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factfile3.17 Output to Print

 

Preparing images for print involves a number of factors, depending on whether output is to a desktop
printer, or to a professional print shop. Print resolution is much higher than the resolution needed for
screen.

Desktop printer
For your school or home desktop printer, which could be laser or ink jet, the optimum resolution is typically 300 to 400 DPI (dots per inch) – but check with your ICT teacher.

Professional print shop
For professional print output you should always consult the company to find out their exact specifications. For professional print jobs it may be up to 8000 DPI (dots per inch), sometimes also measured as LPI (lines per inch). A print shop prepares image files for printing, converts them to film, and then transfers the film to colour plates. The plates are used with screens to transfer the inks to paper. The International Color Consortium (ICC) has developed a cross-platform colour management system that is widely used throughout the industry.

Paper quality
Outcomes also depend on paper quality – will newsprint or glossy coated stock be used, for example? Lower grade papers need larger dots and fewer lines per inch because the ink bleeds. Desktop printers reproduce colour through dots of cyan, magenta, yellow and black ink. You will need to select different setting if printing onto acetate, glossy photo paper, specialist card or ordinary printer paper, for example. What are the different settings on your printer?

CMYKChoose the right colour mode
CMYK is a colour process that uses Cyan, Magenta, Yellow and BlacK (known as Key) colour variables for offset printing using process inks. CMYK is known as a subtractive colour process because printing inks absorb light. When printing using this model the more ink that is applied, the darker the colour. All four inks combined produce black; while white is created simply by not adding any ink at all. Subtractive colours

subtract from white to create other colours, and the subtraction of all the maximum colour values makes
black. In a CMY image subtracting 100% cyan, magenta and yellow results in black. When 'prepping' for high-end professional printing the image is separated into four different plates, one for each colour. Serif programs let you choose whether to make a composite copy (one page), or colour separations (4 pages) for sending the print job to an image setter or plate setter.

To print in high quality colour professionally you must convert your artwork to CMYK colour mode, but because this format allows fewer colours than RGB, the colours in your image could be dramatically altered. To avoid this it is advisable to choose the preferred colour mode at the very start of your project if professional printing is planned.

Resolution - calculate required size
If you know that your graphic must have a resolution of 300 dpi and you want the image to measure three inches across, it will be 900 pixels wide. To calculate this, multiply the resolution by the number of inches you want to cover.

Resolution multiplied by inches across = number of pixels wide

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