Digital Art Guidelines Tsg

7/30/2019 Digital Art Guidelines Tsg

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Introductionration into pages for electronically composed publications. Our objectiveis to use submitted art files whenever possible and to reproduce files as trueas possible to the originators intended appearance.

Unfortunately, however, not all submitted digital art has been prepared ina fashion that permits files to be usedof these, some can be convertedand amended; others cannot. At issue, primarily, are technical limitations(e.g., digital file format incompatibility with composition software) and aes-thetic considerations (e.g., insufficient image resolution for acceptableappearance in print). Also, for those files that, as supplied, may not meetcriteria but can be converted, modifications may be laborious and costly.

These guidelines are intended to improve awareness of successful digitalart file preparation methods and to convey optimal characteristics forsubmitted digital art files. As a consequence of observing recommended

specifications, a greater opportunity to use original submitted digital artfiles can be expected. As well, the ability to render art in print may satisfymore favorably the expectations of the author/creator.

Digital Art Guidelines

DIGITAL ART GUIDELINES

Introduction

1

The Sheridan Group welcomes the submission of digital art files for incor-

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File Format Digital art files should be saved as TIFF or EPS format.Submission as native file formats, or submission as any format other than TIFF or EPSis not recommended.

Images should be flattened prior to submission; that is, files should not contain lay-ers and/or transparent objects.

ImageResolution

Raster (scanned) image files should adhere to resolution guidelines specified forthe publication in which they will appear.Typical recommended image resolutionspecifications are as follows:

q 900ppi-1200ppi for monochrome (1-bit) imagesq 300ppi for tones (either grayscale or color)q

Imagesize/crop

Digital art files should be cropped to remove non-printing borders.

Art should be created or scaled to the size intended for print.

Image orientation should be the same as intended for print.

Color Black and white raster images should be submitted as bitmap (1-bit) mode formonochrome, and grayscale mode for tones or combination tones.

Color images should be submitted as CMYK color mode. Files should not be sup-plied as RGB color mode or as other than bitmap, grayscale or CMYK color.

Files should be free of color functions, including PostScript color management,

transfer curves, halftone screen assignments, and black generation functions. Filesshould not include references to ICC profiles.

Total Area Coverage (TAC) for black or dark elements or for black areas withincolor images should not exceed 300%.

For color images, black text and lines should be specified to overprint.

Text/LinesFor vector EPS files, fonts should be embedded or converted to outlines.

Lines or rules should not be defined as hairline width.Recommended minimum linewidth is 1/4 point (i.e., 0.0035 inches).

For digital art files not supplied same as print size, the effect of scaling reductionshould be considered for small text and for thin rules or lines.

Proofs A clean proof same size as the digital art should accompany file submissionforcolor images, the supplied proof should be color.

To ensure color match, the accompanying proof should be generated using aSWOP-certified (Specifications Web Offset Publications) proofing system andshould be produced in accordance with the SWOP ADS (Application Data Sheet).

In case that the digital art file cannot be used as provided, or the file cannot be

converted/modified, the supplied proof will serve as original art for scanning.

Submission Raster images may be compressed using LZW method for TIFF format.Digital art files may be compressed as archive format using WinZIP or PKZip for PCor Aladdin StuffIt for Mac.

File submission can be accomplished using standard removable storage media(e.g.,high-density floppy disk, Iomega ZIP, or CD-R), or as e-mail attachment or FTPby arrangement.

Digital Art: General Guidelines


Guidelines

2


500ppi-900ppi for combination tones (either grayscale or color)


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Information

Digital Art: Information

Color CMYK vs. RGB color mode: Computer monitors emit color as RGB (red,green,blue)light.Although all colors of the visible spectrum can be produced by merging red,green and blue light,monitors are capable of displaying only a limited gamut (i.e.,range) of the visible spectrum.

Whereas monitors emit light, inked paper absorbs or reflects specific wavelengths.

Cyan, magenta and yellow pigments serve as filters, subtracting varying degreesof red, green and blue from white light to produce a selective gamut of spectralcolors. Like monitors, printing inks also produce a color gamut that is only a subsetof the visible spectrum,although the range is not the same for both.Consequently,the same art displayed on a computer monitor may not match to that printed ina publication. Also, because printing processes such as offset lithography useCMYK (cyan, magenta, yellow, black) inks, digital art must be created as CMYKcolor or must be converted from RGB color to enable use.

