Back when we all worked with physical (rather than digital) photographs, there was never any question about how a photo should be reproduced because the photographer, client and prepress technician were all looking at the same physical print or transparency. With digital photography, since everyone is going to look at your picture on a different monitor, the only way it’s going to be properly reproduced is if everyone’s monitor is calibrated to the same standard.
What makes calibration a requirement? It all comes down to a difference of opinion on what a given color should look like. Given identical RGB values, two different uncalibrated displays will display different colors. This is a problem, so calibration exists to bring those monitors to a universal standard (called the reference space) before they can be used without incident.
How does it happen? First, the monitor is profiled. Your colorimeter’s software displays color swatches on your screen and the colorimeter itself measures the color’s show. This is used to make a chart of the monitor’s display characteristics. Using this chart, the monitor’s output is then altered to more closely match the CIE reference color space, to which all other calibrated devices are also matched. The monitor’s display can be altered in two ways – either the monitor itself alters the colors(available on high-end monitors) or it is altered through the computer’s GPU using a look-up table or LUT to change the colors it received from the computer into the colors that the monitor needs to display the correct pixel values. In the former case, the GPU works as a translator, taking input values and creating output values that are adjusted based on the profile built by your colorimeter
The complexity of this process has a lot to do with the quality of the monitor, the available gamut of your display, and the type of screen you’re working on. But the basic principle is always the same: measure and modify to produce accurate color.
STEP 1: THE RIGHT TOOLS
The first step is to make sure you have a monitor that’s worth calibrating. Some cheaper monitors may not be able to render the full range of colors or contrast contained in most photos, so all the calibration in the world won’t make them display your pictures properly. Selecting the right monitor is a post in itself, but suffice it to say that a professional photographer needs to have a professional monitor. You can expect professional results from brands like NEC or Eizo in nearly all their product lines, and expect to pay $500 to $1,000. You’ll get the best results from Eizo’s ColorEdge or NEC’s Spectraview series, but that comes at a price. However, regardless of the amount of money you spend and the assurances you receive from the manufacturer, a monitor without calibration is limited in its usefulness.
WHAT SORT OF MONITOR SHOULD I GET?
Basically, the best one you can afford. There are a few basic things to look for. At minimum, your monitor needs an IPS panel and an LED backlight. It should also have a resolution beyond simple HD, 8-bit, if not 10-bit color depth and a 12 or 14-bit 3D look-up table. Also, keep in mind that every monitor on the market will say it can display 16.77 million colors, but cheaper monitors get there differently. Cheaper monitors use 6 bits per channel and take advantage of the same optical illusion that movies use to produce the other colors, quickly cycling subpixels back and forth to achieve colors they would otherwise be unable to show. While this likely improves the web-browsing experience, it is not appropriate for color-critical work.
CALIBRATION TOOLS
Here at Wonderful Machine, we use the Spyder 5 Elite to calibrate our Apple Cinema displays. While we can comfortably recommend that tool, Color Munki’s higher-end products are also great, and if you make prints for anything more than casual viewing, you’re going to want a tool that profiles printers as well as monitors, which the Spyder does not do. If you don’t make prints, you’ll be fine getting a more basic calibrator that only calibrates monitors.
Don’t just buy the most expensive one: in this arena, more money doesn’t necessarily equal better performance in all cases. What it does get you is a more advanced set of tools that can take advantage of a more expensive monitor’s great flexibility, so monitors without those capabilities won’t gain anything. Choose a tool that’s commensurate with your monitor’s features and price. For example, using a $2,500 LightSpace CMS colorimeter isn’t going to get you better results than a $199 Spyder 5 if you’re just using a $250 Dell UltraSharp.
STEP 2: PROPER MONITOR PLACEMENT
Little things matter a lot in the way that humans perceive color. We’re wired to be most attracted to the brightest, most saturated colors, so we often surround ourselves with such things. As pretty as these things are, having them near your monitor is a bad idea. A red stress ball at the base of your monitor can have a serious impact on the way that you perceive color, and you don’t want to go through all the trouble of fine-tuning your monitor just to mess it up with your desk flair.
Going further, it’s advisable to remove as many colorful or distracting elements from your field of view as possible. This includes the brightly-painted surface behind your monitor, the mirror mounted on your door and the LED clock you hung on the wall. Not only do these things draw the eye, but they can impact color perception just as much as something right in front of you. Professional graphics houses often go so far as to paint the walls of their editing rooms 18% gray to avoid even a hint of color bias. There’s only so far we’re each willing to go for accurate color, but take the time to do the easy stuff – clear out anything bright and distracting.
Lighting is also important. You want to be able to see the space around your monitor, but because the screen itself is a glowing box, having other glowing things competing with it makes it more difficult to accurately perceive what’s on the screen. Make sure that no bright lights are directly visible are around your display, and dim the lights that are illuminating your surroundings. Many calibrating tools also include an ambient light sensor or lux meter, but you can also use your camera to measure the ambient illumination. The generally recommended ambient light level is about 32 to 64 lux. 4 EV is right in the middle, so the exposure should be about 1.5 seconds at f/5.6 and ISO 100, or the equivalent. Use the spot meter function on the camera to be sure you’re getting an accurate result, and make multiple measurements. If you have a light meter with a spot attachment, you can use that to measure lux directly and save yourself the step.
Additionally, be certain to avoid glare on the monitor. How do you find out if you have glare? Turn off your monitor and check to see if there’s any color visible in the display’s reflection. See a bit of orange? Turn off the lamp and see what happens. Little blue at the bottom? Close the shades further and check again. Having light reflecting off your monitor is going to have bad results, so get rid of it. You can also use a monitor shade, so if your monitor can accommodate one, make sure to use it.
