Profiling, Step-by-Step

The creation of a printer profile consists of 5 individual steps, some of which can be skipped with certain printer models (we will discuss this later).

Step 1: Preparation

The first step is probably the most obvious one: make sure the printer is working properly and handles the material such that it performs optimally. Every printer has manual or automated processes to ensure all working fine, and to compensate the material feed  paper and ink. Since there is no profile or software magic that will be able to fix machine problem blanket, rollers and materials that used for testing.

Once everything is set up correctly, Make sure to check (and double-check!) these settings; 

1. Machine performance (speed, trial run etc..)

2. Blanket quality and tightness

3. Roller setting

4. Ink swipe setting or zero setting

5. Raw material selection

6. Working condition and environmental aspects 

Step 2: Ink Restrictions

Once we have determined our print priorities, and ensured our printer is running smoothly, we have to verify that the printer is laying down correctly calibrated ink amounts. The first step of this process is to make sure that all ink channels are restricted to meet the desired target. Most RIP software will set the target at the point where the dark colors (cyan, magenta, yellow and black) reach the ‘tipping point’. This tipping point occurs when adding more ink starts to cause image quality issues, or no longer adds any additional color and only makes the print darker. Most RIP software's also use the measurements taken during this step to set the light ink amounts and light ink mixing levels. It’s important to remember that 100% light ink is as much liquid as 100% dark ink and since we are fighting ink amounts here, it is critically important for the light inks to be set correctly.

As you are probably beginning to see, ink restrictions are a giant topic all on their own. Most RIP software will set them automatically with good results, but there are a lot of great tricks you can play once you have an advanced understanding of the mathematics behind them. Let us know through the poll below if you want to know more about them.

Step 3: Linearization

After the ink restrictions have been set, and we have found a new 100% for each color channel, and the dark and light inks are mixed, we are ready for the next part of the process: making sure that each step in between the material color (0% ink) and the maximum ink amount (our new 100%) prints correctly. This is fairly simple: the RIP software generates a chart with multiple steps for each ink color channel. Note that this chart looks almost the same as the one we measured in step 2, but this time the ink channels are clipped to the new 100% values we found and the light inks are mixed into the dark inks. Most RIP software produces a chart that contains 20 or 33 steps per color channel. By measuring each step and comparing the values to the target, the software calculates the correction it needs to make in order to reach the desired target. Imagine that our target is to get a linear result, this means that when we ask the printer to print 50% of a certain color, it will print enough ink to produce 50% on the material. This sounds easy, but keep in mind that materials absorb ink (and some more than the others). Also aging of printheads and changes in environment will have an impact on how inks dry up. For that reason, it is recommended to linearize the printer regularly.

Some printers do have built-in measurement devices that are capable of performing this calibration all by themselves. There is no guarantee that this will work as well as an external measurement device, especially when calibrating materials with uneven surfaces, such as textiles, mesh banners, or anything transparent or reflective. We are planning another Deep Dive article about the profiling of transparent and backlit material. Keep an eye on this blog!

Step 4: Ink limits

This step sounds simple, but can be very complicated. The simple version is that you print a specifically designed chart from the RIP software, and pick the last value in the row that does not show issues. The complicated version is that it is never that easy and that this is the only step of the profiling process you have to decide all by yourself, without the help of measurement devices.

We have focussed on individual ink channels so far, but now it is time to look at what happens when we start mixing inks. Creating red, green, or blue, requires us to mix 100% cyan, 100% magenta, and 100% yellow, resulting in a 200% ink load. If we then want to make dark red, dark blue, or dark yellow, we will have to mix in one of the other colors (magenta or cyan), until the combination turns so dark that we start calling it black. This results in a 300% ink load. The problem with most inkjet inks is that the combination of cyan, magenta, and yellow will not create a deep dark black, and for that reason, we will start adding black inks until we reach the point where the ink amount becomes so high that we will start seeing issues, or where inks no longer dry in time.

Our goal is to define ink limits as high as possible - yes, higher is better! It is a myth that lowering the ink limit will save tons of ink. There are better and more efficient ways to achieve ink efficiency, without compromising the quality of the profile.

Step 5: ICC Profiles

We are almost done, and in some ways we already are! We created a setup that prints with the speed we desire, the amounts we need, and the result looks great already! There is one problem: up until now we have adjusted amounts of inks, but we haven’t looked at the colors yet. The most common method is to create an ICC profile, a standardized file format and method of creating a digital color snapshot of a device that creates or registers color. Printers are obvious, but also displays, projectors, cameras and scanners can be profiled with ICC profiles.

