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While GIFs are an appropriate format for logos, typography, and illustrations, the JPEG format is usually preferred for photography. It is impossible to shift colors to the web-safe palette in a JPEG. Again, this limitation of the medium is accepted or ignored by most users. But GIF images should generally be shifted as closely as possible toward the Color Cube. In the next sections, we will talk about ways of doing that.
Gamma Gamma Hey!
Gamma is a measurement of light, and different platforms come with different standard gamma settings. The Macintosh has a System Gamma setting of 1.8. Put simply, it looks bright and has a wide range of light-to-dark variance unless Mac users adjust their display to some other setting. Silicon Graphics Machines (SGI) have a System Gamma setting of 2.4. Their default output is darker than that of Mac OS.
The Windows, Linux, and Sun operating systems run on PCs. PCs and their components are built by a wide variety of manufacturers. While this keeps end-user costs down, it also means that PCs have no standard hardware gamma correction. Typically, their System Gamma is estimated at 2.4— darker than Macintosh. In practice, PC gamma can be all over the place, but it is always darker than that of Mac OS.
What does this mean to web designers? It means that if you do not compensate for this cross-platform gamma variance, the subtle “study in earth tones” that looks so moody and mysterious on your Mac will probably look like a “study in mud” on most PCs. Because PCs are used by at least 90% of your audience, a study in mud is not what you want.
In the late 1990s, Microsoft and Hewlett-Packard (www.w3.org/ Graphics/Color/sRGB.html) came up with a gamma standard called standard RGB (sRGB) that gives Windows machines a common gamma setting of around 2.2—at least in theory. Of course, it doesn’t work if users don’t select it. And if they haven’t calibrated their monitors, it still won’t really work. But at least it gives us something to aim for. Windows-based web designers should calibrate their monitors, set their machines to sRGB, and find something else to worry about.
60 WHY: Designing for the Medium: Color My Web
There are three ways for Mac-based web designers to compensate for gamma issues.
The simplest is to download and install GammaToggle FKEY (www.acts.org/ roland/thanks/), a $5.00 shareware control panel created by Roland Gustafsson in the mid-1990s. After it's downloaded and installed in the System folder, this simple control panel allows you to toggle between your Mac gamma setting and a representative PC gamma setting at the touch of a command key. The software works flawlessly, the $5.00 shareware fee is optional (but how could you not pay the man?), and this tool has proved sufficient for hundreds of thousands of web designers since the earliest days of professional design on the Web. Another advantage to GammaToggle FKEY is that it is software-independent. In other words, you can toggle from Mac to PC gamma whether you’re working in Photoshop, using a browser, or simply have the kooky urge to push a Command key in the middle of a slow day.
The second solution is to download the Furbo Filters Webmaster pack (www.furbo-filters.com), created by Iconfactory’s brilliant Craig Hockenberry with kibitzing from your humble author. Unveiled in 1997, the Furbo Webmaster pack is a constellation of Photoshop plug-ins that (among other things) allows web designers to switch between Mac gamma and three kinds of PC gamma. The software also lets you preview the effects of various types of GIF and JPEG compression, and an included Web Scrubber (based on the pioneering efforts of user interface guru Todd Fahrner) lets you selectively shift your images toward the Color Cube. The shareware costs $40, and may be downloaded and used indefinitely for free. A nag screen helps your conscience decide when it’s time to pay for the software.
In 1998, Adobe got wise to this whole cross-platform gamma issue (and related web design issues) and came out with ImageReady, a Photoshoplike application for creating and exporting web graphics. Like Furbo Filters, ImageReady lets you preview the effects of gamma differences and compression settings on your images, and it also lets you shift your colors closer to or further from the Color Cube.
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In late 1998, with the release of Photoshop 5, Adobe made it possible to compensate for gamma differences between platforms using Photoshop alone. This is largely because Adobe supports the sRGB standard in Photoshop (even on Macs), and Apple supports it through the system’s included ColorSync control panel.
Mac users, here’s how to put sRGB to work:
1.Open the RGB Settings preference in Photoshop 5 or higher and select sRGB as your working environment.
2.Photoshop will prompt you to set up your System Gamma if you have not done so already. In Mac OS 8 and higher, you can set your Mac’s System Gamma to sRGB using either the Mac’s built-in ColorSync control panel or the Adobe Gamma control panel that comes with Photoshop.
3.Set your Mac to sRGB, and you will always be inside the Windows gamma space. If you prefer, leave it at typical Mac gamma (or some custom setting), and Photoshop will magically shift your images from the Mac to the Windows color space.
Choose Your Gamma
If you continue to design for print as well as the Web, stick with Apple’s default settings and let Photoshop toggle you back and forth between Mac and sRGB gamma settings. If you’re biting the bullet and plunging into full-time web design, by all means set your Mac to sRGB and be done with it. After you get used to working inside a slightly darker color space, it will look just fine to you, and you’ll never have to worry about gamma compatibility again.
ImageReady 2.0 is included in Photoshop 5 and higher. Photoshop 5.5 is much more web-savvy than its predecessor, and Photoshop 6 is even more so. We heartily recommend these later versions of Photoshop. If you use an older version, by all means try GammaToggle FKEY or Furbo Filters.