Register Guidelines E-Books Search Today's Posts Mark Forums Read

Go Back   MobileRead Forums > E-Book Readers > Kobo Reader

Notices

Reply
 
Thread Tools Search this Thread
Old 12-25-2012, 12:31 AM   #1
xuyn2003
Connoisseur
xuyn2003 might easily be mistaken for a Texanxuyn2003 might easily be mistaken for a Texanxuyn2003 might easily be mistaken for a Texanxuyn2003 might easily be mistaken for a Texanxuyn2003 might easily be mistaken for a Texanxuyn2003 might easily be mistaken for a Texanxuyn2003 might easily be mistaken for a Texanxuyn2003 might easily be mistaken for a Texanxuyn2003 might easily be mistaken for a Texanxuyn2003 might easily be mistaken for a Texanxuyn2003 might easily be mistaken for a Texan
 
Posts: 71
Karma: 18140
Join Date: Jul 2011
Device: PRS-T1&KOBOTOUCH
A pessimistic guess about Kobo Glo's brightness limit.

Dear all,
Many people have asked KOBO for a less bright light at the minimal light level,
but till now KOBO never said anything about it.
I'm afraid the bright limit is denpend on hardware, not software.

I hope this is not real!
xuyn2003 is offline   Reply With Quote
Old 12-25-2012, 01:38 AM   #2
stewacide
Groupie
stewacide ought to be getting tired of karma fortunes by now.stewacide ought to be getting tired of karma fortunes by now.stewacide ought to be getting tired of karma fortunes by now.stewacide ought to be getting tired of karma fortunes by now.stewacide ought to be getting tired of karma fortunes by now.stewacide ought to be getting tired of karma fortunes by now.stewacide ought to be getting tired of karma fortunes by now.stewacide ought to be getting tired of karma fortunes by now.stewacide ought to be getting tired of karma fortunes by now.stewacide ought to be getting tired of karma fortunes by now.stewacide ought to be getting tired of karma fortunes by now.
 
Posts: 162
Karma: 1051770
Join Date: Jul 2012
Device: Kobo Glo, Kobo Touch
I bet they could lower it, but I can think of two reasons they might not want to:

1. Lower brightness would make the lighting look uneven, which people will complain about and might cause returns of people with unreasonable expectations
2. If they're using PWM to control the LEDs, going too low might make 'strobing' apparent

p.s. perhaps an easier to implement solution is a white-on-black mode: if they did this at the display driver level would seem trivially easy to implement. It's how I use my iPhone and laptop in the dark comfortably (although on a laptop this is sub-optimal since it messes up the sub-pixel smoothing, which with eink is not a factor)

Last edited by stewacide; 12-25-2012 at 01:58 AM.
stewacide is offline   Reply With Quote
 
Advertisement
Old 12-25-2012, 09:05 AM   #3
murg
No Comment
murg ought to be getting tired of karma fortunes by now.murg ought to be getting tired of karma fortunes by now.murg ought to be getting tired of karma fortunes by now.murg ought to be getting tired of karma fortunes by now.murg ought to be getting tired of karma fortunes by now.murg ought to be getting tired of karma fortunes by now.murg ought to be getting tired of karma fortunes by now.murg ought to be getting tired of karma fortunes by now.murg ought to be getting tired of karma fortunes by now.murg ought to be getting tired of karma fortunes by now.murg ought to be getting tired of karma fortunes by now.
 
Posts: 1,424
Karma: 3095950
Join Date: Jan 2012
Location: Australia
Device: Kobo: Not just an eReader, it's an adventure!
Quote:
Originally Posted by stewacide View Post
2. If they're using PWM to control the LEDs, going too low might make 'strobing' apparent
I think the Glo is using PWM. I noticed that after reading in the dark for a while, when I turn off the Glo, I see a strobing in my eyes for a while, which is very similar to what I get when I stop watching TV.
murg is offline   Reply With Quote
Old 12-25-2012, 10:03 AM   #4
Uschiekid
Evangelist
Uschiekid ought to be getting tired of karma fortunes by now.Uschiekid ought to be getting tired of karma fortunes by now.Uschiekid ought to be getting tired of karma fortunes by now.Uschiekid ought to be getting tired of karma fortunes by now.Uschiekid ought to be getting tired of karma fortunes by now.Uschiekid ought to be getting tired of karma fortunes by now.Uschiekid ought to be getting tired of karma fortunes by now.Uschiekid ought to be getting tired of karma fortunes by now.Uschiekid ought to be getting tired of karma fortunes by now.Uschiekid ought to be getting tired of karma fortunes by now.Uschiekid ought to be getting tired of karma fortunes by now.
 
