Preflight for CMYK 0,0,0,100?

[mykee]

I not only make covers, but also book interiors, where printing with black ink only is essential. So it can only contain elements that cannot contain CMY colours, only K.

Is there a preflight option that I can use to filter out elements that meet this requirement?
Unfortunately, the printer has repeatedly rejected the preflight because Publisher sometimes makes vector images stroke a non-CMYK 0,0,0,100, or if a K-only image does not have 100% opacity properties, the program will mix in a CMY value.

Press can find these straight away using Acrobat, but I can't. It would be nice to filter this out before sending to the press.

[Old Bruce]

1 hour ago, mykee said:

I not only make covers, but also book interiors, where printing with black ink only is essential. So it can only contain elements that cannot contain CMY colours, only K.

I am going to assume that the Covers are CMYK. So my advice is to make two documents, the Cover in CMYK and the Interior in K only.

[David in Яuislip]

Try Ghostscript for a poor man's report on ink coverage per page

Document CMYK US Web coated SWOP V2 saved as Konly.pdf
Contains same image on each of 3 pages with settings noted below

This is the report using gswin64 -dSAFER -sDEVICE=ink_cov -o Konly.txt Konly.pdf

Image1 set to K only
 0.00000  0.00000  0.00000 61.27310 CMYK OK
 
Image2 with B&W adjustment
42.69350 37.05737 35.53457 14.81541 CMYK OK

Image3 with desaturation adjustment
48.45574 49.59304 49.69440 32.78706 CMYK OK

[lacerto]

13 hours ago, David in Яuislip said:

Try Ghostscript for a poor man's report on ink coverage per page

It IS a poor man's report tool because it will signal K100 in any PDF with ICC embedded (the default setting of Affinity apps when exporting to CMYK) as a four-color black (similarly as Adobe Acrobat Pro, if the implied but not explicitly stated target profile is not selected as the simulation profile).

A good question is: will this be four-color black also on plates, or does it depend on skills of print-shop personnel that native colors will be output despite of ICC-dependent input ("input" in context of imposition software)?

[lacerto]

3 hours ago, mykee said:

It would be nice to filter this out before sending to the press.

In lack of proper preflight tool, you could open your exported PDF in an Affinity app, and get pretty reliable interpretation of color mode of objects in the PDF (things like overprint status would not be read, at all, but you should be able to detect things like K100 vs. four-color-black).

[thomaso]

3 hours ago, mykee said:

printing with black ink only is essential. So it can only contain elements that cannot contain CMY colours, only K.

With certain settings you can export a PDF that contains the K ink channel only. This post has a K only profile attached, note @lacerto's hints above and below this post:

[mykee]

Thank you for your feedback! It was not clear to me in the first place why once I set a vector to 0,0,0,100, it converts it during the Affinity export, even though I stay in color profile. Or if I set the opacity, why does it convert the CMY values if only the K value was set in the first place (i.e. why is the opacity in this case not x % of the K value?).

So I'm reading the comments and trying to learn how to make a perfect K 100 only export from Affinity with CMYK profile.

 

[mykee]

On 3/16/2024 at 8:04 PM, lacerto said:

In lack of proper preflight tool, you could open your exported PDF in an Affinity app, and get pretty reliable interpretation of color mode of objects in the PDF (things like overprint status would not be read, at all, but you should be able to detect things like K100 vs. four-color-black).

I wonder how I can test this. In Photo has a meter, but I can't measure each image one by one, and sometimes it also converts the vector strokes to CMY values. I read in one of your comments that other tools have such a tool that measures CMY values that don't match, one of these would be good for Affinity Publisher.

[Old Bruce]

Just now, mykee said:

Thank you for your feedback! It was not clear to me in the first place why once I set a vector to 0,0,0,100, it converts it during the Affinity export, even though I stay in color profile. Or if I set the opacity, why does it convert the CMY values if only the K value was set in the first place (i.e. why is the opacity in this case not x % of the K value?).

So I'm reading the comments and trying to learn how to make a perfect K 100 only export from Affinity with CMYK profile.

Are you starting with a Publisher document that is CMYK?

[mykee]

7 minutes ago, Old Bruce said:

Are you starting with a Publisher document that is CMYK?

