[poppler] Implement overprint in qt interface?

Sat Oct 20 08:36:22 PDT 2012

On 16.10.2012 22:57, Albert Astals Cid wrote:
> El Dilluns, 15 d'octubre de 2012, a les 07:15:51, Thomas Freitag va escriure:
>> On 14.10.2012 22:58, Albert Astals Cid wrote:
>>> El Diumenge, 14 d'octubre de 2012, a les 19:41:26, Thomas Freitag va
> escriure:
>>>> On 14.10.2012 17:21, Albert Astals Cid wrote:
>>>>> El Diumenge, 14 d'octubre de 2012, a les 13:47:29, Thomas Freitag va
>>> escriure:
>>>>>> Hi folks!
>>>>>>
>>>>>> Is there anybody in the community who wants the possibility to simulate
>>>>>> overprint in qt library?
>>>>>> With the implementation of DeviceN support in splash this is quite easy
>>>>>> now, so I can upload a patch.
>>>>> Sure, why not? Let's see the patch :-)
>>>> Okay, here it is.
>>> The two new methods are missing @since markers (and also i think the
>>> documentation of the two methods could be a bit more explanatory)
>> @since: I thought that You insert it when You commit it. If I would
>> insert 0.22.0 You have to change it if You will not have the time to
>> commit it :-) or I need to change it and have to upload a new patch if
>> You will not have the time :-(
> Well, if you do it, it's less work i have to do and thus it's easier i'll have
> time ;-)
Because I removed these two new methods now there is no need to comment 
them anymore :-)
But I introduced a new (static) method "okToUseOverprint" which just 
proofs if poppler is compiled with SPLASH_CMYK, and there I add the 
@since comment now.
>
>> Explanatory: Okay, but this will be hard. For those who know what
>> overprint is the documentation is self-explanatory, for others I need to
>> write reams. What's about to insert the link to
>> http://en.wikipedia.org/wiki/Overprinting?
> To be honest doesn't seem to make things much clearer to me :D
Okay, let me try to explain it in my own words:
First of all, in the normal behaviour, if something is painted 
everything previously painted at this place is knocked out. This is 
rather simplified, because we ignore functionality like transparency, 
blending modes etc. Now let us have a look at the printing process with 
4 different colour plates Cyan, Magenta, Yellow and Black. Without 
setting the overprint mode, the behaviour is the same:  if something is 
painted everything previously painted on every plate is knocked out. But 
when overprint mode is enabled, and i.e. in a DeviceN colorspace with 
only one process colour, let us assume Cyan, the Magenta, Yellow and 
Black plates kept untouched and only previously painted objects on the 
Cyan plate at this position are knocked out. But when You paint in 
DeviceCMYK, the behaviour remains the same (all is knocked out) even 
with overprint on, unless You set overprint mode to true in addition. 
With overprint mode true You need to look at the colour components You 
use for painting: if the a component is 0 the corresponding colour plate 
is left untouched again, if it is not 0 it will be knocked out again on 
this colour plate.
If there is a additional spot colour plate, it is similar: overprint 
false: everything is knocked out, overprint true: if You paint with 
process colours only this spot colour plate is left untouched, if You 
paint with this spot colour, the process colour plates remain untouched 
but on this spot colour plate previously painted objects are knocked out.
As I said, this is rather simplified, there are special rules for 
images, blending modes and so on and so on. A complete explanation can 
be found in the PDF specification.
As overprint just works on colour plates, You'll see no effects when You 
print in RGB as on a monitor, therefore You have to simulate the effects 
(overprint preview :-) ) if You want to see them on a monitor.
> Ok, let's leave the docu as it is
>
>>> Also why are you calling it "overprint preview"? How is it a preview?
>> To be honest, I haven't really thought about that. Probably I choose
>> that name because it is also introduced in GlobalParams with that name.
>> But also in the acrobat reader preferences it is called "Use overprint
>> preview". And because not all RIPs support it (i.e. RGB printers) it is
>> indeed something like a preview (for RIPs which support it).
> Ok, let's leave it with that name (but maybe make it a RenderingHint as Adam
> suggests?).
I tried to understand what You meant with RenderingHint and made it, 
hopefully it is what You meant. I attach the changed patches (poppler 
and okular).

Cheers,
Thomas
>
> Cheers,
>    Albert
>
>>> Given that overprint only works if defined(SPLASH_CMYK) you should make
>>> the
>>> setter return a boolean that says if the set worked or not (i.e. make it
>>> fail if !defined(SPLASH_CMYK))
>> Gotcha. I thought about that and disable / enable the option in okular
>> if the format generator doesn't support it. But because I'm not familiar
>> enough with okular I defered it and then forgot it...
>> I'll insert it in QT when I get answers to the other points.
>>
>> Cheers,
>> Thomas
>>
>>> Cheers,
>>>
>>>     Albert
>>>> In a few places it has already a similar
>>>> implementation than in bug 50992 (thread safe), because changing the
>>>> overprint option also meant that we need a different SplashOutputDev
>>>> instance. But You probably also want to test it in okular? Even if we
>>>> are here not on an okular list, I attach the okular patch here, too.
>>>> Also here, it has already the changes from bug 50992. But because
>>>> POPPLER_QT_THREADSAFE is not defined here, it doesn't make any
>>>> difference, so I let these changes as they are. BTW, I'm not really
>>>> familiar with qt programming, so most changes in okular are more or less
>>>> a (hopefully) best guess.
>>>>
>>>> Cheers,
>>>> Thomas
>>>>
>>>>> Cheers,
>>>>>
>>>>>      Albert
>>>>>> For everybody who doesn't know anything about overprint I attach three
>>>>>> screenshots which shows the implementation in okular.
>>>>>> (This is not fake, I made a small apprentice piece today morning :-) )
>>>>>>
>>>>>> Cheers,
>>>>>> Thomas
>>>>> _______________________________________________
>>>>> poppler mailing list
>>>>> poppler at lists.freedesktop.org
>>>>> http://lists.freedesktop.org/mailman/listinfo/poppler
>>>>>
>>>>> .
>>> _______________________________________________
>>> poppler mailing list
>>> poppler at lists.freedesktop.org
>>> http://lists.freedesktop.org/mailman/listinfo/poppler
>>>
>>> .
>> _______________________________________________
>> poppler mailing list
>> poppler at lists.freedesktop.org
>> http://lists.freedesktop.org/mailman/listinfo/poppler
> _______________________________________________
> poppler mailing list
> poppler at lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/poppler
>
> .
>

-------------- next part --------------
A non-text attachment was scrubbed...
Name: qtopnew.patch
Type: text/x-patch
Size: 11096 bytes
Desc: not available
URL: <http://lists.freedesktop.org/archives/poppler/attachments/20121020/c9286b37/attachment-0002.bin>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: okular.patch
Type: text/x-patch
Size: 12343 bytes
Desc: not available
URL: <http://lists.freedesktop.org/archives/poppler/attachments/20121020/c9286b37/attachment-0003.bin>