Print to black and white PDF no longer working

[jderhake]

We commonly use print to PDF to resize scanned music images in our publishing business. Until this week, printing to black and white caused no serious problems. Now all of a sudden, using the same procedure introduces unwanted gray in the output file. Has a recent update degraded this functionality? Thanks in advance for any advice on how to fix. I have already tried repairing my Acrobat DC installation twice. See screenshots for step by step process.Output has grayscale and poor qualityOriginal scan, crisp b/wPrint to PDF settings 2Advanced PDF settingsPrint to PDF settings 1

[jderhake]

In case it is helpful, I've attached the original scan to this reply. Thanks-Joe Scan 

[Luke Jennings3]

Page 1 of your PDF is RGB and pages 2 & 3 are black only. The images appear to be scanned at 612 ppi, try printing your PDF as an image at 612 ppi. Alternately, you can try using a preflight fixup (Tools> Print Producton> Preflight) to convert your PDF to BW. This will produce a small amount of noise, probably jpeg artifacts, which can often occur when RGB is converted to CMYK. I don't know if there is an easy way to eliminate it in Acrobat. The left screen shot is the converted PDF, the right screen shot is the original (RGB) PDF.

[jderhake]

Thanks for the suggestions, Luke. Unfortunately, both methods were still creating gray artifacts and degrading the image quality. I did finally stumble across a very time-consuming solution, however. Perhaps one of the other fixups does exactly this?

1. Saved as PNG with settings: Color Management >> RGB Embed profile, Grayscale Off; Conversion >> Colorspace Monochrome, Resolution 600 ppi

2. Opened each PNG with image editor and changed the color mode from RGB to indexed using a black and white (1-bit) palette

3. Recombined PNG files in Adobe.

4. Printed to PDF following my original procedure, output was perfect. Desired output 

Luke, is there a way to emulate this process with a different (or custom) preflight fixup? I really appreciate your help! -Joe

[Luke Jennings3]

I tried a different preflight and it appears to convert the RGB images to grayscale without producing any artifacts, probably because there is no RGB to CMYK conversion.

You can use the Acrobat Action wizard to create an action that uses the preflight, this will allow you to run the preflight on a file, or a folder of files with one or two clicks.