Spot colors: Digital art that is com-prised of spot colors (e.g., specialcolors: any colors that are notCMYK process colors), generally

require conversion to the CMYKcolor space to enable file use.Because color gamuts for spotcolor libraries, such as those associ-ated with the PANTONE MATCHINGSYSTEM, usually extend beyond theranges of the CMYK color gamut,some spot colors may not be rep-resented effectively using CMYKprocess inks.

Halftoning: In offset lithography, the density of CMYK inks can not be varied in con-tinuous fashion across an image, so a range is produced by means of halftoning.In halftoning, translucent CMYK ink dots of variable size are printed in overlappinggrids. Grids are placed at different angles for each of the ink colors. Smallerhalftone dots absorb less light; thus, as a result of an increase in the amount ofreflected light, apparent density is decreased and the object appears lighter.

yellow

green

cyanred

blue

magenta

monitorCMYK

PANTONE

visible spectrum color gamut comparison

halftoning screen angles (133lpi 40% screen enlarged)

15 75 90 45

CMYK

3

cyan(C)

magenta(M)

yellow(Y)

black(K)

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Information


Total Area Coverage: Because process color ink pigments are imperfect,pureblack cannot be achieved by overprinting CMY inks. Consequently, black (K)ink is introduced in addition to, or in substitution for, CMY inks. The combinedvalue of all CMYK inks for a particular area or object cannot exceed a spec-ified amount, however, or ink may not transfer effectively and printed sheetsmay not dry properly. This specified amount, referred to as Total AreaCoverage (TAC), typically is limited to 300% for offset lithography using coat-ed paper. Compensation for TAC limitation is accomplished during the sepa-ration process, by which RGB color is converted to CMYK, by means of UCR(undercolor removal) or GCR (gray component replacement).

For some of the same reasons that printed digital art may not match the same artviewed on a color computer monitor, digital art printed to a dektop inkjet printeror another printing device may not match when compared to the same art print-ed using CMYK lithographic processes---for example, color gamuts may vary foreach. Consequently, to ensure that color gamuts are comparable, proofs shouldbe produced in accordance with SWOP (Specifications Web Offset Publications)

guidelines. For contract color proofing (i.e., proofs that serve as a contractbetween the provider and the printer that an acceptable reproduction can beachieved),since the proof is expected to serve as a predictor of CMYK offset lith-ographic press output, the proofing system used must have been SWOP-certified,and proofs must have been produced in accordance with the SWOP ADS(Application Data Sheet).

Color management: Because proofing devices can vary significantly relative tocolor reproduction, due to toner/pigment and paper/substrate differences, andbecause significant variations exist for monitor to proof,and for proof to press,colormanagement techniques have been developed. However, in order to reconcilethe differences between input and output device color gamuts, chosen devicesmust be capable of consistencyafter having been qualified as reliable, each

device is calibrated to the defined standard. Devices are subsequently charac-terized by comparing device output against a standard color gamut, the out-come of which is an ICC (International Color Consortium) profile or tag that servesas a color space description for the device. Conversion is achieved when varia-tions between the input device profile and the output device profile are recon-ciled by means of a CMM (Color Management Module). Currently, assignment of

created using different color management systems may not convert satisfactorily.

color separations (UCR employed to accomplish 300% TAC)

cyan(C)

magenta(M)

yellow(Y)

black(K)

CMY

CMYK

Proofing

4


ICC profiles to digital art image files is not recommended, in part because profiles

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File Sourcesprofessional graphics applications (e.g., Adobe Photoshop and/or Illustrator).

Word processors and spreadsheet or presentation applications, although suitablefor creating files for office or internet use, are not recommended for creating dig-tial art for print. Microsoft Office applications are included in this group. In some

cases, however, such files may be converted so as to enable use.


Image Types Digital images generally can be classified as one of two types: vector or raster.

Vector graphics typically are generated using drawing or illustration programs(e.g., Adobe Illustrator) and are composed of mathematically-defined geometricshapeslines,objects and fills. Since vectors entail both magnitude and direction,vector elements thus are comprised of line segments whose length representsmagnitude and whose orientation in space represents direction.

