Additional Resources


UPDIG Guideline Excerpts

UPDIG refers to the Universal Photographic Digital Imaging Guidelines, a set of best practices for digital photography that have been put together by a group of working photographers, manufacturers, and trade groups. Included here are some UPDIG excerpts that are relevant to color management.

The following is an excerpt from the guidelines available at http://www. updig.org. Used with permission.

The Primary Goals

  • Digital images look the same as they transfer between devices, platforms, and vendors.

  • Digital images are prepared in the correct resolution, at the correct size, on the devices(s) on which they will be viewed or printed.

UPDIG Guidelines for Meeting the Goals

  1. Manage the color. ICC profile-based color management is the standard.

  2. Calibrate the monitor. Monitors should be calibrated and profiled with a hardware device.

  3. Choose a wide gamut. Use a wide-gamut RGB color space for capturing and editing RGB master files. We recommend Adobe RGB (1998) or ProPhoto RGB.

  4. Capture the raw data. For best quality, digital cameras should be set to record RAW files.

  5. Embed the profiles. All digital files should have embedded profiles (should be "tagged"), unless otherwise noted. Photoshop's Color Management should be set to "always preserve embedded profiles" and the "ask when opening" boxes should be checked to alert you to profile mismatches and missing profiles. When profile mismatches occur, you should elect to preserve the embedded profile.

  6. Color space recommendations:

    1. For the Web, convert images to sRGB and embed sRGB profile before delivery.

    2. For display prints from professional digital color labs, if a custom profile is available, use it for soft proofing. Then submit either sRGB or (more rarely) Adobe RGB with embedded profiles, as specified by the lab. If a lab does not have a custom profile, it's usually best to use the sRGB color space with that profile embedded.

    3. For display prints from many consumer digital-print vendors, a database of custom profiles is available. Otherwise, deliver files in the sRGB color space with embedded profile.

    4. For offset printing, it's always best to begin by asking the printer or the client's production expert what file format, resolution, and color space they require. RGB files contain many colors that cannot be reproduced by conventional CMYK printing. This has often led to a situation where the final result looks nothing like the screen version of the file, or the ink-jet print of the file. There are two ways to avoid this confusion:

      • Files can be delivered as CMYK files. This is the "safe" way to go, because the image itself will contain no colors that can't be reproduced by the CMYK process.

      • Files delivered as RGB files can be accompanied by a cross-rendered guide print that includes only colors reproducible in CMYK.

      Files can also be delivered in both CMYK and RGB. This allows the photographer to make the artistic decisions about color rendering, and gives the printer more tools to recover from mistakes the photographer may have made in converting RGB to CMYK.

      Ideally, CMYK image files should be converted from RGB using the printer's CMYK profile with that profile embedded in the file. It is not always possible to get the printer's profile, either because the printer does not have one or the client does not know who will print the images. In such cases, it's often best to deliver an RGB master file, with an embedded profile and a ReadMe file that explains that "for accurate color, the embedded RGB profile should be preserved" when opening the file.

    5. For ink-jet and dye sub printers, use a wide-gamut color space, such as Adobe RGB, for the source space. Use a custom profile for the printer-paper combination in the print space to get the best quality and the best match to a profiled monitor.

  7. Formats and names. File formats should always be denoted by standard, three-letter file extensions.

    1. For the Web, use JPEG files.

    2. For print, uncompressed TIFFs are best. Use JPEG only when bandwidth or storage constraints require it. Use the highest JPEG quality setting possible. We recommend not using less than "8" quality.

    To avoid problems with files that will be transferred across computing platforms, name files with only the letters of the alphabet and the numerals 0 through 9. Avoid punctuation marks (other than hyphen and underscore), accented vowels, and other special characters. Keep the full name (including extension) to 31 characters or less for files on a network or removable media and to 11 characters or less (including the three-letter file extension) when burning to CD-R, in case a recipient's computers don't support long filenames. For the complete guide to file naming protocol, see the Controlled Vocabulary website (http://www.controlledvocabulary.com/imagedatabases/filename_limits.html).

  8. Appropriate resolution. Resolution of digital images is described by three numbers: height, width, and ppi (pixels per inch). Beware: it's easy to confuse ppi with dpi (dots per inch), which refers to the resolution of a printing device, or with lpi (lines per inch), which describes a halftone grid or screen used for printing images on a press.

