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Colour mixing

Posted by Eddie 
Colour mixing
March 19, 2012 06:26PM
Hi Finn,

I have a pond which displays (and also prints) green.
In Ocad it is fine. The blue is layered above yellow (Open).
There are also a number of instances where areas of green change shade due to underlying yellow.
Is there anything I have missed in Condes?

Regards

Eddie
Attachments:
open | download - Fallowfield 2012.ocd (262.2 KB)
open | download - qaz.wcd (3.2 KB)
Finn Arildsen
Re: Colour mixing
March 19, 2012 06:57PM
Hello Eddie,

What you see is most likely the overprint effect.

Very briefly, overprinting colours is what you see when you print your map with offset printing, 5 colours (black, brown, green, yellow, blue). If you print an area with yellow ink on top of an area with blue ink, the result is a green coloured area.

Overprinting colours is actually good, and we use it because we want for example brown contours to become slightly darker when they traverse a green area. This makes the map more readable.

However, we don't want yellow and blue to mix into green, so that a blue stream becomes green when it traverses a yellow field. Here, we want the blue colour to "knock out" the yellow.

In the olden days, when we drew maps with pens on films, we had to meticulously cut out the yellow area where the stream crosses.

OCAD and other drawing programs support that this can be done automatically. Thus, in OCAD, for each colour layer you indicate whether the colour should "knock out" the underlying colour layers, or it should "overprint".

In the normal viewing mode, OCAD for some reason does not show overprint, but you can change to "spot colour mode" in OCAD and it will show you.

Condes respects the overprint settings in the OCAD map file, and it therefore shows the overprint effect.

There are two solutions to your problem: The best one is probably to modify the map file so that only the colour layers where you really want the overprint effect, are marked with overprint. The "lazy" solution is to use the Canvas / Map menu in Condes and uncheck the option "Make overprint effect for overprint colors in OCAD maps". This will solve the immediate problem, but you will also lose the overpritnt effect for those colours where you really want it.

I hope this is helpful.

Best regards,
Finn
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