The role of grayscale levels
Print resolution is undoubtedly a critical aspect of quality control and preflight processes. This concept is relevant both in graphic software and during lithography, and its correct setting can significantly enhance the quality of the final output. However, it’s often misconfigured. This raises the question: on what basis are resolution values determined, and what values should be set?
The answer lies in the structure of the human eye and its ability to distinguish colors in "grayscale levels." Furthermore, fundamental principles in color management and the brain's color perception are also dependent on the number of levels the eye can discern.
To illustrate this process, let's consider a simple example using black, white, and gray. For the human eye to perceive an image as continuous and analyze it, it requires a limited number of dark and light levels. After that, the perception of color is analyzed based on the definition of brightness in the brain's system. Let's examine this division from pure white to pure black to see how accurately the eye can distinguish these levels and subsequently colors.
Initially, we place seven levels between black and white. Each level gradually transitions towards the other color. We increase the number of levels to eleven, fifteen, fifty, and one hundred, but a banding effect or step pattern is still observed between black and white. This indicates that more levels need to be added between the color origin and destination to create a smoother color surface, allowing the eye and brain to perform a more accurate analysis of the image.
When the number of grayscale levels reaches 256, the eye perceives the necessary quality for a smooth visual appearance of the color surface. Any more levels are difficult for the human eye to distinguish and are generally unnecessary in printing. Pay close attention to this number, as it is crucial in determining file resolution in design and print resolution in lithography. It can also prevent many problems during the production process.
The Grayscale Levels Formula
Now, let's explore a specific formula used in defining halftone structure and its connection to the number 256. In a lithography machine, the laser produces a series of dots that combine to form a continuous image. However, each halftone dot is created within a pixel grid, and as discussed in the halftone section, increasing the number of cells and microdots improves the quality of the final halftone.
The creation of halftone cells in a matrix can begin with different numbers of rows and columns and gradually increase in this experiment. This process initially starts with a 4x4 matrix and eventually reaches 17 states. This quantity is insufficient to produce a halftone with a shape that can provide suitable quality in the final output.
We continue this process up to 16 units, and after color testing in printing, it becomes evident that this number of cells creates a satisfactory quality for printing. However, we also arrive at a familiar number: 16*16=256. This figure is the same as the number of grayscale levels the eye requires to perceive an image smoothly. Therefore, we stop increasing the number of cells at this point. We add one unit for white to this formula, resulting in the following:
(Halftone Cell)^2+1 = Gray Levels
Meaning of the Formula
This formula states that to achieve grayscale levels for proper visual perception of a continuous image, each halftone dot must have a certain number of cells in width and height. In this way, the golden numbers 256 and 16 appear, which will be used extensively in subsequent discussions. This formula and its numbers are crucial in defining the role of print resolution in the LPI section and file resolution as PPI.
The number 256 is suitable for defining both the meaning of color and light in the human eye and as a criterion for creating a halftone matrix in lithography. Meanwhile, the number 16, which is part of the microdot production process, is used in determining file resolution.
In this process, understanding the formula and how halftones are created can prevent problems such as dot gain, banding, and choosing the wrong file resolution for printing. Moreover, it improves the understanding of the color management process for more accurate production.