Vector graphics usually are easily modified within the creating application andgenerally are not affected detrimentally by scaling (enlarging or reducing theirsize). Because vector elements are mathematically-defined, scaling simplyrequires modification of their mathematical locations.However, vector files do notsupport photographic imagery well and often can be problematic for cross-plat-form exchange.Vector graphics typically are saved as EPS format.

Raster images are produced by digital image capture devices: digital scanners ordigital cameras, or by pixel editing programs (e.g., Adobe Photoshop). Rasterimages are composed of a matrix (grid) or bitmap of digital picture elements (pix-els). Pixels are squares or rectangles described as black, white, gray or color.

Raster images typically are saved as TIFF format, but can be saved as EPS as well.Whereas conversion from vector to raster is easily accomplished, raster conversionto vector is much more difficult (and often is not possible). Raster images typicallyare easily shared across various platforms, but can be more difficult than vectorgraphics to modify. As well, raster graphics are impacted by scaling.

Information

Vector Raster

Screened original art: Images scanned from screened original art (i.e., scannedfrom halftone film, or scanned from a previously-printed publication or from artproduced using a device that employs halftoning or another pattern method ofapplying toner/dyes to a substrate) can be reproduced by either copydot scanor descreen scan methods.The objective of copydot scanning is to preserve exist-ing halftone dots, whereas the objective of descreen scanning is to remove dotsor other structure and subsequently apply halftone screens prior to print.

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For preparing digital art intended for print, The Sheridan Group recommends using



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Information

head

gutter

face

figure 1

head

gutter

face

figure 1


filetype

fileformat mode

suggestedresolution

monochrome

tone

combinationtone

TIFF

TIFF

TIFF

bitmap

grayscaleor

CMYK

grayscaleor

CMYK

900-1200ppi

300ppi

scan (raster) imagefile types

Raster images can be classified as either monochrome, tone, or combination tone.

Monochrome (1-bit) images,typically scanned from line art and/or text originals, arecomprised of a single bit of data. Since each bit (binary digit) can be representedonly as either a zero or a one, pixels within a monochrome image can have only twostates: black or white. Monochrome images generally require higher resolution

(more pixels per inch) than tone images in order to prevent aliasing (stairsteppedappearance) of diagonal lines.

Tones, typically captured from continuous-tone photographs, are comprised of 8-bitdata (represented as 256 different levels for grayscale images). Color tones containeight bits of data per channel (i.e., per color); thus, a CMYK tone contains 32 bits ofinformation (and 256 levels each for cyan, magenta, yellow, and black).

Combination tones contain both tone and text/line art elements. Consequently, liketones, combination tones are comprised of 8-bits of data per color channel. Thus,combination tones are saved as either grayscale or CMYK color mode. Becausecombination tones contain text/line art elements, however, the level of resolutionemployed must be compromised to address aliasing versus physical file size.

RasterFile Types

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500-900ppi

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Vector graphics are resolution-independentthus, their resolution is determinedonly by the output device.Because vector elements are mathematically-defined,scaling (enlarging or reducing their size) simply requires modification of their com-ponent mathematical descriptions.

Whereas vector graphics are resolution-independent,raster images are resolution-

dependentthe number of pixels that occupy a given space must be defined.Consequently, raster image resolution is specified in pixels per inch (ppi). However,although the term is not effective, image resolution commonly is referred to in dotsper inch (dpi)dpi more appropriately is attributed to device resolution or outputresolution, where the number of dots an output device is able to produce withinan inch represents the resolution of the device.

Division of the number ofpixels in the height and inthe width of a raster orbitmap by its resolutiondetermines the physicalsize of the imagee.g., a

300ppi raster image thatis 900 pixels wide and 600pixels high is 3 inches by 2inches in size:

900 pixels 300ppi= 3 inches wide

600 pixels 300ppi= 2 inches high

Monochrome (1-bit) image resolution for images intended for lithographic print is900-1200ppi. In general, monochrome image resolution should be equivalent tothe resolution of the intended output device. Output resolution for computer-to-plate devices (i.e., platesetters) typically is about 2400dpi; however, because nosignificant visible improvement is realized when 2400ppi and 1200ppi mono-chrome images are compared, the range for monochrome image resolution issuggested as 900-1200ppi.

