I am amazed how different actually the printing from the screen world is. It is not just a matter of different colour spaces.

http://www.23hq.com/andrewagill/photo/2947647

This brochure should have used rich black. You can see that the black is actually printed on top of other colors, and you can actually see the other colors through it.

http://www.23hq.com/andrewagill/photo/2947644

An example of misregistration. Look at the white gap in the lower right corner of the green boxes. I can’t tell if it really was trapped or not. but increasing trapping would remove the gap.

http://www.23hq.com/andrewagill/photo/2947643?

An example of good trapping. There’s a very small border where the circle touches the graphic around it. You can see that no matter where you move the circle, it will still have that border.

I have the feeling that people around here do know a lot of things about this and other image editing stuff, and I think that is great the way you are sharing those knowledge…

Thanx!

@Andrew.
Thanks for the link to prepressure.com It contains a wealth of information. I will order “Getting it printed”. A second hand for just $12 is a bargain. Thanks again.

First, rich black:

http://www.prepressure.com/design/basics/richblack

The other inks make the black appear darker than it should, and you get funky effects. I saw an example once where someone overprinted 100%K on two other colors, you could see little shapes of other colors running through there.

I’ll see if I can’t whip up and example for you guys.

And here’s one for trapping:

http://www.prepressure.com/design/optimize_design

If you have a two colors that touch, it’s often useful to create a very small border between them of both colors. Again, I’ll see if I can whip up an example.

You can take a look at these pictures on http://www.23hq.com/jaims/album/2944601

You will found something extrange there: the cmyk-converted ones, can’t be displayed at all by the browser! Or, at least, I haven’t been able to do so, I’ve tried with firefox and with iexplore too.

That being said, Rolf: I don’t understand either how come photoshop saves jpg with cmyk. I have no idea. But it does

Alexandre: I have read something ’bout the importance of prepress, but I have to confess that I can hardly understand much of the stuff on the cmyk topic, the ‘trapping’ thing that you mention and all.
Do you think that working in rgb mode with the colour proof filter set to cmyk can do the trick?

Please ask him for permission to publish these images. If he is reluctant, let him slap his logo/copyright over it to make them useless for other purposes than making a point.

What I still don’t understand is savin CMYK in a JPEG. Isn’t JPEG strictly RGB?

Finally I’ve been talking to my drawer friend.
I wanted to explain him every suggestion you have put in this thread, and to find up what is his workflow to explain it to you.

So, with the workflow:
-> he’s delivering his works to several editor companys, which in turn release them to their printers.
My friend is aware that printers often allow to print an image from rgb color, but in the particular case of his customers, all of them happen to work with printers that need to be fed with cmyk images.
This seems to be the most common scenario with professional printers here in Barcelona (Spain).
My friend has had plenty of problems with the results of his works being printed, and the best approach to avoid them is releasing cmyk images.

-> therefore, hi works on his drawings with cmyk from the very beginning.
He also states that a common mistake is to work with rgb and convert to cmyk just prior to send the works to the editor/printer, as one can find nasty surprises with colors being very different from the intended ones, and then he can lose all the job done.
But we have found a really nice surprise here.
I told him yesterday to download the adobe cmyk file mappings and to use view/display filters/add proof color -web coated fogra28 (iso 12647-2:2004)- intent=relative colorimetric…
Et voilà! He’s able to work on a cmyk basis, and he likes it! Many thanks to David Gowers here, as he suggested this point.
One extra would be that you can have a 2nd view of the drawing (through view/new view), which allows to work with 2 instances of the drawing in parallel: rgb and cmyk.
There’s one thing missing here, though. It is that in the pallette he can pick up colors on a rgb basis, which are not the cmyk colors he’d be ‘brushing’ on the cmyk-filtered drawing.
This is not so important because he says he knows very well the colors he need, even on a rgb basis, and then I suspect that maybe I’ll find a workaround for this.
He says that having a real cmyk pallette would be a commodity, but he can work without it in the meanwhile.

-> so far, so good; the main issue now would be the ability to save the image as cmyk.
He can work with the cmyk filter, but he still can’t save the job as cmyk.
So this would be the main reason not to use the Gimp.
I know that there are a couple of plugins that would allow to save as cmyk.
I’ll have to invest some more time on this, as the one I have tried (separate) doesn’t work 100% ok, and it should be able to save the image as jpg (not tiff).

I have also explained to him the upcoming GEGL library stuff (thanks to be given to Andrew A. Gill for his nice webcast) and he’s looking forward to the next versions of the Gimp working with that.
He has just sent me a mail this morning, he says he’s happy with the Gimp now that he knows it a bit more in deepth, and he ensures that he’ll be using it; but that he knows that he’ll still have to use other apps to do some stuff.
He has also told me that he’ll be investigating on the (many) features on the Gimp, as he feels it’s really powerful.

By the way, he has sent me several of his drawings to make his points clearer (rgb, cmyk by phoshop, cmyk by corel painter…)
If you feel that it would be nice to take a look at them, I can ask him for permission and publish them (on 23hq.com for instance).

Well, this is a long enough post.
I hope I’ve been able to make these points clearer (sorry for my english when it is not good enough), as I think they can be illustrative for an (hypothetical ) chapter of mtg on cmyk.

Very kind of you, thank you very much.

Rolf, I think that the original question is broadening, now we have to learn/clarify stuff on cmyk but also in colour management.

But I think that from this thread some interesting stuff is being revealed as subject to study and get understood.

And I also feel that everyone here is being kind and helpful, which is always something good.

Andrew: thank you for making the effort, I’m downloading your the stuff, I’ll give it a deep look when I finish my work. And I never thought you were going to get heated on that, just happened to think that it’s better to be careful. Not only ’cause the hypothetical holy wars with other readers in this thread, but because the gimp developers deserve all my respect, I don’t want to sound like I’m complaining or I’m so picky

Thank you all, more on this later

So I would like to hear someone else talk about it.