Are K-only Images always K-only?

[waltonmendelson]

I am curious about K-only images.

Yesterday, I asked about how to create K-only images in Affinity Photo. Thanks to Walt.Farrell, I found out was both surprisingly easy and quick. Things took an interesting turn when I started playing around with them.

I have believed the Info windows. Move the cursor around a K-only image and you get K-only numbers no CMY. I’ve done the same in Acrobat with K-only PDFs, using Output Preview.

Photoshop

I made a K-only image in Photoshop:

• Mode > Grayscale (Discard color information? To control the conversion, use Image > Adjustments > Black & White. Discard/Cancel . . . Discard)
• Mode > Monotone (a “subset” of Dutotone),
• Mode CMYK (with Custom CMYK set to GCR, Black Generation set to Maximum).

This produces a grayscale image with K-only values. Saved as a PDF, K-only values. Saved as a JPG, K-only values.  But . . .

When I open that JPG (produced in Photoshop) in Affinity Photo the grayscale has CMYK values!

 

AffinityPhoto

I converted the same image as I used above, to K-only: using the magic K-only button.  It had K-only values in the exported JPG and PDF.

When I opened the JPG in Photoshop, I got a warning: “This file contains file info data which cannot be read and has been ignored. OK”  I clicked okay, and the image has K-only values. The Affinity Photo > PDF is also K-only. 

The Affinity Photo methods appears to be more reliable than Photoshop.

 

Question

How do CMYK values show up when the Photoshop K-only image is opened in Affinity Photo?  Is it possible that Photoshop does not discard the color information?

 

[David in Яuislip]

This jpg was produced in PS CS2 using a new CMYK image, the numbers were coloured by entering K values in the colour picker dialog
APhoto registers them precisely, dunno if this proves anything

CMYKcolours.zip

[waltonmendelson]

Interesting.  Perhaps the difference here is that you created the K-only values, where I was converting a color image to K-only values. Also, your image is not a K-only image, although it contains K-only values. It is also possible the PS CS2 (ver. 9?) was a better program, at least more stable, than version Photoshop 24.1.1! 

walton

[lacerto]

Obsolete.

[waltonmendelson]

@ Lacerto . . . It's going to take a bit of rewatching and rereading to follow the video. Thank you very much for attaching it.  

Meanwhile the image that I created in Photoshop:

• Color to Grayscale
• Grayscale to Monotone
• Monotone to CMYK where I had a custom CMYK with the GCR set to Maximum Black.

I saved it as a PSD, JPG, and PDF.  All three show CMY values of 00 and K 0-100. Opening it as a PDF in Acrobat, it was not listed as indexed.

 

But at this point, I'm confused (maybe when I understand more of the video, I'll understand more in general).  

Up until the last few years, although I did play with Serif Photo, I used mostly Photoshop.  My concern with K-only images is this:

• When being printed by KDP/Amazon, IngramSpark, etc., where we get virtually zero information, to get grayscale images with the best potential for "good," predictable results, I have found . . .
  •  Although KDP prints from RGB noticeably better than CMYK, the exception to that is grayscale images prepared for black ink books
  • Grayscale images in CMYK are more reliable . . . . reliable in the sense that the printed images better match the print-ready PDF.
  • K-only images in CMYK are more reliable still  . . . . reliable in the sense that the printed images better match the print-ready PDF.

But it sounds like I'm chasing a myth. Are you saying that K-only is only is a simulation or emulation of some sort and that it does not really exist? 

The Affinity Photo K-only test images, when either exported to JPG and opened in Photoshop or exported to PDF and opened in Acrobat, read with K-only values . . . but the Ouput Preview does say "simulate." In Acrobat the color space is device CMYK.  It seems Photoshop thinks it's K-only!? 

Again, thank you for the video and the explanatory information. 

Walton

[waltonmendelson]

I am willing to accept that the Info window is giving some sort of simulation.  But after looking at the video, I thought to look at the channels.  The C, M, and Y channels appear to contain no image information.  This strongly suggest that the K-only conversion is a true K-only conversion.

I understand that it is in CMYK color space.

Walton

[lacerto]

Obsolete.

[waltonmendelson]

There may be two problems.  

Me:

• I have relied mostly on the Info windows in Photoshop, AffinityPhoto, and Acrobat. My bad.
• With regard to Grayscale I was using Mode > Grayscale, or equivalent, to make the conversion. For K-only I used the process I listed above.  
• After your first video, I realized I should have been double checking Channels. If for nothing else, thank you.

Photoshop:

• For some years, and two computers, Photoshop has not been stable.  I would like to blame everything (perhaps even Covid) on Adobe.
• In short, there may be problems with Photoshop and grayscale/k-only, maybe not (as me: something I'm doing wrong), or even a combination.

The problem with KDP/Amazon is that it is incredibly and obsessively secretive. Before CreateSpace was absorbed into KDP, I had phone and email access to the Executive Team and Technical Support. They were still secretive, but this access opened the door a little.  KDP's printing is in some ways better, and in others bordering on outright bad compared to CS.  With KDP, no one has access beyond Customer Service, and they are woefully undertrained. 

I am trying to write out the best way to prepare grayscale images for print-on-demand printing . . . I got sidetracked with the grayscale/k-only/differing-info-window values thing. 

Walton