Color on iPhone
This Month's Feature Article:
Color on iPhone
by CHROMiX's Steve Upton
The iPhone has been out for over a year now and I'm surprised how long it took us to come around to writing an article about its color handling abilities (or lack thereof).
From the outset, Apple has told us that the iPhone runs Max OS X and, while it has many unnecessary pieces removed, it is essentially the same core code that we enjoy on our desktop computers. Days after its initial release I hurried over to our local Apple store and iPhone-surfed over to the ICC's profile evaluation page to see if ColorSync was something that Apple decided to leave in or take out. It was immediately evident that Mobile Safari, the iPhone's version of the desktop web browser, did not support color managing images. The desktop version does.
Fast forward to today. The iPhone is on its second generation in both hardware and software. It seems like we cannot put off a comprehensive evaluation of color on this new platform any longer. We have been experimenting with the iPhone for quite some time now. So here it is.
What to manage?
We can't evaluate the iPhone without first enumerating the components that might be color managed. And while we're at it, let's cover what we mean by color management.
Color Management, constrained to the iPhone's mobile platform, would consist of the following features:
- Capture - images snapped with the iPhone's internal camera would either have an embedded ICC profile OR EXIF tags configured to correctly describe the color space in which they reside.
- Display - images (and possibly other elements) which contain ICC profiles will be converted to, presumably, a canned ICC profile which describes the iPhone's screen.
- Conduit - images which pass through the iPhone will not have their color management information stripped off or altered so they may be forwarded to other systems intact.
Printing and proofing functions are outside the scope of the iPhone's functions (at least at this time) so we don't expect these features to exist yet.
How did the iPhone do?
It's fair to say that color management does not exist on the iPhone in any but the most basic form...more on that below.
I also need to say here that I didn't expect the iPhone to have any color management capabilities, nor do I think it is essential to the success of the platform. I like my iPhone very much, thank you, and we are providing this review as an informative overview for those color geeks who want to know what's going on under the hood.
iPhone 1.x, 2.x
For the record, the iPhone we tested was a 1st generation phone updated to OS version 2.0.1. We were able to perform some tests on photos from the previous 1.x OS version. We have seen no evidence that there are any color differences between the two OS versions.
The applications and functions we tested include:
- Mobile Safari
- iPhone's photo browser
- Mail - image viewing
- Mail - PDF viewing
- iPod cover art
Let's break this down by the functions listed above:
Images snapped with the iPhone's internal camera are NOT tagged with an ICC profile NOR do they contain any EXIF data. We didn't expect to see an ICC profile but we assumed there would be some EXIF data. The lack of EXIF data is not necessarily a problem as EXIF can only contain references to the sRGB or Adobe RGB color spaces and I expect neither of those represent the space of captured images. Interestingly iPhoto gets involved in the process when images are transferred from the phone. More on that below.
The only way to get images onto the phone with embedded ICC profiles intact is over the web through Safari or emailing them. In both cases, the iPhone ignores the embedded profile(s) in image and PDF files. Transferring images via iPhoto or as cover art with music files results in stripped profiles. Again, iPhoto/iTunes gets involved (see below).
Images & PDFs which are emailed to the phone and then email-forwarded to another account arrive with their embedded color information intact. With the iPhone 2.x upgrade came the ability to tap a picture and then add it to the images in the phone. The image is stripped of its ICC profile, resampled, and dropped into the "camera roll" list as if the iPhone's camera itself had taken the picture. The stripping of profiles and resampling of the image is somewhat destructive though. I wouldn't recommend it for anything other than the most basic snaps.
iPhoto / iTunes
We would be remiss if we didn't mention the role that the desktop applications iPhoto/iTunes play in transferring images to and from the iPhone.
- First, when photos are transferred TO the iPhone through the iTunes syncing process, they are converted to an unknown color space prior to transfer. This has led some to believe that the iPhone is performing color management when test images in different color spaces (and with correctly embedded profiles) end up looking the same on the phone. Instead, all images are converted to the same space prior to transfer and, therefore, they look the same. Sometimes this process of converting all images to the same space is referred to as "normalizing" the images.
- Second, images transferred FROM the phone to your computer via iPhoto/iTunes undergo a somewhat mysterious conversion and end up with the computer's system profile embedded in them. They also gain EXIF data in the process, though the color space itself is listed as "untagged". When I tried to replicate the conversion process (Generic RGB to my monitor profile, & others) I was unable to determine which profile is used to represent the iPhone's source color space.
