SERIES OVERVIEW

This is Part II of a com­pre­hen­sive multi-part arti­cle series with in-depth mea­sure­ments and analy­sis for dis­plays on the Google Nexus One and the Apple iPhone 3GS. It is pro­duced as a col­lab­o­ra­tion between DisplayBlog and DisplayMate Technologies. We will show you the good, the bad, and also the ugly unfin­ished rough edges and prob­lems lurk­ing below the sur­face of each of these dis­plays and dis­play tech­nolo­gies. Each arti­cle will be intro­duced and dis­cussed on DisplayBlog by me, Jin Kim, fol­lowed up with a detailed tech­ni­cal analy­sis and mea­sure­ment data on the DisplayMate web­site by Dr. Raymond Soneira. There will be three parts to this series:

• Part I: Google Nexus One (Part Ia, Ib, Ic, Id)
• Part II: Apple iPhone 3GS (Part IIa, IIb, IIc, IId)
• Part III: Detailed Point-For-Point Shoot-Out Comparison

Parts I and II will be rolled out and expanded in sev­eral stages over a period of about a week, so be sure to check each day for updates.

INTRODUCTION

What more can be said of the iPhone than what has already been said. The gist of it is: Apple com­pletely rev­o­lu­tion­ized the smart­phone mar­ket with the iPhone. No ques­tion about it. There is much going for the iPhone: Multitouch that actu­ally works. An ele­gant and beau­ti­ful device. A legion of devel­op­ers cre­at­ing hun­dreds of thou­sands of apps that enhance the iPhone’s capa­bil­i­ties. And lit­tle things like visual voice­mail, the iPod app, and mobile Safari that makes brows­ing on the lit­tle dis­play as pain-free as can be, etc. But not every­thing is per­fect. And in this arti­cle we will be look­ing very closely at the dis­play: the 3.5-inch 480xRGBx320 pixel for­mat TFT LCD.

Everyone seems to think all dis­plays regard­less of plat­form need to have a 16:9 aspect ratio. Hogwash! The most applic­a­ble is the TV but even then if you’re watch­ing a lot of film you’re bet­ter off get­ting one of those incred­i­bly wide Philips TVs with a 21:9 aspect ratio. Aspect ratio is just one small part of the entire expe­ri­ence of a display-based device. Take for instance the iPad: it has a 1024xRGBx768 pixel for­mat and that’s an “old” 4:3 aspect ratio. But think about the usage sce­nario for the iPad. I haven’t used one so I can’t say for sure but I think I’ll be using it for more than watch­ing the occa­sional video: blog­ging, check­ing email, read­ing e-books, flip­ping through pho­tographs, etc. Books aren’t wide. Most pho­tographs aren’t wide. I’d rather have a por­trait dis­play for blog­ging. I do think email might ben­e­fit from a wide dis­play but if you’re the type of per­son who prefers writ­ing dis­ser­ta­tions to tex­ting, the por­trait mode will pro­vide a bet­ter more focused expe­ri­ence. So clearly, the dis­play on the iPad needs to fit in with all of its usage sce­nar­ios. The same logic applies to the iPhone: the 480xRGBx320 pixel for­mat has a 3:2 aspect ratio and it works quite well.

I have often hoped that Apple would raise the bar and incor­po­rate an OLED dis­play on the iPhone. There are many ben­e­fits of using an OLED on the iPhone: superb con­trast, deep blacks, a thin­ner dis­play, bet­ter power man­age­ment via UI tweeks, etc. There are some draw­backs too: lim­ited life­times rel­a­tive to LCDs, dif­fer­en­tial aging of the pri­mary col­ors’ phos­phors, more power draw if UI isn’t tuned for OLEDs, etc. Even though we have seen some imper­fec­tions on the OLED imple­men­ta­tion in the Nexus One, I still hope Apple puts an OLED dis­play into its next-generation iPhone. The Nexus One is the result of many com­pa­nies work­ing together and from what I have seen recently it seems that Apple’s approach of tak­ing total con­trol (sans the wire­less car­rier part) over bring­ing a smart­phone to mar­ket results in a bet­ter expe­ri­ence. So it is just my guess that Apple would be the com­pany to cor­rectly imple­ment an OLED dis­play into a smart­phone. I could also be com­pletely wrong: Apple could use a 24-bit IPS TFT LCD instead.

