by Thomas Bachand, ©2002-2005
In no small measure the dot-com crisis is a critical mass of false promises. Key to the computer's success has been the allure of greater efficiencies and the promise of increased productivity and capability. Many of us have reluctantly boarded the bandwagon, determined to bring ourselves in line with our modernizing world. Yet, anyone who has attempted to set up an accounting package or a database of clients knows that when it comes to computers, rarely is there an easy solution. Sticking with a typewriter and an accountant may not have been such a bad idea after all.
Even so, try and find a traditional color printer and you'll discover that the digital imaging train has already left the station. The color fidelity and print control are irresistible. And for those exhausted by the prospect of dealing with inexperience lab help, the ability to bring this subjective process in-house is revolutionary. Be forewarned, though, of the elusive but holy grail of desktop printing - color management.
On the face of it, your typical trade show huckster makes it sound quite simple. Click a button here to make your scan, do an adjustment there, click print, and bingo - a full-color, 8x10 glossy ready to knock the socks off art directors and patrons alike. Begin putting the digital studio together yourself and you discover that in the literal world of computers, we creative humans have created a nightmare of digital complexities.
The difficulties begin with how each device you attach to your computer sees color and interprets it. Scanners, displays, and printers all rely on different technologies. In short, a scanner interprets a transparency or print as a series of dots, assigning each one a color value. The computer's CPU (central processing unit) translates those values to a form your display can understand. Third-party image editing applications, such as Photoshop, allow us to alter those values, translating our changes in real-time to the values posted to the display. Finally, the printer software translates these color values again to produce a reasonable representation of the digital file - all in a perfect world, that is.
Of course, we don't live in a perfect world. All the aforementioned devices have their own gamut, or color space - the physical number of colors the device can interpret. A scanner that can assign 8 bits of digital information to a dot cannot represent color as accurately as one that can assign 16 bits. Likewise for displays (and the video cards that drive them). An image editing program that can handle 16-bit images, such as Photoshop, will make more precise edits than one that clips the file to 8-bit. This is why many imaging professionals work in very large color spaces, such as Adobe 1998 or ProPhoto. Finally, the printer has the herculean task of translating the larger working spaces to the limited gamut of ink and paper.
In addition to the gamut issues, is the one of color bias. From brand to brand, model to model, each piece of hardware has a penchant for some colors over others. Some biases are inherent to the device, others are built in. Print drivers, for example, often increase saturation and contrast to disguise a the printer's limited gamut.
Years ago, as computer chips, graphics applications, and printers became more powerful, it became apparent that desktop publishing would be unsuccessful without reliable color management. With Colorsync Apple Computer tackled the problem head on by providing a system level color interpreter that followed international color standards. Through the management of device profiles Colorsync is able to translate color between devices and applications. A profile not only describes a device's color space but also its bias. For display correction and image manipulation, Apple supported video cards utilize video LUTs (video look-up tables) - three tables (red, green and blue) of 256 possible values by which to describe the color on the display. Display calibration is done by recalculating the video LUT based upon the display's measured output. A secondary video LUT is made available to image editing applications so that display color and contrast can be adjusted to reflect image edits. By tying the video LUT to the video card, Apple allows for those running multiple displays to calibrate each separately. Because of Colorsync and video LUT technology, you'll find color management support slanted toward the MacOS.
While Colorsync utilizes device profiles to coordinate color throughout your workflow, a third party software program is required to create and edit these profiles. These programs work in conjunction with a colorimeter (a device for measuring color values from a display), an IT8 target (a film or print color target produced by film manufacturers for calibrating your scanner to a particular film family), and a spectrophotometer (a strip-reader for reading color swatches output by a printer).
Unlike scanner and printer calibration, there is no work around for display calibration. It is mandatory. If what you see on your display does not accurately represent your image file, there is little point in image editing. Additionally, display and printer profiles do not directly affect the image file, only the device output - whether it be the image on the screen or the print on the paper. The image file itself remains untouched. In fact, the term "printer profile" is a misnomer for it is the print settings and paper stock you are profiling. Each combination of printer, print settings, ink type, and paper stock requires its own profile. When any of these variables are changed, the rendered color changes - blue on a matte paper is not the same blue on glossy paper. Printer manufacturers incorporate automatic color management into their print drivers to coerce a pretty picture out of the printer, correct settings or not. This color management must be turned off for your profiles to work correctly.
Unlike these other devices, the scanner's profile is applied directly to the image file so as to correct for the scanner's bias. As the printer profile is unique to output settings and paper, the film scanner profile is unique to the scanner settings and film type. As IT8 targets are calibrated against the film's image forming dyes, one target can be used for an entire film family. Some claim that an E6 IT8 will be work for any E6 film, regardless of the manufacturer.
For most people, system calibration begins and ends with display calibration. If one is out-sourcing both scans and prints, a correct viewing environment is all that is required. The low-end calibration tools serve this market well. Typically, the user is first prompted to select the color temperature of their display and the white point (6,500° and 2.2, respectively, are considered standard). Next the user adjusts the brightness and contrast of the display. If you find that you are adjusting the brightness toward to top of the display's range, the display may be nearing the end of its useful life. For CRT's, a white luminance greater than 75 is bad news. Likewise, if you set brightness and contrast too high, you'll be unnecessarily stressing your display's hardware. The final step is to place the colorimeter onto the display's surface and let the software do the rest. The software will display a range of colors while the colorimeter tests their accuracy. When all is completed a display profile will have been created and installed into your Colorsync folder (on Mac). Your display should be calibrated biweekly.
For display profiling I have used the Monaco Optix by X-Rite and found, once familiar with the interface, display profiling to be simple and straight-forward. The Monaco Optix works on both CRT's and flat panel displays, Mac and Windows, with equal ease. I typically run display calibration first thing in the morning while reading my email.
Keep in mind that, no matter how you are calibrating your display, the profile (and your color workflow) will only be as good as the display you are using. Do not expect profiling to rescue your color workflow from an old CRT or a laptop display. If you have not yet jumped on the flat panel bandwagon, perhaps because of the superior luminescence of the CRT, keep in mind that CRT's have virtually gone out of production. The higher quality flat panel displays are reported to offer an equal gamut. Early brightness issues have been resolved, allowing for finer adjustment and, thus, a closer match to print reflectance. Flat panel display's also don't come with the heavy metal, radiation, and eye-strain issues that plague the CRT. Some of the new flat panel's include an integrated calibration system, thus taking the calibration process down to the hardware level. Yet, don't expect these benefits from laptop displays or the low-end flat panel's. Do your research. I concluded that I will not be using my laptop's LCD for color critical work.
One of X-Rite's low-end colorimeter competitors offers printer and scanner calibration through the software. Be wary of these units. The unit I tested profiled a test file designed to be printed and then scanned back into the computer. The resulting digital file was compared against the original digital file to produce a profile of the printer. I cannot recommend this method as it does not correct for the bias of the scanner. In fact, the scanner's bias will be added to that of the printer. Another product got around this problem by supplying a reflective IT8 target (for flatbed scanners). Once scanned, the IT8 target can be compared against a data file of the target's known values to create the scanner profile. The printer is profiled by printing out the digital IT8 benchmark file along with a swatch file, and then scanning this output to create digital comparison files for profiling.
Display calibration easily becomes a mine field when using multiple color management applications as these programs step on each other as their extensions load, the later ones calibrating against the former. Before you install any display calibration software be sure to remove the extensions of any other - including Adobe Gamma.
Thomas Bachand has been both Editor and Webmaster for ASMP Northern California. When not consulting on computer and Internet projects, he can be found photographing landscapes, travel and architecture.