Tech Talk: Creating a Proofing Workflow

KEY TO SUCCESS

Contractor: Rich Adams

Project: Proofing

Key to success: Show customers prints from a low-cost, easy-to-operate printer that exactly matches the output of your expensive production printer.

In the last two parts of our Digital Basics series we looked at color management for monitors and printers, respectively (see S&DG, “Tech Talk,” Jan. and March issues, 2010). We saw how a color-profiled monitor provides a true “window” on an otherwise invisible digital file, but doesn’t necessarily show how it will look when printed. We also saw how a color-managed printer can match the original file as closely as possible. So what’s missing to get the monitor to look like the printer? A proofing workflow!

One reason ICC-based color management became so popular is the ability to get proofs that match press sheets. Proofs are single (or a few) copies of color separations (known as scatter proofs) or pages (page proofs) that will be printed, usually by offset lithography. Proofs can be design or concept pre-proofs used by designers to get an overall feel of documents, or contract proofs that the customer signs to indicate acceptance of color.

In traditional printing systems, proofs are important because traditional presses are expensive, require specialized training to operate, and are usually tied up with production printing. It’s not cost-effective to print one or several copies for approval on a press that requires several dozen sheets of paper just to get the color adjusted correctly.

PROOFS IN DIGITAL PRINTING?

Do you have a printer that’s more expensive than most? Does it require specialized training to operate? Does it take a long time to set up? Is it tied up with production most of the day?

What if you could show customers prints from a low-cost, easy-to-operate printer that exactly matches the output of your expensive production printer? What if you could get accurate monitor previews? What if the customer could get previews in his or her shop? Enter, the ICC proofing workflow!

ACCURATE COLOR PROOFS

Color-managed workflow uses a source-destination-simulation workflow. Color files come from a “source,” such as a digital camera, scanner, or (in the case of preexisting files) a standard working space. In workflow, the files go to “destinations,” such as monitors, printers, or proofers. And finally, the ICC adds “simulation,” a third element for the workflow. Simulation means that when files get to the destination, they look like files from something else. In other words, prints from a small inkjet printer could look like those from your expensive production printer. And likewise, a monitor preview could look like output from the printer. The setup is easier than you might think.

WHAT YOU NEED

Let’s assume that you have a large digital printer that is used for imaging signs, posters, banners and similar prints. To set up proofing, you will need the following:

A small inkjet printer, such as an Epson, HP, Canon, or similar printer. When purchasing the proofing printer, consider the size of documents you want to proof. Do they need to be actual size, or will smaller-sized desktop versions suffice?

Proof media that matches the whiteness, brightness, and gloss of your production media as closely as possible, providing a realistic simulation of the actual print.

A workflow program such as Adobe Photoshop, or a RIP to drive the printer. Almost all RIPs today use the ICC profiles and the simulation workflow necessary to match color on the proofer to that of the production printer.

ICC profiles for the standard working space in which your documents are stored, for your production printer and for your proofer. Printer and media profiles may be available free from the manufacturers. If not, you may need to make them using a color measurement instrument and a color profiling program.

COLOR PROFILES

Inkjet inks have color characteristics much different from those of industry-standard lithographic printing inks. The color match you get with an inkjet printer is highly dependent upon the proper use of accurate ICC color management profiles. For the close color match you want for final comps or contract proofs, you’ll need four profiles:

Proofer profile—This is an ICC profile for your inkjet proofer. It should be made with the same ink, media, and RIP (or driver) you use to make proofs. Your printer or media manufacturer may offer free profiles on its Web site or on a CD that comes with the printer. If not, you’ll need a color measurement instrument and application capable of profiling printers.

Printer profile—This is an ICC profile for the production printer, the color of which you want to match. Again, depending on the printer, media, and RIP you use, the manufacturer may offer free profiles on its Web site.

Monitor profile—If you’re a designer or photographer, or output technician pre-flighting customer files, you’ll undoubtedly want to proof your work on-screen. For this you’ll need a monitor profile, along with the press profile. You can make a “poor man’s monitor profile” by using a free visual calibration application like Adobe Gamma or Apple ColorSync, but for the most accurate monitor profile you need to use a monitor colorimeter and profiling program.

Figure 1: Standard working space profiles that became available in Photoshop 5 (1998) are standard monitor profiles that are widely distributed and available to everyone. They represent places to store color data until you know what you want to do with it, such as display it or print it. The standard working space profile could be both a source profile (such as when displaying or printing a file) and a destination profile (as when saving a camera or scanner file).

Standard working space profile—A standard working space is a place to store data until you know what you want to do with it (display, proof, or print it). Adobe Photoshop and other applications support several standard RGB working spaces, including (from largest to smallest) Adobe RGB, ColorMatch RGB, and sRGB (see Figure 1). Most content creators today use Adobe RGB. Users with CMYK workflows can use one of Adobe’s standard CMYK working spaces, such as U.S. Sheetfed Coated or U.S. Web Coated (SWOP). Of these, Sheetfed Coated has the larger gamut, but SWOP is more common. SWOP (Specifications for Web Offset Publications) was the first color specification developed.

PROOFING WORKFLOW

Profiles. To use your color profiles for accurate final comps and contract proofs, you’ll need to establish a color-managed workflow that uses the four profiles described above—proofer, printer, monitor, and standard working space. Three terms are used to describe these profiles when used in a workflow:

Source profile—This profile describes the color space that the image is currently in—generally a standard working space profile. It could also be a scanner or digital camera profile. Ideally the standard working space profile should be embedded into files, so users can identify it down the line. If you or your customer don’t know what standard working space was used, you won’t be able to get matching color.

Destination profile—This profile describes the device to which the profile will be output. The destination could be a color monitor (for display), an inkjet printer (for proofing), or a production printer (for final output).

Simulation profile—This profile describes what device the image should look like when proofed. When proofed on a small inkjet printer, for example, the simulation profile would be that of the production printer.

Figure 2: Most RIPs today, such as this ColorBurst RIP, have implemented the ICC workflow and include the “source-destination-simulation” model that enables proofing.

RIPs used for proofing will generally have a place to specify the three types of profiles above (see Figure 2)

RGB or CMYK workflow. The first decision you should make is whether to use an RGB or CMYK workflow. RGB standard working spaces typically have bigger color gamuts than CMYK working spaces, so are good for getting the most color saturation. This is useful for repurposing content, e.g., from print to web. Your company or client may want a CMYK workflow, which will also work but is not going to keep all of the color saturation of the original images.

Soft proofing in Photoshop. To view accurate proofs on the monitor, your viewing program needs to convert color from the standard working space to the monitor profile. Say you want to see how a document in Adobe RGB will look on the printer. Open the document, select View > Proof Setup > Custom, and select the printer profile (see Figure 3). Photoshop will convert color from the standard working space profile (source profile) to your monitor RGB (destination profile) with reference to the printer profile (proofing profile).

Figure 3: Photoshop’s View > Proof Setup dialog box is Adobe’s implementation of the “simulation” profile that enables proofing, both on-screen and when printing.

Printing a proof with Photoshop. To print a proof to your inkjet printer from Photoshop, you will most likely be printing with the manufacturer’s driver. Open the document you want to proof, as discussed in the Soft-Proofing section above. If you haven’t already done so, select View > Proof Setup > Custom, and select the production printer profile (see Figure 3). Then, select Print with Preview. Check Show More Options and select the Color Management popup. The Source Space should be listed as Proof with your production printer profile selected. In Destination Space, select the profile for your proofer.

Printing a proof with a RIP. Most large-format printer RIPs have proofing capability. When printing a proof in the RGB workflow, the application or RIP needs to be set for the standard working space (source profile), the proof printer (destination profile), and the production printer profile of the device to be matched (proofing profile, see Figure 2).

Figure 4: Changing the rendering intent of a proof from relative colorimetric to absolute colorimetric tints the background to match the color of the production paper, if it is not white. Good examples are newspaper ads and fine-art prints made on antique paper.

Rendering intent. One feature of inkjet proofs is that they can be set up to match the color of paper being proofed. If you’re proofing a job for canvas, vinyl, fine-art paper, or other media with a color cast, you can make an inkjet proof on white paper in which the background has been tinted with ink to match the job’s paper stock (see Figure 4). Some customers like background tinting, while others find it distracting. Either way, background tinting is controlled by the rendering intent.

Rendering intent describes the way out-of-gamut colors are moved into gamut with color management. If you use the large Adobe RGB standard working space and want to print on a press using uncoated paper, which has a much smaller gamut (compare the gamuts of Adobe RGB and U.S. Sheetfed Uncoated as shown in Figure 1). To be represented in the print, all of the colors outside the uncoated paper’s gamut must be either lost or moved inside the gamut.

FINAL OUTPUT

For final output, use perceptual rendering, which moves colors relative to each other to maintain their distinction (see Figure 5). For proofing, however, where you’re generally moving from a small gamut to a larger one, use colorimetric intent, which matches colors “by the numbers.” The ICC recognizes two types of colorimetric intent: absolute and relative. Relative colorimetric intent readjusts the white point of the file to that of the substrate, while absolute colorimetric does not. The bottom line is, if you use absolute colorimetric rendering, the proof will be tinted to match the paper of the press, while if you use relative colorimetric, it won’t be tinted.

Figure 5: Four standard rendering intents defined by the ICC are used to bring out-of-gamut (non-printable) colors into the printer’s gamut so they can be reproduced. These include perceptual, relative colorimetric, absolute colorimetric, and saturation intents.

Proofing PANTONE colors. Some inkjet printer RIPs have automatic Pantone calibration for printing spot colors. Depending upon the ink and paper used, some can accurately reproduce 70–90% of Pantone colors. To use this feature, define Pantone colors as named spot colors (not as CMYK or RGB process) and save in EPS or PDF format. The RIP’s lookup table converts named colors to the closest-matching CMYKcm (or other ink set) values based on the color profile selected.

To soft-proof Pantone colors, open the document in Photoshop in LAB mode, set the Proof View to the printer profile, and turn on the Gamut Warning feature. Out-of-gamut Pantone colors will be grayed out (see Figure 6).

Figure 6: Photoshop’s View > Gamut Warning feature grays out out-of-gamut colors that cannot be matched on the printer or monitor. This is a good way to see whether or not Pantone colors can be printed.

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Tech Talk: Creating a Proofing Workflow

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