Glossary

CMYK Color Model

CMYK (cyan, magenta, yellow, black) color model refers to the four color components frequently used in printed media such as books, magazines, brochures, and ink-jet printing to produce full-color images. 

Adding together the four colors in varying quantity produces millions of visible colors. Not all colors can be faithfully reproduced, however, due to limitations of inks, the printing process, and paper characteristics.

CMYK color is the standard color model for documents produced for print, through there are other color models. Providing images in CMYK color mode often limits flexibility for image manipulation, color correction, delivery via digital media, and conversion for use in digital media.

Modern graphics software allows documents to be fully produced using RGB images, with conversion to CMYK occurring immediately prior to printing, under the control of the printing vendor.

Alternate color models include RGB, Grayscale, and Lab.

Cropping

Cropping is the deliberate act of framing the most desirable portions of an image, usually to improve composition or to fit a layout.

Cropping can be done while taking the photo, by manipulation in a photo editor, or during layout.

It is recommended that you provide loosely cropped images for publication which contain extra image around the subject, which allows latitude for additional cropping during layout.

False Resolution

A poor quality high-resolution image, caused by resizing an low-resolution up to a higher resolution. The resulting image rarely improves upon the original and can introduce new artifacts into the image.

False resolution image are deceptive. When evaluating for resolution alone they appear to satisfactory, and when displayed at smaller sizes on screen the loss of quality may not be visible.

Grayscale Color Model

Grayscale color model refers to images produced using only shades of gray, white, and black.  

Grayscale data can include over 65,000 levels of gray, dependent on the bit-depth of the data frequently described as 8-bit or 16-bit gray.

Grayscale color can be used for either digital or print production.  In digital distribution, the grays are converted to RGB color mode; in print distribution, the grayscale data can be used with any number of inks or ink combinations to produce color images.

Alternate color models include CMYK,  RGB, and Lab.

.JPG or .JPEG Image format

Joint Photography Group (or Joint Photography Experts Group) is one of several file types for storing photographic images.

JPG files are lossy, meaning that image quality can decline during editing and multiple resaves.

JPG images can be saved with various levels of quality/compression. Some software describes quality on a scale of High to Low, or using a numeric system of 12 down to 1 (twelve is the highest quality with the least compression.)

Caution is advised when resaving JPG images: the compression used to reduce file size can introduce disruptive artifacts that become visible at lower resolutions or with lower-quality compression. Multiple saves tend to exaggerate these artifacts even further. 

When providing JPG images for publication, it is best to provide the original image from the camera or imaging device. 

Other common photo formats include TIF, PSD, and GIF. Less common formats include RAW, BMP, and PCT.

Lines Per Inch (LPI)

A unit of measurement specifically describing the linear number of halftone dots at a particular dimension (in this case, inches.) 

LPI applies exclusively to print materials on standard printing presses. It does not apply to photographic prints, ink jet prints, or digital display on TVs, tablets, or phones.

Most book printing uses a halftone dot pattern (“Screen”) containing 150 LPI, while screens of 175 LPI and 200 LPI are not uncommon. 

LPI can also be described as “Course” (65 LPI used commonly for lower print-quality news papers) and “Fine” (200 LPI) used primarily for art reproduction and high quality books and magazines.

Publications printed using a fine line screen can reproduce detail more clearly than a course screen. A fine line screen (LPI), when used to reproduce a low-resolution image (PPI) can reveal the artifacts contained in the original image.

The dot pattern in printing can be seen by the naked eye or using a simple magnifying glass.

Frequently confused with Pixels Per Inch.

Pixel

The basic measurement unit used in a digital image or output device. The word pixel is a contraction of Picture Element.

Every image is created with thousands (or even millions) of pixels. A 7.5 Megapixel camera, now common in consumer-level cameras, captures images containing 7.5 million pixels.

‘Pixels’ is commonly used to describe the resolution of an image: your 1080p TV displays an image that is 1920 x 1080 pixels dimension. 

Pixels Per Inch (PPI)

An image measurement specifically describing a particular resolution (pixels) at a particular dimension (in this case, inches.) 

Example: a 300 ppi image contains 300 pixels per each inch in layout.

PPI is used almost exclusively for print, where the printed dimension is fixed and being reproduced using a halftone dot. By contrast, an image displayed on a digital device may be displayed very large (ie on a TV) or small (ie on a phone.)

There is a strong correlation with Pixels. An image for print could be described as 4″ wide at 300 ppi, while describing the identical image as 1200 pixels wide.

Frequently confused with Lines Per Inch.

Resolution

The number of pixel elements used to capture or output an image. Resolution can be described somewhat loosely (ie: high resolution, low resolution) or specifically (ie: 7.2 Megapixel, 300 pixels per inch at 6″ wide, a 1080p TV screen.)

It is important that images provided for print or display on monitors, tablets, or smart phones be adequate resolution to faithfully reproduce important detail within images, and to have pleasing clarity on screen.

RGB Color Model

RGB (Red Green Blue) color model refers to the three color components used in digital displays, televisions, smartphones, tablets, and similar devices to produce full-color images. 

Adding together the three colors in varying quantity produces 16.7 million visible colors. Modern monitors are capable of displaying a wide color range, though not all colors can be faithfully displayed due to a restricted gamut.

RGB color is the standard color model for digital images, through there are other color models. Providing images in RGB color mode usually allows the most flexibility for image manipulation, color correction, delivery via digital media, and conversion for use in print media.

Alternate color models include CMYK, Grayscale, and Lab.

.TIF or .TIFF Image format

Tag Image File (or Tag Image File Format) is one of several file types for storing photographic images.

TIF files are loss-less, meaning that image quality is preserved during editing and multiple resaves.

TIF images can be saved with no data compression, or with a compression called LZW to reduce file data size on your computer.

Other common photo formats include JPG, PSD, and GIF. Less common formats include RAW, BMP, and PCT.