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Why Are My Prints Too Dark?

By Andrew Rodney

One of the most compelling features driving the usage of color management is the goal of What You See Is What You Get, also known as WYSIWYG. You want to view your images on-screen and know how those pixels will translate into a print, making as few test prints as possible. Calibrating and profiling a display, using good ICC printer profiles and setting up Photoshop’s soft proofing is well documented and embraced by many users. Yet a great many encounter a severe disconnect between what they see on-screen compared to what they see on their prints. The complaints heard are common; my prints are too dark. This article will attempt to pinpoint why so many are encountering this problem, where the problem may manifest within the workflow and what can be done to fix these issues. 


Prerequisites:

It should go without saying that you must calibrate and profile your displays using quality instrumentation and software. You need to calibrate and profile such devices on a regular basis because displays are unstable and greatly differ from one another. You also need good quality ICC profiles for the printers and papers you will use and work with ICC aware applications that support soft proofing, such as Adobe Photoshop. 

It is not assumed you have a proper setup for viewing your prints next to your display. Or you have full control over the ambient lighting conditions in this environment. It is absolutely critical to have well-controlled print viewing conditions next to the display! An open window behind the display, overhead lights that can’t be controlled, an inexpensive desk lamp is all sub optimal. You need a light source that ideally has a suitable spectrum, which I will discuss later. This light source shouldn’t spill light onto your display, and preferably has some way to control the intensity reflecting off your prints. This print viewing conditions, the print station if you will, is as important as the display system in terms of producing a successful print to screen condition. You would never consider using a night light or the headlights off a bike to view your prints next to your display. You should assume other light sources could be equally unsuitable. Some argue that an idealized print viewing condition is unnecessary because clients will view these prints in another environment with different lighting. This logic fails to account for the initial goal of matching a display and a print. These two items, the display and the print viewing conditions are tightly interconnected. 

Are my prints too dark?: The number one complaint heard on various on-line forums discussing color management is “My prints are too dark”. There is no question that you can encounter situations where prints are too dark. Before rushing to alter the RGB values in these documents, a highly questionable “fix“ suggested by some, it’s necessary to determine that the print is actually too dark. Move the print to a number of other locations where you can view it under differing illuminants. Go outside during the day, into the kitchen, another area of the office, next to a window. Do the prints look too dark no matter where you view them? If so, you need to ascertain why it is too dark and if this is true for all documents printed the same way. It is possible the RGB values do need adjusting. Or that a print driver setting was incorrectly configured. There could be an issue with the printer itself. The output profile could be the culprit. However, when I ask users to examine prints in different lighting environments, nine times out of ten, they tell me the prints are not too dark.  Instead, they discover the prints are much darker than the display, often by a large factor! While these users have calibrated their displays, they didn’t calibrate them correctly with the print viewing conditions in mind. Would you agree that viewing a print illuminated only by a small candle would appear very dark? Of course it would. That doesn’t mean the prints are too dark outside this environment. 


Calibration:

Many people who tell me their prints are too dark compared to their display also tell me they have calibrated their displays. Calibrated to what target aim point? When calibrating a display, the software used to conduct the calibration has to be set for specific calibration target settings. You are asked to define a white point, a TRC gamma value** and the display luminance. If one group of values worked for all users, you would not be asked to specify these important target settings. The settings make a significant difference between prints that appear too dark, too warm or cool or those that match your display. 

**TRC or Tone Response Curve.

Often incorrectly referred to as Gamma. Various values for gamma produce different curves. So we can use a single number to describe this type of curve. However, many devices do not follow this formula, their curves are far more complex and are not gamma curves nor should we use gamma to describe them.

The most critical calibration target to set is the luminance (what some incorrectly call brightness*). Most calibration products ask you to set a value for display luminance, specified using candela per meter squared (cd/m2) **. This is simply a unit of measurement like feet, or liters but in this case, a unit that defines the light intensity of your display. Many software products, and imaging ‘experts’ will tell you to set your display for this or that cd/m2 value as if its to be written in stone. Such target values for luminance often lead to the dreaded “My prints are too dark” problem. How can anyone suggest a setting for the display luminance without first accounting for the conditions under which the print is viewed? Because modern LCD displays are capable of very high luminance, and because users do not configure the calibration of luminance to match their print viewing conditions, most users see an enormous dissimilarity between the perceived brightness of their display and their prints. The display appears so much brighter than the print that the print therefore looks dark. The solution is easy. Lower the display luminance and/or raise the print viewing luminance until the two visually match. The correct value for luminance is one that produces a visual match. You can start at the so-called “recommended” value, which is often in the neighborhood of 120-140cd/m2. That value may need to be lower or higher. You will need to adjust the display luminance until you get that visual match. 

