image editing in RGB and manual separations to CMYK for press

[Typothalamus]

We're asking if the following workflow and division of labor is advisable, as it's our most readily available option: Can we execute all needed image aesthetics editing in RGB (mostly B&W architectural images) under our careful eye with our retoucher first, then send the image files to a color corrections color space conversion expert (RGB to CMYK, manual conversions/separations) to manually convert and translate that work accurately to CMYK for high-end offset printing? This is as opposed to having one vendor do it all. We'd place the manual color space convertor's work back into our ID doc and export to pdf using the printer's Fogra 51 profile.

Is this division of labor between two parties (a retoucher, and then a color correctionist/separator) before printing not advisable? Ask any clarifying questions.

[rob day]

Can we execute all needed image optimizations in RGB (mostly B&W architectural images)

In almost all cases RGB B&W images will convert to CMYK using all 4 plates. If handled correctly that can get you more dynamic range on press, but you run the risk of color casts. For color work, color correcting in a large RGB space (ie, AdobeRGB, ProPhoto RGB, etc) with View>Proof Colors turned on is the preferred workflow.

There is no guarantee the color will print accurately—how you handle your display matters. All color in the Adobe print apps is converted into your system’s monitor profile for display—profiled RGB to Lab to the monitor RGB profile, or profiled CMYK to Lab to monitor RGB profile. If the system’s monitor profile does not accurately represent your monitor’s properties (gamma, white point etc) your color correction preview will be less accurate. Typically hardware calibrators are used to generate the most accurate monitor profiles.

[Typothalamus]

Rob, thanks for confirming the workflow and highlighting the 4-plate conversion complexity for BW images. For our BW image enhacements in RGB, the photo editor, who doesn't work in print, is focused on tonal editing—highlights, shadows, midtone gradations, sharpness, and texture preservation rather than color correction.

The division of jobs (BW photo editor in RGB → expert CMYK conversion) seems to make sense since managing 4-plate CMYK conversion for 240 images requires print-specific expertise our RGB photo editor doesn't have. This reinforces that manual conversion by a 2nd specialist after him is needed, as opposed to 1-click ID auto conversion.

Does that sound advisable? Not sure if the wider color space is still key for BW though.

[BobLevine]

@Typothalamus Are you aware that every time you edit your posts a new email is sent to those of us monitoring this community?

An edit or two? Fine but 16? Please stop. 

[Typothalamus]

@BobLevine, I apologize for the excessive edits. I wasn't aware each edit generated email notifications. I'll be more careful about finalizing posts before submitting. Thanks for letting me know.

[rob day]

This reinforces that manual conversion by a 2nd specialist after him is needed, as opposed to 1-click ID auto conversion.

...printer's Fogra 51 profile

You apparently know the final press profile is Fogra 51. The conversion from your chosen RGB editing space to Fogra 51 CMYK can happen anywhere—in Photoshop, on export to PDF, or in the RIP—the ICC color management system produces the same result in all three cases.

The problem with converting invidual images in Photoshop—besides the labor of doing them one at a time—is you convert for a single press condition. What if you end up choosing a different printer using a different press profile? Or, is the person manually converting to CMYK going to make post CMYK color corrections? If that is needed, it would indicate either Fogra 51 is not the actual press profile, or the system monitor profile is wrong and is displaying a misleading soft proof.

[Jeffrey_Smith]

Rob, for images that are colorful and not neutral, I agree with your statement of CMYK conversion can happen on PDF export, Photoshop, and in RIP.

But with B&W architectural images (as OP described) in RGB colorspace, is there any profile that will convert these neutral images into CMYK with a higher percentage of black, and lesser percentages of CMY (example: 40C 40M 40Y 90K)?

[rob day]

is there any profile that will convert these neutral images into CMYK with a higher percentage of black, and lesser percentages of CMY (example: 40C 40M 40Y 90K)?

The amount of black generation is built into the profile, so yes the problem with letting B&W RGB go to the RIP is with a light black generation, the press gray balance would not have to be very far off to produce a color cast. Black Generation is built into the profile, and most ICC press profiles output a light black plate.

You could convert the B&W images to a custom profile with a heavy black plate, which you can make with Photoshop’s legacy Custom CMYK setup, but getting those CMYK values to the press plates unchanged would require good comunication with the printer.

