Snow Leopard makes images darker--on purpose

Jake Widman
Wednesday, 09 September 2009 02:09

IT Industry - Development

The new version of Mac OS X changes the Mac's default gamma from 1.8 to 2.2. Don't know what that means? Let Adobe's Lars Borg and John Nack explain it.

Buried deep in settings most computer users never see is their display's gamma setting, a number that determine's how the system compensates for the nonlinear response curve of CRTs.

Since they first came on the market, Macintosh computers have used a gamma value of 1.8, a number chosen to reflect the dot gain of a typical printing press. Windows, on the other hand, uses a gamma value of 2.2.

(For more about the history of gamma choices, see the conversation between Adobe's John Nack and Principal Scientist Lars Borg on Nack's blog.)

The result was that images looked darker on Windows machines than they did on Macs. As the Web grew more and more popular, this became a bigger and bigger problem for Web designers.

With the release of Snow Leopard, the Mac has adopted the 2.2 gamma value "to better serve the needs of consumers and digital content producers." Most images created in the past decade have either a color profile or color space tag, which enables the operating system to compensate for the change in gamma. In short, most images for most users will look the same on screen.

But images created earlier than that may appear darker than they used to. Applying an appropriate color profile to the image will reverse the change; Apple describes how on the "About gamma 2.2" page.

The other group affected will be Mac-using Web designers, who will have to get used to their CSS-specified colors looking darker than they're used to. The compensation, of course, is that they'll look the same as they do on Windows machines.

As Nack puts it, "At least now we'll be less likely to hear complaints about colors 'getting screwed up' when going from Photoshop to the Web."