Print resolution related to file quality
As we know, the structure of a printed image is composed of small dots called halftones. These dots play a crucial role in forming print resolution, which is a key factor in quality control. In this article, we will explore how the final plate resolution in lithography affects the file resolution for designers and how important it is to control this factor.
A halftone dot appears as a small shape such as a circle, oval, square, or other form. However, each of these dots is defined in a matrix grid called a Halftone Cell. This matrix consists of smaller squares called microdots or Pixel Spots. The greater the number of these microdots, the more accurate the final shape of the halftone dot will be, and ultimately, the better the print quality.
Print Resolution: DPI
A very important factor in defining print resolution and creating halftone dots is the number of microdots per inch, referred to as DPI. A laser lithography machine can define the final resolution or required DPI for producing microdots per inch at predefined levels such as 2800, 2400, and other values. Of course, the selection of these numbers is coordinated with the capabilities of the lithography machine, and it cannot be arbitrarily defined at very high levels without a reason.
Each dot indicates the presence or absence of a pixel unit for file information and its registration in the halftone matrix. The number and structure of microdots have been examined and evolved over time by various companies, and the halftone matrix grid is still being refined and changed in detail. This can play a key role in producing rosette patterns and forming a halftone angle in a grid in a uniform manner.
Print Resolution: LPI
Another key unit in halftone structure and final resolution is the number of lines of halftone dots defined per inch. For example, after preparing each halftone dot and defining its matrix grid in DPI, it is now time to arrange each dot in a row next to other dots. The number of rows formed is known as lines per inch or LPI. In this case, by increasing the LPI value to 150, 175, or other defined values, the size of the halftone dots changes.
Of course, increasing print resolution means reducing the size of halftone dots, and the smaller the size, the more attention must be paid to the quality of the ink and the final material. Also, keep in mind that the correct definition of LPI depends on the DPI value and is a number that is selected in grayscale levels suitable for the human eye.
Increasing or decreasing the print resolution in the halftone structure through LPI and DPI, even considering the material, type of printing press, and the capabilities of the lithography machine, is also defined. Increasing the resolution indicates a smaller halftone dot size but cannot be directly related to increasing print quality.
The higher the resolution, the more skill is required to control the file in lithography and printing, and the production material must also be selected with greater care. Increasing LPI unnecessarily can cause problems such as color banding, dot gain in colors, and an unnecessary increase in file size for RIP.
File Resolution: PPI
After defining the quality level as LPI and DPI in lithography, it is time to set the file resolution for graphic designers. It should be noted that all these units are related to each other, and choosing an arbitrary quality can sometimes damage the standard quality control process.
The key point is that the print resolution is defined first, and the file resolution changes according to the process you will see later. For a standard print, we use various criteria, one of which is called the "Quality Factor." This coefficient can be defined as 1, 1.5, 2, and in very special cases 2.5. This factor is multiplied by the print resolution or LPI, and the result is the quality of the digital file in design, known as PPI. For example, if the lithography resolution is 150 LPI, with a factor of 2, you can achieve a file resolution of 300 PPI.
The appropriate number:
The question that arises here is choosing the appropriate number for the quality factor in printing. Because with the default 150 LPI, you can reach different numbers such as 150, 225, 300, and 375 in pixels per inch or PPI through the quality factor!!!.
The answer to this question depends on the lithography. That is, the quality of the printing material, the type of printing press, the ink volume, the laser capability of the lithography machine, and even the type of graphic elements in the design such as gradient and texture can play an important role in selecting LPI. This is where we see that the issue of selecting file resolution should not be initially defined by designers, and the main criterion is in lithography and with regard to the production discussion.
Finally, it should be noted that unnecessarily increasing the resolution without coordination with production managers and print quality control managers not only does not increase production quality but can also cause dot gain, banding of gradients, set-off, and other damages in the production process.