So: gray walls and dark lights. What a happy, vibrant space! You don’t have to take all these recommendations to the extreme, but it’s useful to know that when you need to do some serious color-correct work, you should take down the flashy posters and dim the lights.
A WORD OR TWO ON STANDARDS
The standards chosen for monitor calibration are somewhat arbitrary. The sRGB profile was created based not on what humans could see, the most commonly encountered colors, a camera or scanner’s gamut, or the colors seen in negative or slide film. Rather, sRGB is based on the colors that early CRT monitors were able to display best. The D65 white point was created similarly – it was the “whitest looking” white point that a CRT monitor was capable of. As ridiculous as that may be, we’re stuck with it – imaging and display manufacturers have been using these standards for a long time, and they’re not likely to change. On the other hand, other standards, such as those created by ISO and CIE, are very much created based on scientific evidence. These varied standards all come into play when discussing color calibration, and it’s important to realize that while they are all important, they have different levels of impact.
STEP 2: CALIBRATING THE MONITOR
This is the easiest part of the process. There are several colorimeters you can use to calibrate your monitor and most of them are very straight-forward. The instructions are clear, include pictures and are written in plain English. If you encounter problems it’s very easy to get a YouTube video with further explanations, and manufacturers often go out of their way to make the software easy to use. The details of the exact steps below may vary based on the calibration tool you select, but the basic elements will remain the same.
First, plug the colorimeter into your computer’s USB port and start up the software. You’ll be allowed to choose some settings, including white point, brightness, and monitor type. D65 (a.k.a. 6500°K) is a good starting place for white balance, and you’ll want to choose a brightness around 100 or 120 cd/m2. Make sure to select the appropriate type of monitor, if that’s an option.
Many calibration tools will then take an ambient light reading. If you have not already done so, adjust your lighting to the level you expect it to be when editing photos. This may impact your monitor brightness – follow what the software says.
When prompted, you’ll need to place the calibrator on the monitor. The colorimeter will hang from its cable, which will have a counterweight on it. Pull on the weight while holding onto the cable to move it up and down the wire. Make sure it’s far enough from the meter to go behind your monitor, but not so far as to not work as a counterweight. It can also be helpful to lean your monitor back slightly so the meter rests flush against the monitor screen.
The software will then take over the screen and flash a bunch of color patches for a few minutes. This is the measurement phase. It’s best to just let your computer be while this happens so you don’t accidentally interfere with the process. It should take about 10 minutes.
When this process is done, you’ll be asked to save the profile – give it a descriptive name – and then shown a photo that’s designed to show off your monitor’s new calibration. You will probably see an obvious if minor difference when flipping back and forth. Revel in the splendor of your calibrated screen!
GAMMA, WHITE POINT, GAMUT AND BRIGHTNESS
If print-to-screen matching is not required, your monitor should be calibrated to D65 (6500°K white point), 2.2 Gamma for the majority of uses. If you’re working in an ultra-wide gamut like ProPhotoRGB, 1.8 gamma is recommended. When print matching is required, calibrate your monitor to D50 (5000° white point). Keep in mind you can’t (and shouldn’t) just flip between gamma settings when you change color profiles and expect to get accurate results. Shifting gamma and brightness alters other variables in the system, so your monitor needs to be calibrated with those specific parameters in play. Generally, 2.2 gamma is considered the best general point, so don’t meddle with it if you don’t have a good reason to.
Regarding monitor brightness, you should be shooting for about 100 to 120 cd/m2 when not matching to print, and 80 cd/m2 when you’re trying to match a printed output. Again, you can’t change the brightness and expect good results: you need to calibrate the monitor at the brightness level you plan to use.
STEP 4: KEEP IT UP
Monitor calibration tends to drift over time. Digital though they may be, monitors rely on physical components to show light, and like all things in this world, those components will degrade over time. Generally, it’s recommended that you recalibrate your monitor every 200 hours of use, or every 30 days, whichever comes first. But like changing your oil, many people wait a little longer than suggested. Just make sure to recalibrate your monitor before doing any color-critical work if it’s been longer than 30 days since your last comparison.
MATCHING PRINTS
The discussion of creating color-accurate photos is a whole separate beast, and as such, I won’t go deeply into print viewing and matching. However, I do want to make mention of some less obvious information.
Matching prints to your monitor is a complex and detailed process requiring careful control of lighting conditions and digital displays. To correctly view a print on paper, you must view it under correctly calibrated lighting.
This requires creating a viewing booth that uses lighting that meets the standards specified in ISO 3664:2009. There are two ways to get there: you can build your own, or purchase one.
Buying your own is far, far easier. GTI’s PDV-3 is an excellent, if expensive, tool. GrafiLite’s Ott-lite is also frequently recommended and can produce good results, but doesn’t sufficiently block surrounding illumination to be a universally excellent tool.
When building your viewing station, you need to get the right lights – and not any 5000°K light will do, especially not the commonly available ones. The standard specified by ISO 3664:2009 requires lights balanced at the D50 white point with even distribution and a significant UV component to correctly illuminate the optical brighteners embedded in most photographic papers. Such lighting can be purchased from GTI Graphic Technologies or JUST Normlicht. The tubes themselves should be printed with “ISO 3664:2009″. Anything else is just a gamble.
Also keep in mind that a monitor transmits light, while a print reflects it. The two are fundamentally different and will never match identically. However, you can get the relative color tones to be the same. It’s like looking at a transparency and then looking at a press print – the two are just different.
FURTHER READING AND SOURCES