ABOUT PRINTING Printing in its broadest sense, is any process whereby one or more copies are produced from master image.Image transfer from master to copy is usually accomplished with inks and the transferring agent is a mechanical press.Most commercial printing is achieved through one of the following process. They are Relief printing, Offset Lithography and Gravure printing. PRINTING PROCESS AND TYPE Tthe printed communications begins with a plan that is followed by or jointly prepared with the words and illustrations needed to accomplish the goals of the communications. •Due to the invasion of digital media (offset printing) made the production •Even more preparing printed media using computers. •We have many process, but the best is Photo offset Lithography or offset process. This uses metal images to carry ink to paper from a flat surface. •Offset printers work with the basic principle that water won’t mix up with oil. The printing plate holds ink because the image area is treated so that it is receptive to oil based ink not to water. •A multi-color offset press has a separate printing unit for each ink being printed. •The steps involved are:- Plate making. Wetting. Inking. Offsetting. Printing. •Wetting is a process in which the plate is mounted on a rotating cylinder. When the press starts, the plate comes into contact with the water rollers first. •Dampening solution flows constantly from a tray like fountain through series of rollers wets the entire printing plate, except where the plate has been treated to resists water. •Plate making is a process whereby a printer exposes the reversed image from a film separation (negative) onto a flat plate with light-sensitive coating, and then develops the plate. •The image area of the plate — now a readable positive is coated with a chemical that attracts ink but repels with water. •Offsetting is where the final roller, which is a rubber blanket, will be pressed against the printing plate and carries away a reversed inked image. •The rubber blanket has some flexibility and gives slightly when pressed against paper, so the image can transfer evenly to both smooth and textured paper. •Printing -In the last step, the paper in individual sheets or on a continuous roll passes between the rubber blanket and an impression cylinder. •The inked blanket cylinder with its reversed image presses against the paper, printing the +ve image. CALIBRATING YOUR SYSTEM The first step in Color separation is calibrating Our devices (monitor, printer, scanner) and have Correct system-wide color calibration. Calibration is of two types viz, device calibration And system calibration. Device calibration works with monitor and making adjustments for the image setter that we’ll use when we do color separation. System calibration is adjusting the Adobe Photoshop settings that affect the image when it has been converted from RGB to CMYK. Calibrating an image won’t affect it in RGB, because monitors are RGB devices. Changes are only for CMYK. Don’t set changes in CMYK, always comes to RGB and then change the mode. Producing a best scan. Although Photoshop corrects scanned images, it cannot correct images which doesn’t have much color details init — either because it was scanned at a too low resolution or because it lacks detail In the highlight and shadow areas. To make good second originals, do the following steps properly: Steps Determine the exact scan resolution for according to your requirements. Take care of size of the image according to the scan resolution. Scan always by using the file size settings. Eliminate the unwanted color casts by calibrating Your monitor. Separation setup adjustments. The settings in the Separation Setup dialog box along with the settings in Printing Inks dialog box control how CMYK plates are Generated. The Separation settings include the method used for Black generation, under color removal and total ink limit for the press. When Adobe Photoshop converts an RGB image in to CMKY mode, the program converts the values Using information in the Monitor setup, Printing ink setup and Separation setup dialog boxes. The first two settings will provides a closest match for the onscreen and final output image. The separation Setting will give the precise CMYK value chosen for a given RGB color. Color separation is based on the principle of translating the three additive colors — red, green and blue — into their subtractive colors- Cyan, Magenta and Yellow. Theoretically, equal Parts of cyan, magenta, yellow combine to Subtract all light and create black. Due to certain impurities present in all printing inks, however a mix of these colors instead yields a muddy brown. To compensate to this deficiency, we add black ink to the final image output. There are many ways that a given color can be translated from RGB mode to CMYK mode. Pre-Press operators typically use one of two styles of color translation. They are 1.Under Color Removal (UCR) 2.Gray Component Replacement (GCR) For both UCR and GCR, the black generation uses the ink settings we enter in the Separation Setup Dialog box. (Black ink limit is 100 and total inkLimit is 1000.)
|
No comments:
Post a Comment