    The following target resolutions are meaningful only when paired with the height and width at which an image will appear in the final form:

    1. Low (monitor or "screen") resolution is defined as less than 100 ppi.

    2. Ink-jet prints normally need resolutions of 180360 ppi.

    3. Continuous-tone printing requires resolutions of 250400 ppi.

    4. The offset-printing standard is often considered 300 ppi. But resolutions of 1.32 times the halftone screen for the project are considered safe. If the images will be printed at 150 lpi, the appropriate image file resolution range would be 195300 ppi.

  9. Sharpen last. All digital images require sharpening, during capture or after, and the correct amount to apply depends on the type of use and size of the final output. For most uses, it's best to sharpen little or none during capture with a camera or scanner. Sharpening is an art, and requires study and practice. There are several schools of thought regarding proper sharpening. One recommended method is to remove capture softness using a gentle sharpening pass followed by local sharpening and/or output sharpening. Sharpening should be the final step in reproduction, because resizing and contrast adjustment affect an image's sharpness. Sharpening is best evaluated at 100 percent and 50 percent views on your monitor, or by making a print. The most common sharpening method is to apply an "unsharp mask" filter (higher settings for higher-resolution files) to images, but other sharpening methods and Photoshop plug-in programs can be useful, too. Oversharpening creates obvious halos around edges within images.

  10. Delivery. Digital image files may be delivered on removable media (removable hard drive, CD-Rs, or DVD-Rs), or via File Transfer Protocol (FTP) or email. If files are delivered on CD-R, the standard disc formatting is ISO 9660 or "Mac OS extended and PC (Hybrid) CD." When delivering images on a DVD-R, make sure the recipient can read the chosen format, since there are multiple standards. Often speed and convenience require delivery by FTP. Although not a preferred method, email delivery usually works if image files are small in number and size, and both sender's and recipient's Internet service providers permit large attachments. Email delivery sometimes works better if the image files are first compressed using RLE compression software such as WinZip or StuffIt. Check to make sure the recipient can access your specific version of compressed files. Delivery by FTP or email usually precludes delivery of a "guide print" (discussed later in this Appendix), so a disclaimer should always be included that states accurate viewing and reproduction depend on the recipient properly applying ICC color management.

  11. File info. All digital image files should have embedded metadataincluding copyright, usage license, and contact informationthat conforms to the IPTC or the newer IPTC Core standards (http://controlledvocabulary.com/imagedatabases/iptc_naa.html). Photoshop users can input and edit this information by choosing "File Info" under the File menu. Adding caption, title, origin, and keyword data enhances searches and organization with digital asset management applications.

  12. Describe what's there. Provide a ReadMe file in either PDF, HTML, or TXT format with all files delivered for output. Such files should specify image size(s), color space(s) and any licenses granted, the copyright owner's contact information, and, if certain rights are being withheld, the words "other uses, reproduction or distribution are specifically prohibited." The ReadMe file should also include disclaimers noting recipients are responsible for following an ICC-based color management workflow.

  13. Send a guide. Whenever possible, include a guide print with digital image files. A guide print is typically an ink-jet print that serves as a color reference for reproduction of a digital image file.

  14. Disk labels. Do not use adhesive labels on optical media, since they may separate and damage an optical drive. Printing directly on ink-jet-writable CD-Rs or DVD-Rs is a good way to provide information such as your copyright, usage license, file lists, and disclaimers.

  15. Long term. Archiving responsibilities should be clearly stated in writing for everyone involved. Photographers should note that charging for archiving could mean assuming liability for maintaining such archives. Prudent photographers keep backups on external magnetic drives, as well as on optical media and, if possible, also keep duplicate backups offsite.

UPDIG Guidelines: Supplemental Information

Monitors

Computer monitors must be calibrated and profiled before they can be part of a professional workflow. Accurate monitor calibration and creation of a display profile requires a hardware device, such as the GretagMacbeth Eye-One, Color Vision Spyder2, or Monaco Optix XR. Another useful tool is a Profile Verification Kit. This is a digital file with an accompanying proof or print. After profiling your monitor, you view a comparison between the digital file displayed in Photoshop (or other professional-imaging software), and the proof print, as viewed under 5000K/D50 lighting, to indicate whether your monitor profile is accurate.