Tone image resolution is recommended as 300ppi. This recommended resolution,as well as ranges suggested for other file types, assumes that images have beenscanned at the same size intended for print (e.g., the typical image width isapproximately 20 picas ,or 3 1/3 inches, for a single-column image that will appearin a double-column standard size publication).



Information

ImageResolution

7

300 pixels

3 inches

300 pixels 300 pixels

300

pixels

300

pixels2

inches

effect of insufficient resolution for combination tone image (simulated)

high resolution low resolution



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Information

Since raster images have a specific resolution (i.e.,a specific number of pixels perinch), scaling a raster image involves the distribution of available pixels across thedesignated space. Image resolution subsequent to scaling is referred to as effec-tive resolution. If an image is enlarged, unless additional pixels have been addedby means of interpolation (resampling), then accordingly the size of each pixelmust be increasedconsequently, the enlarged image will have fewer pixels per

inch (lower resolution). Conversely, if an image is reduced, unless existing pixelshave been discarded (downsampling), the size of each pixel must be decreased(higher resolution).Although scaling reduction generally is less problematic regard-ing visible defects, unnecessary resolution can contribute to excessive physical filesize. Cropping the scanned image to the size intended for print also will benefittoward the reduction of physical file size. If an image will require scaling, scanningresolution should be adjusted accordingly.

Imagesize/crop

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text and/or line art components, sufficient resolution is required for combinationtones to counter the effect of aliasing (i.e., stairstepped appearance or jaggies);however, higher resolution equates to larger physical file size. Consequently, forcombination tones, a compromise is achieved that balances the issues of aliasingand physical file size.

Quality (halftoning) factor: During the process of halftoning, series of pixels aretranslated to halftone dots of varying sizes and position. Improved results areachieved when more than a single pixel is available to describe the density of agiven halftone dot. Consequently, a quality factor can be assumed to enabledetermination of the suggested resolution for tone images.

For tone images that will be halftoned at 133lpi (lines per inch) or higher,a qualityfactor of 1.5x is applied. For images that contain geometric objects: lines, repeat-ing patterns, diagonals, etc., a quality factor of 2x the halftone linescreen is bene-ficial. Below 133lpi, a quality factor of 2x is recommended, since halftone conver-sion to proper densities is less accurate for lower linescreen rulings.

Because halftone linescreen usually is not known at the time of scanning, 300ppi is

assumed to be a reasonable guideline for grayscale or color tone image resolu-tion. images that have been created or modified for internet display, typically72ppi, do not possess sufficient resolution to enable effective print. Employing thequality factor and subsequently adhering to image resolution recommendationsensures an appropriate balance between print quality and physical file size.

effect of scaling forraster tone images

image at 100% size

image scaled 200%

(effect exageratedfor display)


Combination tone image resolution is recommended as 500-900ppi. Because of

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File Formats


Information

image type source characteristic resolution file format

vectordrawing/

illustration appl.mathematically-

definedindependent eps

rasterscan/pixel edit

applicationpixel-based dependent tiff/eps

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TIFF or EPS file formats only are recommended for submission of digital art filesintended for high-resolution print. A primary issue concerns compatibility with com-position software, for which imported image file format often is restricted to TIFF(tagged image file format) or EPS (encapsulated PostScript). Internet graphics(e.g.,GIF or JPEG formats),clip art,screen captures,and files generated from officeapplications typically are not suitable for use, unless files have been converted toTIFF or EPS format and can be modified to accommodate recommended digitalart file specifications and to satisfy aesthetic requirements.

PDF (Portable Document Format), although the de facto standard file format forpage file submission for prepress and print, is not suitable for digital art image filesubmission. Image files as PDF format should be converted to TIFF or EPS to enablecompatibility with composition software.

Application file formats may be effective within the environment of the authoringapplication; however, recipients of native file formats must have the same versionof software as the creator,plus must have access to graphics and utilized fonts.Aswell, same platform, operating system and associated utilities may be required toenable accurate file replication. Consequently, conversion by the file originator to

recommended file formats is necessary, if possible, to ensure proper digital artreproduction.

Because modern prepress systems utilize composite page workflows,digital art filesshould not be saved for submission as separated or multi-channel formats, such asDCS (Desktop Color Separations).As well,although DCS is a version of the standardEPS format,color and other detail may be lost due to composition software incom-patibility.

