Black problem in CMYK printing

[Gianni Becattini]

The printer is asking me for a problem. He says that "The backgrounds are in 0-0-0 RGB (black). This will be 100% black in CMYK, but certain "black" pages also have images with a black background.
This then becomes a build-up color black (not 100% K but also some other C, M or Y values) resulting in tint differences clearly visible in the final product."

I believe I understand that:

• I have a black page, obtained with black rectangle
• over i I placed a photo (see an example below).

But which could be an alternative to that? Maybe that the problem was that I have two black rectangles superimposed?

Thanks

[thomaso]

19 minutes ago, Gianni Becattini said:

But which could be an alternative to that? Maybe that the problem was that I have two black rectangles superimposed?

If the RGB black in the images have different values than your CMYK black Rectangle fill colour then it may result in different blacks in a PDF export.

Alternatively you could either …

… select the Rectangle layer + use the Colour Picker Tool to assign the image's black as the Rectangle's fill colour.
… increase the black background of the image file + don't use an additional Rectangle object fill colour.

 

 

 

[loukash]

2 minutes ago, thomaso said:

Alternatively you could either …

… 3) flood erase the black background of your image so that it transparently floats over the K100 background shape (what I would do)
… 4) enlarge the image background by stretching its pixels so that it fills the whole spread (old school pre-transparency workflow)

[thomaso]

7 minutes ago, loukash said:

… 3) flood erase the black background of your image so that it transparently floats over the K100 background shape (what I would do)

Sure you would? – It could get tricky at dark edges like these:

btw, your 4.) seems to be my 2nd.

46 minutes ago, Gianni Becattini said:

• I have a black page, obtained with black rectangle
• over i I placed a photo (see an example below).

Actually I would expect to see at least two slightly differing blacks in your APub screenshot but it looks rather like identical blacks. What is your document's colour space and what the Rectangle's black definition in the Colours Panel (with the lock disabled)? What PDF version (e.g. 1.7 or /X-4 ?) and in what colour space/profile did you send to the printer?

Also I wonder how the black background in the image was created. It looks so perfect that it might indicate it was created manually (not just shot on a black ground). If this was the case then it may indeed be an easier option to set the image's background to transparent and cause the black page background via the Rectangle object only.

p.s.: the blue device top left is missing bleed, right?

[loukash]

12 minutes ago, thomaso said:

btw, your 4.) seems to be my 2nd.

Perhaps, depending on what you meant by "increase the black background". I understood it as if the background was already there but cropped.
But point taken. 

16 minutes ago, thomaso said:

It could get tricky at dark edges like these

Sure.

[Gianni Becattini]

I understand my limits.... but I must solve this problem. Thank you very much for your patience. 

The color space is this?

However, with the color picker, black is always 0,0,0 - with the small lock open or closed.

But I suppose that the printer problem is that I have a picture and behind it a black background, but it is impossible to think creating (600 pages!) a special black background for every page with a hole for the images... isn't it?

[thomaso]

7 minutes ago, Gianni Becattini said:

However, with the color picker, black is always 0,0,0 - with the small lock open or closed.

But I suppose that the printer problem is that I have a picture and behind it a black background,

The setup is not the problem and can 'generally' be used without issues. But currently you seem to have deviating colour spaces and/or different profiles involved.

Okay, your screenshot shows a document's colour space RGB with an sRGB profile. – Is this the setting for the image source file or for the layout document or for both?

And what object does show the picker with RGB 000: the image or the Rectangle or both?

And what colour space & profile does the printer get from you? Does it have image colours converted? And does it have a profile embedded, either for the image or for the document or for both and/or does it include an output intent (PDF/X)?

20 minutes ago, Gianni Becattini said:

it is impossible to think creating (600 pages!) a special black background for every page with a hole for the images... isn't it?

Agreed, and it will not be necessary, too. – Do all the images have the same/identical black background colour definition … or do their background blacks vary across the entire layout document / pages?

[loukash]

1 hour ago, Gianni Becattini said:

The color space is this?

Making a print layout in RGB/16 is asking for trouble. Unless you're going to print it on your home inkjet, you want to be working in CMYK/8.

[Gianni Becattini]

I didn't change it, I neither knew that it existed... 😀

But can I change it?

For the photos, I was forced to change the color profile because my PowerMac M2 get crazy with the iPhone defaults - see this:

Often I user Image P3, which works well. Or I left the default sRGB IEC61966-2.1.

[loukash]

27 minutes ago, Gianni Becattini said:

But can I change it?

Of course. in Publisher: File → Document Setup → Color
If you have already consequently applied CMYK colors to your layout objects, their CMYK values should stay intact when converting the document from RGB/16 to CMYK.

[R C-R]

@Gianni Becattini, totally off topic & not an issue I can help with but your images of old tube-type Tektronix oscilloscopes brings back fond memories of using them in my college years ... & the one time I totally ruined the plug-in input amp & some other parts of a very expensive high-end model when a 30KV pulse arced over the voltage divider I was using to step it down to measure its duration & went directly into the amp!

The resident shop wizard who was responsible for maintenance & repair of all the college's electronics said it was the first time in his experience that anyone managed to kill a Tektronix oscilloscope so thoroughly since they were built so well.