There are two types of display technology in use today: cathode ray tube (CRT) and liquid crystal display (LCD). CRT displays are rapidly being replaced by LCD monitors. In fact, professional-grade CRTs are no longer being made.

  • CRT monitors should be calibrated before they are profiled since they have hardware controls that affect the RGB amplifiers as well as controls for black level and luminance. The hardware device and software are used first to adjust the RGB guns to the desired white point (color temperature) and black point (if available on your display system), and then the calibrated CRT is profiled. The display profile is then used by color-savvy programs such as Photoshop to display accurate color.

  • LCD displays often only have brightness controls, although some also have a contrast control. Some LCDs have color temperature controls; however, they actually only adjust the CLUT (color lookup table) and, if much different from the native color temperature, can cause reduced color gamut and banding. For that reason, when profiling an LCD, it is best to adjust only the brightness control and contrast control, and let the profiling device set the desired white point through the display profile.

  • DDC (direct digital communication) allows for the brightness, contrast, white point, and gamma to be adjusted through the profiling device and software. This will save time and improve precision when calibrating and profiling monitors. When shopping for a new monitor, it's best to choose a DDC-compliant display, if possible.

In choosing white point and gamma settings, the whole concept of monitor calibration and profiling is to create a situation where the image on your monitor is a close match to the image as a print, a proof, a press sheet, or if your work is destined for the Web, as viewed on the average uncalibrated PC or Mac monitor. The white point may range from 5000K (more yellow/red) to 6500K (bluer), and the gamma may vary from 1.8 to 2.2. The luminance may vary from 80 cd/m2 to 140 cd/m2. There is not a single standard for white point, gamma, or luminance because there is not a single standard for what you are trying to match. If you are working in prepress, you will want to match press proofs and press sheets. For this, you may find that a white point of 5000K or 5500K and a gamma correction of 1.8 will give you the best match of monitor to proof or press sheet as viewed under a 5000K light or booth. The appropriate luminance may be around 100 cd/m2. If you are preparing files for ink-jet or light-jet printing, you may find that a white point of 6000K or 6500K will give you the closest match, although you should always view the prints under the color temperature of the lighting that will be used to view them. One reason that a higher (bluer) white point often works best for display prints is because optical brighteners are often used in display print media. Once again, monitor luminance should be chosen to match the appearance of the display prints in the viewing condition. The gamma correction (1.8 lighter, 2.2 darker) should also be evaluated with the viewing conditions and the contrast characteristics of the printer in mind. Image files being prepared for the Web should be prepared to the sRGB standard gamma of 2.2, and a white point of 6500K. This will be a compromise between the uncalibrated Mac gamma standard of 1.8 and the uncalibrated PC standard of 2.4. It is also a reasonable compromise between a prepress monitor calibrated to 5000K, and an uncalibrated PC monitor, which may be in the 7300K9300K range.

For native white point, there is a good argument for keeping things simple with the current crop of LCD monitors, and simply profile using native color temperature, and native gamma, and letting your eyes adjust to the difference between the monitor and the print/proof. The strength of this argument is that using this method will ensure that you get the widest dynamic range the monitor can produce, and also minimize artifacts, banding and posterization, which can occur the farther you force a monitor (especially an 8-bit monitor) from its native white point and native gamma. If you do choose a custom white point and gamma, it is a good idea to evaluate the resulting profile with a utility such as those found here:

  • http://www.drycreekphoto.com/Learn/Calibration/monitor_black.htm

  • http://www.drycreekphoto.com/Learn/Calibration/monitor_gradient.htm

There are more choices than gamma 1.8 and 2.2. Some calibration software allows you to choose a custom gamma. Other software allows you to edit the gamma curve, and one software, ColorEyes, has something called L* gamma, which is unique to that software. L* creates separate tonal curves for the shadow areas, midtones, and highlights, providing smoother transitions, and therefore more accurate color reproduction (http://www.integrated-color.com).

The current LCD technology uses a white fluorescent backlight. NEC has produced a new type of LCD that uses red, green, and blue LEDs (light-emitting diodes) that combine to produce a white backlight. The advantages are a wider color gamut, greater dynamic range, and the ability to adjust the white point without compressing the color gamut. NEC offers a white paper that explains this new technology and its advantages (http://www.necdisplay.com/corpus/S/6/LCD2180WG-LEDTechPaper_121605.pdf).

