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		What should I know about screen angles? What is dot gain? What is optical dot gain? What is mechanical dot gain? What are our high performance screen types? What is conventional screening? What is GeometricDOT screening? What is FULLtone screening? What is High Definition screening? What are colour control bars for? What is grey balance? How can I get the best results in a duotone?
	TO TOP	What should I know about screen angles?
		The screen angles for process colours should be 30° apart, with the yellow placed 15° from the other colours and between the cyan and the magenta or the cyan and the black. It is often acceptable to place the yellow on the same angle as the cyan or black, depending on the dominant colours in the picture, with one of the colours at a different line screen. It is desirable to have the dominant colour (magenta in most cases) on the 45° angle. When significant grey component replacement (GCR) is used, and if black becomes the dominant colour, black should be printed at the 45° angle in place of the magenta. Screen angles are best left to Repros who deal with them as a matter of course when outputting to film.
	TO TOP	What is dot gain?
		Dot gain is the apparent increase in dot size, or tone value, measured on the press sheet compared with size specified in a digital file or measured on the film separations. The increase is caused by two types of gain which are always present: optical and mechanical. Total dot gain (tone value increase) varies with the type of paper and line screen being used. Dot gain is higher with uncoated paper or newsprint. In the past, printers have compensated for increased dot gain by using coarser screen rulings that produce lower dot gains. To some extent, this can be compensated for with digital high performance screen types and calibrations. Printing by offset lithography is generally easier to control when the dot gain is in balance for all process colours. The cyan, magenta, yellow printing sequence facilitates a more uniform dot gain between colours. It also helps the press operator maintain grey and colour balance when printing.
	TO TOP	What is optical dot gain?
		This is the pnenomenon caused by light being absorbed and scattered by paper. The light is diffused around the dot, which makes the tone appear to be darker. Thus the dot appears and measures larger than its physical size as viewed through a magnifier. Optical dot gain is highest in the midtone areas where the dots have the largest circumference.
	TO TOP	What is mechanical dot gain?
		The physical change in dot size as a result of film and plate exposures and printing conditions such as ink amount, pigment strength, ink tack and water balance, ink temperature, blanket, plate and impression cylinder pressures, plate types, blanket types, doubling, slurring, paper surface smoothness, absorbency and brightness. This physical change in dot size is called mechanical dot gain.
	TO TOP	What are our high performance screen types?
		No single screen can do justice to all images and all printed jobs. You have to match the screen to the job. And Scitex Class Screening offers a choice of screen types that allow you to reach the highest levels of colour quality regardless of the image types and press conditions. You can choose the ideal screen to match the job, such as one that gives the best quality on inexpensive stocks or one that reproduces the fullness of continuous tone images on the best of printing stock.       Scitex Class Screening features high precision and several high-performance screen types: Conventional GeometricDOT FULLtone High Definition
	TO TOP	What is conventional screening?
		The dots (round, diamond, square, composite and gravure) have a remarkable, uniform shape with sharply defined edges, resulting in a superior image quality. Our conventional screening features less noise and graininess in the film separations, and smoother transitions in vignettes.
	TO TOP	What is GeometricDOT screening?
		Designed to print smoother, high-quality images on lower-quality stocks. Consisting of a new, elongated dot shape, it results in a clean and smooth dot structure without the usual rosette pattern. Coarse screen rulings appear much finer, and are free of typical moire effects often found in fleshtones (reds and yellows). GeometricDOT has excellent highlight, midtone and shadow detail, and a sharp, crisp appearance. Minimises dot gain on low quality stocks.
	TO TOP	What is FULLtone screening?
		Similar to, yet better than, random (stochastic) screening, FULLtone varies both the size of the dot and it's placement. Free of moire and other unwanted patterns, it gives exceptional detail rendition. It can be used for fine type and vignettes. Screening is fast since it needs no additional computer time. FULLtone sceening is designed for high-quality reproduction of continuous tone and line art images, with the closest possible simulation of continuous tones. Screen ruling and angles are no longer a consideration, making it ideal for reproducing pictures with intricate textures and fabrics. Check with your printer before ordering film.
	TO TOP	What is High Definition screening?
		Allows you to image line screens up to 625 lines per inch with reduced rosette pattern or traces of moiré and without lots of the problems associated with these fine rulings (i.e. dot gain or loss). It is ideal for fine art reproduction and other jobs demanding the highest quality color reproduction. Check with your printer before ordering film.
	TO TOP	What are colour control bars for?
		To facilitate colour control on the press, colour control bars are positioned in the non-image areas across the entire press sheet, horizontal to the direction of the travel. Colour control bars range from 1/8th of an inch to 1/2 an inch deep. Larger control bars are generally more useful, but require more space in the non-image area. Colour control bars include a repeating pattern of small patches of image elements that can be measured to detect the variables that will affect the printed colour. Those patches include a solid and several halftone tints for each process colour and black. 50%, 75% and 40% tints and solid patches are required to measure ink levels. Process ink patches can be measured to determine their hue errors and greyness. Two-colour solid overprint patches provide a place to measure ink trapping and secondary hues. Three-colour overprint patches facilitate the control of grey balance. Microline images allow the detection of slur and the doubling of halftone images during printing.
	TO TOP	What is grey balance?
		Grey balance is the ability to reproduce a rich neutral black and varying amounts of neutral greys using the correct amounts of yellow, magenta and cyan. If grey balance can be maintained throughout the job, the rest of the printed colour gamut will follow. The factors that affect grey balance are colour density, colour purity, total dot gain, paper and the viewer's colour perception. Control bars make grey balance possible.
	TO TOP	How can I get the best results in a duotone?
		The two screen angles for duotone printing should be 30° apart, with the black at 45°. Screen angles and rulings should be such that no moiré pattern appears in the film, proof or print. Generally electronic files should not include screening parameters and dot shape. When plates or film are made by Repros, we generally report moiré pattern problems to you and help resolve the problem whenever possible.
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