TWNA Recommended Practices For Digital File Formats

Compiled By Tom Kelley

As digital images become more of a fact of life in the print publishing world, it becomes necessary to arrive at some standard format. Widespread confusion, amongst both experienced graphics persons and non-graphics personnel in the editorial and public relations communities, results for every participant knowing enough to do their own jobs, but not truly understanding the entire digital file workflow. This is not a criticism of anybody's expertise, it's merely a fact of life during the early stages of any emerging technology.

To provide a common denominator such that image producers in the PR community and image users in the publishing community can be reasonably sure that electronic images will be distributed in a useable form, TWNA has set out to develop a list of standards and recommendations.

The information below is the condensed form of the specifications for the benefit of those participants who only wish to know the basics, or need to pass them along as requested. Following the condensed specification, we are providing some of the supporting details used to arrive at our recommendations, along with some further suggestions pertaining to digital formats and distribution. Finally, we are providing a list of links to some of the resources used in the project for the benefit of anybody who wants to learn more.

FILE SPECIFICATIONS

Continuous-Tone/Photographic Images For Print Use - Hi-Res
TIFF format, uncompressed, of sufficient resolution to provide 300 dpi output at the published size (about 2,400 pixels on the long side of the image, or 8-10MB for a half-page standard magazine photo), scanned/saved in a "wide(r)-gamut RGB colorspace" (such as Adobe RGB 1998).

 

Continuous-Tone/Photographic Images For Preview/Placement/Web/E-Mail Use - Lo-Res
JPEG format, uncompressed or minimal compression, of sufficient resolution to provide 72 dpi output at the published size (about 300 pixels on the long side of the image, or 700KB to fill 1/4 of a typical computer monitor screen), scanned/saved in a "narrow-gamut RGB colorspace" (such as monitor RGB).

 

Line Art & Other Vector Images
EPS format, uncompressed, of sufficient resolution to provide 1,200 dpi output at the published size, ASCII encoded, preferably with a TIFF preview.

 

Press Releases & Other Text Communications Via E-Mail
Raw ASCII text-only format, as an attached file, or more preferably as "inline" copy in the body of the e-mail. Available artwork pertaining to the release should be referenced at the end of the copy, with a link and/or instructions for retrieval. Never send hi-res images without a specific request from the recipient and refrain from sending any type of images as part of a mass e-mailing.

 

Suggested Method Of Distributing Digital Files With Press Kits
One or more CD-ROM discs containing un-embedded (not animations or presentation formats) data files of all press release copy in ASCII Text format along with both hi-res (TIFF) and lo-res (JPEG) copies of any images. Some presentation formats, such as Macromedia Director, will archive all graphics and text as standard (tiff, jpeg, txt) files that can be easily downloaded from the CD-ROM, while other formats, such as Microsoft PowerPoint, embed the source material inside their own proprietary file format, preventing extraction for any use in print publishing.

 

Text File Notes
Do not send/distribute text information as an MS Word DOC file, many versions of Word are completely incompatible with other versions of Word and most versions of other word-processing software. The most useful output format is "Text Only" in MS Word and "Generic Word Processor Text" in WordPerfect. Don't use two spaces after a period (this is a holdover from the typewriter days that causes problems in some typography software). Don't use extensive formatting in text communications. Make press releases archived on websites available in ASCII Text format, HTML placed inside a "table" format (hanging indent to accommodate navigation bar at left) is difficult to extract for use. Include relevant links and contacts.

 

Image File Notes
No embedded images (PowerPoint, MS Word, Acrobat PDF, etc). No proprietary formats (Corel Draw, Kodak PhotoCD, etc). Don't confuse scanned resolution with published resolution. Don't try to up-convert lo-res formats. Never significantly enlarge (more than 10%) an existing image file (re-scan at higher resolution if necessary). Don't apply any size/resolution-dependent filtering (unsharp mask, etc) prior to distribution. Don't re-save JPEG images in multiple generations (compression degrades image more in each generation).

 

Industry suppliers of digital images are advised to make their original scans of the film at resolution equal to or better than that of the film (4,000-5,000 dpi) to allow maximum use from a single scan. Publishing production operations, knowing the required output size, are advised to scan film/photos at a resolution that will produce a 300 dpi image at the finished size. Preserve edit-ability and view-ability throughout the digital image workflow (from scan, to editorial, to production, to printing). Archive editorial-sized hi-res print and lo-res web images in a media-accessible website for retrieval as needed.

 

Supporting Details

Transparency Film Is Still The Standard For Magazine Illustration
Even in today's digital age, transparency film is still the "reference" standard for high-quality color magazine publishing. Covers and two-page spreads typically begin their lives as transparency (slide/positive) film up to 8" x 10" in size. Many less-than-full-page illustrations are originally generated as medium-format (roughly 2" x 2") or large format (4" x 5") transparencies. Timely coverage and availability of a professional photographer sometimes dictate that 35MM (roughly 1" x 1.5") film be used, although the smaller original will not produce as good an image as the larger film.

