Display

Another huge axis of improvement lately has been the mobile display category. It’s an ironic turn of events which has led to the mobile side being where all the improvement is taking place for displays in general. On one side of the industry we have the PC display market, which is currently locked in a dramatic race to the bottom (1080p 27" displays, decline of the 16:10 aspect ratio, etc.), and on the other side we have mobile displays where OEMs are rushing to outdo each other every major product cycle. In fact, 2012 might go down as the year when mobile display resolution eclipses the desktop.

Back on topic however is the Galaxy Nexus display - it’s a 4.65" diagonal, Super AMOLED HD 1280x720 affair. If you’ve followed Samsung’s AMOLED naming scheme, you can pretty much tell everything that there is to superficially know about the display just from the name. Super connotes an optical bonding (read: no air gaps or their pesky 4% Fresnel reflections) of the display and the entire stack above it, consisting of capacitive layer and top glass.

HD connotes, well, 720p HD, and finally the absence of Plus connotes the presence of PenTile RGBG. On that last note, we made a prediction that PenTile would be very hard to see on the Galaxy Nexus based on some pixel pitch calculations, and this turns out to be the case.


Decently close to the Galaxy Nexus display with a macro lens - hard to make out any subpixels

For me at least, the Galaxy Nexus display exceeds my visual acuity - I cannot pick out subpixels at all on the Galaxy Nexus. Quite literally, the RGBG subpixel stripe is now small enough that it is beyond visual acuity at standard viewing distance (1 foot).


Extreme macro shot of the Galaxy Nexus' display for illustrative purposes showing PenTile RGBG

If 2011 was the year where OEMs countered the iPhone’s retina display with qHD panels, 2012 is the year where they finally start to exceed that 330 ppi number. It seems as though 1280x720 WXGA will be the new WVGA or qHD for 2012, and already there are a bunch of 720p devices arriving on the market - phones like the HTC Rezound, LG Nitro HD, Galaxy Note.

Last time we compared pixels and subpixels per inch in the diagonal on a few phones. Many people pointed out alternative ways to compute everything, but in the end the aim was to set expectations for how visible PenTile would be, and the conclusion was: not very. This time, I think it makes sense to compare the actual angular subtense of the subpixels so we can appreciate whether they’re visible or not, rather than deal with another back and forth about whether measuring along the diagonal is valid or not anymore. It's easy to be lazy and just do things entirely wrong, but the actual angular subtense of a subpixel should be the canonical measure we use to determine whether you can see pixels or not, since that's the annoyance after all. Visual acuity for the average human eye is 1 arcminute (something drilled into my head from endless optical engineering classes), and perfect human vision is just below that at around 0.7 arcminutes. I have 20/15 which puts me around 0.75 arcminutes, and I can't see subpixels on the Galaxy Nexus unless I really, really try. 

It’s actually a challenging thing to codify whether or not you’ll be able to see PenTile, since color (wavelength) makes a huge difference. Further, visual acuity is itself a hard thing to qualify - for example, consider how much resolution is enough to identify versus detect something, and then how human vernier acuity (aligning something) is very good, and all of this is a function of the light's wavelength. For example, the on-off pattern when looking at solid green is just about the worst case possible - it’s a square wave (100% modulation) in the green right where the eye is most sensitive. In the past, it struck me that other members of the tech press were perhaps unconsciously taking photos of the green battery indicator to show the presence of PenTile or not since that's where subpixels are most visible. As an aside, most of the UI is now blue in 4.x (including battery indicator) which the eye does not have very good sensitivity to - just try focusing on something entirely blue -  is this a coincidence or conscious decision to mask bad displays? For comparison, when displaying white obviously subpixels largely disappear into a sea of light. If you look at a green solid region now, you’d be hard pressed to make out the individual subpixels, and the table explains why:

Display Subpixel Angular Subtense lower is better, human eye ~1 arcmin)
Phone X subpixel angular subtense at 12" Y pixel angular subtense at 12"
HTC Rezound 0.280 0.839
iPhone 4/4S 0.290 0.869
LG Nitro HD 0.293 0.878
Motorola Droid 0.361 1.082
Motorola Atrix 2 0.373 1.118
Galaxy S II 0.440 1.320
Galaxy Nexus 0.454 0.907
Infuse 4G 0.461 1.382
Droid 3 0.520 1.040
Droid RAZR 0.559 1.118
Droid Incredible 0.568 1.136
Nexus One 0.568 1.136
Galaxy S / Nexus S 0.614 1.228

