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Online User Guide - BodyShots Business
For additional information, please see the BodyShots Frequently Asked Questions.

3. Resolution explained

Much computer terminology is confusing to the novice user, even though he or she may have considerable experience of graphic design and prepress jargon. Of all computer terms, perhaps the most confusing is "resolution" ­ throughout the process of preparing an image for reproduction, from image input to output, there are no fewer than five different interpretations of the term: image input resolution, display resolution, image output resolution, halftone screen resolution, and imagesetter resolution.

Image input resolution

This generally describes the resolution of the device (such as a scanner) which is used to read the original image, and often refers to the number of reading heads, or the number of points at which an image is read, expressed in pixels, or dots, per inch (ppi, dpi). Generally speaking, the higher the resolution of the scanning device the more information that is captured from the image, allowing a greater possibility of faithful reproduction.

Display resolution

This is the resolution at which a monitor displays an image. It can mean two things ­ the resolution of the displayed image, expressed in dpi (monitors are typically 72dpi), or the "bit depth" of the monitor (but not the image). Bit depth determines the number of colors a monitor can display ­ an 8-bit monitor can only display 256 shades of gray or 256 colors, whereas a 24-bit monitor is capable of displaying as many as 16.7 million colors. BodyShots images are 24-bit color images, and are consequently best displayed on a 24-bit color monitor. If you want the displayed image to match as closely as possible the printed output, you should calibrate your monitor. However, BodyShots images are carefully color-corrected to low dot-gain proofs, and in normal use you will not need to make further corrections.

Image output resolution

This is the number of dots per inch in the image before it is output as a halftone image. Typically, image output resolution is double the line frequency of the halftone screen to be used ­ thus an image to be reproduced with a halftone screen ruling of 150 lines per inch (lpi) should be output at 300dpi. All the BodyShots images have a resolution of 300dpi.

Halftone screen resolution

If an image is to be printed on paper it must first be broken up into a pattern of dots of varying size. This pattern of dots is applied, traditionally, by using a "halftone screen." In electronic image output the halftone screen is generated via an imagesetter. Halftone screen resolution ("ruling") is measured in lines per inch (a line being a row of halftone dots), and an image reproduced in 4-color typically has a halftone screen ruling of 150lpi, although very high-quality printing will tolerate rulings of twice this frequency.

Imagesetter resolution

This refers to the dot frequency that an imagesetter uses to generate high-quality output on film or bromide. Imagesetter resolution determines the number of shades that can be achieved in any single color, and image output from imagesetters is generally around 2540dpi ­ but see the next chapter for qualification.


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