Resolution Of (Data Volume Contained In) Fuji Velvia 50 ASA Film As A Comparison Baseline
Among professional photographers who shoot cars and trucks for a living, Fuji's Vevia 50-ASA slide film is pretty much the de facto standard film choice. Velvia's tight grain and exaggerated color rendition, make it the perfect choice for making three-dimensional, multi-hued vehicles look as impressive on the printed page as on the highway.

 

Fuji Velvia film has a resolution of up to 160 lines per millimeter. Multiply that times the 24mm x 36mm image area of a 35 mm slide, gives you roughly 22 mega-pixels in a 35 mm film transparency image. Multiply that times three color channels (RGB), and do the math to convert from bits to bytes (divide by 1024) and then megabytes (divide by 1024 again) gives an approximate figure of 64MB of data in a 35mm Fuji Velvia slide. Expressed in dpi, the 160 lines per mm resolution of the film would work out to 4000 dpi. This is the approximate digital resolution that will match the original film and produce a 64MB file. At the extreme, a high-quality drum scanner can extract as much as 100MB of data from a 35mm slide.

 

Pixels, DPI & Line Screens
The dpi spec is actually used for output (printers), with ppi (pixels per inch) being the appropriate measurement for input (scans). However, as the actual definition of the two terms is roughly parallel, and dpi is the commonly used term for both input and output, we'll stick with dpi. The rough equivalent of these measurements in the offset printing world is a "Line Screen."

 

Most magazines outside of the art and architecture topics will typically use a screen of 150 or less lines per inch (lpi). The generally accepted ratio between lpi and dpi or ppi is 2 to 1, thus requiring a digital image to be 300 dpi/ppi at the printed size, for acceptable reproduction. In some instances, the ratio can be lowered to as little as 1.5 to 1, but this is somewhat dependent on content of each specific image, so 2 to 1 is considered to be the accepted standard.

 

Up-Conversion & Down-Conversion
When 300 dpi is given as a required spec for digital images, it refers to 300 dpi at the printed size. Enlarging a 35mm slide to half page output is an enlargement of roughly 500%. Accordingly, to produce a 300 dpi half-page image, the image at the film size would need to be 1500 dpi.

 

If an image is to be published smaller than half-page size, the end-user can reduce the file and output size without deteriorating the image quality. Conversely, starting with a smaller file size will NOT allow enlargement without decreasing the image quality substantially.

 

Retaining Flexibility In Digital Files
If the original film scan is made at 4000 dpi or above, to capture all of the available image data, then theoretically, anything that could be produced from the film original, could also be produced from this master file. This would include slide dupes from a film recorder, large-format graphics for posters and trade-show use, and any advertising purposes. Although it's likely that most uses will only require film-size resolution of around 1500 dpi, it's easy to make a 1500 dpi file from a 4000 dpi scan, on the other hand, it's impossible to make a 4000 dpi file from a 1500 dpi scan.

 

Digital retouching at the original film scan stage should be limited to those changes that are not size/resolution/output sensitive (Photoshop's unsharp mask is an example of a size/resolution/output sensitive modification).

 

Using a worst case scenario, let's look at using a 35mm slide for a full bleed 8 x 11 cover. Assuming no cropping of the original illustration, beyond fitting the cover's aspect ratio, and a 175-line screen (printed size dpi should be twice the line screen rating), the appropriate megabyte math gives us a required file size of just under 31MB. More likely for editorial use would be a half-page (5 x 7) 150-line screen illustration within an article. This half page editorial image works out to about 9MB.

 

So, for supplying editorial images, the average requirement for most magazine uses would be an 8-10MB file. Expressed in pixel dimensions, the image should measure at least 2,400 pixels on the long side of the image. This 8-10 MB file can easily be created from the 64-100MB file generated by the original film scan. Given the widespread availability of broadband internet access today, an 8-10 MB file is compact enough to allow for downloading in a few minutes or less. Although it would make sense to archive a copy of the image at cover size (30-32MB), the limited use of this size would suggest that its distribution be by user request only.

 

Thumbnails & FPO Copies
As an alternative, supplying the image in two sizes, one for web/thumbnail/FPO use and one for magazine-quality reproduction, would allow for quick previewing before downloading the hi-res file. Given that most web images are no larger than quarter screen, a file size of approximately 700KB (0.7MB) is sufficient for the lo-res version.