The interesting thing about the table is that it very much backs up my subjective impressions of just how visible subpixels were on previous phones. The Nexus S / Galaxy S had comparatively gigantic subpixels, and I can't stand looking at those displays to this day. Move up the line and you get increasingly better (I've sorted by x/horizontal angular subtense), with the HTC Rezound exceeding the iPhone 4S. Note that you have to consider the adjacent unlit subpixels as well to really arive at a conclusion for how visible things are going to be - on the PenTile RGBG displays, that means one adjacent unlit subpixel, and on RGB stripe, two unlit subpixels (assuming we're talking worst case 100% Green, 0% Blue, 0% Red). 

While Samsung has been able thus far to increase its AMOLED pixel pitch considerably, it has come with one unintended effect. That effect is a bit of pixel inhomogeneity which results in a somewhat grainy look to the display under certain circumstances. While neither device we tested had it, others have reported lines or splotches. There’s a word for these inhomogeneities in display luminance, and it’s “mura.” The variance is no doubt very minor, but the eye is great at picking out these small changes, and it’s particular visible in certain contexts, like the grey loading screen on the Android Market. So far getting a good photo of this effect has eluded me, however, it looks like a light film grain. Stated another way, it's like a fixed pattern noise that exists at all times on the display, which seems particularly visible at some brightness levels. To be honest, it doesn’t annoy me any more than IPS display “grain” annoys me - you just get used to it after a while.


Photographing the mura on the Galaxy Nexus' display has proven a challenge

These inhomogeneities also sometimes manifest themselves as visible strips of different luminance. I haven't seen any on either of the Galaxy Nexi we have, but if you do get hardware with annoying inhomogeneities, I recommend just swapping. Again, getting photographs of the grain has proven challenging. 

The display’s surface is curved, though the radius of curvature is nowhere near as curved as some of the early teaser photos would’ve had you believe. Total sag ends up being around 1.5 mm, giving a radius of curvature around 1.5 m - needless to say, it’s a very gentle curve. The other noteworthy thing about the Galaxy Nexus is Samsung’s choice of glass. Lots of people have noted that the Galaxy Nexus isn’t adorned with Corning’s popular Gorilla Glass, though it’s still a kind of fortified (and no doubt alkali-aluminosilicate) glass. It’s impossible to tell exactly what kind of glass is on the Galaxy Nexus without destructive testing on either Samsung’s or Google’s review unit. That said, if anyone breaks a display, send me the broken top glass and I’ll be able to do some compositional analysis. As an aside, compositional analysis of the top glass from different phones is something I’ve wanted to do for a while now, but requires sourcing broken glass.

We’ve also done all the usual measurements on the Galaxy Nexus - luminance and color temperature at different brightnesses selected in settings, and a run through HCFR using Francois’ excellent Screen Test Patterns app.

First off are the display charts taken at a number of different brightness settings by dragging the slider around in settings. Traditionally AMOLED has struggled to keep a flat white point. Here the Galaxy Nexus isn't bad at all, hovering just below 6500K.

White Chart White Brightness

The Galaxy Nexus manages to stay reasonably close to 6500K even as brightness changes across its full range. The brightness curve is also nice and linear, though it tops out at just over 200 nits at maximum brightness.

Brightness (White)

The HCFR plot and color.chc file tell an even more interesting story. The CIE chart shows how AMOLED continues to have a gamut much larger than sRGB (which is the inner triangle). It’s awesome to have more spectrum, but bad when mapping sRGB to this color space without more management, and leads to AMOLED’s oversaturation stigma.

There are more interesting things inside, too. Color temperature at 100% brightness and displaying different shades of Gray stays pretty close to 6500K as well. Gamma ends up almost all over the place, unfortunately.

The nice thing about ICS on the Galaxy Nexus is also increased color depth in many places. Previously Android’s gallery many times appeared in RGB 565, leading to visible banding. This is now almost entirely gone as well.