Basically, Apple has chosen to offload much of the image processing to the desktop machine and pre/post-process images in iPhoto / iTunes instead. Overall, this makes sense though it is a bit mysterious as to which profile is used when converting to and from the iPhone's images. Also, now that the iPhone has the ability to directly email iPhone-captured images or upload them to websites* AND grab images emailed to the phone for other uses, there are ways of bypassing the desktop-sync process. This leads to inconsistent results and end user confusion.
- (Uploading images directly to web sites is available in some 3rd party iPhone apps.)
An example of this is when an image is captured with the iPhone's camera. If emailed to my desktop it arrives without any EXIF data (so none of the new GPS information is available) and without any profile. If synced to my desktop and exported from iPhoto, it contains EXIF fields including GPS data, etc. AND an embedded ICC profile - that of my desktop monitor. As a result, these images look a bit different in various applications such as Preview.
Also, iPhoto is part of Apple's iLife bundle, which is only available on the Mac. I assume that iTunes for Windows performs similar functions but was not able to test it in time for this review.
The iPhone's Display
The iPhone's LCD 3.5 inch display is 480x320 pixels at a remarkable 163 ppi. From a color standpoint I would call it hot and blue. By hot I mean that at maximum brightness it puts out 375 cd/m2 which rivals the brightest desktop displays. Granted, it's easier to obtain that brightness over 38 cm2 than the 1420 cm2 of a 21" desktop display. Also, the Auto-Brightness setting tends to keep the output down to a less scalding 33-50% overall.
In our testing I was pleased to see that the white point of the display is fairly consistent over the wide range of brightness levels. At maximum brightness, the white color temperature was measured at 7855K; a very blue version of white. The white point ranged between 7680K-7960K for brightness settings between maximum and minimum, which is pretty good for varying brightness so much on this type of display. Also, though the white point of the iPhone never struck me as blue prior to this testing, in visual comparison with other displays it's a bit bluer than our 6500K EIZO display, but not objectionably.
We subjected our iPhone to a battery of measurements, and also constructed an ICC profile which is available for download from our Maxwell online color system. (more below)
The gamut of the display, as calculated using ColorThink Pro, is a respectable 576,800 which is larger than an LED MacBook Pro display's 537,500, and smaller than an EIZO CG-series display's 828,000 and sRGB's 832,000. For a hand-held device (I have trouble calling it simply a phone) it's a gamut capable of displaying a good range of natural and custom(brand) colors.
The iPhone display's gamma is 1.8, which is to be expected from Apple. The rest of the world is calibrating to 2.2 but Apple remains firmly entrenched in 1.8. THAT argument will have to be left for another article.
How to manage color with the iPhone
I expect this section to be relevant mostly to website and application designers, but anyone wanting to maximize the color fidelity of images sent to the iPhone can use these techniques.
Creating color FOR the iPhone
Download and install the iPhone profile directly from our Maxwell online color system:
When preparing images for use on the iPhone - whether they are interface components, photographs or other graphics (buttons & such), convert to the iPhone profile with the relative colorimetric intent. Then save the file without an embedded profile. We recommend saving all converted images in a separate area on your hard disk or perhaps including a note in their name about their color space. Images without profiles can create confusion, so be careful. You may want to create a Photoshop action to save time converting images.
Preparing Custom Palette Colors
To determine the best RGB combinations for iPhone interface elements or other artwork, follow these steps:
- Create a new RGB document or open an existing RGB file,
- Set the document's profile to the iPhone ICC profile using Edit:Assign Profile,
- Open Photoshop's color picker,
- Click on "Color Libraries",
- Select your color in the Pantone or other libraries supplied with Photoshop (if you have Lab values for your colors you can enter them directly into the color picker dialog),
- Click on "Picker" to return to the normal Photoshop color picker dialog. (Photoshop will have calculated the RGB color values for the iPhone.)
- Make a note of either the decimal RGB values or the hexadecimal values depending on your requirements.
You will now have custom colors formulated specifically for the iPhone.
Handling color FROM the iPhone
For images that have been emailed from the iPhone or uploaded directly to a website (and then transferred to your desktop):
- Open image into Photoshop,
- Assign iPhone ICC profile,
- Save image to disk, embedding the profile.
The image can now be used in your color-managed workflow.
The iPhone is a remarkable achievement in software and hardware engineering. So much has been written about using it, touching it, controlling it. It's about time we knew what to do so our creations look good ON it.
I hope you have found this article informative. If you have further questions or want to engage in other color discussions, we recommend you visit ColorForums.com. It's a great place to get answers and exchange ideas about color and color management.
Thanks for reading,