Yes, of course. I working with CMYK only in Publisher. I made covers and interior too with CMYK profiles. (I use FOGRA39)

[pbasdf]

As a quick visual check, you can switch to the Photo persona, then in the Channels panel, switch off visibility for the K channel.  Then scroll through all the pages.  If you have any rich black text/images, they will still be visible.  Everything that is pure K will disappear.  Remember to switch the K channel visibility on again before switching back to Publisher persona - I always forget that.

That won't overcome the export conversion issues highlighted above and elsewhere, but it will at least give you a visual check that you are starting the conversion process with pure K in the right places.

 

[lacerto]

8 hours ago, mykee said:

I wonder how I can test this. In Photo has a meter, but I can't measure each image one by one, and sometimes it also converts the vector strokes to CMY values. I read in one of your comments that other tools have such a tool that measures CMY values that don't match, one of these would be good for Affinity Publisher

As stated above, if you have Photo, you can use Channels panel and/or histogram. But you can cope with mere Publisher, as well, as you can use the Color panel to check color values of text objects (and vector objects), and adjustments like Channel Mixer to reveal color in parts that look black (K-only) but involve multiple channels.

 

As for causes Publisher will convert K-only to CMYK (multi-channel), there are various, three of which are mentioned in the video clip.

One further, very common reason, is applying any adjustment or blend mode on text or native K-only objects, causing rasterization to CMYK. Applying F/X effects will often also do that, even if outer effects and Gaussian Blur might survive non-rasterized. Using opacity percentage, too, would cause rasterization to CMYK in case  PDF output does not allow live transparency.

Last but not least, Affinity apps by default embed document ICC in a PDF export, which will cause incorrect readings in tools like Adobe Acrobat Pro in case "wrong" simulation profile is active, or when using Ghostscript for separation.

[mykee]

11 hours ago, pbasdf said:

As a quick visual check, you can switch to the Photo persona, then in the Channels panel, switch off visibility for the K channel.  Then scroll through all the pages.  If you have any rich black text/images, they will still be visible.  Everything that is pure K will disappear.  Remember to switch the K channel visibility on again before switching back to Publisher persona - I always forget that.

That won't overcome the export conversion issues highlighted above and elsewhere, but it will at least give you a visual check that you are starting the conversion process with pure K in the right places.

 

It works perfectly well, I have Photo, so that's what I had in mind when I raised the issue. I can also check the PDF file back with this, thank you very much!

 

9 hours ago, lacerto said:

As stated above, if you have Photo, you can use Channels panel and/or histogram. But you can cope with mere Publisher, as well, as you can use the Color panel to check color values of text objects (and vector objects), and adjustments like Channel Mixer to reveal color in parts that look black (K-only) but involve multiple channels.

One further, very common reason, is applying any adjustment or blend mode on text or native K-only objects, causing rasterization to CMYK. Applying F/X effects will often also do that, even if outer effects and Gaussian Blur might survive non-rasterized. Using opacity percentage, too, would cause rasterization to CMYK in case  PDF output does not allow live transparency.

Last but not least, Affinity apps by default embed document ICC in a PDF export, which will cause incorrect readings in tools like Adobe Acrobat Pro in case "wrong" simulation profile is active, or when using Ghostscript for separation.

The only thing I don't understand is that if I told the program to use only K-only for the images, it shouldn't include CMY when exporting, since the K-only option is inherently higher level, prohibiting the use of CMY (it was designed for that). So if I'm using effects or opacity, it should just modify based on K regardless of CMYK profile, even by rasterizing the image, since there is an option to rasterize what the PDF doesn't support. I don't usually use ICC embedding, I always turn it off because the press wants it that way by default, I guess because of the compatibility you mentioned. Is it perhaps worth turning off colour conversion when saving?

[lacerto]

31 minutes ago, mykee said:

The only thing I don't understand is that if I told the program to use only K-only for the images, it shouldn't include CMY when exporting, since the K-only option is inherently higher level, prohibiting the use of CMY

That is not how it works, though. If you want to apply K-Only on an image and have it exported on K plate, it must be the sole operation on that image layer. You could apply K-Only, then apply adjustments (which cause the image to be handled as an RGB resource), and once finished, rasterize and convert the resulting pixel layer back to image resource, and then apply K-Only again, to force pixels on K plate. Or, you could export a K-Only image with adjustments explicitly to grayscale. That is admittedly quite convoluted.

[mykee]

However, the problem is that you can't really make any changes to a K-only image, because the program will export it incorrectly to the CMYK profile. So that means you should make any changes before you paste the image, then paste it, and then K-only. For example, in the case of opacity, why can't a K-only image be made to take x% of 100 as the export value, since black is greyed to white during opacity. So 100 opacity is 100 K, 25% opacity is 25 K, or no?