This is a visual analysis of colors and transitions

This step also requires a measurement device and software that allows you to create ICC profiles. Most modern versions of RIP software do have this capability built in. The first step is to print the so-called “ICC target”, a file that contains between 1,000 and 2,000 colored patches. The number of patches depends on the type of printer you have. If your printer has additional colors, besides the CMYK colors, such as orange or green, the number of patches could increase to more than 3,000. Make sure all the patches are smooth, clean, and dry before measuring. Some inks will have drastic color changes while drying, and measuring too early will result in a snapshot of your printer which is inaccurate.

Let it dry, measure the patches, and move on the next step: setting the ICC parameters. Now this is where things become more complex. All the various RIP software and profiling solutions offer a wide range of settings and tools to optimize the results, but we will cover the detailed ins and outs of ICC settings in a separate blog post in the future.

Anyone who has printed a picture knows that what you see on your computer or cellphone screen almost always looks very different in the final print. With family photo, we often shrug our shoulders and accept this as inevitable - after all, the moment the picture captures is often more important than what it looks like, right?

However, the story is ENTIRELY different when printing is your business and the color you print is part of the branding of your customer. Similarly, both professional and amateur photographers are constantly striving for better quality and more accurate color in their photos. Simply put, outside of your family photo albums, color becomes critical.

In this episode, we dive deeper into the mechanics behind digital color conversion and will explain rendering intents - the 'black magic' at the core of this process.

Every imaging device is different

Let’s stick to the example of printing a picture. Pictures nowadays are captured by digital cameras, and cameras use imaging sensors. These sensors capture light and turn it into digital information. Light consists of three color components: red, green, and blue, and we shorten this to RGB. That is why color scientists and color management professionals call cameras “RGB devices”. Files coming out of a digital camera are called “RGB files” for that exact reason. Your computer screen consists of millions of light-emitting elements which create the colors and images we see and for that reason, a computer screen is also an RGB device.

And this is where the challenge starts: cameras and computer screens are different devices and the red, green, or blue of a digital camera might look different from the red, green, and blue of a computer screen. Imagine a wall of televisions at your local store: they all show the same image or movie, but all look slightly different. Different components, settings, price levels, and technologies mean that those different RGB devices all have a different color gamut.

What's a color gamut you ask? A color gamut, or color space, is the total range of colors that can be reproduced (or in the case of a camera, captured) by a device. When using multiple color devices (cameras, screens, printers etc) converting color information between these different gamuts is - needless to say - not always seamless.

How conversion between devices works

This is the reason we need conversion and it is also the reason we need to find a way to describe what a certain device is capable of producing, or which colors it captures. Luckily there is a standard that has been adopted by all major players in the computer industry. It is called an ICC profile and it helps computers understand what color is and what a certain device is capable of. These ICC profiles are attached to image files in the background of your operating system, or stored in the computer applications you use. When you open an image, the ICC file attached to it is used to read the RGB values in the file and translate them into digital colors (also known as LAB values).

Your computer screen also has an ICC profile attached to it, not physically but digitally in the operating system of your computer. The color management system in Windows or macOS uses both of these profiles to convert the RGB values in the files to RGB values for your screen, with the goal to reproduce the colors. This could result in different RGB values since red on your screen might be different from red in your camera.

Doing the impossible

This conversion is easy when you are converting from a small color space to a large color space, as all colors can be reproduced and nothing will be lost. It becomes a challenge when the color space of the file is very different from the screen, or the printer. In reality that is what happens with almost every digital camera to printer conversion: most cameras capture so many colors that only 50% of them can be reproduced by a normal color printer. Also: using a different material or paper will have an immediate effect on the number of colors you are able to print. Imagine the difference between printing on high-glossy photo paper and toilet paper: the latter is designed to absorb, which results in images with very low saturation.

In color management, we use so-called “rendering intents” to convert from one color space to another. Rendering intents are not optional, meaning that they are always applied, whether you are aware of them or not. Think of them as a strategy on how to deal with colors. Their effect is most noticeable when you are converting from a large to a small color space, because that is when you are in trouble, 99% of the time. It is almost like someone that tells you “alright, this is an impossible color, what do you want me to do with it?”.

The different rendering intents

Rendering intents are mathematical methods of mapping colors from one color space to another. Both colors that are in gamut and out of gamut are being mapped. The rendering intent has a direct influence on how this is done. There are 4 official (read: ISO standardized) rendering intents defined, which we'll go through one by one.

