Amoled display issue

[Eugiaz]

Hi everyone i would like to know if what i'm going to describe in the next ilnes is a common problem due to the amoled screen or it's just my nexusone that has this problem:
I have to say that when I'm watching pics or movies the screen is awsome and has a very good resolution. For all the rest the screen seems a bit dotted and grainy, especially with text. For example in the app launcher where the app's names are written in white and the background is black the text is not extremely clear and if I take a closer look theres seems to be little pink dots on the letter's edges. I can notice this thing almost evrywhere but I think it's a lot more clear to see with text.
It's not a big deal I can get used to it but i just wanted to know if it's only my phone that has something wrong, so could you please check if even your nexusone is like this?? Thanks

If I can i'll post a pic of what I tryed to describe

[phunds]

That's not normal. Most likely a defective N1. You should contact HTC.

Also I wouldn't mind seeing a screenshot of this issue.

[Eugiaz]

Thanks for your quick reply, i've not been able of taking a pic in which you can see this problem but searching the web I found this Nexus One Organic LED Detail on Flickr - Photo Sharing!
in that picture I think you can understand what I'm saying.
Since I live in Italy it would be a bit difficult to get a replace so i'm hoping that my nexusone is not a faulty phone....

[abirkill]

Hi there,

The photo linked to above is mine, thanks for the extra traffic today!

I would agree that the Nexus One screen can appear grainy at times -- more specifically, it's not the entire screen, but it's text. It appears to affect grey text more than it does pure white text, and it's a minor issue, but it is noticeable to those who are used to high-resolution LCD displays.

I have taken a couple of better photos to try and show the grainyness issue -- as I said on my Flickr comment, I believe this is completely normal behaviour, and an effect of the pixel layout of the OLED screen, possible combined with the sub-pixel anti-aliasing that the Android OS performs. Apologies for the quality, I took them in a rush so they're a bit out of focus at the edges.

[kc.rkitek]

who really gets that close to the display to look at it?? i usually hold mine about a foot away from my eyes and it looks pretty darn good! just sayin...

[abirkill]

Originally Posted by kc.rkitek

who really gets that close to the display to look at it?? i usually hold mine about a foot away from my eyes and it looks pretty darn good! just sayin...

It depends how good your eyesight is and how picky you are, I think. I noticed it within 5 minutes of getting my Nexus One -- it doesn't bother me, but I was aware of it.

Looking closer at my photos I think there is actually a bug in the sub-pixel font anti-aliasing which is causing this, I'm investigating further.

[Eugiaz]

Originally Posted by abirkill

Hi there,

The photo linked to above is mine, thanks for the extra traffic today!

I would agree that the Nexus One screen can appear grainy at times -- more specifically, it's not the entire screen, but it's text. It appears to affect grey text more than it does pure white text, and it's a minor issue, but it is noticeable to those who are used to high-resolution LCD displays.

I have taken a couple of better photos to try and show the grainyness issue -- as I said on my Flickr comment, I believe this is completely normal behaviour, and an effect of the pixel layout of the OLED screen, possible combined with the sub-pixel anti-aliasing that the Android OS performs. Apologies for the quality, I took them in a rush so they're a bit out of focus at the edges.

Thanks, that's exactly what I was talking about and I'm happy to know that has nothing to do with my nexusone. I can finally start enjoying my phone and stop thinking about this problem

P.S. It would be nice to know if this is caused by a software bug so that it could be solved in some way

[abirkill]

OK, I've done some more investigation. I'll post my findings here, you need to have a reasonable understanding of how

subpixel font anti-aliasing

Subpixel_rendering

works to understand it.

First, we need to see how the Nexus One screen differs from typical LCD screens. In a normal LCD screen, each pixel is made up from three subpixels, a red, a green and a blue. These are typically ordered the same way everywhere, so if you look very closely (through a magnifying glass or similar) at a white screen, you'll see the pattern RGBRGBRGBRGB across it. (Some LCD displays use a BGR arrangement but these are rare).

The Android OLED screen differs from this, however, as can be seen below:



As you can hopefully see, there are in fact twice the number of green pixels as there are red and blue pixels on the N1's screen, with the pattern going RGBGRGBG etc. I've yet to figure out what a 'pixel' on this screen is, as having four pixels across is too wide compared to one pixel up. Interesting.

Incidentally, I believe the reasoning for this is that the green LED pixels aren't capable of going as bright as the red or blue ones, so in order to even this out at high brightnesses, they need twice as many green pixels. I think this slightly over-compensates as at full brightness the N1 screen has a very distinct green colour bias.

Now if we look at some text, we see some interesting artefacts:



For the most part, this image looks correct, but we can see there are some artefacts where we have outlying blue or red pixels that do not have the green pixel in between lit. I've highlighted some examples below:



I believe this the main cause for text appearing 'grainy' when viewed up-close.

I have two possible theories for why this is happening:

1. The sub-pixel rendering engine in the N1 is not aware of the different pixel layout of the N1's screen, therefore it's not aware that the missing green pixel needs to be lit to correctly perform sub-pixel smoothing. This could be fixed in software.

2. The green pixels require more current to start to light. In this case, the N1 could actually believe that it was lighting the green pixels at a dim setting, but in actual fact they are not being lit at all. This may or may not be fixable in software -- it depends if they can apply a correction factor to the brightness of green pixel to supply more current to a pixel that should be dimly lit, whilst keeping the current to a more brightly-lit pixel the same. I don't know enough about the video driver to know if this is possible.

Personally, my belief is that the second issue is the cause behind this. Take the clock application, which has a 'super-dim' mode for use in low-light conditions. Activating this mode makes the screen not only go dim but also become quite red -- it's possible this is intentional to prevent loss of night vision, but I suspect it's because the green pixels are prematurely shutting off.

Anyway, as said, it's a very minor issue and not worth being concerned about. There would be a slight increase in text quality if this was resolved, but nothing major.

Does anyone know if Google have a public Android bug tracker that I could submit this to? I doubt it'll get fixed but you never know...

[abirkill]

Finally, it is worth pointing out that the gap between pixels on an OLED screen is far larger than on an LCD screen, as can be seen in the following two photos -- the OLED screen (top) has far more 'black' area between pixels than the LCD screen.





Obviously this makes the individual pixels more discernable to the human eye and hence will generally increase apparent 'grain' across the screen, regardless of the text rendering issue above.

[Eugiaz]

Thank you very much for this explanation, I think it's very interesting
I also found this where they talk about subpixel pattern in the nexus one Nexus One display and subpixel pattern
For the bug tracker I think you can post this issue here : Issues - android - Project Hosting on Google Code