Life is full of colors and nuances. As we know, the colors can give feelings of joy, sadness, calm, fear, etc.; it depends through which eyes we are looking. The same happens in the printing market, even if someone prints single-color or multi-color job, the feeling and perception can be completely different from one person to another or equally within oneself taking into consideration one’s mood or the time of day.
Color perception is different for everyone but can be measured. Everything that can be measured can be controlled allowing us to transform colors (subjective concept) into numbers (objective criteria). This creates a base for color conversion with the best possible colorimetric results and also obtains better printing results, which will be the same for everyone, irregardless if LAB, LCH, XYZ, etc. is being used.
One of the best printing methods that exists today is the extended color gamut that has been used for many years in the graphic arts industry. The extended color gamut can be compared with the recent advancements in medicine, which has reached a high level of knowledge and is able to predict, treat and prevent a large number of diseases, even though there are diseases that remain untreatable. The same happens with extended gamut: we can predict the results, prepare the job and prevent problems but not all projects can be printed and sometimes the treatment is not correct.
Due to all these reasons, it is a plus to have control of the prepress and printing process strictly in order to achieve good machine characterization and color management. How can we achieve this? First, we need to define our standard machine parameters, those that we know will not fail. After this, we need to calibrate and define screens, dot shapes, angles, minimum printing dot, dot gain curves, colors, etc. In the end, we are able to obtain the color profile that will be the prepress base to prepare the projects.
Although we have the best machine calibration in the world, results are not guaranteed. The key to success is to know the limitation of extended gamut and use it correctly to avoid any kinds of issues. Not all colors will fit in the gamut of our printer although there can be very important tonal variations.
In the example, we have a spot color reference with a gradient and on the right side, the conversion of extended gamut with orange, magenta and yellow. Although the solid color are correct, we see that the color difference deviates considerably and the orange and yellow are more prominent than the magenta. This is due to the tone overlapping between the three inks not being the same. In this case, the linear passage is from 100% to 0. This occurs more often than it may seem.
This is just an example of one of the extended gamut limits. This limitation stops with awareness, allowing us to control and correct it, as well as being able to match the different color tonalities. Keeping colors with a linear tone is at the core for optimal printing.
Looking at the picture above, there may be a high color quality of magenta, cyan and yellow, but due to these colors being nonlinear, the difference of tones from 100% to 0 is very likely. To maintain a linear tone of the different colors, even if they are CMYK or extended gamut, it is necessary to control the dot gain curve.
There are different methods to control the linearity of the tone with dot gain such as an ISO 12647-2, which defines a group of curves according to the material and the ruling on which it is printed to maintain linear tone.
However, this is not the best method to ensure a high standard of tone linearity because we are seldom able to simulate the same conditions which the ISO standard has tested. Other methods are more accurate, such as calculating the dot gain through the percentage of ΔE or SCTV. The ΔE is generally used to describe the difference between two colors, but it can also be used to calculate the difference between a color and the substrate. This allows us to maintain a stable color tone by calculating the percentage of ΔE in the transitions from 0 to 100%, where 0 is the material and 100 is the solid.
This method is specified for extended gamut extra colors since there are no standard processes to ensure the linearity of the color.
By having control of color tones, we will achieve a wider gamut, natural colors and avoid greyscales losses. Through prepress, the printer will be able to print with stability, giving predictable results that can be identically repeated as many times as necessary. The brand owner will obtain the best possible results according to the machine’s capabilities, and these results are measurable, therefore everything is equal.