different darkness threshold: doc/docx auto font color
inverted
Classification: Application
Product: Writer
Version: AOO 3.4.1
Hardware: All
OS: All
Status: CONFIRMED
Severity: normal
Priority: P3
Component: code
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Created attachment 80384
--> https://issues.apache.org/ooo/attachment.cgi?id=80384&action=edit
Test document: text should appear white.
Apparently OOo and MS-office have a different threshold to determine what
should be considered dark.
As mentioned in a LibreOffice list:
Neither the OpenDocument spec nor the Office Open XML spec define
what background colour should be considered "dark", leaving it up to the
implementation.
OpenDocument v1.2 section 20.385:
http://docs.oasis-open.org/office/v1.2/os/OpenDocument-v1.2-os-part1.html#__RefHeading__1420234_253892949
Luke Deller made an interesting analysis which I will quote here:
___
Word 2010 appears to treat a background colour as "dark" if:
130*red + 255*green * 51*blue < 105*255
Where red, green, blue are the RGB components of the background colour as 8-bit
integers (ie in the range 0 to 255).
(I arrived at this formula by:
- collecting some data points by experimentation with Word 2010
- guessing the form of this formula
- using linear algebra with the data points to work out the coefficients
- double-checking using more data points)
the LibreOffice formula (from code) is:
77*red + 151*green + 28*blue <= 38*256
I notice that both Word and LibreOffice formulae use weights proportional to
the "Rec. 601" coefficients for Luma shown here:
http://en.wikipedia.org/wiki/Luma_%28video%29
ie Luma = 0.299 R' + 0.587 G' + 0.114 B'
(Actually LibreOffice would match these coefficients more accurately if it used
76*red + 151*green + 29*blue)
Anyway the main difference is that LibreOffice considers Luma <= 38 (out of
255) to be dark, whereas Word considers Luma < about 61 (out of 255) to be
dark.
______
The proposed change in LibreOffice is to change slightly the coefficients in
tools/inc/tools/color.hxx Color::GetLuminance()
change 28 --> 29, 77 -->76
tools/source/generic/color.cxx Color::IsDark()
Change the threshold from 38 --> 60 (or maybe just 50?)
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