Working environment is critical. No matter how good your monitor or how well you have it calibrated and profiled, you must take care that your working environment is subdued neutral lighting that does not vary throughout the day. Your computer desktop should be set to a neutral gray, and you should avoid having areas of bright color within your field of vision, or reflected in the monitor.

Cameras

Professional digital cameras have selectable color spaces. Photographs intended for print should be captured in a wide-gamut space, such as Adobe RGB (1998). Photographs intended only for the Web can be captured in the narrower-gamut sRGB color space. It is possible, but not strictly necessary, to create custom camera profiles. When such profiles work, they can speed workflow and yield more accurate colors. Adobe's Camera Raw program allows for calibration of a digital camera, creating in effect a custom profile.

It's essential that a photographer choose the correct color profile when capturing JPEGs or TIFFs, because the camera will process images into these formats using the specified profile.

Capturing images in a RAW file format offers post-production flexibility to create the best-quality images.Photographers capturing RAW files can choose color space, white balance, and to some extent, exposure value (ISO speed setting) after the capture via the image-processing software. In addition, many RAW processors have sizing algorithms that (some say) are superior to interpolation in Photoshop, since they are working with the RAW datathe actual pixel data captured by the camera's imaging sensor. RAW files also offer more bit depth than JPEG files, allowing more aggressive editing, both in the RAW software and when imported as 16-bit files in Photoshop.

Many camera manufacturers have created proprietary, undocumented RAW file formats. Adobe has offered an open source RAW file format called Digital Negative (DNG). If adopted by camera makers, it would create a standard RAW format that would simplify access to older RAW files as we move into a future of changing software and filing systems. A good first step would be for camera makers to provide open documentation of their RAW file formats. In the meantime, many photographers are converting proprietary RAW files to DNG format before archiving.

Digital cameras and digital-imaging software programs are evolving rapidly. Signal-to-noise ratios continue to decrease, yielding cleaner, higher-quality files at a given megapixel rating. Interpolation algorithms are improving. This makes it unreasonable to specify a certain megapixel rating as a minimum standard tied to any given file size or printed output size.

Scanners

Scanning software, like that for digital cameras, allows a choice of color space for the resulting files. A wide-gamut space for print (such as Adobe RGB) and the smaller sRGB color space for web are the standards. In addition, a scanner should be profiled for maximum color accuracy.

Print or proof-viewing area

The ideal standard is a viewing booth with a dimmable D50 light source. Alternatives to a viewing booth are halogen lights rated at 4700K or 5000K, or full-spectrum fluorescent lights rated at 5000K. A Profile Verification Kit includes a print that incorporates a GATF RHEM light indicator, which indicates whether your viewing area is D50. The inside-back cover of Real World Color Management by Bruce Fraser, Chris Murphy, and Fred Bunting (Peachpit Press) also has a GATF RHEM light indicator.

Professional digital color labs

Most professional digital color labs that do have an ICC workflow usually require sRGB as the color space to send to their RIP or other printer software. A few labs will work from Adobe RGB files, so it is best to ask before submitting files. Those labs that offer custom profiles provide them as "soft-proofing" profiles only, since they update their actual profiles on a regular basis, when they change chemistry, paper batches, or software versions.

Consumer photo lab digital printers

There is a free database of ICC printer profiles for digital labs worldwide at the Dry Creek Photo site (http://www.drycreekphoto.com). The printers covered include Fuji Frontier, Noritsu, Agfa D-Lab, LightJet, Durst, and Chromira printers, among others. Because these printers do not recognize embedded profiles, it is necessary to convert your files to their profiles, and then save them with the profiles embedded. Converting to these profiles will give you the best color fidelity and allow you to soft-proof your digital files before committing them to print. Labs that don't use profiles usually require that submitted files be converted to sRGB. To avoid confusion on your end, it's still best to include the embedded profile, even if the lab will ignore it. Using the sRGB color space instead of a custom profile may yield less accurate color that doesn't take advantage of the full gamut such printers can produce.

