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Author Topic: How does altering a smart phone's gray-scale on help with battery life?  (Read 10880 times)

Offline McKay

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Greetings. The gray scale mode of the new Samsung Galaxy S5 is really bothering me.
Many people, without deeper knowledge and understanding, automatically think that a grayscale screen will  require less power - but is it true?
Lets see:
First of all, the screen is not black and white, but grayscale - there is a difference.
In order to get a gray pixel, all three sub-pixels (RGB) must be active (if all are at max levels then it will be white.. as gray is dark-white). And from the looks of it, the images on such a grayscale mode screen are mostly .. gray, not fully black.
Wouldnt a, for example, dark blue tone need less power than a gray tone, as it would need only one color sub-pixlel to be active?

What does actually reduce power consumption:
*Reduce the color depth (grayscale probably does this, but it is not advertised as such) - less bits per color to be stored in video RAM and processed.
*Reduce the brightness of the screen. (the grayscale seems a bit darker, but the screen can be made darker keeping the colors and, perhaps, adjusting contrast for better viewing)
*Reduce the resolution - less pixels to be processed and stored in RAM (damn, people want 4K screens in their devices and cry about how bad the accumulators are, phew)
*Make the screen ACTUALLY black with some white (or gray, or single color) marking what needs to be seen.
*Reduce the refresh rate, perhaps.
*What else.. ?

All this can actually lower the power consumption, but how exactly does simply making the screen gray-scale helps?
« Last Edit: 12/06/2014 09:37:18 by graihagh »


 

Offline evan_au

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Re: Galaxy S5 gray scale screen actual physics
« Reply #1 on: 08/06/2014 04:43:42 »
Reducing the CPU load to render colours and do gamma correction must save some power.
Less memory and fewer refresh cycles on the screen must also save some power too.

Traditional colour LCDs have a uniform white backlight, then pass the light through red, green and blue filters, then through LCD to let through a variable amount of each colour. This results in a display that is about 6 times less efficient than necessary.
If you made a greyscale screen by dropping the RGB filters, you could get away with 1/3 of the power to the backlight. (just using the LCD in on/off mode to produce a black and white display would halve the power again.) However, I see that greyscale is only used in power-save mode, and at other times it still has full-colour. So this can't be the method... 
 

Offline McKay

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.. However, I see that greyscale is only used in power-save mode, and at other times it still has full-colour. So this can't be the method... 

Exactly.
The grayscale mode seems a bit over rated.
It would be a different story if the screen was actually made to be purely grayscale or black & white.
« Last Edit: 13/06/2014 12:40:02 by McKay »
 

Offline zacsaturday

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Re: Galaxy S5 gray scale screen actual physics
« Reply #3 on: 29/12/2014 21:50:34 »
Reducing the CPU load to render colours and do gamma correction must save some power.
Less memory and fewer refresh cycles on the screen must also save some power too.

Traditional colour LCDs have a uniform white backlight, then pass the light through red, green and blue filters, then through LCD to let through a variable amount of each colour. This results in a display that is about 6 times less efficient than necessary.
If you made a greyscale screen by dropping the RGB filters, you could get away with 1/3 of the power to the backlight. (just using the LCD in on/off mode to produce a black and white display would halve the power again.) However, I see that greyscale is only used in power-save mode, and at other times it still has full-colour. So this can't be the method...

(do correct me if i am wrong) This only happens in LCD displays (pretty much any phone apart from most Samsungs), not AMOLED screens, like Samsung Galaxy series.
 

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Re: Galaxy S5 gray scale screen actual physics
« Reply #3 on: 29/12/2014 21:50:34 »

 

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