Or whatever I set on the image (contrast, opacity) it will first execute and then finally drag the K-only "layer" on top.

[Alfred]

5 minutes ago, mykee said:

For example, in the case of opacity, why can't a K-only image be made to take x% of 100 as the export value, since black is greyed to white during opacity. So 100 opacity is 100 K, 25% opacity is 25 K, or no?

No. K100 with 25% opacity will look the same as K25 with 100% opacity, but only in isolation. 25% opaque is the same as 75% transparent, so any objects underneath will show through quite strongly, whereas 100% opacity will result in underlying objects being completely hidden where they overlap with the object on top.

[lacerto]

1 hour ago, mykee said:

For example, in the case of opacity, why can't a K-only image be made to take x% of 100 as the export value, since black is greyed to white during opacity. So 100 opacity is 100 K, 25% opacity is 25 K, or no?

But doesn't it behave that way? Layer opacity does not cause a K-only image to become converted to CMYK. Layer adjustments (and most of the F/X blend modes) do:

 

[mykee]

Interesting, but then it seems that masking can also cause such distortion in the colours, because I put in an image, masked the frame, and set it to K-only, and set it to 75% opacity. So the masking can be a problem on export.
Thanks for the video, I absolutely understand what to look out for then.

[lacerto]

2 minutes ago, mykee said:

Thanks for the video, I absolutely understand what to look out for then

You're welcome. You could also colorize K-only images, e.g., making them K100 using the Color panel (instead of being void of fill), and then applying swatch opacity, would equally retain the K-Only images as K-Only.

[mykee]

Great trick, I will check it soon, thank you! This would solve my image editing problems. I'll solve the PDF back-testing with the Channels panel (like you did in Acrobat), and then I can actually use normal effects on the embedded images later.

Does Total Area Coverage, which is in Acrobat, also exist in Affinity? Or should I add up the percentages in my head?

[mykee]

I couldn't wait, so I tried your trick. It's brilliant. I would never have thought that by following these steps I could keep the K-only ability and still be able to tone down the greys. I'm posting the steps here for posterity:
- CMYK project
- paste the image
- K-only button pressed
- select the image
- in the Color panel, select CMYK mode and set CMY sliders to zero, K to 100
- in the Color panel you set the Opacity slider (not the opacity of the image layer!)
- when export your project use Convert image colour spaces option for perfect CMYK export

I tested the exported PDF, and in Affinity Photo, turning off Composite Black in the Channels tab makes the image disappear, i.e. it only contains K.

[thomaso]

In addition to @lacerto's hints: Compare the attached PDF files exported from a CMYK .afpub + a placed RGB image in 4 variations.

• Both PDF are exported as PDF/X-4 but only 1 got "Convert image colour spaces" activated. The one which does not did export the RGB images as RGB and thus causes their K-only settings to result in CMY + K.

• If you open the PDFs in APub the Resource Manager lists one image as Grayscale and three as colour images. The grayscale is the one with K-Only and no fill colour.

k-only & colour _cmyk X-4.pdf

k-only & colour _cmyk X-4 convert.pdf

[mykee]

@thomaso Thank you very much for the video and the use of the switch is now clear. So even if the project is CMYK and the fill is only K, if the image color space is not converted when exporting, the switch is essential when using PDF export. It is safer to leave the switch always on. I added your step to my comment. Thank you very much!

[thomaso]

18 minutes ago, mykee said:

the image color space is not converted when exporting

Just note, a PDF file may contain multiple colour spaces/profiles, even PDF/X * regardless of its output intent.
(advantage: required colour conversion happens in a late/last state of a print process to avoid multiple conversions)
[* only PDF/X-1 must not and exports as CMYK (+ spot colours) exclusively]

[lacerto]

Interestingly, forcing conversion of image color spaces in context of PDF/X-based export methods also seems to restitute the "K-Only" effect for "K-Only" images that have adjustments applied (and which otherwise result in conversion to four-color state when exported). When examined in Adobe Acrobat, such objects seem to have both grayscale and K-ink version of a CMYK image included in PDF/X-4 and all non-PDF/X based export methods, but the values show as K-values only in PDF/X based versions. PDF/X-1 and X-3 only have the CMYK K-ink included. This is quite confusing (and also feeble, knowing the restrictions involved in PDF/X-based export methods).