Xante Accel-a-Writer 812 Manuel utilisateur

____________________________________ 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

( )2+1

Introduction

To take full advantage of your Accel-a-Writer 812’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 Accurate Calibration Technology. The second half 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 resolutions on your Accel-a-Writer 812 are 600 x 600 dpi and

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 75 line screen, the

image produced has 65 levels of gray (600/75 = 8; 8 x 8 + 1 = 65). If

you want more levels of gray at 600 dpi, the line screen or lines per

inch (lpi) has to be reduced.

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 812’s

1200 x 1200 dpi with the same 75 line screen. You would now have

approximately 256 levels of gray (1200/75=16; 16 x 16 + 1 = 257).

Use the following table as a guide when working with levels of gray.

LPI ToAchieve 256 Levels of Gray

Printer

Resolution LPI

1200 x 1200 dpi 75

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 and 95 for 1200 dpi. Trying these line screens generally

gives you a more precise idea of the optimum output for a particular

image.

Note: Your Accel-a-Writer 812 features XANTÉ’s new enhanced

screening technology which lets you select different gray

level and gamma correction combinations to further fine tune

the quality of your output. See “Gamma Corrections” and

“Enhanced Screening” later in this chapter for more details.

____________________________________ Advanced Imaging 7-5

Scanner Resolutions

Another way to insure high quality output for your images is to

determine the optimum scanning resolution.

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 812

in the 600 x 600 dpi mode, the scanner resolution should be set at

600 x 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 formulas for scanning in this section are 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 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 provides a sophisticated

gamma correction feature. This feature allows you to change

midrange contrasts by adjusting gray-scale 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 or use the software printer setup to select a new gamma

setting to lighten and enhance the details. Gamma correction brings

out details that can be lost when printing at higher line screens or

when dark photos are scanned.

Your Accel-a-Writer 812 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. Chapter 5,

“Configuration,” contains details on where to find the gamma

options in the menu structure and how to make the selections.

Output Levels

Gamma 0

Black White

Input Levels

Black White

Fig. 7.1 Gamma Correction 0

7-8 Advanced Imagingbb ___________________________________

Output Levels

Black White

Input Levels

Gamma 6

Black White

Output Levels

Black White

Input Levels

Gamma 5

Black White

Output Levels

Black White

Input Levels

Gamma 4

Black White

Output Levels

Black White

Input Levels

Gamma 3

Black White

Output Levels

Black White

Input Levels

Gamma 2

Black White

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 1200 dpi

145 70 140

197 60 120

256 53 106

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, use the following procedure 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, use the following procedure 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.

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