Posts: 453
Karma: 478836
Join Date: Oct 2012
Device: Kobo Glo
Quote:
Originally Posted by stewacide View Post
p.s. perhaps an easier to implement solution is a white-on-black mode: if they did this at the display driver level would seem trivially easy to implement. It's how I use my iPhone and laptop in the dark comfortably (although on a laptop this is sub-optimal since it messes up the sub-pixel smoothing, which with eink is not a factor)
I wonder about this though....the only time I notice ghosting (besides when using the browser) is when there is white "text" on black background. I wonder if having the black background would make the letters illegible if not on every page refresh......
Uschiekid is offline   Reply With Quote
Old 12-25-2012, 11:21 AM   #5
xuyn2003
Connoisseur
xuyn2003 might easily be mistaken for a Texanxuyn2003 might easily be mistaken for a Texanxuyn2003 might easily be mistaken for a Texanxuyn2003 might easily be mistaken for a Texanxuyn2003 might easily be mistaken for a Texanxuyn2003 might easily be mistaken for a Texanxuyn2003 might easily be mistaken for a Texanxuyn2003 might easily be mistaken for a Texanxuyn2003 might easily be mistaken for a Texanxuyn2003 might easily be mistaken for a Texanxuyn2003 might easily be mistaken for a Texan
 
Posts: 71
Karma: 18140
Join Date: Jul 2011
Device: PRS-T1&KOBOTOUCH
Quote:
Originally Posted by stewacide View Post
2. If they're using PWM to control the LEDs, going too low might make 'strobing' apparent
Oh my god!'strobing'!
Meaning that lower bright is achieved by slower LED flashing speed? not by lower electric voltage? That's harmful to eyes!
xuyn2003 is offline   Reply With Quote
Old 12-25-2012, 12:34 PM   #6
DNSB
Bibliophagist
DNSB ought to be getting tired of karma fortunes by now.DNSB ought to be getting tired of karma fortunes by now.DNSB ought to be getting tired of karma fortunes by now.DNSB ought to be getting tired of karma fortunes by now.DNSB ought to be getting tired of karma fortunes by now.DNSB ought to be getting tired of karma fortunes by now.DNSB ought to be getting tired of karma fortunes by now.DNSB ought to be getting tired of karma fortunes by now.DNSB ought to be getting tired of karma fortunes by now.DNSB ought to be getting tired of karma fortunes by now.DNSB ought to be getting tired of karma fortunes by now.
 
DNSB's Avatar
 
Posts: 2,319
Karma: 6142827
Join Date: Jul 2010
Location: Vancouver
Device: Kobo Aura HD, Glo, Nexus 7 HD, iPad Air
Quote:
Originally Posted by xuyn2003 View Post
Oh my god!'strobing'!
Meaning that lower bright is achieved by slower LED flashing speed? not by lower electric voltage? That's harmful to eyes!
Sheeshh,....

Their most likely method of controlling the LED brightness is using PWM. There will be no change in the flashing rate when using PWM as the brightness change will be done by modifying the amount of time the LED is on during each cycle.

If they are using PWM at 1KHz (a 1000 microsecond cycle width), I somehow doubt that anyone is going to notice any strobing effect or suffer any ill effects. Now if they were using between 5 and 30 pulses per second, you might have a case (and for the photosensitive epileptic, a seizure).

Say you are using a 1000 microsecond cycle and a resolution of 100 microseconds, you would get 11 steps from 0 microseconds on (dark) to 1000 microseconds on (full brightness) without having to change the cycle time.

Perhaps next time before getting angry, you should try getting educated?

Regards,
David
DNSB is offline   Reply With Quote
Old 12-25-2012, 12:45 PM   #7
DNSB
Bibliophagist
DNSB ought to be getting tired of karma fortunes by now.DNSB ought to be getting tired of karma fortunes by now.DNSB ought to be getting tired of karma fortunes by now.DNSB ought to be getting tired of karma fortunes by now.DNSB ought to be getting tired of karma fortunes by now.DNSB ought to be getting tired of karma fortunes by now.DNSB ought to be getting tired of karma fortunes by now.DNSB ought to be getting tired of karma fortunes by now.DNSB ought to be getting tired of karma fortunes by now.DNSB ought to be getting tired of karma fortunes by now.DNSB ought to be getting tired of karma fortunes by now.
 
