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Question

Can I convert images that are in Photoshop's Grayscale mode to CMYK within InDesign?

Forum|Forum|3 years ago
June 14, 2022
7 replies
3300 views

I'm close to finishing a proofable version of a photo book of black-and-white images and plan to publish it as a paperback on KDP.

In the KDP forums, another photographer/author has found that for some images, submitting the PDF with RGB images works better than in CMYK. He suggested I do a test book with duplicate files, one set in RGB and the other in CMYK, and output to PDF/X-3. The images are now in Photoshops Grayscale mode, using the Gray Gamma 2.2 profile.

I'd like to test this. It occurred to me that instead of producing a sample book with image files in two (or is it three?) color spaces, I could print three books, one with the Gray Gamma files, one with images converted to RGB, and a third with images converted to CMYK, and that I could do the conversion to the different color spaces in InDesign rather than creating a new set of files in Photoshop.

Is this possible? It seems, when I experimented, that I could get RGB output by specifying the RGB transparency blend mode and then converting to and specifying sRGB as the output space. But I haven't been able to figure out how to convert to CMYK.

When I convert a few test images to CMYK in Photoshop and then output a test file to PDF/X-1a or PDF/X-3, the CMYK images look right in the Acrobat Reader, but the unconverted images that are still in the Gray Gamma space look washed out, which tells me they are not probably not converted. Also, the PDF output file is only increased by additional size of the test CMYK images.

What am I doing wrong? Or is it not possible to get InDesign to do a bulk conversion of the images to CMYK?

Thanks in advance for any help with this.

This topic has been closed for replies.

rob day

Community Expert

Just to clarify Uwe’s post, you can convert a placed flattened, grayscale image into a different color space inside of InDesign by direct selecting the image with the white selection tool, and apply an InDesign native color or swatch—the mode of the swatch determines the mode of the image in the exported PDF.

If you Export to the default PDF/X-4 preset with No Color Conversion, AcrobatPro will inspect the image color mode as the applied swatches’s space. The exception is—RGB or Lab black can’t be absolute black. So here I’ve placed the same grayscale 3 times, with the top version’s fill set to 1|0|0 RGB, the middle version is set to 40|35|35|100 CMYK rich black, and the bottom version set to 0|0|0|100 [Black].

AcrobatPro inspects the top image as profiled RGB using the document’s assigned RGB profile, the middle as DeviceCMYK, and the bottom image as DeviceGray:

If I check the 50% gray patch in Separations view, the top version is showing the color managed conversion of the ProPhoto RGB color into the US Web Coated SWOP Output Intent profile 50|42|42|5:

The middle version is showing a 50% tint of my 40|35|35|100 rich black CMYK swatch—20|18|18|50:

And the bottom version is showing the original 50% gray as 0|0|0|50:

My example files:

https://shared-assets.adobe.com/link/f5a3b216-e040-403e-452e-9a14d480f31a

D

DavidOfMAAuthor

Known Participant

Thanks. I will use this technique to refine the images, once I have a better idea of how they print with just the K channel. Someone on another forum suggested the same technique, but at with higher values for CMY, and the results were discouraging.

I am guessing/hoping that I can use this method to create slightly different blacks within the same InDesign file, should I want to do that, without having to alter the source, or to give all the images a slight tint, right? That had never occurred to me to do until just now, but it's something I may think about. Do I need to reduce the K if I add significant amounts of CMY?

rob day

Community Expert

Do I need to reduce the K if I add significant amounts of CMY?

I don’t think so, isn’t your complaint that the grayscale’s appear washed out? The point of adding CMY would be to give the grayscale more dynamic range. Offset inks are transparent, so absolute black in CMYK printing would be black + CMY, not black by itself.

You might have to lighten the grayscale’s midtones to compensate for the added CMY, but you want the image’s black point to be 100% black plus CMY.

I think testing the different color modes is a good idea, but I’m sure every job you send to Amazon is output on a different device, so I don’t think you can get too fussy with color management.

James Gifford—NitroPress

Legend

CMYK images, for color at least, should never be used in KDP uploads. They're accepted, and converted as part of the process, but the KDP print process (and Kindle, of course) are optimized for RGB.

That said, grayscale — which as Willi points out are K-only CMYK in format — is pretty much the same no matter what you upload. It would all be in balancing the tonal range at the Photoshop level before export from InDesign. I am not sure if KDP has either color profiles or other specs — that are accurate and up to date, anyway; docs tend to lag way behind tech — to give any guidance for optimizing B+W images.

That is the downside of all the POD wonder: you pretty much have to take what you get. Which is fine for text, line art and snapshots, but not so good for any kind of art photography.

—

D

DavidOfMAAuthor

Known Participant

Thanks. I just bought your book! Once I've gone through it, perhaps some of the questions that mystify people like me will be clarified. I've also submitted three copies of the book, in CMYK, RGB, and Grayscale, to see if there are any subtle differences.

One question came from this process: the RGB version of the PDF is much, much larger than the Grayscale or CMYK. I find this perplexing, since it's dealing with only three channels compared to four for CMYK. Do you have any idea why that is happening? I output all the PDFs using InDesign's PDF/X-3 preset. I had to downsample all images to 300dpi just to get the RGB file size down below KDP's limit (most were around 350dpi), whereas with the other color spaces, the default compression was fine.

James Gifford—NitroPress

Legend

I'm not heavy on image management issues, because KDP isn't. It's a given that everything changes, more or less continuously, and the docs/help info never comes close to catching up, and when you find an optimized solution, the goal posts move (different print tech, different bureau, different settings). I'm not sure there is any approach except "do your best and take what you get... every time."

