Whenthe Repeat edge pixels option is active, the pixels along the edge of the
`image are repeated across the space in the direction the selection is offset. This
`
`can create a bandingeffect if the edge pixels are different colors. ,ieee eea
`
`Original selection
`
`Repeat edge pixels, horizontal value: 50;
`vertical value: 0
`
`The Wrap around option makes the image wrap around thepart of the image
`opposite the selected area. You can use the Wrap aroundoptiontocreate a pattern
`that tiles correctly. Often when youcreate a pattern, the seams where the elements
`of the pattern join togetherare visible and detract from the pattern’s appearance.
`You can use the Offset filter and the Wrap aroundoption to expose the seam in a
`pattern, adjust the pattern to remove the seam, then define the pattern as your
`custom pattern using the Define Pattern commandin the Edit menu.
`
`When The Wraparoundoption is active, the Adobe Photoshop program wraps
`the imagein the specified direction to fill the space left by the selection. Hereis
`an example of how the Wrap around option works. If you select the lowerright
`corner of an image and specify 0 for the horizontal offset and -100 for the vertical
`offset, the Adobe Photoshop programfills the space with the part of the image
`that appears 100 pixels down from the upperright corner of the image. If you
`select the same lower right corner of the image and enter 100 for the horizontal
`offset (to move the selection to the left) and -100 for the vertical offset, the
`program fills the space with the part of the image that appears 100 pixels to the
`
`right and 100 pixels down from the upperleft corner of the image.
`
`Original selection
`
`Wraparound, horizontal value: 50;
`vertical value: 0
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`To use the Offsetfilter:
`
`1. Select the part of the image you wantto offset.
`
`. ChooseFilter from the Image menu.
`3. Choose Offset from the Filter submenu.
`
`The Offset dialog box appears.
`
`© Wrap around
`
`Offset...
`Horizontal: [| (pixels right)
`Vertical: [ (pixels down)
`Undefined Areas:
`
`@ Set to background
`© Repeat edgepixels
`
`Cancel
`
`. Enter the number of pixels you want theselection to be offset in the horizontal
`direction. Enter a positive value to movethe selection to the right; enter a nega-
`tive value to move theselection to theleft.
`
`5. Press the Tab key or click in the Vertical text box.
`6. Enter the numberof pixels you want theselection to be offset in the vertical
`direction. Enter a positive value to movethe selection down; enter a negative
`
`value to movethe selection up.
`
`
`Original image with selection
`
`Horizontal Offset value: 30
`Vertical Offset value: -20
`
`.
`
`If your selection appears near the edge of an image, specify how the undefined
`areas will be treated by clicking the Undefined areas option you want.
`. Click OK.
`
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`The Add Noise filter
`
`Noise in an imageis represented by pixels with randomly distributed colorlevels.
`The Add Noisefilter can be used along with the painting tools on a gray-scale
`image. The painting tools apply paint thatis free of noise. Therefore, if you apply
`paint to an area in an image that contains some noise, you might select the area
`you painted, and use the Add Noise filter to make the area blend in better with
`its surroundings.
`
`When youuse the Add Noisefilter, you can select the method that determines
`how thecolor values of the noise pixels are distributed in the image. The twodis-
`tribution options available to you are Uniform and Gaussian; you can experiment
`with these two options to achieve the effect you want.
`
`When Uniform distribution is active, the value you specify for the amount of
`noise is the maximum value. The color values of the noise are determined by
`calculating random numbers between 0 and plus or minus the specified value.
`
`When Gaussian distribution is active, the distribution of color values are distrib-
`uted along a Gaussian (bell-shaped) curve. In this case, the value you specify for
`the amount of noise is used as the standard deviation of the color values of the
`noise. The standard deviation is a statistical calculation that represents how widely
`the values vary.
`To add noise to a selection:
`
`1. Select the part of the image to which you wantto add noise.
`
`2. Choose Filter from the Image menu.
`3. Choose Add Noise from the Filter submenu.
`
`The Add Noise dialog box appears.
`
`© Gaussian
`
`fidd Noise...
`
`Amount:
`
`Distribution:
`
`@ Uniform
`
`4, Enter a value from 1 to 999 for the amountof noise you wantto add.