COLOR & IMAGE QUALITY

The iPhone 3GS makes use of 18-bit color plus dither­ing to emu­late 24-bit color. Each color (Red, Green, Blue) has 64 inten­sity lev­els. 24-bit emu­la­tion has been imple­mented well on the iPhone 3GS with artifact-free pho­tographs and test pat­terns that show smooth inten­sity scales. In gen­eral the qual­ity of images and UI ele­ments are very good across the board. The weak link would be under-saturated col­ors and less-than-ideal con­trast. Although scal­ing always takes away some qual­ity the engi­neers at Apple have done a solid job, how­ever, there were minor com­pres­sion and/or scal­ing arti­facts show­ing up on 480×320 images. These images were imported into iTunes, synced to the iPhone and then dis­played using the Photos app.

The DisplayMate Multimedia Edition for Mobile Displays test pat­terns we were able to show some inten­sity scale irreg­u­lar­i­ties in 256-level inten­sity color ramps due to the lim­i­ta­tions of 18-bit plus dither­ing. At low inten­si­ties there were screen mot­tling and irreg­u­lar­i­ties. And even with images at the display’s native 480×320 pixel for­mat there were rescal­ing and/or com­pres­sion artifacts.

The iPhone 3GS was com­pared side-by-side with a pro­fes­sional Sony high def­i­n­i­tion stu­dio mon­i­tor using a large set of DisplayMate Calibration and Test Photographs. The results were less-than-ideal: images were under-saturated and exhibit low con­trast. In other words, the images looked washed out. The cul­prit? A small color gamut and shal­low inten­sity scales.

When a new prod­uct is immi­nent Apple engi­neers fly to Asia and live there for weeks to make sure every­thing is per­fect. Overall fac­tory cal­i­bra­tion and qual­ity con­trol for the iPhone 3GS’ dis­play is very good. White point, color and grayscale track­ing is accu­rate and images are rel­a­tively free of arti­facts. We will dig deeper into color gamut but even with a less-than-ideal color gamut col­ors on the iPhone 3GS are accu­rate. The shal­low inten­sity scale resulted in low con­trast and under-saturated col­ors. This could be cor­rected by chang­ing the gamma curve to track closer to 2.2.

DISPLAY TEST RESULTS

Peak Brightness: 428 cd/m²

This level of bright­ness is excel­lent and is at the high­est level for mobile dis­plays. You will be able to see the dis­play in all ambi­ent light con­di­tions except when the sun is hit­ting it straight on.

Black Level Brightness: 3.1 cd/m²

You want black to be black. On the iPhone 3GS black is dark gray and a lot grayer than you’d want. Overall image qual­ity suf­fers because of a rather high black level brightness.

Contrast Ratio: 138

Because of the high black level bright­ness con­trast ratio is low. Images look washed-out.

Screen Reflectance: 9.2%

Screen reflectance is the most impor­tant spec­i­fi­ca­tion for a mobile dis­play and the iPhone 3GS does excep­tion­ally well and cou­pled with very high peak bright­ness allows you to view the dis­play in bright ambi­ent environments.

High Ambient Light Contrast Rating: 47

A rat­ing of 47 is excel­lent and rates as one of the best mobile dis­plays for view­ing in bright ambi­ent light envi­ron­ments. Clearly Apple was think­ing about users in sunny envi­ron­ments, like Cupertino, CA. For mobile devices like smart­phones, high ambi­ent light con­trast rat­ing is a much more impor­tant spec­i­fi­ca­tion than con­trast ratio, unless of course you’re almost always in a rel­a­tively dark room.

Dynamic Color and Dynamic Contrast: n/a

The iPhone 3GS does not make use of dynamic color and con­trast, a good thing since this fea­ture often dis­torts images.

WHAT’S UP NEXT

In the next sev­eral days Dr. Raymond Soneira and i will be adding more inter­est­ing dis­play test results for the iPhone 3GS:

• Part IIb: Color Temperature and Chromaticity, Color Gamut, Intensity Scale and Gamma
• Part IIc: Brightness Decrease with Viewing Angle, Contrast Ratio Shift with Viewing Angle, Color Shift with Viewing Angle
• Part IId: Display Power Consumption, Display Spectra

For screen cap­tures, more tech­ni­cal and in-depth expla­na­tions please visit DisplayMate.