I've done three books with significant images and never had any problems just using defaults and no special attempt to game the profiles, settings, standards etc.

I know I've read a lot of complaints from people trying to do high quality/art image work, all touching on things above. I will be interested to see if you can get optimized results, especially for B+W, and if you can continue to get consistent results across time.

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Jumpenjax

Community Expert

If you send the job through preflight it will tell you what photos are rgb. Then you can either open original and change to gray scale. But like Willi said it is only grayscale you need.

Lee- Graphic Designer, Print Specialist, Photographer

rob day

Community Expert

I could get RGB output by specifying the RGB transparency blend mode and then converting to and specifying sRGB as the output space. But I haven't been able to figure out how to convert to CMYK.

Hi @DavidOfMA , Keep in mind that the Transparency Blend Space only affects spreads containing a transparent object—if the document has no transparency the blend space is not used.

Also, with print documents you have to be careful using an RGB blend space or setting the export Destination to an RGB profile—if you are using black text, it would output as 4-color CMYK and likely cause registration or "bolding" problems on an offset press. Setting the color of the placed grayscales as Uwe suggests would not affect the color space of other objects on the spread.

D

DavidOfMAAuthor

Known Participant

Thanks for this. It may be why, when I used a PDF print driver to output a book created in Word, the text looked semi-bold. In any case, I've gone to using PDF/X-3 to prevent that problem, though this seems to render the images much lighter than I intend them to be. Next round of testing, I'll try the select-and-apply-rich-black trick described above.

rob day

Community Expert

though this seems to render the images much lighter than I intend them to be.

With PDF/X exports grayscales get previewed via the CMYK Output Intent profile, which would not be the Gamma 2.2 profile you are using in Photoshop—Gray Gamma 2.2 is not a print profile. Applying a rich black CMYK color will darken the image because of the added CMY.

More on InDesign grayscale profiling and soft proofing here:

https://community.adobe.com/t5/indesign-discussions/greyscale-jpegs-or-psd-images-are-going-much-darker-when-dropped-in-on-indesign/m-p/11152264

L

Laubender

Community Expert

"What am I doing wrong?"

I do not think you are doing something wrong.

If you want to output RGB with InDesign for a grayscale image, simply select the image, not its container frame, and fill the image with a black RGB color swatch.

Leave it as that when you like to convert the black RGB to a rich black CMYK when you export to PDF and the conversion is done in the PDF. InDesign's export will do this right if you are using a PDF/X preset with color conversion.

EDITED:

Seems that I was wrong if the RGB values for this black are exactly 0|0|0. Then InDesign will treat the black as [Black] 100%. Not only in the Separation View, but also if you export to PDF/X and you do a color transformation to CMYK.

Solution: Use RGB 1|1|1 for example.

( See Rob Day's post and experiments below. )

FWIW: If you do not fill the grayscale image with a swatch, InDesign handles the color as if it is [Black], the K channel for the black ink of CMYK. So you get no rich black if you output to PDF and do a color conversion to CMYK at the same time.

Regards,
Uwe Laubender
( Adobe Community Professional )

rob day

Community Expert

Hi Uwe, I’m not sure if this is a bug or a feature, but if I "fill" a grayscale with RGB 0|0|0 and check its output values in Separation Preview, 100% gray still outputs as 0|0|0|100.

But, if I make an RGB swatch that is not absolute black (e.g., 1|0|0) I get a conversion into the document CMYK profile’s black point—so for default US Web Coated SWOP I get 75|68|67|90. I checked back to CS6 and it seems like it has always worked this way.

Another option, if you know the printer is going to output the provided CMYK values, would be to apply a rich black CMYK swatch, which would allow more control over relationship of CMY to Black—something like 40|35|35|100 would probably have a better chance of remaining neutral if the gray balance is off:

L

Laubender

Community Expert

Hi Rob,

wow, thank you for testing this. I see the same. Also with InDesign CS6.

A RGB black with 0|0|0 will be treated as 100 K in separation preview.

One with 1|1|1 will be separated to a rich black.

Regards,
Uwe Laubender
( Adobe Community Professional )

Brad @ Roaring Mouse

Community Expert

Greyscale images do not convert in InDesign. They are essentially "black" so will print as such in a CMYK workflow.

Regardless, KDP is an RGB workflow, so all your colours are converted to the sRGB space anyway, including your greyscale. If you send pre-converted CMYK (shudder) it may cause inappropriate color shifts that wouldn't happen if you started with RGB images.

Personally, I would convert all your greyscale images to RGB now and be done with it.

D

DavidOfMAAuthor

Known Participant

It's unclear to me whether KDP print is RGB or CMYK. How have you been able to determine this? In the readme files to their templates, and on their website, they say they want CMYK, at least for the covers (I can't find any specifications for interior images). However, as you suggest, with covers, they do a better job with RGB. With grayscale, it's unclear. I've seen examples of grayscale images printed at KDP from CMYK images that have a wider dynamic range than the same RGB images.

What they seem to be is a CMYK process that's optimized for the sRGB gamut. I'm going to test this. I created three identical copies of my book, one with Grayscale images, one with RGB, and a third with CMYK, and am in the process of uploading them to KDP. Once I have all three proofs in hand, I'll report back here with the results.

Willi Adelberger

Community Expert

Grey images are technically seen as cmyK, only K channel used. I see never a need to convert them to CMYK. The policies are to keep values. But I can apply any color to K images and another to their frames. No need to convert them before plaing them.

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