Viewing angles on the Galaxy Nexus, like other AMOLED devices, is superb as well. There’s practically no shift in either horizontal or vertical angles. Outdoor viewing has gotten better on AMOLED with a bunch of improvements - better AR coatings, no more air gaps, and other coatings. Out in the brightest of sunlight it can still be hard to read, however.

Camera - Stills and Video Cellular Performance and Call Quality on Galaxy Nexus
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  • zorxd - Friday, January 20, 2012 - link

    They can have some differences (cache size, memory bandwidth, neon instructions) but the A9 is not an ISA. ARMv7 is.

    Given that it has the same configuration, an Apple A5 behave the same as a TI OMAP4 or a Samsung Exynos of the same clock speed. I beleive nVidia tegra2 lacks the neon instructions so can be slower in some cases. There is an article on Anandtech about this.

    Given that the iPhone 4S is only 800 MHz it is the slowest A9 CPU by far.
    Reply
  • pSupaNova - Friday, January 20, 2012 - link

    The GPU's on the IPhone uses Tiling so in most GPU rendering tasks it will be a lot faster, However spit lots of Triangles at it and then see how fast it really it is. Reply
  • StormyParis - Wednesday, January 18, 2012 - link

    It's not all about performance, at least if you don't do FPS games. The screen on the Nexus is much bigger than on the 4S for example. For me, it's not about performance at all. I went for the GN for its even bigger screen, and that criteria alone was 95% of my decision, the remain 5% being "... and the rest don't suck", and "has xda-dev support'. Reply
  • humancyborg - Wednesday, January 18, 2012 - link

    Once you start accelerating the entire interface, performance becomes much more significant than just FPS games. There's a reason Apple uses such a gigantic and powerful GPU in their devices, and it's definitely not only for FPS gamers.

    Agree with you on the rest, there are other good reasons to buy this phone, just a shame that they skimped here. I have the 4S, GN and Lumia 800 currently and constantly switch around between them.
    Reply
  • metafor - Wednesday, January 18, 2012 - link

    It doesn't really take a whole lot of resources to render a 2D interface. Just about any ol' GPU with OpenGL ES 2.0 support will do it.

    About the only thing where the GPU is the limiting factor is rendering 3D games. And even then, most if not the vast majority of games on the market will continue to be written for this level of hardware for at least the coming year.

    Honestly, people take benchmarks way too seriously.
    Reply
  • doobydoo - Thursday, January 19, 2012 - link

    Actually, you're absolutely wrong.

    In fact, the GPU slowness is cited in this very article for causing slowdowns in situations where no 3D gaming is being done.

    Remember, the operating system as a whole is hardware accelerated, so every thing you do - animations, transitions, task switching, etc are carried out by the GPU. With the higher screen, the speed of the GPU becomes even more relevant.

    The combination of a high resolution screen and a low powered GPU is a bad combination and materially affects the performance of everything you do on the phone.
    Reply
  • zorxd - Thursday, January 19, 2012 - link

    Do you remember the iPhone 4? Who complained that the GPU was slow? It was much slower than the SGX540 in the Galaxy S. Reply
  • metafor - Thursday, January 19, 2012 - link

    Speculation in an article isn't exactly proof of concept.

    Alpha blending, panning, compositing are very light tasks for a GPU pipeline; it's only a problem when a GPU is TMU-limited. And if it's TMU-limited, it would be obvious all the time.

    I don't think you quite grasp exactly what parts of UI rendering are handled -- or could be -- by the GPU and just how trivial it is compared to rendering a 3D game.
    Reply
  • trob6969 - Wednesday, January 18, 2012 - link

    What i don't understand is why would samsung give the gn 1gig of ddr2 ram then give it an inferior GPU? But to be fair, Apple is no better. Why give iphone 4s a powerful GPU then give it only 512 mb of ram?! My old-ass og moto droid from over 2yrs. ago had that much! Reply
  • doobydoo - Thursday, January 19, 2012 - link

    As alluded to by numerous posters, including one in this comments section, iOS handles memory usage more efficiently than Android so it doesn't suffer any performance penalty as a result of having less RAM. Reply

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