15. Computer-To-Plate: Called CTP, by this technology the design to be printed is directly transferred on to the plate by digital process thus eliminating the traditional use of process camera to prepare positives and negatives followed by plate making process with the use of chemicals. Earlier the direct computer to film technology called CTF, was introduced to directly get the negatives or positives, which lead to the development of CTP by which even plates for the Intaglio process have been made possible. While negatives and positives are eliminated for making plates for Dry Offset process, in the case of Intaglio process printing the images are directly engraved on the Intaglio plates thus eliminating hand engraving process in a single die from which several moulds are taken, assembled and master plates prepared by electrolysis process for producing multiple plates for Intaglio printing. Again while the CTP is based on chemical free technology, and eco friendly, this will not suit small presses due to the cost involved in establishing such equipments. Some of the leading firms which offer varieties of CTPs and CTF technology includes Agfa, Fujifilm, Glunz & Jensen, Heidelberg, Kodak, Mitsubishi Imaging, Screen (USA), KBA Giori, Komeri etc.
16. Contrast: The tonal range of a original i.e differences between the lightest and darkest colors in an image can be expressed as contrast. A good contrast original will have the tonal values gradually flowing from light to dark in several areas, where as the flat original will have less graduation from light to darker areas. You can see the illustration below to understand the term contrast in an original. In general three tones govern the contrast. They are called Highlights, Middle tones and Shadows. If you see the grey scale given below you will understand the three terms. In an original the tonal values should gradually flow from highlight areas to shadow areas to give clarity to the images. Unless the original will have contrast the print result will be flat. A full contrast artwork will have complete range of tonal values, from white through middle tones to dark areas called shadows. The light and dark areas of the original contribute more to the success of a original's composition than any other factor, including color. Therefore contrast is an important tool to guide the for the designer/artist in forming an image for reproduction. Similarly the term also guides the photographers to take correct pictures. Even if the picture has less tonal differences, to some extent they can be corrected in the process work while taking negatives or positives for printing. They can be adjusted by suitably changing the apertures to control the reflected light for highlights and shadows.
17. Cover Paper: Heavyweight paper that is commonly used for printing book covers, file folders, presentation folders, greeting cards, business cards, postcards, brochures . The cover paper comes in different qualities, thickness, finish and colors to match the printed book paper colors and finishes.
18. Crop Marks: This is nothing but marks meant for trimming. They are printed as lines , cross marks etc at the edges of a printed sheet indicating where the paper is to be trimmed. Some of the printers prefer to use the crop marks as register marks instead of separately using a register mark.
19. Carbonless Paper : Special variety of paper coated with chemicals on its back side to produce second or third copies with pressure from writing or typing thus avoiding use of Carbon paper for making multiple copies. The paper is coated with micro encapsulated dye or ink or some sort of reactive clay , but the coating will remain invisible to naked eye. With pressure from the tip of the pen or typewriter keys, the micro-capsules of color dye breaks and develops images by a chemical reaction with the color acceptor on the surface of the next front coated next sheet below. These paper eliminates the use of carbon ribbon or carbon paper thus increasing the efficiency of the user as time to keep the carbon paper, then removing it etc are saved. These are used by business concerns to produce duplicate, triplicate copies in the business deals.
20. Chalking : This is one of the defects attributed to Ink-Paper relationship. The images on the printed stocks appear to fade away or show dusty image after the sheets are printed. The deterioration on the printed image is caused by ink carrier vehicle that gets absorbs into paper too fast leaving the ink pigments in semi wet condition on the paper surface or not getting properly absorbed into the surface of the paper thus causing improperly-dried ink being easily rubbed off the paper. This powdering defect is due to the ink that has not been properly formulated to suit the paper. The other possible reasons for this defect could be acetic paper, fountain solution too acetic (in wet offset ), formulated as too soft an ink which emulsifies etc.
21. Coarse Screen : This term is applicable both in Process reproduction as well as Silk Screen printing. The continuous tone originals are converted into printable form by the use of something called halftone screen. The halftone screen breaks the tonal values into minute dots of varying sizes while preparing negatives through process camera. The halftone screens are made up of fine ruling of lines that cross each other leaving small gap between them. Such screens are made with different screen rulings available for use. The resolution of a halftone screen is measured in lines per inch which is indicated by the term ‘lpi’. Therefore the resolution of the screen is written as "150 lpi" or "150#". The term Coarse screens refers to screens having 65, 85 or 100 lines per inch. For finer work fine ruling screens such as 250 lpi and up to 400 lpi are used.
22. Color Separation : Color separation is the process by which original color artwork is separated into individual color components for printing. The components are cyan, magenta, yellow and black, known as CMYK. By this process the colored originals are converted to printable image using a process camera or a scanner. Though traditionally process color separation has been done photographically by using different colour filters, the manual process is being replaced slowly with electronic scanners. Four halftone negatives are prepared to print yellow, cyan, magenta and black colors on paper to render the true colour image as per original copy. In order to achieve it, color filters are used in the colour separation process to produce four separate negatives or positives to print yellow, cyan, magenta and black colors on paper. Each filter would expose only that primary color in the image as a film negative, and the resulting film positive would contain the complementary—or opposite—color. Thus:
Since the colour separated negatives or positives will not be defect free, the negatives or positives are manually corrected wherever it is necessary to bring it closer to the original before final negatives or positives are made. However in the scanners, this correction is automatically done as the original is read by the scanner and necessary corrections automatically carried out to produce color separated negatives or positives.
- The yellow filter is used to make a negative to print Black colour.
- The Red filter is used to make a negative to print Blue (Cyan) colour.
- The Blue filter is used to make a negative to print Yellow colour.
- The Green filter is used to make a negative to print Red (Magenta) colour.
............Additions to alphabet C to be continued under C/3