`5. Select either the Uniform or Gaussian option to distribute the noise in the
`selection.
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`
`
`6. To apply the Add Noisefilter, click OK.
`
`The Add Noisefilter is applied to the selection.
`
`Image with uniform sky
`
`Add Noise: 30
`
`Using the High Passfilter
`The High Passfilter retains the high frequency part of the image and suppresses
`the low frequencyparts of the image. High frequency areas coincide with sharp
`transitions that generally occur around the edgesof distinct parts of an image, for
`example, where the ram’s head shownin the followingillustration meets the
`darker background. The low frequency areas occur where there are smooth,grad-
`ual transitions between the brightnesslevelsof pixels, for example, on the surface
`of the ram’s head.
`
`To determine how much of the high frequency information to retain and how
`much of the low frequency information to suppress, you enter a value in the
`High Passfilter dialog box. The value you enter in the dialog box determines the
`amount of low frequency information that is suppressed. Enter a low value to
`suppress a large amountof low frequency information; enter a high value to
`suppress a small amount of low frequency information.
`
`To use the High Passfilter:
`
`1. Select the part of the image to which you will to apply thefilter.
`
`2. ChooseFilter from the Image menu.
`
`3. Choose High Pass from the Filter submenu.
`
`The High Pass dialog box appears.
`
`High Pass...
`
`Radius:
`
`(pixels)
`
`4, Enter a value from 0.1 to 109.0.
`5. Click OK.
`
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`The High Passfilter is applied to theselection.
`
`
`
`
`ue
`
`High Pass value: 80 pixels
`
`High Pass value: 10 pixels
`
`Using the Customfilter
`The Custom filter allows you to create a special filter to suit your needs that can
`be saved andloaded into another documentfor use. Using the Custom filter, you
`can create special effects by changing the brightness values of pixels according to
`a mathematical convolution kernel that you specify. As an example, you can de-
`fine a filter that showsoff a selection in highrelief orafilter that creates a motion
`blur effect.
`
`Thefilter uses a grid consisting of text boxes. The grid acts as a template thatis
`applied to each pixel, one at a time, in the image. The center text box in the grid
`represents the current pixel, the pixel whose new brightness valueis currently
`being calculated; the text boxes aroundit represent the pixels surrounding that
`pixel. The values you enter in the text boxes apply a designated weight to the
`pixel represented by that text box. If you enter a high value, that pixel is heavily
`weighted and is more influential in the brightness calculations than pixels that
`are assigned lowervalues.
`
`The Custom filter works as follows. You enter values into the grid text boxes and
`the Scale and Offset boxes. The values entered for Scale and Offset are applied to
`the value that results from the mathematical operations involving the values in
`the grid text boxes. The Adobe Photoshop program multiplies the brightness val-
`ues of the center pixel and the surrounding pixels by the respective values in the
`grid text boxes.
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`As an example, if you enter “1” into the center text box, the program multiplies
`the current pixel’s brightness value by 1. The program then addstheresulting
`brightness values ofall of the pixels involved, divides that value by the Scale
`value, andfinally adds the Offset value. The current pixel’s brightness is changed
`to this final value.
`
`
`
`Below are some examples of custom filters and their effects on an image.
`
`
`Scale value: 1; Offset value: 128
`
`Custom filter applied
`
`LTJE JL IL IC4
`LJeJe IeIC4
`LIeOBIEIC4
`LJbIe IE IC)
`LICICIC IC)
`
`Scale value:1; Offset value: 0
`
`Customfilter applied
`
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`To create a custom filter:
`
`1. Choose Filter from the Image menu.
`2. Choose Custom from the Filter submenu.
`
`The Custom dialog box appears.
`
`Custom...
`
`offset: [|
`
`nooo
`
`MSS
`RIE II
`
`LTJE Je ILIC4
`L JLJILJLICI
`Scale: (|
`
`3. Click a text box representing a pixel to which you want to assign a weightedvalue.
`4, Enter the value by which you want the pixel in that position multiplied. The value
`can be an integer between -999 and 999. For example, if you want the brightness
`value of the pixel to the immediate right of the current pixel multiplied by 1,
`enter “1” into the text box to the immediate right of the center text box in the
`grid.
