Editor’s note: Chromaticity experts will address questions from the pressroom to the plateroom, addressing such topics as prepress, workflow, proofing, digital photography and color management. Submit a question by going to www.chroma-tech.com and choosing the trial question option. Please make sure to note that you are submitting a question for Newspapers & Technology.

Q: I have been creating profiles for quite some time, but occasionally get strange results. Is there a process that I can use to verify the profile before I introduce it into the workflow?

A: Yes, there is. Before we go into that process, let’s review a concept first. An ICC profile is nothing more than a snapshot of the device’s behavior at the time the profile is created.

If this is a press or printer profile, then it should be run to shop standards or to the printer’s optimized state when printing the profile patches. At the time of printing the profile target patches, there are several test targets that could be used to verify the accuracy of the printed output.

One is the ChromaChart Tone file, available at either Color Source’s or ColorSync’s Web sites. (See end of reply for Web address that will allow you to download the target file.)

This test image helps define five key attributes of an output: density, tonality, secondary colors, total ink limit and gray balance.

In addition to those attributes, tone value increase, trap, print contrast, hue error and grayness also can be evaluated.

If your output’s key attributes are acceptable, then you can use this information to check the integrity of the profile.

The first thing to check on a printer profile is neutrality, or gray balance. As mentioned earlier, the ChromaChart Tone test image contains color patches that will print as a neutral gray assuming an optimized print condition.

The CMY values for this optimized condition are as follows:

Quarter-tone gray – 25 percent cyan, 19 percent magenta and 19 percent yellow should closely approximate a 25 percent black.

Midtone gray – 50 percent cyan, 39 percent magenta and 39 percent yellow should closely approximate a 50 percent black.

Three-quarter-tone gray – 75 percent cyan, 63 percent magenta and 63 percent yellow should closely approximate a 75 percent black.

This close approximation is based upon weight and a neutral color cast. If a color cast is detected, then the profile must correct it.

For example, let’s assume that your device exhibits a red cast in these three tone ranges and that it is more than a slight cast, appearing very warm when viewed.

We know from color theory that printing inks absorb and reflect the visible color wavelength. We also know that cyan ink absorbs the red color wavelength, magenta ink absorbs the green color wavelength and yellow ink absorbs the blue color wavelength.

Seeing that we have a red cast, we either need to add cyan, or, alternately, reduce magenta and yellow.

This question is answered by asking if our grayscale patches are too dark or too light.

Let’s assume for the sake of discussion that the patches are too dark when compared to the black patches. In this case, we would remove weight, which means we would remove magenta and yellow. What this comes down to is that the values displayed above do not work for creating neutrals on this device and must be altered.

We will use a simple process within Adobe Photoshop 6x or 7x to determine if the profile can create proper neutrality.

Make sure that you have the printer profile installed on your workstation so that Photoshop can access it. Additionally, ensure that you have a valid RGB working space such as ColorMatch RGB or Adobe RGB loaded within your RGB settings. Create a new RGB document 10 inches by 3 inches at 100 dots per inch and set the default colors to black-and-white.

Create a gradient from black to white along the 10-inch direction of the new document. Check to ensure that white is displayed at 255, 255, 255 RGB, and black is displayed as 0, 0, 0 RGB.

Access the Image>Mode>Convert to Profile option and load the printer profile. Using either the Relative Colorimetric or Perceptual Rendering Intent, convert the image to the CMYK printer space that you wish to evaluate.

Use your eyedropper to evaluate the RGB along with the CMYK values of the color space transformations. If, as outlined above, the neutrals exhibit a red cast, we would expect cyan to be higher, or magenta and yellow to be lower than the values seen on the printed sheet.

If the values do not conform to your inspection of the printed target or the onscreen display is not neutral, or gray, then you very likely have a bad profile.

Ideally, this test grayscale can be printed to the device after the color space conversion to verify the accuracy of the profile.

There is an old saying that says if you cannot print gray, you cannot print color. Obviously, there is more that you could do here, but this issue is the cause of many of the problems we see with profiles: They will show a total ink limit that is too high or too low and black generation settings that are optimized or less than optimized.

For more information, visit the ColorSync Web site, http://www.apple.com/colorsync/stories/bohnen/testprofiles/index.html and read the article, “Testing Your Profile.” The test target can also be downloaded here.

Roy Bohnen
rbohnen@chromaticity.com

Q: We are supplied with images in the CMYK color space. Quite often, these images print incorrectly on our press. How do I ensure that the images can be printed correctly prior to going to press?]

A: There are two ways you can accomplish this. For the first method, you need to create a proof that emulates, or simulates, the press condition or output. This is easily accomplished using inkjet technology, enabled and controlled using traditional color control or ICC profiles.

The traditional approach relies upon setting the correct densities and tone curves in order to emulate the press.

The ICC approach uses profiles to accomplish this task.

A second method that may be as effective, or a necessary precursor to hard proofing, is soft-proofing within Adobe Photoshop 6x or 7x.

Photoshop has very powerful tools, which allow users to preview the effects of the final output. The soft-proofing process is enabled by ICC profiles. In order to accomplish this task, the color settings within Photoshop will need to be configured the same on all workstations.

This setup can use default settings or profiles specific to your location. Once the setup has been created, it can be saved and loaded to the other workstations.

Upon opening the image in question, access the View>Proof Setup>Custom dialog. Once this dialog is opened, load the profile of the press. Note that the relative colorimetric rendering intent has been automatically selected. This is the default and correct setting for most soft-proofing.

Click the Preserve Color Numbers option below the loaded profile.

Let’s look briefly at the concept of the preserve numbers. The same numbers, or ingredients, will print differently on each device. By selecting the Preserve Color Numbers option, we are soft-proofing the output as it will be printed on the press. We must view color as device-based and device-dependent and we need to use the profile of the output device to successfully soft-proof. If you follow all the steps, you’ll see a good approximation of what your press will produce.

Richard Lerner
rlerner@chromaticity.com