*Brightness is a perceptual, subjective phenomenon while Luminosity (luminance) is the measure of total radiant energy emanating from a body or object like our displays. 

** The candela per meter squared (cd / m2) is the standard unit of luminance. It represents a luminous intensity of one candela radiating from a surface whose area is one square meter.

Many new LCD displays cannot achieve low cd/m2 values. Many users upgrading from the older and dimmer CRT displays try to calibrate these LCDs to 90 cd/m2 and find that these new LCDs simply can’t be calibrated to such low luminance. Many new LCDs will have difficulty being driven much lower than around 120cd/m2. This would only be a problem if you could not control the print viewing conditions to produce a match. This is why having the ability to control the luminance of the viewing booth can be so useful and will be discussed later. The point is, no specific cd/m2 target will necessary be correct without taking the print viewing conditions into account. Very low cd/m2 values are not necessary better, however the lower you can calibrate the display luminance, the longer that display will last. Displays do wear out. 


White Point

Like the target calibration for luminance, the white point can play a role in print to screen matching albeit a much smaller one. Once you have produced the correct display luminance to match your prints, you can adjust the white point to produce a visual match of the paper white color. Some will state you must calibrate to D65, or you can never calibrate to D50. Taken at face value, this is untrue. The correct value will be the one that produces a visual match. It might be D50, or D55, or even a correlated color temperature, such as 5750K. The specific values are rather meaningless until you produce that visual match to the print. The numbers do not have to be a value that matches “daylight”. Since the print viewing conditions could be any number of florescent “daylight” blubs, halogen bulbs, possibly LEDs, its not possible to define the ideal white point without taking the viewing conditions into account. By using a trial and error approach, you can try different white point settings until you see a visual match between the display and the print. Most modern LCD displays have a native white point around D65 and that’s a good starting point to begin the calibration process. Additionally, your eyes will adapt to the white of a viewing booth shortly after looking at the display. Dissimilarities between display and print white point are far less an issue than big differences in luminance. With products that allow multiple calibration target aim points with associated ICC profiles, I find it useful to tweak the white point calibration for a specific paper for a visual match. 


TRC

Lets skip lengthy discussions about the TRC gamma settings for calibration. 2.2 will work equally for Mac and Windows users. It is useful to discuss a feature some higher end calibration products provide over the contrast ratio of the display calibration. Many display manufacturers specify very high contrast ratios in their marketing materials with the goal of enticing sales. You would assume that if one brand has an 800:1 contrast ratio, the competitor’s display at 1000:1 must be that much better. Not so! If you measure the contrast ratio of a glossy photo print, it may at best have a contrast ratio of 350:1. Matt papers would have significantly lower contrast ratios. Here we find yet another significant disconnect between the print and the display. Some displays provide the ability to control the black level as well as white luminance rather than driving the unit at maximum contrast ratio. Consequently, Photoshop’s Customize Proof Setup has two check box options called Simulate Paper Color/Black Ink. Many users ignore these settings because they make the images on-screen appear muted and dull, since part of the Simulate functionality is to adjust for the contrast ratio of the soft proof to match the print. Calibrating the display to account for the contrast ratio of the print, rather than fully adjusting the soft proof using the paper profiles greatly reduces the visual differences seen when the simulation is invoked. It is important to understand the role of soft proofing, dynamic range simulation and proper image viewing when attempting that screen to print match. See: 

http://www.ppmag.com/reviews/200409_rodneycm.pdf

http://www.ppmag.com/reviews/200410_rodneycm.pdf

http://www.ppmag.com/reviews/200411_rodneycm.pdf

While these PDFs from 2004 cover older versions of Photoshop, the functionality has not changed. 


Getting the Print Booth and Display to Match:

I’ve been able to produce very close screen to print matching both in my office and for class demonstrations using the method to follow. A few items are necessary before I even start the calibration and profile process. First I need a good reference image to view in Photoshop. There are a number of free images available listed below, but for this step by step demo, I’ll use my own Printer Test File which can be downloaded at...

http://www.digitaldog.net/files/Printer_Test_file.jpg.zip.

