Welcome back to the wonderful world of ICC Profile editing. In last month's article, I presented an overview of the more common edits that can be made to ICC profiles. This month, we'll examine some of the less-often-used editing tools available in most of the profile editing packages.
First, we'll look at ProfileMaker from X-Rite (formerly GretagMacbeth). Remember, profile editing is no substitute for accurately calibrating and profiling your devices but, rather, is used when you have done everything correctly but still need to squeeze that last little bit of color accuracy out of your system.
Last month's editing examples used the global and curve editing tools. This month we begin with the selective color tool (Figure 1). Anyone who has performed selective color editing in Adobe Photoshop will be familiar with the concept of this tool. It is used, as an example, when the entire image doesn't need more yellow but, instead, only a few select reds or greens.
The easiest method to use in selecting the color you wish to edit is to open a sample image and use the eyedroppers in section "A." The left-most eyedropper, when used to click in an area of the sample image, will load the LCh or L*a*b* value for that pixel into the editor. The plus and minus eyedroppers allow you to click on additional areas of the image to expand or contract the range of colors to which you wish to apply the edit.
You can also use the small triangular range sliders shown in Figure 2 to expand the color range. Separate sliders are available for each of the channels. You can also select the desired base color by simply entering the appropriate numerical values in the corresponding windows in section "B" in Figure 1.
After you have loaded the desired color and set the range of colors you wish to affect, you use the sliders in section "C" to modify the base color. The amount you move these sliders will modify the base color by 100 percent and feather off proportionately to modify the other colors contained within the range sliders.
If you opened an evaluation image within the editing interface (Figure 3), moving the sliders on the top and left-hand side of the window will allow you to see the before and after effects of not only the selective color edit being described here, but any of the edits you are applying to the profile.
Checking the Range Preview box in "D" in Figure 1 will highlight the colors that will be affected by the edits much like the gamut-warning feature in Adobe Photoshop (Figure 4).
The before-and-after numerical data for the selective color edit will be listed in the upper window, "E" in Figure 1. The buttons in section "F" can be used to add selections for editing, remove selections, save, or load the edit list. You can add multiple selective color edits to your list, as shown in Figure 5.
I recommend that you use caution and add only one or two selective color edits at a time, save the profile and test the results. Making too many edits at one time can lead to poor results and a situation where you don't know which edit caused the problem.
White point editor
If you use the Absolute Colorimetric rendering intent, you may find that the simulated white point is not as accurate as you would like. Enter the white point editor (Figure 6). When you launch this module the current white point of the selected ICC Profile is automatically loaded and displayed. Make small moves and test the results when using this tool as your eyes are very sensitive to changes in the white point.
You also need to think about whether you are editing a source or a destination profile for this or any edits since this will dictate how your edits are made. For example, if the white point simulation is too light and you are editing the source profile, you would reduce the "L" value in the white point editor. If, on the other hand, you are editing the destination profile, you would raise the "L" value.
The logic is that by lowering the "L" value in the source profile, you are telling the system to darken the white point simulation. If you raise the "L" value of the destination profile, you are telling the transform that the media you are printing on is brighter than it actually is, which will force the transform to darken it. Either task will give you the same results. It's up to you to determine which profile makes the most sense to edit.
Correctly saving edits
One other little "gotcha" to keep in mind is to make sure you save the edit into the correct rendering intent (Figure 7). Save the profile with the wrong rendering intent selected and you will not see the changes when you test the results.
Carefully plan all of your edits, execute them one at a time, test and evaluate the results before initiating additional edits. Follow this plan and you will find that you can now wrest that last little bit of color accuracy out of your color conversions.
John Nate is a senior color specialist for FineEye Color Solutions. Contact him at 616.988.6119 or firstname.lastname@example.org