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Commonly used terms explained :-

This is not an exhaustive glossary of the printing industry. It is merely intended as a short listing of the terms you are likely to encounter when dealing with printers such as Caralan.

  • Bitmap   Graphics file format used to store digitised images. As it's name implies it is a "Map of Bits". The easiest way to see a bitmap in operation is to look closely at any computer monitor or tv screen. Imagine each pixel is a single "bit" and you can see how each bit can be specified, ie mapped - (600,437) = RGB(255,255,255). Meaning the "bit" at position (600,437) is white.
  • CMYK   Cyan, Magenta, Yellow, Black. A system used to specify printing ink colours on the printed page. Cyan, magenta and yellow are referred to as "subtractive primaries" because they are the corollaries of RGB but in a subtractive way. That is they specify a light filter, ie the subtraction or blocking of light, rather than a light source. Printing inks are considerably less than perfect so black is added because CMY can only produce a turgid brown colour.
  • Colour Gamut   The range of colours that a particular device is capable of reproducing. For example the colour gamut of CMYK print is about 4 million colours but that of a standard monitor is around 16 million. This means that if you create artwork on your monitor that is to be printed CMYK the colour range usually has to be compressed and effectively degraded.
  • Colour Profile   A file containing data that allows different devices to attempt to render colour in a way that is consistent between devices and systems. The theory is that with the use of the correct colour profiles you can view a file on your monitor, print it on your colour laser and print it on an offset press and they will all look very similar. If you are selecting a colour profile to match sheetfed offset you should be looking for the low gain versions of "Eurostandard Coated", "3M Matchprint" or "Cromalin". Do not use SWOP profiles as these are high gain for newspaper type presses.
  • Compression  Making digitised data take up less space. Generally two types - Lossy and Lossless
  • Digital Print   Term commonly used these days to refer to colour laser printers attached to a computer. This method is currently gaining some ground on the litho market. However, it currently has the following disadvantages compared to litho - inferior quality, far more expensive per copy, much slower, short machine life cycle, limitations of stock weight and coatings. It has the advantage of having no platemaking or makeready and so is much cheaper on short runs - typically 250 or less.
  • Dot Gain  The tendency of printing dots to spread on press during the printing process. Standard gain for sheetfed offset is around 14% which means if you specify a 50% tint you will actually get something like 64% on paper. Dot gain is a variable that changes with paper stock and other press conditions. For example, gain is usually higher on cartridge paper than coated stock.
  • EPS   Encapsulated postscript. A common file format for data exchange. An EPS can only contain one page. Eps files usually consist of a postscript body containing the page data and a bitmap image header to allow previewing of the contents without interpreting the postscript content. DCS (desktop colour separation) is a form of EPS.
  • JPEG, .jpg  A bitmap file format commonly used in print and the web. Jpegs use lossy compression and can save huge amounts of space over uncompressed formats. Jpeg compression is used in postscript level 2 and above and PDF files.
  • Knockout  Artwork. The act of punching an object out of the object beneath it.For example, if you print a yellow object on a blue background you must set it on knockout because if it is printed on overprint it will become a green object.
  • Litho Printing   Also called Offset. Printing using inks on a printing press. This is an old process but currently dwarfs the market presence of all other methods because of it's speed, high quality and low cost per copy. However, litho is only really suitable for larger quantities of 1000 upwards. This is because of the overhead incurred by platemaking and makeready. Litho machines are typically very expensive with a B2 press weighing in at 20-30 tons.
  • Lossless Compression For example, LZW Tiff or Zip files. Lossless compression usually saves less space than lossy but ensures that on decompression the original data is perfectly restored.
  • Lossy Compression For example, Jpeg files. Lossy compression achieves very high levels of compactness by degrading the data in areas where it is judged to have no effect.
  • Overprint   The act of printing one object over another. As opposed to "Knockout" where the top object is printed in a corresponding hole in the object beneath.
  • Overprint Black   It is common and desireable to overprint small black objects, eg type upto 12pt, since doing so usually increases clarity and removes any dangers from slight misregister on press.
  • Overprint White   Never set a white object to overprint unless you intend it not to print at all. This is because white ink is never actually used and the white on your pages comes from the paper it is printed on.
  • Pdf   Portable document format also called Acrobat. Pdf is now the format of choice for data exchange in the print industry. Pdf is a form of postscript. Pdf is NOT infallible.
  • Postscript   Page description language created by Adobe in the early eighties. Postscript saw off it's competitors and is now the basis of all modern offset printing systems. Pdf and Eps files are postscript formats
  • Press Ready Artwork   Artwork is referred to as being "press ready" when it can be printed without modification or further work being required. If you submit your own artwork to us we expect it to be press ready.
  • Proofing   Proofing is a procedure whereby you can see how your job will print before it is printed. Proofing is very important because it enables you to spot problems in your artwork files before significant cost is incurred. Getting a job back from the printer and then sitting down to proof check it is really, really dumb. Viewing your artwork onscreen in the program you used to create it is not proofing. Proper proofing will typically involve following the same procedures as though your artwork were to be printed but then making some form of preview rather than actually printing it. See our Howto page for proofing advice.
  • Pixellation   A term generally used to describe the degradation of an image whereby it's individual pixels can be clearly seen. This happens when a low resolution image is printed on a high resolution device. The high res. device will faithfully reproduce the pixels and the image seems to be made up of square blocks. This is what happens when, for example, a website image at 72dpi resolution is printed on a printing press. You see 72 square blocks for every inch of image.
  • Resolution   Generally refers to the granularity of a bitmap file or bitmap based device expressed in dots or pixels per inch. Examples:- Computer monitor resolution is commonly 72dpi which means there are 72 pixels on every inch of your display. A jpeg file may be at a resolution of 400dpi which means there are 400 pixels of data for every inch of the picture it contains.
  • RIP   Stands for Raster Image Processor. A rip is a program that converts postscript type files to bitmap type files so they can be printed on a bitmap rendering device. That is so they can be printed on paper or viewed on a monitor.
  • RGB   Stands for red-green-blue. This is a system used to specify light pixels in devices such as digital cameras, scanners, monitors etc. Red, green and blue being the primary colours of light.
  • SWOP  Standard web offset process. You will encounter this in lists of colour profiles. It is NOT appropriate for sheetfed offset and if you use such a profile you may see drastic shifts in colour density when your job is printed.
  • Tiff   Bitmap file format commonly used in printing
  • Trapping   Artwork. All presses are prone to slight misregister. To combat this it is common in the printing industry to employ a technique known as trapping or spreading to avoid the appearence of slight white gaps around objects. When an object is set to knockout of a background the whole in the background is made very slightly smaller to produce an area of overlap. Many programs can be set to trap your designs automatically. You can do it manually. For example, in CorelDraw to trap an object you would usually give it a hairline outline.
  • Vector Art   Basically artwork that is a drawing of some kind as opposed to a bitmap. Vector art consists of lines, shapes and fills that are specified mathematically. Vector art is scaleable without degradation because it is a mathematical construct. Fonts are an example of vector art in action. Programs such as CorelDraw and Freehand are vector art editors. The postscript language combines vector and bitmap to describe pages.