I print this image using a good ICC profile, which will also be used to soft proof the image. The print will be placed in the viewing booth and as I calibrate the display using various targets, I’ll examine the soft proof in Photoshop until I produce the desired calibration that results in a match.  

First I’ll start with the so-called recommended target calibrations just to see how much I may deviate to get a visual match. I’ll set the calibration targets aim points for a white point of D65, Luminance of 140cd/m2, TRC gamma of 2.2 and a contrast ratio of 300:1 since my test print is on Luster media. When this initial calibration and profiling process is finished, the software loads the ICC profile for use by Photoshop. I’ll examine the Printer Test File in Photoshop setting the Customize Proof Setup dialog for the paper profile and rendering intent used to make the print. I turn on the simulate check boxes for black ink and paper color. I hit the F-key until the image is in full screen mode and hide all the palettes using the Tab key. This provides a soft proof of the image with no user interface elements. I attempt to set the zoom ratio of the image such that it is scaled on-screen to match the print size as close as possible. For critical analysis, I may trim any white paper border around the image area on the print or better yet, mask the print border with a black frame. Now I simply judge the match or lack thereof between the display preview and my print. I have the ability to alter the luminance of the GTI viewing booth using its LCD control panel. A lower value results in longer lasting fluorescent bulbs and at the booths higher setting, its far too bright. With a setting of D65, luminance set a bit higher at 150cd/2, and the GTI booth digital brightness control set at 50, I get a good screen to print match in terms of the brightness but the image on-screen is too cool. 

In this exercise, I started at D65, which needs to be set to a lower (warmer) value based on the visual match of the print. I see the effect of the white point prominently on light gray and white portions of my test image. Since D65 appears too cool, I calibrate to D55 with the other settings the same. Now the image on-screen is too warm. I have the ability to enter any value for white point into a field in the advanced options of the software I’m using. After two more attempts, entering differing values, I get a match when the CCT** value for a custom white point is set to 5750K. The screen and print match really well, and are not too warm, not too cool. Most importantly, in terms of perceived brightness the settings used are just right. At this point, it’s useful to print the same test image on different paper stocks using good ICC profiles, setting up a Photoshop soft proof and examining the results. I try different images, printed using different profiles but with the soft proof always setup as described above and sure enough, I continue to get very good screen to print matching. Note that altering a warm/cool bias using a CCT value is a viable solution, however, if a cast on the magenta/green axis is seen, this cannot be fixed with sole a Kelvin adjustment. Products that allow editing the white point using x and y axis of the white point on a CIE xy plot will allow colors on these axis to be adjusted.

CCT or Correlated Color Temperature:

Photographers have been taught for years that tungsten film has a color temperature of 3200K (Kelvin; being unit of temperature). Lower Kelvin values appear redder, and as the Kelvin values get higher, the color becomes bluer. In actuality, a color temperature is a range of colors correlated to the temperature of a theoretical object known as a blackbody radiator. The blackbody reflects no light and emits energy in shorter wavelengths as it is being heated. Because natural materials are not theoretical blackbodies, heating them to a specific temperature creates deviates from the theoretical color from magenta to green. It's really much safer to use the term correlated color temperature (CCT) because many colors of white may correlate to the same blackbody color temperature. Also see: http://www.ppmag.com/reviews/200512_rodneycm.pdf


Viewing Booths:

You don’t have to spend hundreds of dollars on a print viewing booth but you do need something that has a well behaved illuminant that can be controlled. I use either a GTI print viewing booth, which depending on size can be somewhat costly, or Solux Halogen blubs, which are more affordable. The advantage of the GTI booth is I can dim or raise the fluorescent lights in a very precise fashion without affecting the color. Many of the companies I deal with in the print and prepress trades have the same viewing booths. I can precisely specify the intensity of the lighting in the booth, providing the ability to setup multiple locations to view prints under the same conditions. Due to the spiky spectra all florescent lights exhibit, and interactions with some papers containing high levels of optical brightening agents, I prefer using true, full spectrum Solux halogen bulbs for print viewing. The downside is Solux bulbs generate more heat than fluorescent blubs and can be more difficult to control. They cannot be dimmed like the GTI booth, as this would affect their color temperature. Control over their intensity can only be accomplished by moving them closer or farther from the print. Yet multiple Solux blubs can be setup to illuminate a very large area for viewing prints that can’t fit under a florescent light box. Either print viewing solution will work and you can build your own if so inclined. Once you have a good print viewing area, you can calibrate your display luminance and white point to produce a visual match.