`5. Repeat steps 3 and 4 for all of the pixels you want to be weighted.
`6. Click the Scale text box.
`
`7. Enter the value by which to divide the sum of the brightness values of the pixels
`in the calculation.
`
`8. Click the Offset text box.
`
`9. Enter the value to add to the result of the scale calculation.
`
`10. Click OK.
`
`11. The Custom filter you specified is applied to your selection.
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`To save the current custom filter:
`
`. Click Save in the Custom Filter dialog box.
`
`The Save As dialog box appears.
`
`. Type the file name in which you want to save the custom filter.
`
`If necessary, use the drive and directory buttons to access the folder in which you
`want to save thefilter.
`
`. Click Save.
`
`To load a previously saved custom filter into the Custom dialog box:
`
`. Click Load in the Custom dialog box.
`
`The Open dialog box appears.
`
`If necessary, use the drive and directory buttons to open thefolder that contains
`the filter you wantto load.
`
`2. Click the filter you want.
`
`3. Click Open.
`
`The values used for the selected filter are automatically entered in the Custom
`dialog box.
`
`Using plug-in filters
`A plug-in filter is a filter that is developed by a third party for use in the Adobe
`Photoshop program. The effects vary according to thefilter. Documentation for
`the plug-in filter is included with the third-party software disk in your Adobe
`Photoshop package.
`
`Plug-in filters are easy to install; once installed, they appear in the Filter sub-
`menu, which is accessed via the Image menu,in the same way as the standard
`Adobe Photoshop program filters.
`
`To install and use a plug-in filter:
`
`. Drag a copyofthefilter from the third-party software disk to the folder that
`contains your preferencesfile (named “PS Prefs” by default).
`
`. Restart the Adobe Photoshop program. You do not have to reboot the Macintosh.
`The plug-in filter will appear in the Filter submenu of the Image menu.
`
`. Select the plug-in filter by choosing Filter from the Image menu and dragging to
`highlight the desiredfilter.
`
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`
`
`
`
`Starting with an image ofplants in bottles, the artist applied the Find Edgesfilter to
`produce a hand-drawneffect. The color balance was adjusted to modify and subdue the
`colors; and the Diffuse filter was applied to roughen thetransitions between colors. The
`leaf image was scanned ona flatbed scanner from an ink drawing. The background was
`created by scanning a small piece of tracing paperin a slide scanner. Both images were
`pasted onto the backgroundusing paste controls, allowing some of the background
`texture to show through the images.
`
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`

`—
`
`Chapter 18: A Printing Overview
`
`This chapter gives an overview of the basic conceptsof printing, describes the
`general printing options, and explains howto print individual channels and
`print images on color printers.
`
`The Adobe Photoshop program allows you to print images in a numberof ways.
`You can create a halftone from a gray-scale image, as well as a color proof and
`color separations from color images using the four process colors. You can print
`halftones and color separations as negatives that an offset printer can use to print
`reproductions of your work.
`
`The Adobe Photoshop program allows you to combinea variety of media—from
`photographs, scanned-in artwork like watercolors and old map fragments, pen-
`and-ink drawings, airbrushedillustrations—and produce them as camera-ready
`artwork, Producing high-quality results, whether a halftone or color separation,
`mandates good planning.
`
`The key to producing a high-quality halftone or color separation is planning and
`testing the processfirst. Before producing camera-ready artwork, you should talk
`with everyone involvedin the printing process, from the graphic designer andart
`director, to the print buyer, color separation house, and print shop, to take into
`account and compensate for any problems that may be encountered in printing
`the job. You should experiment with whatwill work by producing a proof or
`color key, compensating for factors such as paper surface and quality, then stan-
`dardize your printing process.
`This compensation or calibration is largely an iterative process in which youcal-
`ibrate one aspect of the system, print out a test proof, compare the printed results
`to the display on-screen, then make an adjustment, and make another compari-
`son. You may have to perform this process a numberof times to achieve the
`results you want. When you havefinished makingcalibrations to your system,
`it is a good idea to record the date of the calibration and the current settings in a
`printing log. This information helps you achieve predictable results.
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`Someof the problems that can be encountered in printing are poorregistration
`and moirés; banding from dot gain; and the inability to produce or repeat pre-
`dictable results due to imprecise calibrations of equipment.
