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Printing Knowledge for Prepress Printing:Color Separations

Published Time:2016-02-16 Original Source:Color Separations
Printing Knowledge for Prepress Printing: Color Separations
In order to reproduce or prepare a full color image for printing using four process colors, the image must be divided into the the individual subtractive primary color components. The separation process can be accomplished photographically or electronically.
Photographic Separations: Using a large process camera, a full color image is converted into halftone negatives which contain a series of dots of various sizes to represent shades of gray. The dots are achieved with the use of special screens placed over the negative material during exposure. When printed, the smaller dots create the lighter areas of the image, with the lightest appearing white, and the larger dots make up the darker areas of the image, with the darkest appearing black. This system of using the halftone screens directly with the film is known as the Direct Screen Photographic Color Separation method. A halftone negative is made for each of the separate subtractive color components of the image (cyan, magenta, yellow) and black. The four halftone negatives are records, in varying shades of gray dots, for each of the separate color components and are known as "Color Separations".
Another photographic technique known as the Indirect Photographic Color Separation method is also used. The original image is separated into the individual primary color components and continuous tone films are made for each of the separations. From continuous tone films, the halftone negatives or positives are created. The advantage in first creating continuous tone separations before creating the halftones is that the continuous tone separations can be reduced or enlarged and corrected before the actual halftone films are produced.
Color separations created from photographic methods are used to prepare analog plates for traditional printing methods. Each plate corresponds to one of the four colors, cyan, magenta, yellow, or black. The plates are coated with the corresponding ink colors during the printing process and the inked image from the plates is transferred to the substrate. The varying sizes of the halftone dots on the plates determines the amount of ink that will be printed on the substrate. The dots from each of the different colored images overlap to produce the full color image.
Electronic Separations: The electronic separation of an image into its individual color components has become the most popular and labor saving method of producing color separations. The original image is placed in a scanner which stores the image as a digital record. The digital image can be imported into a software program such as Adobe PhotoShop™ where the color separations can be produced with the click of a mouse. The scanned image and/or the color separations can be quickly manipulated and edited in an infinite number of ways with the tools provided with the software. Color separations created electronically can be output to film to prepare analog plates or they can be used for Computer-to-Plate applications and digital printing.