CMYK stands for CYAN, MAGENTA, YELLOW and BLACK (the 'K' stands for black as opposed to 'B' which is blue), which are the 4 colours that are used in full colour, offset printing. CMYK is also known as 'process colour'. If you look closely enough, all printed material is made up of tiny dots of cyan, magenta, yellow and black. Some vibrant and luminous colours cannot be printed using CMYK - in particular bright blues, purples and lime greens. Any full colour images that you have in your CD layout MUST be saved as CMYK.

RGB stands for RED, GREEN, BLUE, the way in which colour is displayed on computer monitors and television screens. RGB images tend to be more vibrant that CMYK images, BUT you cannot print images in RGB! Most image manipulation programs like Photoshop however will default to RGB and all images on the Internet are in RGB.

What's the difference between DPI, LPI and pixels per inch, and what's meant by 'high-resolution' and 'low-resolution' images.

Most offset printing (including your CD covers), are printed at 300 DOTS PER INCH(DPI) resolution. Only images in publications like art books and the like are printed at higher resolution. 300 and up is termed 'High-resolution'.

LPI is a printing and film making term, it stands for LINES PER INCH. To make things confusing, LPI is exactly half DPI. So 150 LPI is the same resolution as 300 DPI. In the digital world, pixels per inch is the same thing as dots per inch, thus 300 DPI is the same as 300 pixels per inch.

Low-resolution is a term given to images that are saved at somewhere between 72-150 DPI. Images that are made to be displayed only on computer monitors will be low resolution, because monitors can only display 72 pixels per inch. Thus the Internet is entirely 72 pixels per inch, (which is why images printed off the Internet look so bad!).

Photoshop and some other image manipulation programs will default to 72 pixels per inch....so beware. If you've forgotten to change the resolution of your Photoshop document to 300 pixels per inch before you start, your carefully layered artwork that has taken weeks of you time to produce will be virtually useless. It doesn't matter if you have scanned in your images at 300 dpi or higher - once you import them into a low-resolution photoshop document they WILL remain low-resolution.

What is 'bleed' and 'registration black'?

Bleed is a safeguard. It's when you take an image or background over the crop marks of a document, so that when it's trimmed after being printed, the colour or image goes right to the edge. If you don't have bleed, then you run the risk of tiny slivers of white paper showing along your edges - as the printer might crop a millimetre out. Usually 3 mm bleed is sufficient.

Registration black is a black that is made up of all 4 colours (CMYK). Usually all trim and perforation marks are selected in registration black. This is so that the marks show up on all four pieces of film. Most page layout programs have 'Registration' as a colour in the default colour menu.

What is an 'Imposition'? and what is meant by 'head to head'? What is a 'double cut'?

Imposition is a printing term meaning 'layed out ready for printing'. CD booklet artwork must be imposed a certain way so that it's ready for the printing press. The more pages a booklet has, the more complicated the imposition will be.

Head to head is a way in which pages are imposed so that they can be printed on both sides easily and economically. It refers to how certain pages are layed out upside down, above others - so that both pages 'heads are touching'. The imposition will change depending on the number of pages the booklet has.

A double cut refers to the space between separate pages in an imposition. Usually a double cut will be either 5 or 10 mm. Check our art specs for details.

What are 'Pantone or PMS colours'? and what is 'Spot colour'?

The Pantone Matching System is a globally recognised standard of colour mixing for printers and designers. EVERY printer and designer will have several Pantone colour swatch books for both spot and process colour. Individual Pantone colours are designated with a numbered code, usually with a prefix of PMS. e.g.: Fire engine red is PMS 032.

Spot colour (unlike process or CMYK colour) is when an individual colour or colours are printed. With spot colour you can nominate a particular or unusual colour and have it pre-mixed, rather than try and reproduce that colour in CMYK. CD discs are silk screened in spot colour. (Although it is also possible to print discs in CMYK).

What is the difference between a 'digital proof', a 'chemical proof' and a 'Chromalin or Fuji proof'

It is standard practice that a colour proof is required by a printer so they can accurately match the CMYK colour balance of the job they are printing.

Traditionally, when the film separations for a print job were made, a chemical proof was generated by making a contact print from the 4 pieces of film. Because a chemical proof can only be generated AFTER the film has been made, any typos or mistakes cannot be corrected without running out new film - a very costly exercise. Chemical proofs are also called 'Chromelin' or Fuji' proofs due to the brand of the proofing paper.

At ACDC we prefer to use a 'Digital Proof' because they can be generated BEFORE the film is run out, so that any changes you might wish to make to your art can be made before the film is generated. (Despite all the proof reading in the world, you would be surprised to learn of the number of mistakes that are not picked up by the client until they looking at a full colour proof of their CD or cassette booklet).

The digital proof is essentially a very high quality, accurate inkjet print, so it is not quite as sharp or crisp as a chemical proof, but it is cheaper and these days all printers are happy to use them. Unlike most film bureaus, the company that ACDC use outputs the digital proof through the same 'post script rip' that the film goes through on it's way to the imagesetter This means that any problems that would've been encountered during the film output, will be encountered and solved in the digital proofing process.

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