Offset printing

We strongly recommend that all offset printers adopt the ICC standards. Currently, there is tremendous variation among offset printers, and nothing can be taken for granted. For many years, offset printers used a "closed loop" color management approach. They scanned film on drum scanners with software that output directly to CMYK. The CMYK was targeted to a proofing device, the customer approved the proof, and the press was adjusted until its output matched the proof. Color profiles were built into the workflow, not applied to files. This meant printers could not offer custom CMYK profiles for digital files created outside their shops.

Today, with 60 to 80 percent of images intended for print arriving as digital files, offset printers are moving away from the closed-loop workflow. A single printed piece often includes digital image files from many different sources. It is increasingly likely that an offset printer will have a CMYK profile that describes its proofing device's color space. As a general rule, an offset printer can match the output of its proofing device.

Two organizations in the United States have produced standards for the printing industry that would allow for standardized CMYK profiles. They are the SWOP Committee (Specifications for Web Offset Publications), covering web presses, and GRACoL (General Requirements for Applications in Commercial Offset Lithography), which covers sheet-fed printing. The two standards, SWOP TR001 and GRACol's DTR004, if widely adopted, would do away with the need to worry as much about custom CMYK formulas.

Outside of the U.S., organizations such as The European Color Initiative are working to support similar standards, such as ISO 12647.

When a photographer has the expertise, it's best to provide the printer with CMYK image files embedded with the printer's custom CMYK profile. If the printer does not have a custom profile, it's best to consult with the printer or the client's production expert to determine the best color space for the delivered files. A standard Photoshop CMYK profile that matches the general press conditionssheet-fed coated or uncoated, or web coated or uncoatedmay suffice, particularly if the printer adheres to SWOP or GRACol specifications. In this period of flux, communication is key.

Many times, digital image files must go to several different printers, or a project is photographed and delivered before a printer has been chosen. In such cases, it may be best to deliver RGB master files. These should always have an embedded RGB profile to ensure accurate color when they are converted to each printer's specific CMYK profile.

Send RGB image files (especially Adobe RGB) to a printer only if the shop has experience converting RGB files to CMYKand then only if the printer will provide a random or contract proof. If a printer has a clear understanding of ICC profiles and requests RGB, it's best to submit files in Adobe RGB or, possibly, the narrower-gamut ColorMatch RGB. If a printer cannot ensure preservation of the embedded profile before converting to CMYK, it is better to provide files converted to a general-purpose CMYK or RGB profile, such as SWOP Coated V2 CMYK, ColorMatch RGB, or sRGB, with the appropriate profile embedded in the file.

Besides color profile issues, perhaps the biggest stumbling block to quality reproduction is inappropriate file resolution. Some digital cameras produce a native file at x inches high by x inches wide at 72 ppi. This sometimes results in printers receiving files of the correct height and width, but at 72 ppi. This mistake is so common that printers have a mantra that all files need to be 300 ppi when the image is sized to the final height and width to be printed. This can be used as a rule of thumb, although if you have good communication with a knowledgeable printer, you can use the more sophisticated standard of 1.3 to 2.0 times the halftone screen ruling (lpi) for the job.

RGB master files

RGB master files are Photoshop (PSD) or TIFF files, optimized in a wide-gamut color space (such as Adobe RGB or ProPhoto RGB), at either at the digital camera's native file size or interpolated to a larger size (consistent with any possible future use) by a RAW file conversion program. They should be left unsharpened or sharpened only on a removable layer, since resizing for future uses is likely. Master files should be archived along with the RAW files for a project.

Ink-jet and dye sub printers

You can easily bring desktop and wide-format printers into a color-managed environment with the help of profiles. If working with the manufacturer's printer driver, turn off all color management and print a copy of the color target file. Next, measure the printed target with a spectrophotometer to generate a profile for accurate output on a particular paper or other medium. Repeat this process for each paper stock you use. Most RIP (Raster Imaging Processor) software offers profiles for a wide variety of papers. Many RIPs will also allow use of custom profiles.

Guide prints

Profiling a desktop printer is critical for photographers who include digital guide prints with their digital filesa key part of these guidelines. This is particularly true with CMYK files submitted to an offset printer. Unless using a SWOP-certified proofing system, photographers should include disclaimers stating that guide prints are for color reference only and are not "contract" proofs.