DNSB's Avatar
 
Posts: 2,319
Karma: 6142827
Join Date: Jul 2010
Location: Vancouver
Device: Kobo Aura HD, Glo, Nexus 7 HD, iPad Air
Quote:
Originally Posted by stewacide View Post
I bet they could lower it, but I can think of two reasons they might not want to:

1. Lower brightness would make the lighting look uneven, which people will complain about and might cause returns of people with unreasonable expectations
2. If they're using PWM to control the LEDs, going too low might make 'strobing' apparent.
Out of curiosity, why would you think that using PWM and going too low might make 'strobing' apparent? Most of the PWM implementations I am aware of use a constant cycle time (cycle = on time + off time).

Regards,
David
DNSB is offline   Reply With Quote
Old 12-25-2012, 07:00 PM   #8
jusmee
Guru
jusmee ought to be getting tired of karma fortunes by now.jusmee ought to be getting tired of karma fortunes by now.jusmee ought to be getting tired of karma fortunes by now.jusmee ought to be getting tired of karma fortunes by now.jusmee ought to be getting tired of karma fortunes by now.jusmee ought to be getting tired of karma fortunes by now.jusmee ought to be getting tired of karma fortunes by now.jusmee ought to be getting tired of karma fortunes by now.jusmee ought to be getting tired of karma fortunes by now.jusmee ought to be getting tired of karma fortunes by now.jusmee ought to be getting tired of karma fortunes by now.
 
Posts: 978
Karma: 203682
Join Date: Oct 2009
Device: Kobo Touch / Astak Pocket Pro
Quote:
Originally Posted by DNSB View Post
Out of curiosity, why would you think that using PWM and going too low might make 'strobing' apparent? Most of the PWM implementations I am aware of use a constant cycle time (cycle = on time + off time).

Regards,
David
And the frequency is way too fast for the eye to perceive. After effects from a TV were mentioned, but the frame rate for most TV systems is 50 or 60 Hz. PWM usually works in the thousands of Hz.

Last edited by jusmee; 12-25-2012 at 08:18 PM.
jusmee is offline   Reply With Quote
Old 12-25-2012, 07:45 PM   #9
EldRick
Addict
EldRick is the 'tall, dark, handsome stranger' all the fortune-tellers are referring to.EldRick is the 'tall, dark, handsome stranger' all the fortune-tellers are referring to.EldRick is the 'tall, dark, handsome stranger' all the fortune-tellers are referring to.EldRick is the 'tall, dark, handsome stranger' all the fortune-tellers are referring to.EldRick is the 'tall, dark, handsome stranger' all the fortune-tellers are referring to.EldRick is the 'tall, dark, handsome stranger' all the fortune-tellers are referring to.EldRick is the 'tall, dark, handsome stranger' all the fortune-tellers are referring to.EldRick is the 'tall, dark, handsome stranger' all the fortune-tellers are referring to.EldRick is the 'tall, dark, handsome stranger' all the fortune-tellers are referring to.EldRick is the 'tall, dark, handsome stranger' all the fortune-tellers are referring to.EldRick is the 'tall, dark, handsome stranger' all the fortune-tellers are referring to.
 
Posts: 384
Karma: 91339
Join Date: Aug 2010
Device: Kobo Mini, Kobo Glo (Sony PRS-950, Nook STR, Kobo Touch, K-DX, K-3)
Every adjustable-brightness LED flashlight in the world uses PWM to control the brightness.
EldRick is offline   Reply With Quote
Old 12-25-2012, 11:08 PM   #10
sysKin
Connoisseur
sysKin knows the complete value of PI to the endsysKin knows the complete value of PI to the endsysKin knows the complete value of PI to the endsysKin knows the complete value of PI to the endsysKin knows the complete value of PI to the endsysKin knows the complete value of PI to the endsysKin knows the complete value of PI to the endsysKin knows the complete value of PI to the endsysKin knows the complete value of PI to the endsysKin knows the complete value of PI to the endsysKin knows the complete value of PI to the end
 
sysKin's Avatar
 
Posts: 56
Karma: 31286
Join Date: Oct 2012
Location: Australia
Device: Aura HD, after a train ate my Glo
So has anyone managed to control the glow by directly interacting with hardware?
Looking at /sys/devices/platform/ -- which should have all Freescale hardware accessible - there exists /sys/devices/platform/pmic_light.1/, which has a virtual file "lit". It *looks* like writing to that file should control the light, just like writing to platform/pmic_leds.98/leds/pmic_ledsb/brightness makes the LED go blue.

