[reportlab-users] CMYK overprinting (colour-separated PDF output)

[Robin Becker]

On 30/06/2010 10:06, Dominique Lederer wrote:

>

> Am 30.06.2010 um 10:45 schrieb Andy Robinson:

>

........

>> Yes, use the CMYKColor class instead.

>>

>> Hope this helps,

>>

>> Andy

>

> thanks for your reply, but i am already using the CMYKColor class, which does not work. Please see my example, maybe i am using it wrong?

>

> cheers

> Dom

........

Hi,

the problem here may be that non-separating overprint is not controllable by the 
pdf definitions; it is a function of the output device.


from the 1.7 manual

> If the overprint parameter is true and the output device supports overprinting, no such erasing actions are performed; anything previously painted in other colorants

> is left undisturbed. Consequently, the color at a given position on the page may be a combined result of several painting operations in different colorants. The effect produced by such overprinting is device-dependent and is not defined by the PDF language.

> Note: Not all devices support overprinting. Furthermore, many PostScript printers support it only when separations are being produced, and not for composite output. If overprinting is not supported, the value of the overprint parameter is ignored.


I looked inside the PDF produced by the example and there is only one setting of 
the overprint control (effectively we set /op true). After that I don't see any 
restore states that affect the simple CMYK drawing; I think we're not doing 
anything wrong. So it could be that the acrobat tools just decide not to show 
this overprint as a colour mix for this case.

That being said there is an additional parameter that affects process cmyk 
overprinting that is the opm value. We don't control that parameter currently. 
According to the manual when OP is true OPM controls the interpretation of zero 
tint values.

Have you tried printing any of this output with a CMYK capable printer?
-- 
Robin Becker