Bug#418708: installation-reports: Dialogs difficult to use on gray-scale monitors
[ As querybts doesn't let me provide extra information (##501285), I'm
trying to add this via e-mail, hope it works. ]
Tomasz Chmielewski <firstname.lastname@example.org> wrote:
> I remember I used d-i to install Debian (arm) on Thecus n4100 - using
> minicom and a serial connection. Navigation in d-i over a serial
> connection / minicom sucks, but that's another story.
> Essentially, a serial connection is black and white only - can it be
> worse than a gray-scale monitor?
In case of a serial connection, the communication endpoint (software or
hardware terminal) can
1) evaluate *all* color/brightness information (it's usually just
black and white with two grades of brightness, digitally encoded
via escape sequences),
2) losslessly reproduce the transferred color/brightness information,
as the terminal (software or hardware) is featured with an
appropriate output device (CRTC in either case).
In case of a gray-scale monitor attached to a (color) graphics card, the
1) usually *not* evaluate all information (at least 16 millions of
colors, split to three different color channels, analogically
encoded), as it often has only one input channel, which is hooked
to the green output channel of the graphics card,
2) *not* losslessly reproduce the transferred information. The input
consists of at least 16 millions colors, which have to be mapped
to just 256 grades of brightness (gray).
Lower-end gray-scale monitors only evaluate the green channel and will
display all colors that don't contain any green (e. g. pure red or pure
blue) as black.
Higher-end gray-scale monitors evaluate all three color channels (red,
green, blue), and map the 16 millions of colors in an
eye-physiologically optimal way to 255 grades of brightness, so that,
for instance, pure red and pure blue are displayed with to different
shades of gray. There are also graphics cards that do that mapping on
their own, if configured so.
Either way, information gets lost or "compressed" so much, that two
different colors can be indistinguishable on a gray-scale monitor.
There are two possibilities after letting the user tell the system
(e. g. via bootloader parameters) about having a gray-scale or
A) For both gray-scale and monochrome monitors:
Use only black and white (with two grades of brightness) and
display the currently selected element with a special formatting,
i. e. inverted or underlined.
B) For gray-scale monitors:
In case the color-to-shades-of-gray mapping is (nearly) the same
everywhere, use more than two colors, but make sure that with the
given mapping, they are well distinguishable.
Option "A" should be totally sufficient for installing Debian.
P.S.: Even today's BIOS setup programs have an option to change
foreground and background colors (incl. black & white) -- which
is good, because otherwise, it could happen that I can't use my
server's BIOS setup, as it's attached to a small gray-scale