Overprinting: a double-edged sword
Overprinting, also known as knockout or knockout color, is a technique used in printing where one color is intentionally printed over another. This can create new colors, enhance visual effects, or conceal registration errors. While overprinting offers several advantages, it's essential to understand its limitations and apply it judiciously. We said many things about overprint before and now we want to talk about newer features.
Four Prohibitions in Overprinting
1. Color Change: One reason to avoid overprinting is color alteration. While black is relatively unaffected by the saturation of underlying colors due to its properties, using overprint on a color like yellow with a blue background can shift the resulting color towards green.
This happens because a portion of the background color is introduced into the foreground color to cover the underlying area, altering the color codes. In such cases where color changes are undesirable, techniques like trapping can be used.
2. Spot Colors: Spot colors are solid, pure colors with high saturation, often used for corporate or brand identities. Overprinting can alter the saturation and properties of spot colors, making them unsuitable for applications where color consistency is critical. In these cases, trapping is a more appropriate technique.
3. Grayscale: Overprinting can also affect grayscale elements. In many cases, grayscale elements are composed solely of black ink. Overprinting can introduce a tint to these grays, diminishing their visual impact. Therefore, overprinting should be avoided for grayscale elements that rely solely on black ink.
4. White or Very Light Colors: Overprinting white or very light colors can cause them to disappear entirely in the printed output. While this might be visible on screen, the overprinting process can eliminate these light colors during printing.
This can happen, for example, when a designer copies a text with overprint enabled and then changes the color to white.
Color Combination in Overprinting
The color combinations resulting from overprinting can sometimes be misleading. If you expect the color to remain unchanged after applying overprint, you might be surprised by the results. For instance, when examining a design with overprint in Adobe Acrobat or Esko Deskpack, the black text might appear to have a slight tint. This is due to the overprinting process combining the background color with the foreground color.
Special Overprinting Techniques
A fascinating technique for quality control and cost reduction is using overprinting for two spot colors. While overprinting can alter colors, it can also be used to create new colors without the need for additional inks. For example, in high-volume print jobs like calendars, books, and labels, designers often limit themselves to two or three colors to save time and material costs.
By using overprinting, a third color can be created by combining the two existing colors. This can be achieved by overprinting yellow on a blue background, for instance, to create a new shade of green. This technique reduces costs by eliminating the need for a third ink. In this regard, it is suggested to check the TIC index before production.
Advantages of Overprinting
- Color Creation: Combining colors through overprinting can create a wider range of hues without introducing additional inks.
- Registration Error Concealment: Overprinting can help to mask minor registration errors, improving print quality.
- Visual Effects: Overprinting can be used to create interesting visual effects, such as shadows or highlights.
- Cost Reduction: In certain cases, overprinting can reduce the need for additional inks, saving on costs.
Limitations and Considerations
- Color Shifts: Overprinting can sometimes unintentionally alter the color of the underlying object.
- Ink Consumption: Overprinting can increase ink consumption, especially when used extensively.
- Technical Challenges: Some RIPs and software may have limitations or compatibility issues with overprinting.
- Specific Applications: Overprinting may not be suitable for all printing applications, particularly those involving grayscale elements or very light colors.
Remember that...
Overprinting is a valuable technique that can enhance print quality and create unique visual effects. However, it's important to understand its limitations and apply it strategically. By carefully considering the advantages and disadvantages, you can effectively use overprinting to improve your printing projects.