`
`Factors that can affect the quality of final printing include the quality ofthefilm,
`ink, and paperthatwill be used in the printing; the concentration, amount, and
`use of the chemicals used in the film processor; and the experience and knowl-
`edge of the print shop. Other factors that affect printing include the calibration
`of the equipment, including the scanner, monitor, proofing system (such as a
`MatchPrint or Chromaline system), and the original image.
`
`To achieve the best results, the output device you use, such as a PostScript
`imagesetter, should be set to the proper density limit and the processor should be
`properly calibrated. If these factors are inconsistent, you cannot achieve predict-
`able results.
`
`Because of the complexity of offset printing, a description of the process of color
`printing is beyond the scopeofthis section. If you are new to color printing or
`have never worked with a professional color-separation house before, it is sug-
`gested that you workclosely with your local print shop.
`
`Printing basics
`To print any type of image, youfirst select any printing options, then specify
`settings for the particular image type. For halftones and color separations, you
`mayhaveto calibrate the variousplates to correct the color. Finally, you print the
`imageas oneorseveral plates.
`
`You can print the three channels of an RGB imageas a single, composite image;
`the three channels are printed as one on a single plate and appear black and white
`if you print them on a monochrome PostScript printer. You can also print the
`individual channels, one channel at a time on separate plates. By converting an
`RGBor indexed color image to a CMYK image, you can print a color separation
`of the image consisting of cyan, magenta, yellow, and black plates.
`
`By default, when you print a gray-scale image on a 1-bit PostScript printer, the
`imageis printed as a halftone, consisting of a series of dots. The size and density
`of the dots vary to create the optical illusion of variations of gray in the image.
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`For both a halftone and a color separation, you can specify the screen frequency
`and angle for each plate, just as if you were using a stat (photostat) camera. You
`can also specify the shapeof the dot used in the screen andprint a calibration bar
`to help you correct dot gain and color inconsistencies between the screen display
`and the printed image.
`
`Forall of the image types, you can print identifying information to help you crop
`and register (align) the image. The printing options appear in the Page Setup
`and Print dialog boxes underthe File menu. Thefollowing sections describe the
`various options.
`
`General printing options
`For any type image you print, you can chooseto print the document and channel
`nameon eachplate, along with crop marks, registration marks, and a caption.
`You can adjust the size of the printed image, print a negative of the image,
`and specify an emulsionside for your film processor. You can preview how these
`options will appear on the printed output by using the page preview box.
`
`The page preview boxis displayed in the lowerleft corner of the document
`window;it displays the size of the image in memory.
`
`For more information about using the page preview feature, see the section,
`“Previewing the page size and layout” in Chapter 14, “Resizing Images.”
`
`The various printing options appear in the Page Setup dialog box undertheFile
`menu. To activate the option, you click the checkbox beside the option.
`
`To display a page preview:
`
`. Position the pointer on the boxin the lowerleft corner of the document window.
`. Press down the mouse button.
`
`The page preview appears.
`
`3. Release the mouse button when you havefinished previewing the page.
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`To activate a printing option:
`
`1. Choose Page Setup from the File menu.
`
`The Page Setup dialog box appears.
`
`LaserWriter Page Setup
`Paper: @ US Letter © A4 Letter
`OUS Legal OBS Letter ©|_Tabloid
`Reduce or
`Printer Effects:
`(Options)
`Enlarge: [oo
`—] Font Substitution?
`Orientation
`x] Text Smoothing?
`Frei
`— Graphics Smoothing?
`g
`[4 Faster Bitmap Printing?
`
`6.0
`
`(J Registration Marks
`
`-
`
`Ctabels
`(] Crop Marks
`Oo Calibration Bars
`
`Ci Negative
`CJ Emulsion Down
`
`2. Click the checkbox next to the appropriate option to selectit.
`
`Printing crop marks
`Whenthe Crop Marks option is checked, crop marksare printed near the edges
`of the image. The crop marks indicate where the imageis to be trimmed.
`
`Printing labels
`WhentheLabels option is checked, the document nameand the channel name
`are printed on the image.
