« Closing the Barn Door | Main | Quote o' the Day: Stanley Greene »

Tuesday, 12 June 2012


Mike, you jumped the gun. B&H is taking pre-orders.

The iPad 3's Retina display has an unusually wide color gamut for a portable device, almost equivalent to sRGB.

Portable devices like laptop computers usually have quite narrow gamuts, as wide gamut LCD panels that can deliver saturated, pure colors require very selective color filters with narrow peaks. Selective color filters thus tend to block a large part of the backlight's light output and require powerful, energy-hungry backlights that sap energy on battery-powered devices.

One annoying issue with the iPad3's display is that its gamma is very different from the usual 2.2 used by sRGB and AdobeRGB.
This results in a quite incorrect contrast curve when displaying sRGB pictures, which are the most common type found on the Internet.

In popular file formats, light intensities are encoded as 8-bit values, ranging from 0 to 255.
"0" corresponds to black.
"255" corresponds to the maximum (100%) brightness the display – LCD, CRT etc. – can output. With non-luminescent, printed media like paper, the 100% brightness is obviously the one determined by the media's reflectance properties.

In the sRGB standard, with its 2.2 gamma, the 8-bit value "118" corresponds to an intensity of 18% of the maximum brightness or luminance of the media. Take a picture of a 18% gray chart, using automatic exposure, and a digital camera should deliver, in sRGB or AdobeRGB mode, a JPEG file whose RGB components are (118,118,118)

The Imaging Resource web site has an interesting page on monitor calibration.
In the "How's your contrast?" section of that web page, there's a "Gamma 2.2 check image"
The surrounding gray area in that check image has RGB values (186,186,186)
On an iPad3, that surrounding area looks much brighter than the central area. This means that the pixel value "186" on an iPad3 is much more bright than what a properly calibrated sRGB display would show. It's also likely that pixel values with values "118" would be brighter than 18% of the display's maximum brightness, resulting in an overexposed look with image files that have been exposed using e.g. an 18% gray chart reference.

The fact that the new Macbook Pro has an IPS display, with their wide viewing angles, is excellent.
It seemed, at one time, that IPS LCD displays were going extinct on laptop computers – they were briefly available, several years ago, only on a limited range of IBM Thinkpad or Hewlett-Packard laptops targeting imaging professionals.

The Retina display's very high resolution is also a nice plus.

But, my main concern is whether Apple got the factory gamma of these IPS panels fairly close to 2.2, so that calibrating a Retina display wouldn't result in a monitor profile requiring large encoding value gaps in the transfer curve mapping an 8-bit sRGB or AdobeRGB file to the binary values accepted by the LCD controller's circuitry...

I'm not crazy about Apple but I laud their effort to get "retina" (high-dpi) displays more mainstream. Right now, all desktop LCD monitors, even the most expensives one, are still low-dpi. As I type this reply I can clearly see the jaggies in the letter 'y' for example. That's why prints look so much better for rendition of fine details.

This is the first non-refurb computer that I've purchased in several years, and it's also the first that I've purchased on the day of release. I think it looks perfect for my uses.

The comments to this entry are closed.