File resolution related to design
One of the most crucial aspects in quality control and standard production processes is examining the file resolution, which is a specific numerical value expressed in PPI (pixels per inch). This value is applied to pixel-based images and is typically set to 300 by default.
However, this number doesn't always accurately represent the print quality, as it needs to be adjusted based on the production process. In simple terms, file resolution and its corresponding numerical value signify the number of pixels within an inch and can be modified within image editing software like Photoshop. However, determining the correct numerical value for image quality involves specific rules.
Beyond the default setting, achieving the ideal file resolution requires a careful consideration of several elements:
- Lithography: The capabilities of your lithography equipment play a significant role in determining the appropriate file resolution.
- Halftone Structure: The arrangement of halftone dots, as discussed in the previous section, influences the overall print quality.
- Printing Process: The specific printing method (e.g., offset, flexography) and the associated equipment have implications for resolution.
- Material Type: The type of paper or substrate used can impact the required resolution.
- Design Complexity: The complexity of your design, including the presence of gradients, textures, and fine details, can influence the optimal resolution.
By carefully considering these factors and understanding the relationship between file resolution, halftone structure, and printing processes, you can make informed decisions to ensure the best possible print quality for your packaging designs.
Every pixel counts. Understanding file resolution is essential for producing high-quality prints. Explore the connections between halftones, LPI, and DPI to elevate your packaging designs.
When you send your file to a lithography, a laser analyzes or maps all the information within it. Each machine in the lithography process, responsible for creating plates (such as clichés, zincs, and cylinders), may have its own numerical guideline for resolution. The higher this number, the more powerful the laser is in mapping and producing halftones. For instance, if a machine's laser resolution is 2400 DPI, it means the laser can create 2400 laser dots per inch to form microcells.
Primary process
In our previous discussions about print resolution, we established that the number 16 represents the grayscale levels that the human eye can distinguish, resulting in a formula: 16*16=256. This formula helps us understand the color depth that our eyes can perceive.
Now, let's introduce a crucial formula that connects the laser resolution to this number 16 and ultimately determines the final output for halftones:
DPI ÷ 16 = LPI
In this formula, LPI represents the Lines Per Inch, which is the basis for the halftoning process. The LPI value is determined based on the printing material and the desired quality of the print. For instance, a coated glossy paper typically requires an LPI of 150 for high-quality printing. But what happens if we choose 175 LPI? The answer lies in the formula we just presented. Let's illustrate this with an example:
If a lithography machine has a resolution of 2400 DPI, and we use the constant value of 16 for the number of grayscale levels, then the optimal LPI for this machine can be calculated as follows:
2400 ÷ 16 = 150 LPI
This device allows you to use a higher LPI, but since it exceeds the optimal level, you may encounter issues like dot gain and banding during printing. Increasing LPI unnecessarily cannot guarantee the desired print quality because the human eye only requires a certain level of grayscale. This also affects the file resolution. Moreover, the machine, when operating at optimal conditions, can accurately produce halftones. Exceeding this limit can damage the dot structure and result in poor print quality.
When using a higher LPI, each dot becomes smaller, requiring greater precision during printing and higher quality printing materials. However, standard conditions are not always achievable, and increasing LPI only harms print quality. To prevent common printing errors, we recommend optimizing the LPI based on the provided formula.
Determining File Resolution
Based on the aforementioned factors influencing print quality, we can easily define the file resolution. The quality of the digital file that designers work with is determined using the following formula:
LPI * 2 = PPI
In this formula, the number 2 is a quality factor. Previously, we mentioned that this factor can be 1, 1.5, 2, or in rare cases, 2.5. The number 2 is the most commonly used value. If you've noticed, considering 150 LPI, which is suitable for most high-quality printed works, we get the well-known file resolution of 300 PPI.
This result has become so widely accepted for production and printing that it has become a general rule, unfortunately being suggested for all types of printing and materials. It's important to note that in lithography, resolution is defined based on the type of material, number of colors, specific printing requirements, and the production machine. To achieve the best quality, the LPI should first be obtained from the lithographer, and then by multiplying it by the quality factor, the digital file resolution for images can be determined.
Resolution Table:
As previously discussed, many factors can influence the determination of the optimal resolution for an image file. However, remember that you should initially have a general guideline for determining PPI in images, and if it conflicts with the lithographer's recommendations, you should inquire about the reason:
|
Material |
LPI |
PPI (min: *1.5 - ideal:*2) |
|---|---|---|
|
Newspaper |
100 |
150 - 200 |
|
Magazine low quality |
133 |
200-266 |
|
Magazine high quality |
150 |
225-300 |
|
Packaging |
175 |
263-350 |
|
Perect printing |
200 |
300-400 |
* In this table, based on the quality factor of 1.5 for the minimum level and 2 for the ideal case, you can determine the optimal file resolution for Sheetfed Offset printing machines. However, for flexographic printing machines, since the presence and accuracy of Anilox, the amount of elastic modulus, various types of HD plates, and flexible materials are highly variable, it cannot be easily expressed in a simple numerical definition. But it's best to consider a minimum initial value of 300 PPI.
Remember:
- The values provided in the table are general guidelines.
- It's always best to consult with a prepress specialist or lithographer to determine the exact resolution requirements for a specific printing job.
- Factors like the complexity of the image, the size of the printed area, and the viewing distance can also affect the optimal resolution.
In conclusion, while the table offers a starting point for determining resolution, it's important to consider the specific characteristics of each printing project to achieve the best possible results.
