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Imaging

Most projects involve much more than just pages of type on paper. There's no limit when it comes to fonts, color, photography or illustrations. There are some details that must be addressed before passing off a project to production specialists. This section will help make the most of a project's graphic imaging aspects.

Color Management

With monitors, printers and presses all using different varieties of color, keeping the color consistent throughout the production of a job is very challenging. A basic understanding of the additive and subtractive color processes is required. A Color Management System (CMS) should be used to get consistent and reliable color.

Different devices (scanners, monitors, printers) use different color specs (CMYK or RGB) and each of those has a different range of colors that each device can display or produce, which is known as its color “gamut” or “color range.” Some devices have limited gamuts and others have very large gamuts, but none can produce the range of colors our eyes can detect. Printers vary drastically in their gamuts, especially if they use different technologies. Changing ink or paper will also make a difference. A color management system converts the device-specific colors into a common visual language that can be used throughout the process to ensure predictable color. When colors in an image cannot be displayed or printed because they are not in a device’s gamut, they are called “out-of-gamut colors.”

When an image is scanned into the computer, only the colors within the scanner’s gamut are saved. When an image is viewed on a monitor or output to a printer, the colors that are produced are the colors within their gamuts. Devices that use different gamuts cannot reproduce each other’s colors exactly. A Color Matching Module (CMM) is then used to perform gamut mapping, which selects the next closest reproducible color.

A color management system can be broken down into three categories: calibration, characterization and conversion:

Calibration is the first step in obtaining color management. It’s the process of tuning a device (scanner, monitor, printer, etc.) to a known or defined standard to ensure that it will meet the manufacturer’s specifications predictably and accurately. It establishes a baseline of operation to ensure that the device doesn’t vary from the standards.
Characterization, also called profiling, is a process that defines the color gamut of a specific device. A device profile is simply a translation table between the standard color space and device-specific CMYK or RGB. Device profiles are used to convert from one device to another. They measure how a device differs from an industry standard, such as the IT-8 standard target. Determining how a device differs is accomplished by sending a target to the device, measuring its reproduction and comparing the measured values against target values. The process is the same for creating profiles for monitors, scanners and output devices.
Conversion is the process of charting or mapping the color gamut of one device to that of another and making the required changes in order for both devices to display or produce a similar color range. The conversion process is also known as gamut mapping. For example, to convert an RGB image to CMYK, the CMM (e.g., ColorSync) looks up the CIELab value to get the equivalent CMYK value. This converts directly from RGB to CMYK, resulting in both having the same color range.

File Format and Resolution

A print project with images is almost always more attractive than one with only text. People prefer and pay more attention to pictures. However, when formatting an image for a project, carefully consider how and why an image is being used. Each instance is unique and the final decision should be based on a number of factors including project stage, image quality acceptable for the graphic’s intended purpose and project budget, among others. But first, it is necessary to have an understanding of the fundamental characteristics of the many formats in which images can be created, edited, transported or viewed.

It’s good to know how to finish the printed piece before starting. Some things to keep in mind are:

PSD (Photoshop Document) or Native - While working on a file, it can be saved in a native Photoshop® format that retains layers, channels and clipping paths. Once the file is completed, save it again as a Photoshop® file and then do a “save copy as,” in order to save it in another format such as TIFF or EPS. When the file is saved in TIFF or EPS format, its layers are flattened, making it difficult to return and edit the file. Because flattening makes editing difficult, an original Photoshop® file should always be kept so additional editing can be performed later.
TIFF - TIF or TIFF format (Tagged Image File Format) is the most common format for saving bitmapped images that will be printed or imported into a page layout program such as InDesign™. It can be used on both the Mac and PC. A TIFF file can be CMYK, RGB, grayscale, index or bitmap.
EPS - EPS (Encapsulated PostScript) format is widely accepted by the graphic arts industry for saving images that will be placed into programs such as Adobe Illustrator®. The EPS format is usually used for vector files but can also be used for raster files. One reason to use EPS in an image-editing program would be to save duotones, as they can only be saved as EPS. If using bitmap mode, the EPS format allows saving the white areas of an image as transparent areas. The EPS format is also used when saving an image with a clipping path.
JPEG - The JPEG (Joint Photographic Experts Group) format/compression technique was developed specifically for photographs. JPEG is utilized to gain high compression levels for photographic images without sacrificing image quality. It’s used exclusively for the compression of 24-bit images and it will not work for images less than 24-bit. It also doesn’t work as well for non-photographic images such as illustrations, cartoons, flat color areas or images with defined edges.
GIF - GIF (Graphics Interchange Format) was originally developed for use on the internet. It was developed as a way to store images in small files that can be quickly exchanged and easily downloaded. GIF files have a color depth of 8 bits per pixel, so the image must be in index color mode to be saved as a GIF. GIF files can be accurately displayed on all systems that can display at least 256 colors, and are also saved as low-resolution, usually 72 ppi. A GIF should never be used for images that will be printed. Using an image for both web and print will require two separate files, one as a GIF and another as a TIFF or EPS.
PNG - The PNG (Portable Network Graphics) format was created to replace the GIF format. It is a bitmapped format that utilizes lossless data data compression. Designed for internet use only, PNG only supports 24 bit RGB color and grayscale images. PNG also supports transparency. PNG images cannot support CMYK, making them not suitable for print work.
PDF - PDF (Portable Document Format) is a file format that allows a document to be viewed on any computer. It will look the same on all computers, regardless of how it was created or on which operating system it is viewed. The PDF format stores all of the fonts, colors and graphics in such a way that these elements will look exactly as they were intended to look. Converting a file to PDF is one of the best options when transferring via email or the web. It ensures that the file will be readable on any computer. In addition, printers will often accept files in PDF format.

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