1. Perceptual (or photographic) rendering intent

This method preserves a relative distance between all colors in a file when being mapped from one color space to another. The best analogy to explain how this rendering intent works is to imagine squeezing a large balloon into a smaller glass box, by letting air out of the balloon. The entire balloon changes, the shape stays the same but just becomes smaller, but it is still recognizable as a balloon. This applies to colors too, resulting in a picture that might look darker/brighter/different than the original, but still has all the correct color transitions and details in dark areas. Hence the alternative naming “photographic”.

Perceptual or photographic rendering intent

Original vs. Perceptual or photographic rendering intent

2. Relative colorimetric rendering intent

This method leaves all colors from the input color space that are fitting into the output color space unchanged. They are exactly reproduced and don’t shift and change. However, all colors that are out of gamut will be placed on the edge of what is possible. This often results in a loss of detail in dark or oversaturated areas. Think of a picture of a car with dark tires with a clearly visible tire profile. Converting this image into a much smaller color space with the relative colorimetric rendering intent will result in a loss of all detail in the tires, resulting in a dark area without any visible details. This is the most used rendering for vector CMYK files because they often contain logos and corporate colors that need to be reproduced as accurately as possible.

original vs relative bpc

Original vs. Relative colorimetric rendering intent

3. Absolute colorimetric rendering intent

This rendering intent does all the same things as the relative colorimetric rendering intent, except for one big difference: it simulates the white point of the input profile. Imagine using an ISO Coated FOGRA input profile. This profile describes a standardized offset printing press, using FOGRA certified CMYK inks, printing on a standardized coated paper. This paper has a particular color and as we all know: white is not just white. The white point tag in a profile describes this white in LAB values. When using the absolute colorimetric rendering intent, the color engine will also convert the white point and will try to simulate it on the printer or display. This rendering intent is used for proofing applications, where an inkjet printer or computer screen is used to predict the output of a production printer. It also works well when trying to mimic the color of a printed sample. The reason is that most inkjet inks are semi-transparent, which makes the color of the paper affect the color you are viewing.

original vs absolute

Original vs. Absolute colorimetric rendering intent

4. Saturation rendering intent

The final rendering intent aims to maximize the use of the output color gamut. This means that each color from the input color space will get converted into the most saturated color possible. This results in bright and saturated colors, but accuracy is often totally lost. This rendering intent is rarely used in production workflows but might come in handy when trying to achieve the impossible in case a requested color is out of gamut. You might get lucky!

original vs saturation

Original vs. Saturation rendering intent

There is also an add-on setting for both the relative and absolute colorimetric rendering intent, called: “Black point compensation”. This setting applies a compression to dark colors that are out of gamut. It basically works like a perceptual rendering intent within a relative or absolute colorimetric rendering intent, but only for darker colors. When a RIP or color manipulation software, such as Photoshop, supports this mechanism, the best results are often achieved by using a relative colorimetric rendering intent with black point compensation. It solves the issues of the details in dark colors disappearing and maintains all colors that are in gamut.

How to apply this knowledge?

This is a lot of information to take in and it is also quite abstract. The best way to familiarize yourself with it is to try it out. Photoshop allows you to convert colors with a preview, which shows you on-screen what happens. Try something extreme, for the best results. Photoshop comes with a standard ICC profile for Japanese Newspaper presses, this profile has a small gamut and it effectively shows what happens when you convert from a colorful RGB picture to a newspaper printing press gamut. The differences are huge and the effects of changing the rendering intents are immediately visible. Also, the use of the black point compensation can be simulated on-screen. Like with everything else in color management: trying and playing around is often the best way to develop a feel!

Rendering intents and printing workflows

The next step for every printing company is to use this new insight and apply it to your daily practice: the printing workflow. We learned here that selecting the correct rendering intent can make a huge difference in output. Picking the correct one is not only important to get the maximum out of your printers, but also to make sure you are able to produce repeatable quality over time. In general, a relative colorimetric rendering intent in combination with black point compensation gives the best results for most printers and materials. Most RIP software will support black point compensation by now, and you can typically find it in the ICC color settings. In case you cannot find it, contact your supplier and make sure you are using the latest version.

ONYX rendering intent profile settings

ONYX rendering intent profile settings

The best result for a consistent print workflow is rarely the absolute maximum color saturation, which you could try to achieve with a saturation rendering intent, but rather a consistent and achievable result, which you are able to reproduce at any given moment in time.

There is nothing magical about digital colors, since it is based upon mathematics, although we believe that color still works magic in our daily lives!

Feel free to contact us if you want to know more about color management, managing workflows, and getting your printers set up for maximum performance! If you enjoyed this article, check out our previous Deep Dive into Printer Profiles, and our tutorial on how to Set Ink Restrictions Like a Pro!