[rob day]

is there any profile that will convert these neutral images into CMYK with a higher percentage of black, and lesser percentages of CMY (example: 40C 40M 40Y 90K)?

The amount of black generation is built into the profile, so yes the problem with letting B&W RGB go to the RIP is with a light black generation, the press gray balance would not have to be very far off to produce a color cast. Black Generation is built into the profile, and most ICC press profiles output a light black plate.

You could convert the B&W images to a custom profile with a heavy black plate, which you can make with Photoshop’s legacy Custom CMYK setup, but getting those CMYK values to the press plates unchanged would require good comunication with the printer.

[rob day]

The other, safer, and easier way to do it is by placing flattened Grayscale images. Flat Grayscale images can be assigned a color or Swatch which can be anything. Here I’ve placed a Grayscale image, selected the image and set its color to CMYK 45|40|40|100:

[Typothalamus]

So, does this route bypass Fogra conversions? Rob, I understand that the grayscale approach can eliminate color casts by defining exact CMYK values. However, determining optimal CMYK recipes for highlights, midtones, and shadows across 130 B&W images from various sources seems to require specialized knowledge. Are we assuming that Fogra 51's automated GCR algorithms will underperform in minimizing color casts while optimizing black usage?

For context, I can soft proof RGB images with Ctrl+Y to preview the Fogra 51 conversion and adjust accordingly. Does the grayscale method offer significant benefits over this profile-based approach that justify the added complexity?

While the Fogra 51 workflow includes soft proofing and a planned scatter wet proof, we may need to adjust CMY values consistently. This might require a hybrid of Fogra 51 and modified GCR, but I can’t become the algorithm myself.. The scatter proof will help us see if Fogra 51's automated method produces acceptable results, but I need a Plan B or C ready for file adjustments if necessary.

[rob day]

Does the grayscale method offer significant benefits over this profile-based approach that justify the added complexity?

The only advantage in placing a grayscale and adding CMY in InDesign, is you can output relatively lower CMY values, which will make the color somewhat less susceptible to color casts because there is relatively more Black in the separation.

But offset printing is not that precise—the color can change depending on the ink densities during the press run—run extra cyan and the gray balance will change. Whether the press actually runs precisely to the Fogra 51 profile is up to the press person.

Here my document’s assigned CMYK profile is PSO Coated v3 (FORGA 51), so with Overprint/Separation Preview turned on I get a PSO Coated v3 preview

If I turn off the Black channel I can see there is less CMY in the grayscale version

And relatively more black

[Typothalamus]

This was a key question, @Jeffrey_Smith  This is precisely what Echelon Color of Venice (CA), admirers of the architect, advised, and though I cannot afford such rates in the tens of thousands for separations work, their results and clientele list also make it clear this is a well-supported direction. Fogra 51 apparently is more refined in this area than prior versions, but not 'intelligent' enough to replace the eye of the artist-technician.

[rob day]

Fogra 51 apparently is more refined in this area than prior versions, but not 'intelligent'

It seems like you might be misunderstanding the function of an offset profile. FOGRA 51 won’t magically produce more accurate color than some other profile—either the press is running to the FOGRA 51 profile or it’s not. The press profile can even change during the run—the press person can manipulate the ink densities during the run and change the running color profile.

A composite printer like inkjet doesn’t have that problem.

[Typothalamus]

Rob, thanks for the clarification on offset printing variables. Your point about press operator adjustments during the run is well taken – profile accuracy means little if the press doesn't maintain consistent ink densities. This reinforces why we're planning the scatter proof early in the process. It'll show us not just how our soft proofing predicts conversion results, but whether this particular printer maintains consistent standards that make our workflow optimization meaningful. 

Fogra 51 probably does have better GCR algorithms than older profiles, I had read, and had that in mind when writing. 

Appreciate the reminder about offset printing limitations.

[rob day]

We'd place the manual color space convertor's work back into our ID doc

Also, in case you are not aware, you can get the expected CMYK conversion for profiled RGB colors without actually committing to the conversion. Here I have Proof Colors turned on with my Proof Setup set to Coated FOGRA39. With my Info panel’s eyedroppers set to Proof Color I can get the expected CMYK values for a conversion to FOGRA39 without committing to the conversion: