Why Color Management Is Important to Graphic Arts Workflow

Digital Photography for Graphic Communications

Chapter 4 • Color Direction

How can you get consistent color from camera to monitor to print? Shouldn't color match by itself? The advent of desktop publishing in the 1990s enabled users to connect diverse "plug-and-play" color peripherals, including cameras, monitors, and printers. Although standards accept helped create uniform colour, one device does non necessarily "know" about the others or the manner they save, evidence, or print color.

One standard that has helped overcome device color differences is the International Colour Consortium (ICC) profile format, which characterizes devices by relating their color to a mathematical model of human being vision. Color profiling is a swell solution to the quest for closely-matching color but can be a challenge to set.

The purpose of this chapter is to help users understand the concepts behind color management. To implement a system, help will undoubtedly be required from systems and peripherals vendors.

ICC profiles capture the colour reproduction characteristics of each device using an industry-standard file format for both Windows and Macintosh computers ( Figure iv-i ). These profiles can be read by ICC-compatible photo-editing, illustration, page-layout, web-blueprint, and web-browsing programs as well as the drivers and raster paradigm processors (RIPs) that control printers.

When because workflow, keep in heed that the goals of using colour management in a digital workflow are to have:

• accurate, consequent color from the original scene, photographic print, or transparency to final output (printed or displayed).
• accurate monitor previews of the original file, terminal output, or proof.
• proofs that simulate press sheets or production printers.

Figure 4-ane. Standard Working Spaces. These diagrams in the CIE xyY chromaticity diagram compare the color gamuts of Adobe RGB and sRGB standard RGB working spaces with those of a color scanner (could also be a digital photographic camera) and a web outset printing press such as would be used to print magazines and catalogs.

The Source-Destination-Simulation Model

The to a higher place workflow objectives are facilitated by four types of ICC profiles:

• source contour—This profile describes the color space in which the image was created or currently exists—more often than not a scanner or camera profile. It could also be a standard working infinite profile. Ideally, all images with a scanner or photographic camera contour should exist converted to a standard working space, and the standard working space profile should exist embedded into files, so users can place it down the line. If you or your customer don't know what standard working infinite was used, you won't be able to get matching color.

• standard working space contour—A standard working space is a place to store data until you know what you desire to exercise with it (display, proof, impress, or archive information technology). Adobe Photoshop and other applications support several standard RGB working spaces, including (from largest to smallest) Adobe RGB, ColorMatch RGB, and sRGB. Most content creators today use the largest, Adobe RGB. Users with CMYK workflows can utilise one of Adobe'southward standard CMYK working spaces, such every bit U.Due south. Sheetfed Coated or U.S.  Web Coated (SWOP). Of these Sheetfed Coated has the larger gamut, merely SWOP is more common. SWOP (Specifications for Web Kickoff Publications) was the showtime colour specification developed.
• destination contour—This profile describes the device or procedure to which the file will be output. The destination could exist a color monitor (for brandish), an inkjet printer (for proofing), or a production printer (for final output).
• simulation profile—This profile describes the device or process that the image should wait like when proofed. When proofed on a small inkjet printer, for example, the simulation profile would be that of the production printer.

The role of the 4 profile types can exist seen in the workflow illustrated in Figure 4-2 . To follow the workflow, think of color image files as "on the motility" from a source (e.g., camera, file) to a destination (monitor, printer, proofer). Each step is represented past a contour. "Assigning" profiles to a file indicates what device it came from, while "converting" changes the color to friction match on an output device.

Figure 4-2. Workflow illustrating the source-destination-simulation colour model. A digital camera file (A) can be converted from a digital camera contour (DCP) to a standard working space profile (represented by the CDs), then converted for output to a monitor contour for display (B), a proofer with simulation of the terminal output, and a printer (C).

Let'south Start with the File . . .

To apply color management effectively in a workflow, the standard file types (TIFF, JPG, PDF, EPS, etc.) you're press should be in i of the manufacture-standard color working spaces, such equally Adobe RGB, sRGB, or SWOP CMYK ( Figure 4-3 ). A standard working space is an ICC profile that has been standardized and is the same for all ICC-uniform applications. Information technology is a place to store colour data until you know what you want to do with information technology, such as print information technology or display information technology.

Figure four-3. A standard working infinite profile is the starting point for a proficient color-managed workflow. This profile acts similar a nametag for the file, identifying its color space for proper matching. This example shows an EFI Fiery RIP'southward setting for default input profile. This profile is assigned to images that don't have an embedded ICC contour.

You will need to cull whether to use an RGB or CMYK working space (see Figure 4-1 ). RGB working spaces generally provide larger colour gamuts than CMYK. They give the greatest color saturation or "pop." Customers may submit files in CMYK, though. In either case, the standard working space profile should be embedded in the image. Embedding the contour doesn't add together much to the file size, and it enables anyone who receives the file to friction match the color on output or brandish, as long as they have an authentic output profile.

If the standard working space profile isn't embedded in the image, virtually workflow applications enable you lot to specify a default source contour (see Effigy iv-3 ). If a customer submits a file without an embedded standard working space profile and you don't know what profile they used, it's best to contact the client and ask. Otherwise, you'll have to cull a contour and the color may non match the customer'south expectations.

Where Did the File Come From?

Photos to be printed may take been scanned, captured with a digital camera, or licensed from an image banking company. Epitome bank photos should have an embedded standard working space profile. To properly start a color-managed workflow, scans and captures should be done with a profiled scanner or photographic camera. If the driver supports ICC profiles, you lot'll be able to assign the profile to images or convert them to a standard working space upon saving. If your scanner or photographic camera driver doesn't back up ICC profiles, you can still profile the device, so assign the profile in Photoshop using the control Edit > Assign Profile ( Figure 4-4 ). (Assign indicates the color space where the epitome came from, or its source; versus Catechumen to, which indicates where it's going, or being output.)

Figure 4-4. Photoshop'south Edit > Assign profile can be used to identify the source profile of a scanned or digitally-photographed paradigm if the scanner or camera driver doesn't support input profiles.

To streamline your workflow, convert all images from the scanner or camera input profile to a standard working space profile. This places all of your images in the same colour space. An exception might be for fine-art photographers or anyone who handles all files in-house and wants extreme colour accuracy. These users may desire to avert the slight inaccuracy of an additional color conversion by leaving images in thecolor space of the scanner or photographic camera profile. Every bit long as the contour is embedded in the prototype, the RIP volition exist able to read it and employ information technology for color matching.

Where is the File Going?

When printed, files volition be output to a printer using an awarding RIP. ICC-compatible RIPs enable the selection of an output contour ( Figure 4-5 ). This profile volition be specific to the printer, ink, newspaper or media, and RIP settings (such as resolution and dot pattern). Selecting the proper printer contour ensures that your images will match the original file as closely equally possible. Using a printer profile alone does non guarantee a match to the monitor, but rather to the original file.

Figure 4-5. Software RIPs, such as EFI Fiery, used with large-format inkjet printers and computer-to-plate platesetters enable selection of an output contour that characterizes its impress characteristics.

Soft Proofing

Before printing images, yous may wish to preview them on the monitor. Soft proofing tin can exist done in an ICC-compatible application or RIP. Most RIPs support color-managed monitors for accurate previewing. To accurately preview files on the monitor, yous will need to accept a calibrated monitor and monitor profile. If the RIP supports monitor profiles, it will catechumen color from the standard working space profile to the monitor contour. This shows that "what you lot meet is what's in the file" (WYSIWIF). If the RIP supports soft proofing, it volition convert color from the standard working infinite to the monitor profile, using the printer profile equally a reference or "simulation" profile ( Figure four-6 ).

Figure 4-6. Simulation contour in EFI's Peppery RIP. The simulation profile enables an inkjet proofer to print colour that looks like information technology came from a lithographic press printing to GRACoL specifications. (GRACoL stands for General Requirements in Applications of Commercial Offset Lithography.)

Printing with Profiles

If you use a digital camera, chances are you may print images using a large-format inkjet printer. These printers have become many photographers' "digital darkrooms." Inkjet printers typically work with computer based raster image processors known as software RIPs. A raster epitome processor (RIP) converts files from vector- and/or bitmapped format into a device-specific bitmap that controls the imaging of inkjet ink spots, prototype carrier halftone dots, or other output reproduction imaging processes.

Many RIPs used in big-format inkjet printing can be used to print private graphics straight from files. For document production, information technology is more than mutual to print to a RIP from an application.

Printing Directly from a RIP with Colour Management. When printing files past opening them in a RIP, the files should have an embedded source profile, or the profile should be identified in the RIP as the default source profile. Choose the correct output profile for the media, ink, printer, and settings (See Figures 4-iii and 4-five ).

Printing from Applications with RIP Colour Management. When press to a RIP from applications, there are three places to set color management profiles: the application, the RIP, and ICM (Windows) or ColorSync (Apple tree). Only 1 conversion should be set to avoid multiple colour transformations. To print a file from an awarding using RIP color management, ensure that the file is in a standard working space, as would a file that is to exist printed directly from the RIP. In the application, set the output profile to "Printer Manages Color," as shown in Photoshop ( Figure 4-7 ) as an instance. This will transmit the file to the RIP with color unchanged, saving the color conversion for the RIP. Second, your RIP may create a Windows printer for each device you lot apply. Windows printers have settings for Microsoft's Integrated Color Management (ICM). If activated, the ICM settings could cause a double color conversion. To avoid this, set Windows ICM to "Application Managed Colors" or "ICM Disabled."

Effigy 4-seven. When printing to a RIP from an application, turn off color management in the awarding by selecting (in this case with Photoshop) "Printer Manages Colors." This passes the file unchanged to the RIP, where colour conversion for accurate output matching takes place.

Printing from Applications without RIP Colour Direction. ICC-compatible applications can print with color matching by converting images from the standard working infinite profile to the printer contour. Using Photoshop equally an instance, in the Print dialog box, select Color Handling > Photoshop Manages Colors and Printer Profile > [select the ICC contour for the printer]. To print to a proofer with simulation of a terminal output device, alter Normal Printing to Hard Proofing. Select the proofer profile in the Printer Profile popup and select the device to simulate in the Hard Proofing > Proof Setup popup.

RGB and CMYK Workflows

Apple tree Calculator discusses dissimilar graphics workflows to use with ColorSync (www.apple.com/colorsync). They coined the terms "tardily-binding" and "early-binding" workflow, referring to the signal where yous "bind," or commit, files to the colour gamut of the printer ( Figure 4-8 ).

Tardily-binding workflow captures, edits, and submits files in RGB style. The service provider then converts files to CMYK using a printer profile. The advantage is that it preserves images' maximum colour gamut until output. This is helpful in getting the best color on different printers, and in repurposing output from impress to web or CD or cantankerous-media publication.

Early-bounden workflow captures images in CMYK, either straight from the scanner or camera, or past converting in Photoshop to a CMYK standard working space profile or printer profile. Its reward is that editing is done in the printer'southward profile, so that the preview more than closely approximates the printed image.

Figure iv-8. Early-binding (carmine) and tardily-bounden (royal) workflows differ as to the point in fourth dimension when the color gamut of files is bound to that of the final output device or procedure. Late-bounden workflow keeps documents in standard color working infinite, preserving the maximum color gamut until converting them to the output device profile at the fourth dimension of printing. Early-binding workflow converts files to the colour gamut of the output device as shortly as possible after capture.

Colour Rendering Intent

Because various imaging devices—scanners, cameras, monitors, and printers—work in different ways, they may non exist able to create the identical range of colors. I reason users are sometimes disappointed in color output is gamut limitations. The gamut is the range of colors reproducible by a device. A device's color gamut is recorded in its profile. RGB-type devices, such every bit scanners, cameras, and monitors, generally accept larger color gamuts than CMYK devices, which include near printers. The chief reason is that RGB devices create colour with lite, while CMYK devices create color with ink on paper.

As images are passed into and out of the profile connection space for "matching," they may be sent to a device with a smaller color gamut. In such cases, color management must bargain with out-of-gamut colors.

Color rendering attempts to find replacements for colors that cannot exist printed. The ICC recognizes four standard color rendering intents: perceptual, relative colorimetric, absolute colorimetric, and saturation.

All rendering intents move out-of-gamut colors within the gamut of the output device. Perceptual rendering scales in-gamut colors to "make room" for out-of-gamut colors. This is more likely to alter colors in the original, but preserves the distinction betwixt colors. Perceptual rendering is used for photographs, which generally contain a broad variety of colors and a diverseness of gradations ( Figure 4-9 , pencils photo).

Colorimetric rendering does not scale in-gamut colors. Thus an out-of-gamut color may be rendered to the aforementioned value as an in-gamut colour, and so that the two colors will no longer be distinguishable. Colorimetric rendering is used for files that contain relatively few and solid colors, such equally logos or PANTONE® colors ( Figure 4-9 , Ryerson logo). Accented colorimetric rendering does not scale the white point of the file, while relative colorimetric rendering does.

Saturation rendering makes images more than colorful by moving in-gamut colors to more than saturated values. Saturation rendering is used mostly for business graphics, where an impact is more than important than color accuracy ( Figure iv-9 , graph).

Figure 4-9. Color rendering intents used for various types of photos: perceptual rendering (pencils, left), colorimetric rendering (logo, upper correct), and saturation rendering (business concern graphic, lower correct).

Making Profiles

Photographic camera Profile

A digital photographic camera profile (DCP) tin be used in shooting camera raw to become a closer match to an original object or scene. X-Rite's free ColorChecker Passport application takes a camera raw capture in DNG format of the MacBeth ColorChecker 24-patch target and creates a DCP profile that tin can be selected in Photoshop'due south Photographic camera Raw plugin > Camera Calibration tab. Information technology should be noted that a DCP profile is not an ICC profile as it is more than tricky and merely useful for specific applications such as fine-art photography, where accurate color matching is a must and digital images are captured in a controllable and consistent environs.  (DNG, or Digital Negative, is Adobe's universal raw format. Proprietary formats like Nikon NEF, Canon CR2, Sony ARW, and others can exist converted to DNG with Adobe's free Digital Negative Converter software.).

1. Ready the photographic camera to capture camera raw.
2. Set exposure (ISO sensitivity, lens aperture, and shutter speed) and white balance using an 85% greyness carte.
3. Capture a 24-patch MacBeth ColorChecker target and save in DNG format by selecting this format in the camera'south settings (if available) or using Adobe Digital Negative Converter.
4. Elevate-and-drop the DNG file of the ColorChecker target into the ColorChecker Passport interface, name the profile, and save.
5. To bank check the quality of the profile, open the ColorChecker target file in Photoshop, select Photographic camera Calibration in the Camera Raw plugin, and select the profile yous made. Note the difference in color ( Figure 4-10 ).

Effigy 4-ten. Photo with (right) and without (left) a digital camera contour.

Monitor Profile

A monitor profile ensures that the on-screen brandish matches the color of the original file as closely every bit possible. Depending upon the operating system, a monitor profile may be gear up automatically or, if not, may be chosen in the display settings or preferences. The monitor profile should not be used every bit a standard working infinite contour because the standard profile should exist one that anybody has admission to. Making a monitor profile requires a color measurement musical instrument capable of measuring emitted color, and a uniform profiling application. Effigy 4-11 shows an X-Rite i1 Pro instrument in the process of calibrating a monitor and making an ICC profile. Earlier making a monitor profile you will accept to choose a quantitative contrast level, known as gamma (usually i.80 or 2.twenty, higher is more dissimilarity), and white point, or grey level (usually 5000–6500 K, college is bluer).

Effigy iv-11. A monitor profile beingness fabricated with an 10-Rite i1 Pro 2 emissive/cogitating instrument and i1 Profiler software.

Printer Profile

Making a printer profile requires an instrument that tin can read reflective color, forth with a compatible awarding. Semi-automated and automatic instruments make it easier to read the hundreds of color patches necessary to narrate a printer. Instruments like the 10-Rite i1 Pro ( Effigy 4-12 ) browse rows of patches and require the operator to move the instrument from row to row. These instruments are referred to as x-scanning or semi-automated. Instruments like the X-Rite iSis ( Figure 4-xiii ) that read an entire printed target autonomously are called x/y-scanning or fully-automatic.To brand a printer contour, commencement print a colour test chart with color management turned off ( Figure 4-fourteen ). And so read the nautical chart with an instrument and uniform profiling application and save the profile.

Figure 4-12. A printer profile is made with X-Rite i1 Pro, or hand-held, musical instrument.  Using the plastic mounting base, the operator volition manually move the musical instrument beyond the colour patches row then move it to the next row to continue scanning the examination target.

Figure 4-13. A printer profile is made with an i1 iSis x/y-scanning, or fully-automated, instrument. The musical instrument reads the set of 800 patches unattended in about 4 min.

Effigy 4-14. When printing a color test nautical chart for printer profiling, exist sure to turn off color direction in the impress driver or RIP. In this case printing to an HP colour light amplification by stimulated emission of radiation printer, the CMYK color has been set up to "Default CMYK+," which is the largest color gamut of which the printer is capable of reproducing. Other settings emulate Northward American, European, and Japanese press specifications and would not be as colorful.

Summary

The graphic arts are notorious for existence concerned with colour and not dealing with it properly at the same time. Because of the number of devices and color modes that a file goes through, a system needs to be implemented to go on color accurate and consequent. ICC profiles are manufacture standard files for capturing color information virtually a file. Substantially, when done properly what y'all typically first preview on a computer screen, volition be similar to what you achieve with the final print. In print production, nosotros are moving from a larger (RGB) to a smaller (CMYK) colour gamut. Seeing that the gamut is being limited downstream, the result is usually less pleasing colour in the final print (less saturated). Often we choose to either stay in RGB for as long as possible to accept more colors to play with or immediately motility to CMYK to amend represent the end results. Either style, ICC profiles piece of work to mimic the images final output and so that color is more than predictable.

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Source: https://pressbooks.library.ryerson.ca/digitalphotographyforgcm/chapter/chapter-4-%E2%80%A2-color-management-reem/

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