 

Some Thoughts On Scanning & Resolution From A Pro
According to Richard Seiling, founder of West Coast Imaging, ". . . for the promise of digital imaging to be fulfilled, there needs to be a change from the "scan many times, for each individual purpose" workflow to the "scan once, purpose many" philosophy. Currently about 99% of digital imaging is done in the "scan many" mode. Each time an image is used, the original film or a dupe is sent out. That film is then scanned for the intended use at "low" resolution in a clipped CMYK or narrow-gamut RGB colorspace that is only good for that ONE use. Just try to use a CMYK scan to make a film output on an RGB film recorder if you believe the scan can be re-purposed."

 

"Usually, technicians perform a limited amount of work on this digital file because it is only good for one use. The amount of time will depend on the client's budget and their quality standards. After the job is complete, the file is discarded, including all the time and effort spent on correcting the image. This is a waste. Future scans and corrections will never match exactly, and repeated handling of the film will damage it."

 

"So what's the alternative? Scan once for many purposes. This means that, beginning with the (original) scan, you make decisions that will allow many uses of the file. First you must make a high resolution scan of your image that captures the practical and usable information in the original. This results in about 100MB of data for 35mm originals and 300MB for 120 and 4x5."

 

Seiling goes on to explain other specifics of the original scan, "It's important to scan on an ultra high-quality drum scanner with a ColorSync input profile. The ColorSync input profile is critical. It makes the digital file match the original film as closely as possible. The ColorSync input profile goes further than just matching color. It allows the scan data to be saved in a Wide Gamut RGB colorspace, or CIE LAB. Unlike all CMYK and most RGB spaces, wide-gamut colorspaces preserve ALL the color information the scanner saw. CMYK, narrow RGB colorspaces, and monitor RGB spaces clip colors and throw them away forever."

 

Digital Compression Schemes (Lossless vs. Lossee)
As the name implies, lossless compression of a digital image does not discard any of the original image data, while lossee compression relies on discarding image data. Because the computer monitor screens used to view the web are relatively low resolution (about 72 dpi), a JPEG image's lossee compression is virtually unnoticeable when viewed. High resolution publishing requires that lossless compression, such as TIFF, be used to preserve maximum image quality and editing flexibility.

 

Because of the wide variations in available file compression utilities (ZIP, Stuffit, etc.), it's a virtual certainty that no matter what utility is used to compress a finished file, it will be incompatible with the system used by the recipient of the file. Accordingly, compression of a finished file should not be used. With the prevalence of CD burners and broadband connections, the trouble created by file compression is not worth the reduction in file size.

 

File, Format & Platform Compatibility

The specifications chosen for TWNA's digital standards are supported on virtually all operating systems (PC, Mac, Unix, Linux, etc.), and are generally supported by all commercially-available image-processing software. Although the Mac operating system is the de facto standard within the graphics community, PCs are generally the standard everywhere else. This, combined with the fact that Macs can read PC files easier than a PC can read a Mac file would suggest that maximum flexibility would be achieved by deferring to the PC format whenever a choice is necessary. Again, staying away from obscure, proprietary file formats (binhex archive, RTF, etc.) will allow maximum compatibility.

 

Digital File Distribution Methods
By a clear margin, the TWNA members surveyed for this project preferred to receive digital materials on a CD as part of a press kit. Those presentation formats that permit the easy downloading of standard format files were widely commended. Another frequent suggestion was that the product manufacturers also make the images and text files accessible in the press area of their websites. As for broadcast e-mailing of press releases, text files or message-body text was the preferred format. Finally, all respondents indicated that they did not want images e-mailed without a specific prior request.

 

 

TWNA Digital Format Recommendation Resources

Real World Scanning & Halftones - 2nd Edition
By David Blatner, Glenn Fleishman, & Steve Roth
Peachpit Press - www.peachpit.com

Real World Photoshop 5/5.5 (Recommended By Adobe's Tech Support Staff)
By David Blatner & Bruce Fraser
Peachpit Press - www.peachpit.com

GRACoL 4.0 - General Requirements for Applications in Commercial Offset Lithography
Graphic Communications Association - www.gca.org

SWOP 2000 - Specifications for Web Offset Publications
SWOP, Incorporated - www.swop.org

The PR Technique Column - PR Week Magazine
www.prweekus.com

Drum Scanning For Top Quality - Outdoor Photographer Magazine
By Michael Frye
www.michaelfrye.com & www.outdoorphotographer.com

Resolution Feature - Digital Camera Magazine July/Aug 2000
By Andrew Rodney
www.photopoint.com/dcm

Other Resources:
www.westcoastimaging.com

www.dcs.ed.ac.uk/home/mxr/gfx/faqs/JPEG.faq

www.digitaladlab.com

 

And finally, in no particular order, the many TWNA members and affiliates who participated in gathering this information: Dave Jacobs, Bill Hudgins, Dave Stolte, Kurt Condra, Marsh Galloway, Stephen Petit, Deborah Lockridge, Tom Berg, Dave Michael, Allison Hatfield, Ruth Jones, Phil Romba, and anybody else we may have forgotten. Thanks to all!