Making a Better Printer Profile
by CHROMiX's Patrick Herold
The science of color management has matured to the point where a novice user can make a dependably good printer profile using any of the software packages available today. But in many cases you have more choices than ever, which can make things confusing if you don't know which options to choose. This article will provide some perspective on what target options are useful and when to use them, tips and tricks to optimize your profile, and we'll watch out for a few pitfalls that still remain in the path to building an accurate printer profile.
Number of patches
Some profiling programs in the past were limited to a few sets of targets. You could either use a "small" set of patches or a "large" one. Most programs you will use today allow you to dial in exactly how many colored patches you want on the target image. It is tempting to think that the more patches you have the better your final profile will be. Like we say in the color world, "Well, it all depends..." Consider the following:
- Say you have an old Epson Rp1280 or some obscure "toner-based-fusion-onto-tile using non-standard colors" printer - or anything that is non-linear and puts out sudden changes in color in an unusual direction. A large patch set is necessary to "capture" the effect of that erratic color blending.
- Some printers (like modern inkjets) have better native printing, are more linear even before profiling, than they were years ago. It really is not necessary to throw 4000 patches at a device that is well-behaved and already reproduces color smoothly. These printers will not benefit from more patches, and instead might suffer from a lack of smoothness if profiled with a large patch set.
- Smoothness vs. accuracy. While we may think we want the most accurate profile, sometimes what we really want is the most pleasing profile. A smaller patch set requires the profile building engine to interpolate more data in-between the measured colors. This will result in smoother transitions. Smoother is better when we want colors in an image to blend smoothly throughout a gradient, from one subtle color to another, without noticeable transitions.
I recommend using between 1000 - 2000 patches for most circumstances. If a program makes use of iterative profile tuning, go ahead and follow the recommendations of the software and use fewer patches. However, even the iterative programs I've used seldom improve things if you are using a reasonably large patch set to begin with.
Scrambled or visual
Profiling targets can either be arranged so the colored patches are in a kind of progressive order, from one shade to the next - or scrambled (some use the term "chaotified") so that the patches are in a random arrangement. If your printing process has any trouble maintaining consistency across a sheet, then using a randomized target can help you get a more representative profile. An offset press would fall into this category. Any inconsistency in the printing across the page will not end up skewing one color group that happens to be in that location on the page. Instead, that inconsistency is spread randomly through the various colors. Spreading fluctuating colors around may not sound like a great idea, but the profile's main purpose is to capture the behavior of the press, and this inconsistent printing is a valid aspect of how the press works. Incidentally, this is also why we like to average several profiling targets throughout a run in order to make a press profile.
A visual target has the advantage of being laid out in a visually organized manner. You can see the progression from one color to another. If you get familiar with the visual layout of your target, you can immediately recognize whether the linearity of the printer is smooth or erratic, if a particular ink is not printing, and where key color patches are located (CMYK, max black and paper white.) These can help you spot errors in printing very quickly and easily (and before you waste more time building a profile.) A visual target is generally used only when the printing consistency is very dependable, such as with inkjet printers, silver halide printing and the like.
Since our eyes are so discerning when distinguishing between subtle shades of gray, the ability of a profile to accurately reproduce neutrals and near-neutrals is highly valued. In the past, programs like GretagMacbeth ProfileMaker used targets that specifically included columns of near-neutral patches in order to 'over-sample' this very important part of the color spectrum. Monaco Profiler targets were laid out in a perfectly uniform grid and seemed to manage neutral rendering very well without these extra patches, perhaps because most users used targets that had a higher density of patches overall.
The newest entry into this field, X-Rite's i1Profiler, uses a combination of these other two tactics. The target generator in i1Profiler creates colors in an evenly-spaced grid. And it will add near-neutral patches into the target as "filler" patches, depending on the exact patch count of the target. If neutral rendering is particularly important in your work, it would be worthwhile to know this formula and choose the patch count of your targets to make the most of this feature. For example, a 1006-patch RGB target made by i1Profiler has no near-neutral patches, while a 1005-patch target has 99 near neutral patches in three columns surrounding the neutral axis. Ironically, if you are wanting to over-sample these near neutrals, you might end up actually choosing a lower patch total in order for the target generator to create more of them.
Confirm no color management
In order to make a good profile, we want the profiling target to capture the 'raw' state of your printing process. In your RIP, you still need to have your ink limiting and linearization turned on of course (in the RGB world this is handled by choosing your media/paper setting) - but any use of ICC profiles (any color management) must be disabled all along the printing path.
This is old news to veterans of color management, but if you are a novice or have inexperienced people printing targets and creating profiles in your organization, it pays to have an easy means to confirm that no color management is left on when printing your profiling targets. If you print with a profile made from a target with color management on, you are basically "double-profiling" and your prints will be desaturated with perhaps a brown or bluish cast - not a good profile at all.
The recent advances in color management have done nothing to make it easier to do this - and some have made it harder. For example, the newest version of Photoshop (CS5) no longer has an option to turn off color management in the printing dialog. So in order to print a target properly you need to use a different program, or a method to work around this limitation. (See here)
There are a couple of easy ways to check your target to verify that color management was indeed turned off when it was printed. With RGB targets, check the 100% yellow patch to see that it contains only yellow ink. If there are droplets of any other inks in there, then that is a clue that something is getting in the printing path and making color decisions. With CMYK prints, find a patch that is supposed to be composed of K (black)-only ink, and check to see that it indeed has only black ink there. (See sidebar) This is another incidence where a visual target comes in handy. But you can also find these patches on a scrambled target by bringing the reference file into Photoshop and using the eyedropper to check the color build of the patches. If you have ColorThink Pro, this task is even easier since you can order the colors in the reference file by color and quickly isolate the strongest yellow, the K-only patches, etc. (Click here for ColorThink Tips and Tricks)
Size of profile
Some profile building programs offer an option for "size" of profile. No, sorry - this is not a magic button that will make your printer capable of reproducing all the colors of the rainbow. This option is not referring to an increase in the color gamut of your printer, but rather how detailed that profile will be. A larger size might have something like a 33 x 33 x 33 grid so that any sudden transitions or irregular gamuts can be accurately reflected in the profile with more detail. But be careful - a bigger profile size results in a larger file size, and with this setting profiles can be made as large as 10 MB or more. (Try embedding THAT into a jpeg you email to your Uncle Lance.) In general, the normal sized profile will work fine for most uses. And besides the larger file size, there is nothing wrong with making a larger profile.
It's great to be part of an industry as it's coming into its maturity. The software that didn't work well is gone and the good software that is still here is still getting better. There are different ways to design a profiling target and more options when building a profile. If we know more about what these choices are intended for, we can make wise decisions which will save us time and effort, and at the same time create profiles in which we can have great confidence.
Thanks for reading,