Moving the Print:

When I discuss screen to print matching, ultimately someone asks “But now what happens when you move that print out of the viewing booth?” The display is now out of the equation; we are not trying to produce a match between two different media. Our eyes adapt to the new illuminant and the print that looked good under the GTI light box, or Solux bulbs, and produced a match to our display looks fine outside those conditions. And this shouldn’t be surprising for anyone who purchased prints at a lab, or artwork from a gallery only to view them in another location. Other than the rare problematic condition called metameric failure, often incorrectly called metamerism** if the print looked good under the viewing booth and matched the display, you will almost always find it looks good under other illuminants. 

** Metamerism is simple: two colored samples with different spectra compared to each other with a given set of viewing conditions produce a match. Metamerism only applies to two color patches when they are compared to each other under an illuminant. It is incorrect to refer to one color from a single ink or paper and say that it suffers from metamerism. A "meterameric pair of color patches" means that they appear to match under a given illuminate. However, they may not appear to match under another illuminate. Metamers ("metameric stimuli") by definition are two different spectrums that appear to be the same color. If they don't look the same color, they are not metamers.  If you are viewing a print (which contains more than just two color samples), and within differing viewing conditions, and there is a mismatch, this could be called a metameric mismatch or metameric failure. This is however not metamerism. 


Not All Displays are Created Equal:

You can buy an LCD display for a few hundred or well over a thousand dollars. This article can’t go into detail about the differences in panel types, gamut and quality, but generally speaking, you get what you pay for. I prefer what are known as “smart monitors”, displays that are designed from the ground up for efficient and easy, high quality display calibration. Such display systems have been available for decades. The NEC SpectraView II systems I use utilize a high-bit panel that is fully controlled by its host software for calibration. I do not have to alter calibration of the display using the On-screen Display (OSD) buttons, I simply set the target calibration values and the software communicates and controls the panel. This level of control is far greater than adjusting the display using the limited and crude controls provided on most displays. I can specify the contrast ratio and the software will control the panels black level and white luminance. The software provides control of the white point by entering CCT values or by entering CIE xy values for colorcasts. Another powerful option provides the ability to build multiple calibration targets with associated ICC profiles. I can then switch on the fly using the host software to a specific calibration aim point. I can calibrate the contrast ratio and white point for a warm white, matt paper and save that target and profile, then calibrate for a cooler appearing glossy paper and switch between the two as the need arises. I can build a calibration target for the Solux print viewing conditions, and switch targets for the GTI viewing booth. If you work in a collaborative group using the same display and viewing booth, you can share the calibration targets, load them onto the various workstations and produce excellent color matching for each workstation. Smart monitors that allows multiple target calibration aim points, with control over contrast ratio and white point settings per paper class is a desirable functionally for print to screen matching. That said calibrating to a single calibration target and placing greater emphasis on individual ICC profiles, using the soft proofing tables could still work well for less demanding and complex workflows. 



Trouble Shooting
:

It is possible your prints appear too dark everywhere you view them. Adjust the RGB values in Photoshop or Lightroom? Not yet. You need to be sure that the problem results from the document. I suggest you write down exactly each step you used to make the print. Create screen captures of every setting configured in both the application you print from and the print driver. Now download one of the image reference files that contain known quality RGB values and make another print, following the steps in your screen captures. If the images print well, you know it’s the RGB values in your document. Why you didn’t see this on the calibrated display would be the next area to examine. How did the reference images you successfully printed appear on-screen? Recalibrate the display and ensure that the display profile is being seen by your operating system and software. In Photoshop, open your Color Settings and examine the RGB Working Space popup menu. Towards the top of the list you will see “Monitor:XXX” where XXX is the name of the display profile. Do not select this profile, just make sure that the correct profile name is shown, as this is what Photoshop uses for all previews. 

