How to get nice dark blacks when printing with KDP?

[Petrichor]

Hi folks. I'm making some coloring books with KDP, but I'm a bit confused about the color black. The book's interior is printed in black and white, and my document has a Generic CMYK color profile.

I've set the book's text to be K100 black (0,0,0,100). I also drew line-art illustrations in Procreate, saved them as png, then imported them into Publisher. The CMYK values for the black part of the illustrations is 75,71,65,80 in Publisher. Will this show up as dark black once printed, or more or a gray? I'd like both the text and images to be a nice dark black. Any suggestions? Thanks!

[firstdefence]

Take a look at this webpage: https://www.bittbox.com/culture/photoshop-101-true-black-cmyk it explains the Rich Black vs K100 but there are a fair few people on here with excellent printing knowledge so they may answer your question more succinctly. 

[Petrichor]

Thanks @firstdefence. That website suggests a "rich black" value of 75,68,67,90. Does this recommendation change if my book is printed on a black and white printer? Since the interior of my book is only grayscale (pretty much just black line art), I'm using the "black and white" interior option from KDP. Does a black and white printer use the CMY values, or only the K?

[lacerto]

If your placed PNG files are in RGB (24-bit or indexed 8-bit), make sure that you apply K-only button (only available on the context toolbar in a CMYK mode document) on all these images after you have placed them. This guarantees that they will be exported in pure black (K-only) as long as you export using CMYK color mode (e.g. using "PDF (press ready)"). If they are in grayscale mode, they will be exported K-only whether the K-only mode is applied or not.

If your drawings are in PNG 1-bit (monochrome) format, make sure that you do not allow downsampling, because for some odd reason Affinity apps will convert blacks of placed monochrome images to 4-color blacks whenever they are downsampled.

Note that if you have four-color (rich) blacks in your PDF delivered to KDP, and you have agreed on grayscale (K-only) printing, and they do not reject the file, the four-color blacks will be converted to grayscale and result in being printed in dark gray rather than 100% black.

kdpblacks.afpub

kdpblacks.pdf

 

[firstdefence]

9 hours ago, Petrichor said:

Thanks @firstdefence. That website suggests a "rich black" value of 75,68,67,90. Does this recommendation change if my book is printed on a black and white printer? Since the interior of my book is only grayscale (pretty much just black line art), I'm using the "black and white" interior option from KDP. Does a black and white printer use the CMY values, or only the K?

If the printer is Mono i.e. no other colour cartridges, just Black, then K100 is the only option. @lacerto gives some sound advice.

[Petrichor]

17 hours ago, lacerto said:

If your placed PNG files are in RGB (24-bit or indexed 8-bit), make sure that you apply K-only button (only available on the context toolbar in a CMYK mode document) on all these images after you have placed them. This guarantees that they will be exported in pure black (K-only) as long as you export using CMYK color mode (e.g. using "PDF (press ready)"). If they are in grayscale mode, they will be exported K-only whether the K-only mode is applied or not.

Hmm, my document is CMYK, but I don't seem to have a K-only button. If I use the "Black and White" adjustment, I get a K value of around 93 by default, while moving all of the sliders to -200% gives me values of K to 98.  I can add a second adjustment (using Levels and Multiply) to get K to 100.  Is this a good option?  If so, can I save these two adjustments as one preset? I don't seem to have an "add preset" button either.

If anyone wants to take a look, I've attached a page below, with the adjustments described above.  Any advice?

sample_page.afpub

[lacerto]

The "K only" button shows if you select the image layer (Verdin.png) -- which is kind of buried as you are using a Picture frame. When you have "K only" button applied, you do not need adjustments to achieve black-only behavior. 

I am not sure if you could achieve K-only effect (from an RGB 0, 0 , 0 value) by using adjustments, but just for information, I think it is one of the sales quirks of Affinity apps to require purchase of Photo to be able to use adjustment presets created in Publisher (by using the "Add preset" button on various adjustment panels), as the Adjustment panel is only available in Photo Persona, as shown in the screenshot below (the screenshot also shows availability of the "K only" button:

[Petrichor]

Fantastic, thanks @lacerto and others! I found the K only button, and it appears to do exactly what I want. And yes, the "Add Preset" button appeared once I installed Affinity Photo. (I already had a license for it, but hadn't install it.)

Thanks again, all!

[thomaso]

4 hours ago, lacerto said:

I am not sure if you could achieve K-only effect (from an RGB 0, 0 , 0 value) by using adjustments,

I wonder if for text + line drawings only it would work to set the document to Black & White to force K only and possibly darker black. Other then expected it results quite different for various image colour spaces. – Can you understand / explain why especially the RGB image (top right) maintains its grays in a B&W document while the CMYK (top center) and the Grayscale image (top left) appears without halftone? (the group on the top left is a grayscale image, not text)

The attached V1 package contains the five images linked and is saved with history for the documents colour space switch.  grays.zip

(click screenshots to enlarge)

->  -> 

[lacerto]

1 hour ago, thomaso said:

I wonder if for text + line drawings only it would work to set the document to Black & White to force K only and possibly darker black.

