3.5.2See Also...International Specification for Orienteering Maps ISOM Index Symbols Index Map type index previous next
revision 01/00
Four colour offset printingThe four colour printing method uses the three basic colours of the additive colour model: cyan, magenta and yellow. In theory a mix of 100% of cyan, magenta and yellow produces black colour, but in reality it will be more of a dark brown. Therefore black is normally printed as a separate colour. After these four colours the model is often referred to as CMYK.
Although four-colour printing requires fewer and standardized inks, the main advantage of using this process is that it allows the inclusion of colour photographs and full colour advertisements at no extra cost.
The use of digital techniques to produce four colour separations has now made it possible to make high quality orienteering maps using four colour printing. This is not the suggested method of printing orienteering maps, it is an alternative. This method will only be acceptable when line quality, legibility and colour appearance are of the same quality as the traditional spot colour printed map.
However, the mapmaker has to take into consideration the limitations and potential errors of this method. The reproduction of very thin lines (contours) requires special attention.
The following table lists the CMYK combinations for the equivalent PMS colours recommended for orienteering maps:
|
Colour |
Cyan | Magenta | Yellow | Black | |
| Black | Process black | 100% | |||
| Brown | PMS 471 | 56% | 100% | 18% | |
| Yellow | PMS 136 | 27% | 79% | ||
| Blue | PMS 299 | 87% | 18% | ||
| Green | PMS 361 | 76% | 91% | ||
| Grey | PMS 428 | 23% | |||
| Violet | Purple | 100% | |||
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The colour mixture can be done either with traditional printing screens or special printing screens with randomly distributed dots called stochastic screens. The latter screens will improve leg ability and make fine lines such as contours more readable, and is therefore highly recommended.
Traditional screens should have a screen frequency of at least 60 lines /cm. For stochastic screens the frequency cy will vary randomly.
To avoid the unwanted moiré effects with traditional printing ting screens 4-color orienteering maps should always use the conventional angle set. In proper stochastic screens the dots are placed randomly, so angles are irrelevant and unwanted moiré effects will not appear.
 |
|||
| Colour | Angle | ||
| Cyan | 15° | ||
| Magenta | 75° | ||
| Yellow | 0° | ||
| Black | 45° | ||
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The appearance of colours is dependent on the printing order. In 4-colour orienteering map offset printing the printing order should always be:
- Yellow
- Cyan
- Magenta
- Black
With traditional spot colour printing inks are physically printed on top of each other. It is possible to simulate the same with four-colour printing technique, and this optimises legibility and gives a colour appearance as close to traditional spot colour printing as possible. To achieve this effect in four-colour offset printing, information underlying (in the spot colour printing order described in 3.5.1) a specific spot colour should not be blocked out (erased /printed white) completely, but should be blended in to produce a new colour for printing.
The use of overprinting effect with 4-color offset printing is recommended for the following solid colors:
Illustration: Contours in dense vegetation printed in 4-colours. Overprinting effect in the right illustration
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Text that is new or revised from ISOM1990 is shown in maroon type.
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This whole section is new
Further advice
on 4 colour printing has been issued (January 2000) link to it here (to follow);
the text will be added to these pages as soon as feasible.