neutralize color casts on greyscale parts of an sRGB image PDF without affecting other colors

[Mattia Battistich]

Hello there,

Not sure where I should post this as I'm new to the forums.

I use both Photoshop CS4 ext and an old version of Acrobat Pro, but this issue is related to several customers of mine.

My company's main area of business is providing "cost per print" printing services to medical imaging customers (private clinics, medical practices etc) where diagnostic images are in the form of low res RGB image files digitized from medical modalities such as CT, MRI, UltraSound etc. Tipically our customers (the doctors) will select some of these images from the medical device's main application GUI, which will arrange them in a predetermined layout, and click a print command that will send the resulting page layout to one of our printers. In other situations the images are exported from the medical device application (usually JPG or PDF to a network folder) with an unknown profile, then opened with a PDF reader application (PDF Reader, PDF Architect, etc) then finally printed.

We generally use Epson WorkForce inkjet printers with standard GDI windows drivers and the OS is typically (a restricted version of) MS Windows 8 / 10.

Most of these images are contain greyscale and a few bits of color used to highlight measurements, blood direction and so on (imagine an x-ray with color marks), here is a good example:

https://www.dropbox.com/s/ekuhapzrzdcauqa/CONEBEAM-2.pdf?dl=0

The MOST important thing for the doctors is to be able to have "neutral" greyscales and as much detail as possible on the prints. Unfortunately the medical device and the likely not calibrated color profiles used by the OS for the file conversions and printing often return RGB greyscale images with color casts on the greyscale parts (i.e. RGB values not exactly like xx/xx/xx) such as 157/157/157 but with small deviations from true sRGB greys, i.e. 157/155/157.

If the images are printed in greyscale the printer only uses black ink and the result is acceptable however this is not viable as the color details of the marks are also needed.

So I'm looking for a way to "neutralize" color casts from the greys (deviations from x/x/x of a certain % or range should be "brought back to" x/x/x) but without color correcting the color parts (reds, greens, etc). All this should happen directly from within a PDF reader sw (maybe using a particular color profile or other middleware).

some Xerox printers have this driver setting ("Print sRGB greys with Pure black") but the Epson printers I am familiar with don't have this.

I hope someone can point me in the right direction.

Thanks and kindest regards

Mattia

PS - I do have an X-Rite i1 Studio but not very familiar on how to use it for this task.

[Abambo]

The question is, where the equilibrium is disturbed. Just looking at your PDF, it looks like a great greyscale image with some colour elements in.

[Mattia Battistich]

Hi there.

My problem is on the prints not on screen. The image I posted is just an example of the many that these customers print from a range of different medical devices so it may in fact be truly neutral sRGB (r=g=b) across the board except for the color parts.

Nonetheless once fed to the Epson driver it will typically transform the neutral sRGB parts in points such as (C=22, M=60, Y= 20, K= 76), causing the casts.

A forum admin suggested that when using PostScript printers Acrobat DC reader and Acrobat pro will enable this setting in Print/Advanced:

“Treat grays as K-only grays”

However this should (and so far I don't think it works) only "capture" true neutral sRGB greys and make them print with K ink only, but it won't "catch" the slightly deviated values (i.e. R=45 G=47, B=45).

Here's the forum thread (maybe an admin should merge the 2 3Ds):

https://forums.adobe.com/collaboration/121960?et=notification.direct.message

Thanks

Mattia

[Lukas Engqvist]

Converting to a Max GCR profile may help. But if the print driver is an RGB driver this is an Epson problem not an Adobe problem. GCR (Grey component replacement) is the process of replacing an acrobatic/neutral part of CMY with pure K. Max GCR means you make the image as black and white as you possibly can and then add what colour can not be produced by black only. (This is a detailed blog post about GCR, but explains the problem well http://the-print-guide.blogspot.com/2009/04/gcr-reseparation-for-ink-savings-and.html)

[Mattia Battistich]

Hi Lukas,

Thanks for your valuable input. I briefly went through the blog post but it's super technical for my current limited skills.

I understand I may need a De Vice-Link profile developed  and embedded in my workflow that typically is:

RGB Diagnostic Images obtained from medical device (unknown embedded ICC Profile) > assembled in multi image A4 layout by Med.Device main application and either printed directly to GDI/PostScript printer driver or printed first to PDF file using standard windows PDF Printers (unknown ICC profile but may investigate) then finally printed through PDF reader.

The workflow should not be altered and ideally the "level" of GCR should be variable to control how many of "close to neutral sRGB greys" should be converted to pure K when printing.

Anyway this is beyond my reach.

Anyway would you or anyone else following this thread be available to provide support to me through a platform like Fiverr or similar? I am quite sure it shouldn't take long to set us up if you know what you are doing. You may also email me to m_battistich at hotmail.com.

Thanks and kindest regards

Mattia

[Luke Jennings]

That PDF was produced from PDF Architect 6. It appears to be indexed color, although it's different from the usual PDFs I've seen, in that when viewed in Acrobat with output preview, the color mode is not readily apparent.

I used Tools> Print Production> Convert colors in Acrobat (DC) using the settings in the attached screen shot, the resulting PDF showed black only in the gray image areas and did not change the color areas to BW. Note the Preserve Black and Promote Gray to CMYK Black at the bottom. You can give this a try.

The Convert colors tool may be in a different location in an older version of Acrobat, but it has been around for a long time. Hopefully your printer will see the black only image and print in black only (which would be ideal), but it might not.

[Mattia Battistich]

Will try and come back, thanks Luke.

I still think though that a specific color profile should do the trick, just don't know who could develop one for this.

Kind regards