Looking at constants from libnickel.so, it seems to do that in a few places:
echo ch %1 > /sys/devices/platform/pmic_light.1/lit
echo cur 1 > /sys/devices/platform/pmic_light.1/lit
echo dc %1 > /sys/devices/platform/pmic_light.1/lit
echo bp %1 > /sys/devices/platform/pmic_light.1/lit

However, it's anyone's guess what %1 should be at those points, and is there some sequence of "ch" and "dc" and "bp" and "cur" commands that need to be run together. My attempts to write numbers or letters there failed, and my attempts to read Freescale documentation on this device were unsuccessful. It seems to be designed for LCD backlight in mind.

It's also perfectly possible that the light is actually not controlled by pmic_light, but instead by one of the mxc-i2c devices or even mxc-pwm.1 device or even something else.

Ideas?

Maybe some linux guru knows a way to capture writes to that "lit" file, somehow, and dump them to a real file instead?
For example overriding "echo" command with our own?

Last edited by sysKin; 12-25-2012 at 11:24 PM.
sysKin is offline   Reply With Quote
Old 12-25-2012, 11:16 PM   #11
xuyn2003
Connoisseur
xuyn2003 might easily be mistaken for a Texanxuyn2003 might easily be mistaken for a Texanxuyn2003 might easily be mistaken for a Texanxuyn2003 might easily be mistaken for a Texanxuyn2003 might easily be mistaken for a Texanxuyn2003 might easily be mistaken for a Texanxuyn2003 might easily be mistaken for a Texanxuyn2003 might easily be mistaken for a Texanxuyn2003 might easily be mistaken for a Texanxuyn2003 might easily be mistaken for a Texanxuyn2003 might easily be mistaken for a Texan
 
Posts: 71
Karma: 18140
Join Date: Jul 2011
Device: PRS-T1&KOBOTOUCH
Quote:
Originally Posted by DNSB View Post
Sheeshh,....

Their most likely method of controlling the LED brightness is using PWM. There will be no change in the flashing rate when using PWM as the brightness change will be done by modifying the amount of time the LED is on during each cycle.

If they are using PWM at 1KHz (a 1000 microsecond cycle width), I somehow doubt that anyone is going to notice any strobing effect or suffer any ill effects. Now if they were using between 5 and 30 pulses per second, you might have a case (and for the photosensitive epileptic, a seizure).

Say you are using a 1000 microsecond cycle and a resolution of 100 microseconds, you would get 11 steps from 0 microseconds on (dark) to 1000 microseconds on (full brightness) without having to change the cycle time.

Perhaps next time before getting angry, you should try getting educated?

Regards,
David
OK, I understand, the flashing rate will not change at different level, but the on-off time was adjusted in one cycle.

Another question, will PWM ,have a minimal on time limit? For example, it had to be on for at least 0.1 microsecond, if the time is less than 0.1 microsecond, it will not be turn on at all?
xuyn2003 is offline   Reply With Quote
Old 12-25-2012, 11:25 PM   #12
GeoffR
Wizard
GeoffR ought to be getting tired of karma fortunes by now.GeoffR ought to be getting tired of karma fortunes by now.GeoffR ought to be getting tired of karma fortunes by now.GeoffR ought to be getting tired of karma fortunes by now.GeoffR ought to be getting tired of karma fortunes by now.GeoffR ought to be getting tired of karma fortunes by now.GeoffR ought to be getting tired of karma fortunes by now.GeoffR ought to be getting tired of karma fortunes by now.GeoffR ought to be getting tired of karma fortunes by now.GeoffR ought to be getting tired of karma fortunes by now.GeoffR ought to be getting tired of karma fortunes by now.
 
GeoffR's Avatar
 
Posts: 1,584
Karma: 3124032
Join Date: Nov 2012
Location: New Zealand
Device: Kobo Glo
Quote:
Originally Posted by sysKin View Post
So has anyone managed to control the glow by directly interacting with hardware?
Not in the way you mean, but I can reduce the (apparent) brightness by holding the hardware further away from my face :-)

When reading most paper books I hold the book quite close in order to see the small type clearly. When I first got my Glo I did the same thing, but then I realised it was much more comfortable to increase the font size and hold it further away. As a result I had to turn up the brightness setting, but that is no problem, the Glo can go brighter that I will ever need.
GeoffR is offline   Reply With Quote
Old 12-25-2012, 11:51 PM   #13
DNSB
Bibliophagist
DNSB ought to be getting tired of karma fortunes by now.DNSB ought to be getting tired of karma fortunes by now.DNSB ought to be getting tired of karma fortunes by now.DNSB ought to be getting tired of karma fortunes by now.DNSB ought to be getting tired of karma fortunes by now.DNSB ought to be getting tired of karma fortunes by now.DNSB ought to be getting tired of karma fortunes by now.DNSB ought to be getting tired of karma fortunes by now.DNSB ought to be getting tired of karma fortunes by now.DNSB ought to be getting tired of karma fortunes by now.DNSB ought to be getting tired of karma fortunes by now.
 