Sorry, I could not follow. Do you mean by "Black and White" document a "Gray/8" document color mode? I could not see any adjustments here (to which I referred in my post).

The document was in CMYK color mode and had Generic CMYK document color profile applied, yet some of the linked images had e.g. ISO Coated and sRGB profiles applied, but were actually in grayscale color mode when opened in Photoshop, so quite confusing. On the other hand, as far as there are (CMYK) profile conflicts (between placed images with embedded profiles and the target profile), I would imagine that there will be export time conversions. The top three images did additionally have RGB 0, 0, 0 fill color applied to them which I think would cause export time conversion and four-color blacks, disregarding K-Only mode applied (when trying to export to CMYK), as I'd imagine that K-Only is applied first and the RGB fill second.

Also, I could not  understand the color markings in the Farbkreis CMYK and Farbkreis RGB images (former being in Grayscale mode and latter in RGB mode); when K-Only is applied on these images, their color values are converted to varied gray values, as expected.

v1105 grays.pdf

[thomaso]

On 8/28/2023 at 1:01 PM, lacerto said:

Do you mean by "Black and White" document a "Gray/8" document color mode? I could not see any adjustments here (to which I referred in my post).

Yes. Your screenshot shows a Levels + a B&W adjustment, which made me wonder if a Gray-8/ B&W document colour space might cause the wanted result without adjustment layers but by its kind of 'threshold / posterize' effect. (as the samples below show it seems to darken even grayscale images)

Sorry for confusion caused by image file names and their use/appearance plus the fill colour assigned to some of them in my .afpub. Below an update of this setup.

My question was / still is why the image top right, an RGB colour image, maintains its halftones in document Gray/8 -> B&W colour space + "K Only" on, while one of the two Grayscale images does but the other does not show halftones then. At least for the last row ("K Only" on, no fill) I would expect either all  Grayscale + RGB images appearing either black or white (as if 1 bit or 100 K / 0 K only) or none of them (= all of them show halftones).

[lacerto]

I am not sure if I got your point but I think that "K-Only" retains its effect even when document color mode is changed so the CMYK and RGB images are still handled as K-Only even when changing to Gray/8 with Black and White profile. The K-Only button is no longer available so you cannot change the handling unless switching back to CMYK mode. This can be beneficial even if the feature is not designed to be used this way.

I did not quite get the point of demonstrating use of a fill color (in this case K100) in context of color images (CMYK and RGB), and have not generally given much thought of using direct fill color with images other than grayscale (either genuine, or ones with K-Only mode applied) -- probably because the way the colors get mixed when not combining just gray values is not clear to me and the effect therefore feels kind of uncontrollable (more so than using direct fill assignments with or blend mode color fill layers on top of grayscales). 

[Petrichor]

Hi all. A follow-up question: are text and image blacks handled differently? I set both my text and images to K100 black. This is confirmed by the Affinity Publisher color sampler. However, after exporting to PDF, the text is a very dark gray instead. The Mac Digital Color Meter identifies the image as 0,0,0 RGB (black), but the text is 26,25,25 RGB (dark gray). Any ideas?

[Catshill]

1 hour ago, Petrichor said:

Hi all. A follow-up question: are text and image blacks handled differently? I set both my text and images to K100 black. This is confirmed by the Affinity Publisher color sampler. However, after exporting to PDF, the text is a very dark gray instead. The Mac Digital Color Meter identifies the image as 0,0,0 RGB (black), but the text is 26,25,25 RGB (dark gray). Any ideas?

From the link posted above…

“The blackest black you can get when printing in CMYK is C-75 M-68 Y-67 K-90. Yes, you can accomplish this by…”

Highlighting the mono image and pressing the K button .

 

[Petrichor]

Thanks Catshill. I'm using the 75,68,67,90 black on the cover, which will be printed in color. The interior of the book will be printed on a black-and-white printer, though, so I thought it was better to use K100 black. But I'm confused why the K100 image (using the K only button) and the K100 text in my document look different once exported to PDF.

[thomaso]

26 minutes ago, Petrichor said:

I'm confused why the K100 image (using the K only button) and the K100 text in my document look different once exported to PDF.

If you apply the K Only button for an image its colours don't get converted to 100 K but to K only, means yellow may appear as a brighter gray than a blue for instance. Also it matters whether the image is in RGB or CMYK colour space: while an RGB image gets a "mixed" result of its 3 channels, a CMYK image gets its CMY inks / channels "simply" ignored + shows its K ink / channel only, and thus may appear lighter then its RGB equivalent. Accordingly for CMYK images it also matters how dark areas were created: either with a lot CMY + a little K or, vice versa, with more K but less CMY.