Color Bar

Color bars are also referred to as color control bars, color control strips, or proofing bars. Color bars are rows of different colored patches printed in the trim area of the press sheet. They are used by proofers and press operators to control the trapping, ink density, dot gain, and print contrast of the proof or the printed sheet. They usually consist of solid and tint blocks of cyan, magenta, yellow, and black; two and three color solids and tints; and additional elements and patterns such as resolution targets and dot gain scales.

Solid process colors ofBlack, Yellow, Cyan, andMagenta. A color bar are used to measure ink densities.

Solid overprint colors include blue (C&M), green (C&Y), and red (M&Y)

Screen tint patches usually 25%, 50%, and 75% of the process colors. A color bar are used to check for dot gain.

A color patch made up of 50C/30M/30Y. A color cast in the patches will show an imbalance in one of the colors, either from incorrect ink density or from dot gain.

There are several different types of color bars and which one to use depends on the type of printing being used. Prepress and print suppliers purchase original film or the rights to digital files of color bars and other test images. The film and files can then serve as constant reference points throughout the proofing, platemaking, and print processes. They are available from GATF (Graphic Arts Technical Foundation), DuPont, RIT (Rochester Institute of Technology), and others.

Color bars are an essential troubleshooting tool. They are easy to analyze, both visually and with a densitometer, which is an instrument used for measuring the relative density of any part of an image.

Color bars created for computer-to-plate (CTP) systems may require additional features than color bars generated for film.

Read more »

Some Digital Questions in Printing

Q: What is the difference between vector graphics and bitmap graphics?
A: A vector graphic is defined in a mathematical nature which makes it resolution-independent. A vector graphic can be printed clearly at any size. A bitmap image is formed by a rectangular grid of small squares, known as pixels. Each pixel contains data that describes whether it is black, white, or a level of color. Bitmap graphics are resolution-dependent they can appear jagged and lose detail if they are created at a low resolution and then enlarged or printed at a higher resolution.

Q: Where do vector graphics come from?
A: Vector graphics are typically created by illustration software such as Adobe Illustrator or Macromedia Freehand.

Q: Where do bitmap graphics come from?
A: Bitmap graphics are typically created by pixel-based image editing software such as Adobe PhotoShop. Additionally, bitmap graphics are generated from digital cameras and scanners.

Q: Can bitmap graphics be converted to vector graphics, and vice versa?
A: Yes. Software such as Adobe Streamline can convert bitmap images to vector images. Vector images can be converted to bitmap images by opening them with Adobe PhotoShop. Please note that converting a vector image to a bitmap image is rarely necessary, removes the resolution-independence of vector graphics, and should only be done if you have a very specific reason to convert the graphic.

Q: What are the different types of bitmap graphics?
A: A one-bit image refers to an image that is a solid color, with no shades of that color. A continuous tone image refers to photographic images, whether they are full color, black-and-white images with shades of gray (grayscale), or single-color images with shades of that color.

Q: What guidelines do you have for bitmap graphics resolution?
A: One-bit images require 600 pixels per inch. Full-color continuous tone images require 300 pixels per inch. Grayscale and single-color continuous tone images require 200 pixels per inch.

Q: Can I resize bitmap graphics in a page layout application?
A: These guidelines are for bitmap images that are used at their actual size. If the image is enlarged in a page layout application, the requirements enlarge by the same amount. For example, enlarging a full-color continuous tone image 225% in QuarkXPress would require a resolution of 675 pixels per inch (the original requirement of 300 pixels per inch multiplied by the enlargement of 225%). It is best to avoid performing scaling in a page layout application, as these programs have no ability to change the actual pixels in an image.

Q: Can I resize bitmap graphics in PhotoShop?
A: PhotoShop can increase the resolution of a low-resolution image, but increasing the resolution of an image scanned or created at a lower resolution only spreads the original pixel information across a greater number of pixels and rarely improves image quality.

Q: I’ve heard Encapsulated PostScript (EPS) mentioned in the context of both vector graphics and bitmap graphics. How can it be both?
A: EPS files act as a container for transferring graphic information. When an illustration software such as Adobe Illustrator or Macromedia Freehand creates an EPS file, it is a vector EPS. When a pixel-based image editing software such as Adobe PhotoShop creates an EPS file, it is a bitmap EPS.

Q: Can I copy a graphic and paste it into my document?
A: While copy-and-paste is supported by most software, you will have much more predictable results by creating a link to your graphic. The graphic then remains outside of your document and is referenced as needed. Please refer to your software’s documentation for full details about creating links to your graphics.

Q: What is a PDF file?
A: Documents in Adobe’s Portable Document Format (PDF) preserve the exact look and content of the originals, complete with fonts and graphics, and can be printed, distributed by e-mail, and shared and stored on network systems (including the internet) for others to use and view. When properly created, PDF files have proven to be an excellent method for generating quality printing.

Q: Where can I find my fonts?
A: On a Windows-based computer, fonts can be located in two different places. First, check Start Menu>Settings>Control Panels>Fonts. Additionally, you may have a folder names psfonts (typically on the C: drive).

Fonts in the psfonts folder are PostScript fonts and require two separate files to accurately define a font’s appearance. The first file, found in the psfonts folder, ends with a .pfb extension. The second matching file is found in the psfonts>pfm folder and ends with a .pfm extension. The font name can be accurately determined by double-clicking the .pfb or .pfm file.

On a Macintosh computer fonts are found in the System Folder>Library>Fonts. In many cases, an alias of the Library folder can be found on the root level of your hard drive, as well. In that case, the path is simply Library>Fonts.

If you use a font management utility on either platform, fonts are found in a location specified by the utility.

Read more »

Colors by its Means

Read more »