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Offset printing technology: NO is not allowed for ghosting and overprinting
Offset printing is known for three major issues: ghosting, overprinting, and bar. These problems can cause the printed image to appear blurry, with distorted tones and poor clarity. To ensure high-quality output, it's essential to identify and address these faults effectively. However, distinguishing between ghosting and overprinting can be challenging due to their similar appearances. Misidentifying the issue can lead to ineffective solutions, making it crucial to correctly differentiate between the two in order to maintain print quality.
Ghosting occurs when faint lines or side shadows appear next to printed dots or lines. These shadows are lighter than the main elements and can result in a loss of sharpness, affecting the overall clarity and color accuracy of the print. Ghosting can manifest in different forms, such as vertical, horizontal, or A/B ghosting. Vertical ghosting appears above and below the original dot, while horizontal ghosting shows up on either side. A/B ghosting is specific to multi-color presses, where the shadow on one side of the sheet appears opposite to the normal dot.
When ghosting affects fine text, it can make the entire layout unreadable, leading to wasted materials. In color prints, severe ghosting can distort the tone, color, and contrast of the image, especially in mid-tones, which are most affected. This can make it difficult to control the desired visual effects and achieve the intended print quality.
Overprinting refers to the process of aligning each color image precisely on the same position during multiple print passes. Accurate overprinting ensures that each color layer overlaps perfectly, creating a clear and sharp final image. When overprinting is inaccurate, the colors do not align properly, resulting in misregistration and visible discrepancies. This can occur due to mechanical issues, improper machine adjustments, or errors in the printing process.
The causes of overprinting inaccuracies include mechanical wear, incorrect machine settings, improper paper handling, and variations in material quality. For example, if the paper is uneven or has inconsistent moisture levels, it can stretch or shift during printing, leading to misalignment. Similarly, improper plate installation or unbalanced ink and water distribution can also contribute to overprinting issues.
While both ghosting and overprinting involve misalignment, they differ in their causes and manifestations. Ghosting is typically related to the physical movement of the blanket or cylinder, causing repeated shadows. Overprinting issues, on the other hand, are often linked to the positioning system failing to maintain consistent alignment between color layers.
In summary, understanding the differences between ghosting and overprinting is vital for maintaining print quality. While they may seem similar, addressing them requires distinct approaches based on their root causes. By identifying and correcting these issues early, printers can reduce waste, improve efficiency, and ensure consistent, high-quality results.