Dot gain adjustment in color profile
When we talk about the control of printed dots, we are definitely facing different issues such as changing the size, angle, and shape of halftones. Tips that each can completely affect the quality of product production. In the meantime, the dot gain is more noticeable because it can be controlled and checked by quality control officials and graphic designers before printing, as well as by the machine during printing. On the other hand, if the lithography operator is skilled, this problem can be checked and controlled.
Dot Gain, which is better to use its equivalent term, TVI (Tonal Value Increase), always happens and is said to increase the size of halftones or printed dots. For example, the value of 15% means the growth of halftones by fifteen percent during printing and enlarging them, which will make the file and shadows appear darker, and of course, the size of the halftones is both different and constant.
In the best state of production, it is tried to control the dot gain and bring it close to the standard level. The amount of dot gain depends on the type of printing machine, material, ink, and other conditions such as humidity, and it can change in different parts of the color. Changing the size and enlargement of printed halftones, if not controlled, can cause shadows to disappear and the final product to be printed darker.
The first step to define and control dot gain is in color management and color profile structure. (Image on the left.) But, this work should consider the type of ink, color separation, the device's ability, and the printed material. The worst way to create a profile and get production quality is to register a low number or choose a color profile with small halftone growth.
In some cases, point gain can be defined by the monochrome color channels or spot colors in Photoshop's color adjustment window. (Image on the right.) But this value must also be defined according to the device and printed materials. Setting it wrong results in a final file with halftone growth. This is meaningless at print time, and it will hurt production.
Dot gain amount
Dot gain (halftone size change) varies depending on location during printing. For example, a 15% value indicates a 15% size increase for midtone halftones (50-65% shadow range) in most cases.
Halftone growth is considered a problem when it exceeds its defined limit and causes color damage in the print. Because the size change always happens and it is not possible to prevent it in all places of bright shadows and zero it.
Another important point in this concept is changing the size of the halftone and its meaning. It should be noted that when a number is mentioned for the growth rate, that number can be divided and controlled in several parts. For this reason, the whole issue of growth cannot be limited only to the time of printing. Part of this size change occurs during file output, part during lithography, and most of it during printing.
Halftone growth refers to the increase in the size of halftone dots during printing. This growth doesn't directly affect the overall darkness of the printed image. Instead, it's a technical aspect of the printing process that can impact image quality.
For example, a 15% or 30% increase in halftone size might not result in a noticeably darker image. However, this growth can still affect factors like color accuracy and detail retention.
QC officer should prioritize checking and controlling halftones during the preflight stage. This helps ensure accurate color reproduction and prevent print quality issues. Likewise, the correct definition of print resolution can prevent unnecessary dot gain.
A few important points
1) We can control halftone growth in three areas: file prep for printing, lithography, and the printing house. Although some quality control officials test this item only at printing, many points can be defined based on ISO standards before production. One of them is the growth of halftone.
2) When you define the color profile on the file, you can set the halftone size change error factor. It should match the type of device and printing material shown in the previous images. The profile setting and change apply to gray and spot channels.
3) Halftone growth rate is not a fixed number for each color. For example, we can monitor, adjust and control the conversion process for each CMYK color individually. Using a fixed number for all colors as a variable is usually not a professional quality control process.
Dot gain control process
- To accurately measure and control halftone growth, specialized tools like iCPlate can be used. These devices allow you to assess changes in halftone patterns and make necessary adjustments. By monitoring the TVI curve and utilizing a densitometer, you can ensure that halftone growth is within acceptable limits and that the printed colors are accurate. This requires a combination of technical knowledge and practical experience in color management and quality control.
- Unlike dot gain, there is also halftone thinning or Loss Gain. It happens less often, but it can be checked in the pre-flight structure and the final print output.
- Normally, a fingerprint can check the device and printing material's ability to control the halftones. By adjusting the cylinder's pressure or changing the printing material, the halftones can be improved.
Not all devices have the same halftone growth. Technical tests define the correct amount. Generally, a 15% growth is often used. However, this is an incorrect figure for quality control.
Dot gain often darkens images and makes shadows disappear. Yet, this can be harmed by improper ink coating, too much pressure, or selecting the wrong anilox in flexo printing.