`
`Printing registration marks
`The Registration Marks option prints registration marks on the image, including
`bull’s-eyes and star targets, to help you register the variousplates that are printed.
`These marks are used primarily for aligning CMYK color separations.
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`Printing calibration bars
`
`The Calibration Bars option prints an 11-step gray-scale. The steps represent a
`transition in density from 0 percent to 100 percent in 10-percent increments.
`
`When you print a CMYKcolorseparation, this step wedge appears only on the
`black plate. However, the cyan, magenta, and yellow plates display screen tints
`of the channel youare printing. Theillustration below shows a sample black
`plate. The illustration on the following page showsthefull-color image with the
`screen tints, called progressive color bars, on bothsides of the image.
`label (filename) crop marks
`
` separation a mark
`
`
`flowers.color
`
`
`
`
`star target
`
`Black Separation Only
`
`
`
`
`caption
`
`calibration bar
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`

`®
`flowers.color
`| ®&
`
`
`
`
`Oe Cyan Magenta ¥»—Black |
`
`CMY
`
`80%
`¥
`MY
`M
`cM
`Cc
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`FINAL
`
`progressive color bars (can be used to calibrate monitors)
`
`Printing a negative
`
`The Negative option prints an inverted version of the image. Only the output
`(not the image on-screen) is converted to a negative when you usethis option.If
`you are printing separationsdirectly to film, you will probably want a negative,
`although in manycountriesit is commonto printfilm positives. You should also
`check with your print shop about whetherit prefers a film positive or negative of
`your image. If you are printing to paper, you will wanta positive. It is recom-
`mended that you print on film to achieve the bestresults.
`
`Specifying an emulsion side
`Emulsion refers to the photosensitive layer on a piece of film or paper. The Emul-
`sion Up option(right-reading) meansthat any type in the image is readable when
`the photosensitive layer is facing you. The Emulsion Down option(right-reading)
`meansthat the type is readable when the photosensitive layeris facing away from
`you. Normally, images to be printed on paper should be printed emulsion up,
`whereas images to be printed on film should be printed emulsion down.
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`
`
`To tell whether you are looking at the emulsion up (emulsion side) or the emul-
`sion down(base), examinethefilm after it has been developed underbrightlight.
`Oneside will appear shinier than the other. The dull side is the emulsion upside;
`the shiny side is the emulsion downside(base).
`
`You should check with your print shop to see whetherit prefers film as a positive
`
`emulsion up, negative emulsion up, or negative emulsion down.
`
`Simulation of a printed page with Negative and Emulsion Downoptionsactive
`
`Printing a border
`
`You can specify the width of a border you wantto appear around an imageusing
`the Border dialog box, The dialog box appears when you click the Border option
`in the Page Setup dialog box. The borderis printed in black. The unit of measure
`is points, inches, or millimeters.
`
`You can select the units of measure you want from the pop-up menu beside the
`Width text box.
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`To specify the width of a border:
`
`1. Choose Page Setup from the File menu.
`
`2. Click the Border option.
`
`The Border dialog box appears.
`
`Cancel
`
`Border...
`
`miathe —
`
`3. Choose the units of measure you want from the pop-up menu beside the Width
`text box.
`
`4. Enter the width you want the border to be; you can specify decimal values.
`5. Click OK.
`
`Printing a caption
`
`You can enter text that will appear below an image using the Caption dialog box.
`The dialog box appears when youclick the Caption button in the Page Setup
`dialog box.
`
`You use the standard Macintosh text editing techniques to edit the text in the
`dialog box. You can print up to six lines of text as a caption; additional text will
`not appear on the image. The text is printed as 9-point Helvetica type.
`
`To define a caption:
`
`1. Choose Page Setup from the File menu.
`
`2. Click the Caption option.
`The Caption dialog box appears.
`
`Caption...
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`3. Type in the text box the text you want to appearas the caption.
`4, Click OK.
`
`Miscellaneous printing options
`Other printing options allow youto print only the selected area on an image, or
`to transfer the image data to the output device in ASCII format. The options that
`control how an imageis printed appear in the lower left corner of the Print dialog
`box. The options that are not currently available are dimmed. The options and
`their effects on the printed image are described below.
