Xante Accel-a-Writer 8200 Manuale utente
____________________________________ Advanced Imaging 7-1
Chapter 7-Advanced Imaging
Chapter Overview
Levels of Gray
Line Screens
Scanner Resolutions
Line Art Scanning
Halftone Scanning
TIFF, PICT, EPS Formats
Gamma Corrections
Enhanced Screening
Accurate Calibration Technology
Page Design
Typefaces and Fonts
Typeface Forms
Other Elements of Design
Orientation
Pitch
Point Size and x-Height
Spacing
Page Design Tips
7-2 Advanced Imagingbb ___________________________________
Notes
____________________________________ Advanced Imaging 7-3
Introduction
To take full advantage of your Accel-a-Writer 8200’s high resolution
and make your images look their best, it is important that you
understand levels of gray, line screens, scanner resolutions, and their
uses within specific applications. The first half of this chapter
explains what levels of gray and line screens are and how to work
with them to achieve the best possible quality of output. It also
covers scanning, selecting formats for your files, and using gamma
corrections, enhanced screening, and XANTÉ’s Accurate Calibration
features. The second half of the chapter covers terms and elements of
page design with tips for adding finishing touches for a truly
professional image.
Levels of Gray
The resolution of a laser printer is measured in dots per inch (dpi).
The standard resolution on your Accel-a-Writer 8200 is 600 x 600
dpi, which you may have upgraded to 800 x 800 or 1200 x 1200 dpi.
Generally speaking, the human eye can detect approximately 200
shades of gray in an image. This means that the higher the levels of
gray (number of shades) used to produce a halftone image, the
smoother the image looks during the transition of changing dot sizes.
The following simple formula can help you determine the shades of
gray used to produce an image:
dots per inch
lines per inch
For example, if you print at 600 x 600 dpi with a 60 line screen, the
image produced has 101 levels of gray (600/60 = 10; 10 x 10 + 1 =
101). If you want more levels of gray at 600 dpi, the line screen or
lines per inch (lpi) has to be reduced.
()
2
+1
7-4 Advanced Imagingbb ___________________________________
Keep in mind that the higher the lines per inch, the tighter the screen
on the image will be. To produce higher levels of gray without using
a lower line screen, you must print at a higher dpi. An illustration of
this would be to print the same image at the Accel-a-Writer 8200’s
optional 800 dpi with the same 60 line screen. You would now have
approximately 170 levels of gray (800/60=13; 13 x 13 + 1 = 170).
Use the following table as a guide to get 256 levels of gray.
LPI ToAchieve 256 Levels of Gray
Printer
Resolution LPI
1200 x 1200 dpi 75
800 x 800 dpi 50
600 x 600 dpi 38
Line Screens
Knowing how many levels of gray you would like to achieve is one
factor in determining the appropriate line screen to use. Depending
on the individual image quality, some degree of experimentation
usually is necessary to produce the best possible output. You do not
always have to achieve 256 levels of gray for the best output. We
have found the following line screens (lpi) to work the best: 60 for
600 dpi, 71 for 800 dpi, and 95 for 1200 dpi. Trying these line
screens generally gives you a more precise idea of the optimum
output for a particular image.
Scanner Resolutions
Another way to insure high quality output for your images is to
determine the optimum scanning resolution.
____________________________________ Advanced Imaging 7-5
Line Art Scanning
For line art, the optimum scanning resolution would be at the same
resolution as the output device, especially when reproduced at the
same size. For example, when printing from your Accel-a-Writer
8200 in the 600 dpi mode, the scanner resolution should be set at 600
dpi.
Halftone Scanning
The resolution for scanning a halftone is usually lower than that of
the output resolution. Black and white images should generally be
scanned at a resolution of 2 times that of the line screen used, if
printing at 100% size. For example, if a line screen of 95 is used, the
scanner resolution should be set to 190 dpi (95 x 2). If that resolution
cannot be selected, choose the next higher resolution available. Also,
scanner resolutions depend on the size at which the output is printed.
If the previous example were to be printed at 75% of original size,
then the scanner resolution should be set to 142 dpi (95 x 2 x .75).
The formula for scanning in this section is used to determine the
optimum resolution possible. Scanning the image at a lower than
optimum resolution results in less detail. Scanning at a higher
resolution increases the file size and the processing time, and it may
only slightly increase the amount of detail. The following is a
formula for scan resolution:
desired lpi x 2 x % of original size
7-6 Advanced Imagingbb ___________________________________
TIFF, PICT, EPS Formats
After creating or scanning the image, you need to decide the format
in which to save it. The three most popular formats are TIFF (Tagged
Image File Format), PICT (from Picture), and EPS (Encapsulated
PostScript) files. If you use a scanning application such as
Photoshop, make sure to choose the appropriate line screen under
Page Setup before saving the image. This is essential for importing
the image into other applications. Some programs do not allow you
to change the line screen of an individual PICT or EPS image once it
is imported.
