9.3

• For pictures intended for on-screen display (in Web layouts), you can adjust the white
point using the Gamma Correction effect. Adjusting the white point controls the brightness
of the picture's display on screen. To use the Gamma Correction dialog box, adjust the
midtones by entering a new value in the Gamma field or by dragging the slider. A higher
value produces a darker picture, overall.
Although modifying gamma gives you some control over picture display, differences
between Windows and Mac OS may still cause issues. Windows uses a higher gamma value
(2.2) for display than Mac OS (1.8), so the same picture will look darker on Windows.
• The Desaturate effect converts a color picture to a black-and-white picture while leaving
the color mode and lightness value of each pixel unchanged. For example, it assigns equal
red, green, and blue values to each pixel in an RGB picture to make the picture appear
grayscale.
• The Invert effect inverts the gray values of each channel in a picture. This effect is
recommended for 1-bit, grayscale, and RGB pictures. Because CMYK pictures contain a
black channel, this effect is not recommended for CMYK pictures. The inversion of the
black channel usually results in images that are mostly black or mostly white.
• The Threshold effect converts color pictures to black and white, without using gray. Enter
a value in the Threshold field or drag the slider; all pixels lighter than the threshold value
are converted to white and darker pixels are converted to black.
• The Posterize effect modifies the tonal levels for each channel in a picture to produce
special effects. To use the Posterize dialog box, enter a new value in the Levels field or
drag the slider. For example, choosing five tonal levels in an RGB image results in 15 colors
(five for each of the three primary colors).
• The Negative effect inverts the brightness and hue of CMYK pictures. Because CMYK
pictures contain a black channel, this effect, rather than the Invert effect, is recommended
for CMYK pictures. The inversion of the black channel usually results in images that are
mostly black or mostly white. If you export the picture in another color mode (File > Save
Picture), the Negative effect is not applied.
Saving and loading Picture Effects presets
To quickly and consistently apply the same adjustments and filters to multiple pictures,
you can export settings as presets. Presets are saved as separate files with a .vpf extension.
To save a preset, apply effects to a picture, verify all the settings and with the picture
selected, click Save Preset on the Picture Effects palette.
To apply a preset, select a picture and then click Load Preset on the Picture Effects palette.
You cannot edit presets. If you need to make changes to settings in a preset file, delete the
existing preset file and create a new one.
By default, when you save presets, they are saved in the "Picture Effects Presets" folder in
the application folder. While you're working on pictures with the Picture Effects palette,
182 | A GUIDE TO QUARKXPRESS 9.3
PICTURES