`
`(1 Correct for Printing Colors
`
`Pages: @ All © From: [ To: [|
`Copies: ||
`Cover Page: @No © First Page (Last Page
`Paper Source: @ Paper Cassette ©) Manual Feed
`
`@ Color/Grayscale © Black & White
`
`(C #iint Selected Area nly
`CJ Print selected Charnne? dnly
`CJ Print Using Color PostScript
`
`Encoding:
`OaAscI
`@ Binary
`
`Printing a selected area only
`
`You can print just part of an image that was previously selected with the
`rectangular marquee.
`
`To print a selected part of an image:
`
`1. Select the part of an image you want to print using the rectangular marqueetool.
`
`2, Choose Print from the File menu. The Print Selected Area Only option is automat-
`ically checked.
`3. Click OK.
`
`Only the selected area is printed.
`
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`Printing with print spoolers and across networks
`
`By default, the Adobe Photoshop program transfers binary information to
`printers. However, some print spooler programs and computer networks don’t
`supportfiles that are binary-encoded. In these situations, you can choose to
`transfer the document in an ASCII format. Files that are encoded in the ASCII
`
`format require about twice as much timeto transfer as binary files, because they
`contain about twice as many characters.
`
`To select the ASCII encoding option:
`1. Choose Print from the File menu.
`
`. Click ASCII.
`
`3. Click OK.
`
`The image information is sent to the printer in ASCII format.
`
`Composite and color image printing options
`If youare printing a color image, you can chooseto print only the active channel.
`You can also compensate for the differences between the RGB colors of the
`monitor and the CMYKprinting ink colors, and send color PostScript language
`informationto the printer if you are printing on a color PostScript
`printer.
`
`Printing individual channels
`
`You can chooseto print one channelat a time. The Print Selected Channel Only
`option is automatically selected when you print an RGB, HSL, HSB, or multi-
`channel image. This option is available when you print a CMYK image, but you
`must select it manually, To use this option with an RGB image, thered, green, or
`blue channel mustbe active. The Print Selected Channel Only optionis not avail-
`able when the RGB display optionis active.
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`To print a single, specific channel of an image:
`1, Choose Channel from the Mode menu.
`
`2. Choose the channel you want to print from the Channel submenu.
`
`Biimap
`Gray Scale
`
`
`jade xed € piper
`RGB Color
`“CMYK Color
`SL [ oipr
`HSE Coler
`Multichannel
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`seutp nbanonbien Magenta
`New Channel
`Yellow
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`Delete Channel
`Black
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`Epinr fable
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`LeeLee
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`Split Channels
`Merge [hanagis...
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`3. Choose Print from the File menu.
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`4. Click the Print Selected Channel Only option, if it is not already checked.
`5. Click OK.
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`The active channel is printed.
`
`Printing a color composite and a color corrected image
`Normally, if you intend to print large quantities of an image on a conventional,
`four-color press, you convert an RGB or indexed color image to a CMYK image
`and then print a color separation that consists of four plates, one plate for each
`of the four process colors. However, if you have a color output device, you can
`print a composite image using the Use Color PostScript option. If you select the
`Use Color PostScript option and print an image on a color PostScript printer
`while the RGB display modeis active, an RGB composite image will be printed.
`
`Whenyou print a color composite, you should use the Correct for Printing Colors
`option in the Print dialog box to compensate for differences between the RGB
`colors and the CMYKprinting ink colors. This option causes the Adobe
`Photoshop program instead of the printer to make the conversion to CMYK
`colors, which usually produces better results.
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`Whenyouselect the Use Color PostScript and Correct for Printing Colors options
`and print on a color PostScript printer, the Adobe Photoshop program prints the
`composite image on one page, The program performs an internal RGB to CMYK
`conversion before sending the data to the printer. The image type of the image
`displayed on-screen remains the same; the image is not converted to a CMYK
`image.
`
`If the Correct for Printing Color option is selected before printing to a color
`QuickDraw printer, the Adobe Photoshop program performs an internal RGB to
`CMYK conversion before sending the data to the printer.
`
`To print a composite color image:
`
`. Open the indexed color or RGB image you want to print; if you are printing an
`RGB image, choose Channel from the Mode menuand select the RGB Channel
`command,
`
`. Choose Print from the File menu.
