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Colour Separation

This is a draft of the section for the main site which explains colour separation and why it is crucial to the print process.

An image that is printed in ink on a page is the result of a variety of processes, each handled by different people using different equipment all of which have the capacity to degrade or impove the image quality.  To understand the importance of colour separation we will look at how and where it fits into the overall process.

Below is a brief description of the graphic arts workflow most commonly in use today.
  1. RGB Image capture.  The most common forms of image capture today are the digital camera and the desktop scanner.  Both yield an RGB digital image file.  In the settings of the camera or scanning software there are various options for how colour is handled.
  2. Design and layout.  The captured image is placed into a page using page layout software such as Adobe InDesign.  In the settings of the page layout software there are various options for how colour is handled.
  3. CMYK press.  The page information including the captured image, text, and other design elements are sent to the software drivers of the printer which controls the actual mechanisms inside the print device which are responsible for applying the CMYK inks down onto the paper.  Again, there are various options for how colour is handled.
In the above simplified description we start out with an image comprised of red, green and blue digital data. Keep in mind, this image does not exist in the real world, the RGB data file is only a series of numbers describing what the image looks like and can only be viewed using additional hardware.  When the printer applies the inks to the paper it must do so using cyan, magenta, yellow and black inks.

Colour separation is the process of interpreting the original image capture's RGB image data to create CMYK image data required by the press.  You can see how this would be a massively important component in the quality of a printed page.  It is analogous to translating from one language to another.  There are many different ways to interpret the original data and the results of the translation will have extremely different results depending on the quality of the translator.

Each of the three steps shown in the description above have the ability to perform the conversion from RGB to CMYK.  Most camera and scanner software has the ability to save out as a CMYK file.  The colour settings of the page layout software also has the ability to make the conversion, and it will do it by default.  If the printer's driver receives RGB image data it will also convert it to CMYK by default.

With modern equipment, the image resulting from allowing the built in software to perform a default colour separation will yield a colour reproduction which will be pretty good so long as it is not compared side by side to a colour separation performed by a skilled colour separator.

A skilled colour separator will prefer to start with the raw image capture data from the camera or scanner image capture and will work to maintain the image information and the intent of the photographer.

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