Converting raster RGB objects to CMYK with no loss of quality

[defaulta6qeln3tquad]

I have yet to find a method of converting raster images to CMYK that doesn't turn them into a pixelated, artifacted mess.  See before and after below:

I have tried Convert Colors, Edit Object, and several different Preflight profiles, all with the same result.  The only surefire method I've found for lossless conversion is to open each image one by one in Photoshop and convert them there.  This gets very tedious very quickly.

Is there anything I am overlooking, or is that really the only way?

[Randy Hagan]

It's the best way, for sure.

You're flipping a big toggle switch when you ask any application to convert colorspaces without any granular controls. Photoshop, for pixel files, and Illustrator, for vector files, have the granular controls to minimize the impact of transiting from the full-range RGB colorspace to more restrictive and reduced color ranges of CMYK reproduction. InDesign does a better job of transiting colorspaces than this, but that's still a relative term.

Randy

[Dave Creamer of IDEAS]

Conversion from RGB to CMYK would not cause pixelization, as conversion would not affect resolution.

Conversion from RGB to CMYK would not cause artifacting, but saving in the wrong format would. Artifacting would be a result of too much JPEG compression, but the image you show should be saved as a PNG if in RGB and TIFF if in CMYK.

The sRGB profile would be the safest before CMYK conversion as it the least color range. What CMYK profile are you using?

[defaulta6qeln3tquad]

We receive these files from outside clients so I have no control over how the original images are saved or what color space they use.  We convert to US web coated (SWOP) v2 for printing.  I don't know how or why the image goes from A to B during conversion.

[Dave Creamer of IDEAS]

Can you upload your files? If you don't want to make them public, you can DM me by clicking on my name.

[defaulta6qeln3tquad]

DM sent, thank you!

[Dave Creamer of IDEAS]

The images were created in Canva and apparently exported as JPEG (or JPEG in PDF "wrapper"). Also, the resolution issue is already there--the pages are 24x18 with a resolution of 4000x2000. That makes the image 166x111 ppi--too low for quality printing. 

Acrobat's color conversion did, indeed, cause artifacting due to the JPEG image conversion. 

Open the files in Photoshop (one page at a time; Photoshop will upacale to 300 ppi), convert to CMYK, flatten the layer, and save as LZW-compressed TIFF. 

Blowup of 1.7x1.3 inches below. 

Original in Photoshop before conversion:

After conversion in Photoshop:

[defaulta6qeln3tquad]

So even if I do it page by page, Photoshop is still the only viable option? That's disappointing but at least I know I'm doing what I can.  Thanks for looking into it.

[Dave Creamer of IDEAS]

From Acrobat, try exporting to TIFF. You can convert to CMYK in the options settings. It seemed to eliminate the artifacts.