`
`If you are printing to a color PostScript printer, click the Use Color PostScript
`option.
`
`. To print a color corrected version of the image, click the Correct for Printing
`Colors option in the Print dialog box.
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`. To print the image, click OK.
`
`Your composite color image is printed.
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`Chapter 19: Printing Halftones
`
`This chapter describes how to print a halftone from a gray-scale image. It also
`covers how to adjust for the gammaof your monitor and compensatefor dot gain
`on press.
`
`A halftone is an image composedofa series of dots of varying sizes. When you
`produce a halftone of a gray-scale image, the variations in size and spacing
`between the dots simulate the changes in gray levels that occur in a continuous-
`tone image. (When you print a CMYK image, the dots determine the varioustint
`densities that occur in each of the four process colors.)
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`19
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`Conventional graphics uses a stat camera to produce a halftone by placing a
`halftone screen between a pieceoffilm and the image, and exposing thefilm. The
`image is converted toaseries of dots. A computer and imagesetter follow a similar
`principle in producing a halftone.
`
`Before printing a halftone, you can calibrate your monitor to correct any discrep-
`ancy in gray-levels, brightness, or contrast between yourscreen display and the
`printed image. The process of printing a halftone begins with a gray-scale image.
`Using the image, youset up your halftone screen includingits frequency, angle,
`and dot shape. Youselect general printing options, including printing calibration
`bars and other identification such as crop or registration marks with the image.
`Then you print the halftone and checktheresults. If the halftone needs adjust-
`ment, you repeat the process.
`
`Several factors affect the quality of the halftone, including attributes of the
`screen. The screen attributes include the screen frequency, screen angle, and dot
`shape. With gray-scale images, the Adobe Photoshop programuses only one
`screen to producethe halftone.
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`The screen frequency controls the density of dots on-screen. The dots are
`arranged in lines on-screen, and the frequency is commonly measured in lines
`per inch(lpi). The screen frequency used is largely dependent on the type of
`paper stock and the quality of the press to be used to print the image. The higher
`the screen frequency, the finer the image produced. Magazines, which normally
`are printed on coated paper stock on high-quality presses, tend to use fine screens
`of 133 Ipi and up. Newspapers, which are normally printed on lower-quality
`
`paper stock, tend to use lower screen frequencies, such as 85 Ipi screens.
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`Screen frequency: 100 lines per inch
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`Screen frequency: 50 lines per inch
`
`The screen angle used to create halftones of gray-scale imagesis usually
`45-degrees.
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`The dot shape also affects the printed image. The shape of the screen dot deter-
`mines the shape of the dots that comprise the halftone. Elliptical-shaped dots are
`commonly used; however, the Adobe Photoshop program also supports round,
`
`line, square, and cross-shaped dots.
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`Ellipse
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`Line
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`In general, you perform seven major steps to produce a halftone. The following
`sections describe the steps in detail. They are:
`
`1, Convert the image to a gray-scale image.
`
`2. Select the screenattributes, including the screen angle and frequency, and the dot
`shape.
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`. Load the transfer function file appropriate for the paper stock on which youwill
`print the image.
`
`. Calibrate the monitor gammausing the Levels dialog box under the Adjust
`commandin the Image menu, and the Gamma Gray Rampfile included on the
`Calibration disk.
`
`. Select the printing options you want, including the Calibration Bar option,
`which is necessary to perform the density calibrations.
`
`6. Print a proof of the image.
`
`7. Calibrate the density of the output of the gray-scale image. This step includes a
`numberof different operations, including:
`
`@ Using a densitometer to measure density levels on the printed calibration bar.
`@ Converting the densitometer readings to percentage values(if necessary).
`
`@ Entering values in the Transfer Function dialog box, whichis accessed through
`the Transfer option in the Page Setup dialog box, to adjust the density levels.
`
`Preparing to print a gray-scale image
`Printing a halftone of a gray-scale imageis a process that involvesa series of steps.
`Thefirst step in printing a halftone of a continuous-tone black and white imageis
`to make sure that you are working on a gray-scale image. You can do this by
`opening the Mode menu and checking to make sure that the Gray Scale menu
`item is checked. Then you set yourscreen settings including the sc