Transparency and/or layers must be flattened prior to image file submission, sincemost print devices, including RIP devices (raster image processors), and Adobe PDFprior to version 1.4 (associated with Adobe Acrobat 5), are not able to accom-modate native transparency data.

File compression techniques can be utilized to reduce physical file size for rasterimage data,and thereby reduce storage space requirements. Compression meth-ods are classified as either lossless, for which image detail is not removed, or lossy,for which detail and color information, if applicable, are removed. Image detailand/or color information discarded (i.e.,lost) using lossy compression techniquescannot be restored.

Welch): a lossless method typically used for compressing images containing largeflat areas of image information, and JPEG (Joint Photographic Experts Group): alossy method used for compressing continuous-tone images (e.g., photographicimages).

image type comparison


Common raster image data compression techniques include LZW (Lemple-Ziv-


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Tables

Digital Art: Tables

picas decimal conversion

to picas/points

Note: Enter data into blue text fields. Result will appear as red text.

point

pica

inch

mm

point pica inch mm

units of measurement conversion table

picas decimalpicas/points

.

picas/points conversion

to points

picas/pointspoints

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Note: Enter data into blue text fields.

Result will appear as red text.

actual

resolution qualifier

desired % scale

actual desired effective

image width (picas)

image resolution (ppi)

image width:

actual = measured width in pica units of origi-

nal digital art image

desired = target width in pica units of final dig-

ital art image (default is 20 picas,

typical width of one column for a

standard double-column publication)

% scale = desired image width divided by

actual measured width

image resolution:

actual = measured resolution in pixels per inch

(ppi) of original digital art image

desired = target resolution of final digital art

image (default is 300ppi, typical rec-

ommended resolution for tone

images)

effective = actual image resolution multiplied

by % scale---compare against

desired resolution


1.00

1.00

1.00

1.00

1.00

12.000

72.000

2.835

0.083

1.00

6.000

0.236

0.014

0.167

1.00

0.039

0.353

4.233

25.400

1.00

1 0

1 0

1 0

12

RESET VIEW CLEAR FORM

20.00 20.00 100.0%

300 300 300

RESET VIEW CLEAR FORM


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Digital Art: Glossary

Glossary

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aliasing Also referred to as jaggies or stairstep-ping. Visible steps along angled lines,objects or edges of text,more noticeableat lower resolutions.Attributed to harshtonal contrasts between juxtaposed pixels.

application file Native file associated with aparticular computer program, usually nottransportable to other applications.

binary The base-two counting system, employedby computers to process data, using onlythe digits 0 and 1.

bit Binary digit. The smallest unit of measure-ment in computer terms; either on oroff.

bitmap A digital image that has been mappedinto a raster (grid) of pixels, each having

been defined by a specific number of bits.CMM Color Management Module. Interprets

the ICC profiles describing the colorspaces used in a color management sys-tem. Enables color space conversion fromsource device to destination device.

CMYK Cyan, Magenta,Yellow, Black. The basecolors used in lithographic printing process-es. CMY are the subtractive primary colorsused in combination with K to effectivelycreate a multitude of other colors.

color gamut A physical plot of mathematicalequivalencies of perceived color, therange of which is associated with a partic-ular device or ink/pigment set.

color management A system by which colorcan be managed across different devices,whether input or output, each of whichmay have a unique color gamut.

combination tone A raster image file type com-prised of both tone (photographic) ele-ments and text/line art.

composite A digital file that contains allrequired high-resolution color plate infor-mation.

contract proof A proof created in accordancewith an agreed upon set of standards orspecifications. The proof may serve as acontract between the provider and theprinter that an acceptable reproductioncan be achieved.

copydot A method by which existing dots (usu-ally halftone) can be maintained duringthe process of digital scanning.Copydotscan files are usually comprised of 1-bitdata for each of the required color plates.