If these reference images print dark, you know the problem is not your original RGB values. The issue may be the handling of the data sent to the printer from the host application or the print driver. Try printing the reference images using a different paper and ICC profile. If still dark, you can probably assume the issue is not a specific ICC profile. If you have more than one ICC aware application, for example Photoshop and Lightroom, try printing with a different product. Could this be just another of those long standing compatibilities between print driver, OS and application? To test this, attempt to print the same document on another computer system, perhaps with a different version of the OS or print driver. If you have more than one printer, do both printers exhibit the same problems? Try letting Printer Color Management handle the conversions instead of Application Color Management, its been known to work. Try converting the image to sRGB and print using a no color management path, setting the print driver for this mode. Are the prints still dark? The bottom line is, don’t automatically adjust the RGB values if the darkness is caused elsewhere in the processing and print workflow. Find the problem and address it at the source. 


Reference Images:

It’s useful to test output with documents known to have certain qualities of RGB values. There are reference images that have test patterns with black to white gradients, memory colors like skin tones and skies that are known to reproduce correctly when properly handled. Such reference images can be found on the Internet that are free to download and use. In addition to my Printer Test File, Bill Atkinson has a number of real world and synthetic images on his download page I highly recommend. 

See: http://homepage.mac.com/billatkinson/FileSharing2.html.

I also recommend the Pixl Test Image. 

See: http://www.pixl.dk/download/ 

The set of Roman 16 reference images are of very high quality digital capture and contain an abundance of different color schemes making them ideal for testing output. The set is not free but for those who can afford them, they are simply superb.

See: http://www.roman16.com/en/



What Works For Me:

 I’m confident that if I setup a display and print station for you with exactly the same equipment and procedures I use, we should both see comparable results. Otherwise what works for me might not work for you. This process is only as effective as its weakest link. Someone on the Luminous Landscape forum wrote, “Soft proofing isn’t as effective as it should be” and to that I partially agree. The technology and implementation need more refinement. Yet when properly setup, soft proofing provides a far greater level of integrity between what is seen on-screen and what comes out of the printer than without soft proofing. You can sweat the small details like painting your studio in a neutral gray, or controlling other ambient lighting aside from the viewing booth. Such factors should not produce as large an impact on the print to screen matching compared to proper calibration for your prints, but can help and should be considered whenever possible. I do believe that correctly calibrating the display for the print viewing conditions, using good ICC printer profiles and properly using Photoshop’s soft proofing is enough to solve the dark appearing print issue. 

I’d like to thank William Hollingworth of NEC, and both Cem Usakligil and Ratko Asanovi from the NAPP forums for providing feedback on this article. 

November, 2010


About Andrew Rodney

Andrew is owner of The Digital Dog, a digital imaging training and consulting business located in Santa, Fe New Mexico. Andrew Rodney, aka the Digital Dog, has successfully provided services and training to photographers, designers, print shops, government agencies, as well as fortune 1000 companies since 1993. Andrew has written in the following publications: PDN, Publish, Photoshop User, Digital Photo Pro, Electronic Publishing, Digital Output, MacWeek, and Professional Photographer. Andrew is the author of “Color Management for Photographers, Hands on Techniques for Photoshop Users” published by Focal Press.He lectures around the country on many aspects of digital imaging and color management. The Digital Dog is devoted to the understanding and adoption of color management. 

Andrew has been a Beta for Adobe Photoshop since version 2.5. and is currently an Alpha tester for Adobe Systems. Andrew is one of the principle partners of Pixel Genius LLC, a company that has created such products as PhotoKit and PhotoKit-Sharpener (http://www.pixelgenius.com/index.html). Andrew was named a "Top 40 Photoshop Expert" by Wacom Technologies. In 2007, Andrew was inducted into the NAPP Photoshop Hall of Fame. Andrew’s web site can be found at http://www.digitaldog.net/.

 

 


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Concepts: Color, Calibration, Gamma correction, Liquid crystal display, Metrology, Printing, Color management, Contrast ratio

Tags: white point, print viewing conditions, luminance, images, color, profiles, match, calibration, prints, contrast ratio, viewing booth, visual match, icc profile, display luminance, Photoshop, dark, soft proofing, RGB values, calibration target, color management, calibrate, print driver, color temperature, displays, reference images, paper, software, correlated color temperature, target calibration, good icc, lcd display, print viewing luminance, GTI viewing booth, print station, multiple calibration targets, display calibration, TRC gamma, icc aware application, white luminance, good icc printer