PageMaker only allows you to change the line screen of a TIFF file.
Do this by clicking the image and choosing Image Control under the
Elements menu. Set the line screen using the formulas in the
previous section, “Halftone Scanning.”
Note: Different versions of PageMaker may work differently. See
the application manual for details.
QuarkXpress only allows you to change the line screen of an
individual TIFF file. Do this through the Style menu. QuarkXPress
gives you a choice of Normal (default), 60, 30, 20 and Other line
screens. You may choose your own lpi through Other. QuarkXPress
goes a step further by allowing you to change the line screen of the
entire document in Page Setup under the File menu.
Note: Different versions of QuarkXpress may work differently.
See the application manual for details.
For more information on specific applications, see appendix B,
“Application Notes.”
Gamma Corrections
XANTÉ Halftone Calibration Technology includes a sophisticated
gamma corrections feature. This feature allows you to change
midrange contrasts by adjusting grayscale values without altering the
black shadow and white highlight values at each end of the scale.
____________________________________ Advanced Imaging 7-7
For example, if a scanned image is too dark, you can use the printer’s
front panel to select a new gamma setting to lighten and enhance the
details. Gamma corrections bring out details that can be lost when
printing at higher line screens or when dark photos are scanned.
Your Accel-a-Writer 8200 offers seven gamma settings, 0 through 6
with 0 as the default. Settings 0 through 5 progressively lighten the
midrange values. If you need a negative (reverse) image, which is
required by some printing processes, you can create one using
gamma 6 rather than using a software application. Figures 7.1 and
7.2 illustrate the effects of gamma correction settings.
1
10
Output Levels
Gamma 0
Black White
Input Levels
Black White
Fig. 7.1 Gamma Correction 0
7-8 Advanced Imagingbb ___________________________________
1
10
Output Levels
Black White
Input Levels
Gamma 6
Black White
1
10
Output Levels
Black White
Input Levels
Gamma 5
Black White
1
10
Output Levels
Black White
Input Levels
Gamma 4
Black White
1
10
Output Levels
Black White
Input Levels
Gamma 3
Black White
1
10
Output Levels
Black White
Input Levels
Gamma 2
Black White
1
10
Output Levels
Black White
Input Levels
Gamma 1
Black White
Fig. 7.2 Gamma Corrections 1 through 6
____________________________________ Advanced Imaging 7-9
If you use gamma corrections in combination with XANTÉ’s new
enhanced screening technology, you can further fine tune your
output quality. See “Levels of Gray” earlier in this chapter and the
next section, “Enhanced Screening,” for more details.
Enhanced Screening
XANTÉ’s enhanced screening allows you to select from the normal
(default) or the enhanced screens defined by 145, 197, or 256 levels
of gray using either the printer’s front panel or via software printer
setup. If you use the front panel, the default enhanced screen is setup
under the MISC:SCREEN menus. If you use the software printer
setup, you can select the levels of gray and gamma settings
simultaneously. Gray level and line screen combinations of enhanced
screens are defined as:
Levels Line Screens
of Gray 600 dpi 800 dpi 1200 dpi
145 70 93 140
197 60 80 120
256 53 72 106
There are nineteen possible gamma correction and levels of gray
combinations from which you can choose to fine tune your output
quality. Depending on your printing environment, Macintosh or PC,
use one of the following procedures to select the enhanced screens.
In a Macintosh environment, to select the enhanced screens
1. Select Print… from the File menu from within your
application. The print dialog box appears.
7-10 Advanced Imagingbb ___________________________________
2. Click Options…. The Options window appears
3. Select the desired screen.
4. Click OK. The print dialog box reappears.
5. Click Print.
In a PC environment, to select the enhanced screens
1. Start your Windows application.
2. Go to the Control Panel and select Printers.
3. Click Setup….
4. Click Features….
5. Locate the Enhanced Screen options and select the desired
screen.
6. Click OK.
7. Click OK.
8. Close the Control Panel window.
Accurate Calibration Technology
XANTÉ’s Accurate Calibration Technology (X•ACT) allows you
easily to calibrate the printer’s engine to print more precise
horizontal and vertical dimensions within the width of one dot.
X•ACT compensates for print engine variations. Every printer prints
in a slightly different way; one engine may print one line a little long
and another a bit short with a usual accuracy of 1 mm ±2 mm. While
this variance is acceptable for many uses, it is unacceptable for color
separations and other jobs where pinpoint accuracy is essential.
Working with X•ACT varies depending on if you are in a PC or
Macintosh environment. Also, after you adjust the printer’s line
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