DNSB's Avatar
 
Posts: 2,319
Karma: 6142827
Join Date: Jul 2010
Location: Vancouver
Device: Kobo Aura HD, Glo, Nexus 7 HD, iPad Air
Quote:
Originally Posted by xuyn2003 View Post
OK, I understand, the flashing rate will not change at different level, but the on-off time was adjusted in one cycle.

Another question, will PWM ,have a minimal on time limit? For example, it had to be on for at least 0.1 microsecond, if the time is less than 0.1 microsecond, it will not be turn on at all?
The minimum on time limit depends on the resolution of the controller. A dedicated controller can easily have an on time of 0.1 microseconds, a controller being run by a microprocessor in software which is handling other tasks is likely to have a longer minimum pulse width. The other limit on the minimum duty cycle would be the LED itself as you generally need higher current at the shorter duty cycles to have the LED turn on and there is a minimum pulse width below which the LED will not turn on. Those numbers will depend on the LED manufacturing process and materials.

Using my 1KHz cycle time, an LED being turned on for 0.1 microseconds then off for 999.9 microseconds is not going to generate very much light. It's more likely to have a minimum pulse width (AKA duty cycle) determined by the minimum acceptable light level and then however many steps the designers felt would be useful between that duty cycle and the maximum duty cycle. If an external PWM controller is used, some of the parameters may be hard-coded into the PWM controller while others would be set by the microprocessor. If not PWM controller is present, the microprocessor would be doing all the control functions.

Regards,
David
DNSB is offline   Reply With Quote
Old 12-26-2012, 04:40 PM   #14
KevinShort
Addict
KevinShort can program the VCR without an owner's manual.KevinShort can program the VCR without an owner's manual.KevinShort can program the VCR without an owner's manual.KevinShort can program the VCR without an owner's manual.KevinShort can program the VCR without an owner's manual.KevinShort can program the VCR without an owner's manual.KevinShort can program the VCR without an owner's manual.KevinShort can program the VCR without an owner's manual.KevinShort can program the VCR without an owner's manual.KevinShort can program the VCR without an owner's manual.KevinShort can program the VCR without an owner's manual.
 
KevinShort's Avatar
 
Posts: 342
Karma: 165069
Join Date: Jan 2012
Location: Virginia, US
Device: Kobo Wifi, Kobo Glo
Quote:
Originally Posted by sysKin View Post
So has anyone managed to control the glow by directly interacting with hardware?
I just figured it out today, see this thread.
KevinShort is offline   Reply With Quote
Old 12-26-2012, 07:46 PM   #15
murg
No Comment
murg ought to be getting tired of karma fortunes by now.murg ought to be getting tired of karma fortunes by now.murg ought to be getting tired of karma fortunes by now.murg ought to be getting tired of karma fortunes by now.murg ought to be getting tired of karma fortunes by now.murg ought to be getting tired of karma fortunes by now.murg ought to be getting tired of karma fortunes by now.murg ought to be getting tired of karma fortunes by now.murg ought to be getting tired of karma fortunes by now.murg ought to be getting tired of karma fortunes by now.murg ought to be getting tired of karma fortunes by now.
 
Posts: 1,424
Karma: 3095950
Join Date: Jan 2012
Location: Australia
Device: Kobo: Not just an eReader, it's an adventure!
Quote:
Originally Posted by xuyn2003 View Post
Dear all,
Many people have asked KOBO for a less bright light at the minimal light level,
but till now KOBO never said anything about it.
I'm afraid the bright limit is denpend on hardware, not software.

I hope this is not real!
You could always wear sunglasses while reading your Glo in the dark...
murg is offline   Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Touch What is the microsd card limit (gb) for the Kobo Touch? Nietzsche Kobo Reader 29 03-14-2014 01:44 PM
Touch Checkers for Kobo Touch and Kobo Glo sergeyvl12 Kobo Developer's Corner 24 01-03-2013 05:36 PM
Glo How to import reading Life Statistics from Kobo Touch to Kobo Glo? the_m Kobo Reader 5 12-13-2012 04:40 PM
Kobo Glo fonts compared to Kobo Touch RobertJSawyer Kobo Reader 3 10-11-2012 01:10 AM
Kobo Glo Vs Kobo Touch Sizes (Want to use my Skindigital cover) Chocky Kobo Reader 3 09-25-2012 11:47 AM


All times are GMT -4. The time now is 01:46 AM.


MobileRead.com is a privately owned, operated and funded community.