Toning Pictures on LCD Screens
When using LCD (Liquid Crystal Display) screens, the viewing angle affects how light or dark the picture appears. Users of flat LCD screens must establish a screen tilt that provides the most accurate view of the picture or they risk having picture tones that appear too light or too dark when viewed on a well-calibrated monitor. Because of the different technology used in Standard CRT (Cathode Ray Tube) monitors, they don't suffer from this problem.
To solve the tilt/tone problem with LCD screens, we created a background graphic file that visually indicates the correct viewing angle for an LCD screen. It is simply a gamma target much like those seen in the Adobe Gamma screen calibration utility but without the adjustment slider.
There are two targets for Macintosh computers depending upon its age. For older Macs (pre-Snow Leopard), there is a gamma 1.8 PICT file of the target. For newer Macs (Snow Leopard OSX 10.6 and beyond), there is a gamma 2.2 TIF file of the target. These files are linked further down in this page.
I have also created a PC-standard gamma 2.2 target for Windows users. Because it is used as a background graphic and can be seen around the edges of a picture, it is always present on the screen to aid judgment.
When the viewing angle is correct, the small squares of grey in the tiled graphic should merge with the background. That indicates that the correct gamma is established and that tones should be correct.
Keep in mind that because the viewer sees the screen at various angles as he/she scans from top to bottom, only a portion of the screen will be seen at the correct gamma. Our experiments with school Macintosh iMacs indicate that the best results are obtained when the screen is tilted so that the squares merge with the background within a band located about 1/3 the way down from the top of the screen. See the illustration below for an example.
Macintosh OSX (on older Macs before "Snow Leopard"
OSX v10.6)
The graphic file named "gamma_18_wallpaper_MAC.pct"
is available on the Bill S server for student use with Mac laptops or iMacs. First copy
the file to your own computer's hard drive (make sure you put it in a place where you can
find it). Then merely drag the file into the preview of the current desktop picture in
System Preferences>Desktop. That installs the file as a repeating desktop pattern.
Macintosh OSX (Snow Leopard OSX v10.6, and newer)
Apple changed the standard gamma
for newer Macintosh computers to be gamma 2.2 - the same as a Windows PC. Also,
PICT files no longer work in a 64-bit system, so the new file,
gamma_22_wallpaper_MAC.tif was
saved in tif format. This appears to work.
Windows
There is also a gamma 2.2 graphic named "gamma_22_wallpaper_PC.bmp"
available for use on Windows computers. To install it, right click on the file when it
displays on the web page, and select Set as Background from the pop-up list.
It will probably be stretched out across the screen, so then right click on a
blank part of the desktop, choose Properties, click the Desktop tab, and then
select "Tile" for the position.
Because the different platforms use different gamma settings, one frequent question is how a picture file can possibly be the same when displayed on a Macintosh vs a PC. In color-managed applications like Photoshop, the screen gamma is taken into consideration and picture tones should closely match on both platforms. However applications that don't color manage (most web browsers, etc.) will indeed show pictures darker on the PC than on older gamma 1.8 Macs because of the gamma difference.
With new Macs now using the same gamma as Windows PCs, the visual differences between platforms should vanish. Even now, in color-managed applications like Photoshop that are aware of the computer's screen calibration, there should be little difference in picture appearance.
TIP: Perception of color in your pictures is affected significantly by adjacent colors like those commonly available as screen backgrounds. If you choose not to use this background graphic, be sure to select a neutral gray background color anyway to avoid unintentional color casts in your picture. Because the gamma targets are gray, they meet this requirement.
This information was published in More Mastering Digital Photography, a special publication of Photo Techniques Magazine in 2004.