DCS Desktop Color Separation. A version of thestandard EPS file format; enables the sav-ing of multichannel files or of process colorseparations. DCS is not a composite file for-mat, in that color plate information mustbe reconciled by printing to separationsfrom the page layout application. Usuallyincludes a low-resolution color preview.

descreen A method by which dots or otherpattern data (such as that applied duringthe printing or proofing process) isremoved or blended during the scanning

process.downsampling The removal of pixel data from

an image, thus lowering its resolution andresulting in less image detail

dpi Dots per inch. The unit of measurement foroutput resolution; a square function of thenumber of dots measured both verticallyand horizontally.

effective resolution A calculated value thattakes into account the actual resolution ofan image and any scaling. Enlarging animage will result in decreased effective res-olution

EPS Encapsulated PostScript. An electronic fileformat used to transfer PostScript imageinformation from one program to another.Includes PostScript data and a low-resolu-tion preview of the image for display.

FTP File Transfer Protocol.A standard means oftransmitting digital information from onecomputer to another via modem or high-speed lines.

GCR Gray Component Replacement. Derived

from UCR.A method by which black canbe generated for print. GCR is used toreplace portions of CMY with K in areas ofcolor as well as in neutral areas.

GIF Graphic Interchange Format. A standardfile format for displaying internet graphics.Usually low-resolution RGB or indexed color,not suitable for print.



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Digital Art: Glossary

Glossary

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grayscale The palette ranging from black towhite. A grayscale image is composed ofvarious levels or shades of gray, 256 levelsof which are available for an 8-bit image.

hairline rule A specified rule that will image at

the finest resolution of an output device(e.g., 1/300 inch for a 300dpi device,1/2400 inch for a 2400dpi device)

halftoning The reproduction of continuous toneartwork, such as a photograph, through ascreen. A halftone simulates continuoustones by using black or overlapped col-ored dots of various sizes and positions.

ICC profile International Color Consortium for-mat. A color space description for a partic-ular input or output device, used in themanagement of color between devices.

interpolation Increase of image resolution bythe addition of new pixels, the color ofwhich is based on neighboring pixels.

JPEG Joint Photographic Experts Group. Formatused to display continuous tone images forthe internet.Unlike GIF format, all colorinformation is retained. Selectively discardsdata to achieve file compression.

lossy Any compression technique (e.g., JPEG)that removes portions of data to reducefile size.

lpi Lines Per Inch. Units of measurement forscreen ruling (halftoning).

LZW Lempel-Ziv-Welch. A lossless compressiontechnique that can be applied to images.Works best for monochrome images withrepeating patterns.

monochrome A 1-bit black and white rasterimage, typically scanned from line artand/or text originals, saved as bitmapmode.

PDF Portable Document Format. Cross-platformobject-based file format from PostScript;can contain all image and font data.

pixel Picture Element. Each pixel is assigned acolor and location value,a grid of whichcomposes a bitmap or raster image.

quality (halftoning) factor A multiplication fac-tor applied to halftone screen ruling todetermine optimum scan resolution.

raster Grid. A bitmap or raster image is com-posed of a grid of pixels.

resolution The number of pixels assigned perunit (usually per inch) of a raster image orassociated with a device. A high resolution

image contains more pixels per inch (ppi).RGB Red, Green, Blue.The primary additive col-

ors of the visible spectrum. Used for displayby color monitors.

scaling Alteration of an images size by enlarg-ing or reducing. Scaling of a raster imageinvolves redistribution of pixels within aspecified space.

spot color A special color; any color other thanCMYK or a CMYK process combination.

SWOP Specifications Web Offset Publications. A

specification employed for offset printing.

SWOP ADS SWOP Application Data Sheet.Presents proofer manufacturers recom-mendations for best match to SWOP speci-fications for density, dot gain, substrate, etc.

TAC Total Area Coverage. Specified as 300% forSWOP CMYK process printing. The totalcombined value of CMYK for the darkestarea of an image or page.

TIFF Tagged-Image File Format. A flexible imagefile format for transferring pixel images

across platforms and applications.

tone Typically captured from photographic orig-inals,a raster file type comprised of 8-bitsof data per color.

transparency An option that enables saving afile as layers instead of with a defined colorbackground.Primarily for displaying over-lapping objects for the web.Transparentobjects must be flattened for print.

UCR Undercolor Removal.A method by whichblack can be generated for print. Black is

used to replace CMY in neutral areas,resulting in less ink and greater depth inshadows.

vector Resolution-independent mathematical-ly-defined geometric shapes (lines, objectsand fills), entailing both magnitude anddirection.

visible spectrum Portion of the electromagnet-ic spectrum visible to the human eye.


Digital Art Guidelines Tsg

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