[Sugar-devel] automatic backlight control

forster at ozonline.com.au forster at ozonline.com.au
Tue Nov 22 23:52:06 EST 2011

Thanks Paul

The logic appears to be buggy, see #11487: XO-1.75 OS12 backlight is off when you come back inside

As it stands, neither the monochrome nor colour modes are OK in full sunlight. The colour mode causes a significant loss of resolution for reading small black text and even more resolution loss with coloured text.

With the monochrome mode, the shadow of your hands as you type is enough to switch mode which is quite distracting

The cutin cutout settings are 50 (bright)and 80 (dark). It does not seem worth raising the 80 figure because there is still visible colour information at 70. The 50 figure could be lowered, direct sunlight is 5-10, so I tried 15, this still could give mode switching from your hands' shadow in direct sunlight.

What I suggest is that the backlight not switch off unless you have been in the sun for (eg) 5 minutes, but switch back on immediately in the dark. I don't have the coding skills or I would have tried it out.

For anybody who wants to try it
powerd is at

the brightness settings are at line1853
monochrome is commented out at lines 1764 &1793

uncommenting these lines reenables monochrome in response to the sensor but surprisingly not the control keys


> forster at ozonline.com.au wrote:
>  > The shift from colour to monochrome is noticable and would be annoying if it 
>  > happened a lot, for example as clouds pass, trees and people move.
>  > 
>  > If the hysterisis, the difference between cutin and cutout brightness is large, 
>  > the change in mode will happen a lot less frequently and not be annoying.
>  > 
>  > I would like to try it switching automatically to monochrome but with large 
>  > hysterisis.
>  > 
>  > I'll wait to try OS12
> you may be in a better position to play with this, geographically
> speaking, than i am -- we're running low on sunlight these days.
> the hysteresis is currently hard-coded in powerd -- you'll find it in
> the function ambient_adjust_init().  it only gets set once, though, so
> after powerd starts, you can change the limits directly and they
> should take effect immediately.
> additionally, to cause auto-monochrome to happen, uncomment the
> obvious lines at the end of set_brightness() and brightness_ramp().
> paul
>  > 
>  > Tony
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>  paul fox, pgf at laptop.org
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