Since ink-jet guide prints made from RGB editing spaces may have wider color gamuts than available from an offset press, a guide print will more accurately reflect what is possible to achieve on an offset press if it is "cross rendered." Cross rendering involves printing from your current output color space through an intermediate output color space to simulate the appearance of the final output space. For example, in the print dialog, the "source" space would be either the CMYK file or the CMYK proof space. Choosing Relative Colorimetric as the rendering intent will limit a desktop printer's color gamut to the gamut of the CMYK file. If you use Absolute Colorimetric (or check the "simulate paper color" box in Photoshop CS2), you may more closely simulate the actual press sheet, since the whites will more closely match the duller white of the actual press stock.

Photoshop's settings for cross-rendering a print can be found in the Print With Preview dialog. Note that Photoshop CS1 does not have the "simulate paper color" checkbox.

A guide print should not be confused with or referred to as a "proof." That term refers to a "random" or a "contract" proof, provided by an offset printer or prepress house, and created from the actual films or plates used for press output. Direct-to-plate workflows create proofs with special printers, calibrated RIPs, and special proofing media to closely simulate the actual press conditions. "Contract proofs" are considered guarantees by printers (or prepress houses) that press sheets will match the proofs.

A SWOP-certified proof provides additional precision when indicating the color of digital files delivered to an offset printer. SWOP-certified systems combine RIP software driving special proof printers. More information on SWOP-certified systems is available.

Workflow

No single workflow suits all photographers or all clients. The ideal workflow should provide the best combination of quality and services to fit a client's budget and needs. Because digital photographic imaging is relatively new, photographers must regularly explain to clients the trade-offs between quality and cost in different workflows.

A film-based workflow is simple. Photographers deliver film, designers or art directors decide how pictures will be used, and offset printers and prepress houses handle conversion of the film to printing plates.

Digital cameras, along with scans from film by photographers and agencies, are now replacing film workflows. While clients have been quick to embrace the speed and convenience of digital capture and delivery, they do not universally understand what is required to achieve the same quality levels that they used to expect from film. With the exception of those involved in high-volume, quick-turnaround workflows, most photographers must decide how to handle file preparation. Some photographers want to avoid the distraction of file preparation. Others have embraced it, because it allows powerful control over the reproduction of their images. Profiles and soft proofing allow photographers to see how their files will look as display or press prints. Looking at soft proofs on their calibrated monitors, those who embrace file preparation can deliver to printers files that will accurately (if not precisely) reproduce on paper the optimized image files the photographers see on their monitors.

When you send an RGB file to an offset printer, the biggest risk is that a prepress worker will open it in the wrong RGB color space, altering the color, and then lock in the mistake by immediately converting the file to CMYK. If the printer receives an untagged RGB file, and there has been neither communication with the printer nor the inclusion of a ReadMe file that indicates the color space of the files, prepress will probably open the file in the shop's default RGB space, which may or may not be the space in which the file was optimized. Even when an image file is correctly tagged and its profile preserved when it's opened, there may be problems if a printer uses a RIP for CMYK conversion. Most RIP software does not use black point compensation, and without it, some conversions can appear flat and unsaturated (muddy).

FOR MORE VALUABLE UPDIG INFORMATION

The material here has been excerpted from the UPDIG Guidelines version 1.0. (September 2005). For the most recent version, please check www.updig.org. UPDIG members include:

  • Australian Commercial and Media Photographers

  • Advertising and Illustrative Photographers Association (NZ)

  • Association of Photographers (UK)

  • Advertising Photographers of America

  • American Society of Media Photographers

  • American Society of Picture Professionals

  • Canadian Association of Photographers and Illustrators in Communication

  • Editorial Photographers

  • International Digital Enterprise Alliance

  • Museum Computer Network

  • National Press Photographers Association

  • Picture Archive Council of America

  • Picture Licensing Universal System

  • Professional Photographers of America

  • Stock Artists Alliance





Practical Color Management. Eddie Tapp on Digital Photography
Practical Color Management: Eddie Tapp on Digital Photography
ISBN: 0596527683
EAN: 2147483647
Year: 2006
Pages: 61

Similar book on Amazon

flylib.com © 2008-2017.
If you may any questions please contact us: flylib@qtcs.net