Why do Photoshop, InDesign, Pixelmator Pro, and Mac Pages all "smooth" my digital photos on export to PDF (how achieve best print preparation)?

Question

I am preparing digital photos for printing and performing various test prints for comparison (with a very cooperative print shop). The print shop only accepts PDF, not direct print from raster format PNG etc. The can handle up to 1200dpi on sizes up to A3, and 1440dpi for A2 and larger (on a separate machine).

My sources are iPhone X photos (super for a mobile phone) and Sony A7Riii photos (42M, utterly stunning).

I am aware that comparing digital images on a display (in my case a 5K iMac) and printed versions is a bit like comparing apples and oranges. That notwithstanding, I am so far disappointed with the printed results from PDF prepared in all of the following tools:

• Mac Pages 7.0 (which seems to pass through Mac OS X 10.13.3 Quartz PDFContext)

• Pixelmator Pro 1.0.9 (which likewise seems to pass through Mac OS X Quartz)

• Photoshop CC (very latest 19.1.3), using Save As to Photoshop PDF.

• InDesign CC (very latest), using Export As PDF.

In all cases the PDF versions, from which the print is made, seem to "smooth" out the original image, resulting in a clear drop in sharpness, at least as far as I can tell comparing display views of the PNG with prints.

For example, in the image below, I have a screenshot from a 5K iMac display of:

1. Left: The Mac Preview view of a PNG. Note the pixelated anti-aliasing around the blue and red spots, which from a distance lends a certain "sharpness". Image (as cropped) is 3835 x 2490.

2. Middle: Mac Pages PDF export, an A3 layout with 5mm margin, with the image scaled to fit inside the remaining horizontal 410mm (pls ignore vertical part). Mac Pages does not AFAICT offer any explicit control over DPI on document creation or export to PDF (unless it is hidden somewhere). Note how the blue and red spots appear smoothed; on printing, the result is a loss of sharpness (at least as I perceive it).

3. Right: Photoshop CC: A4 document created at 600dpi, so for no scaling of the inserted image, it takes up 162.35 mm x 105.41 mm. Document processed as RGB (until export). For the sake of this discussion it seems to make no difference, to the "sharpness", whether export to an RGB profile or a CMYK U.S. Web Coated SWOP (except for colour as seen on a display of course). On export I ensure the images are handled as LOSSLESS (no compression, and no ZIP or JPEG etc.), and with Do Not Downsample.

(I have omitted the result with InDesign CC, with direct insertion of the PNG into a layout document and similar PDF export controls, including 600dpi and 1200dpi throughout. Result is same as Photoshop CC.)

Q1: What am I seeing ? Why don't the images simply propagate through the pipeline otherwise unaffected ?

Q2: How can I ensure the best print reproduction that somehow corresponds to what I am seeing on digital displays (including my iMac, iPhone, and Sony camera displays, all of which are showing higher clarity and sharpness) ?

And for reference: I am using Exiftool to examine metadata. It yields expected DPI indications in the final PDF for Photoshop CC and for InDesign CC such as, for 600dpi pipeline:

X Resolution                    : 600
Displayed Units X               : inches
Y Resolution                    : 600
Displayed Units Y               : inches

But for Mac Pages and Pixelmator Pro, which have no clear PDF export controls, a typical exiftool probe reveals no such indications:

ExifTool Version Number         : 10.80
File Name                       : IMG_XYZ.pdf
Directory                       : .
File Size                       : 2.4 MB
File Modification Date/Time     : 2018:04:08 13:41:54+10:00
File Access Date/Time           : 2018:04:08 13:42:29+10:00
File Inode Change Date/Time     : 2018:04:08 13:42:01+10:00
File Permissions                : rw-r--r--
File Type                       : PDF
File Type Extension             : pdf
MIME Type                       : application/pdf
PDF Version                     : 1.3
Linearized                      : No
Page Count                      : 1
Producer                        : Mac OS X 10.13.4 Quartz PDFContext
Create Date                     : 2018:04:08 03:41:54Z
Modify Date                     : 2018:04:08 03:41:54Z

Answer 1

It is probably a setting in the PDF generation.

Typically, when you use a print-to-pdf (or save-as-PDF) tool, you can enter the settings, and there somewhere (under ‘advanced’ or whatever), you can set the max resolution for images. The default is typical 150 dpi, and the second default is to automatically reduce anything over 200 dpi.
Of course, the details are different for each such software, but the idea is the same.

Check the software you use for PDF generation, and hopefully it exposes those settings somewhere. You should set it to 1200 or 1440, depending on where you eant to print on.

The alternative would be to not use PDF format at all. There is little to gain from embedding an image inside PDF, so if you could extract into a graphic format, it would be easier to accomplish what you want

Answer 2

I suspect there is some scaling to fit the paper size when you are exporting to PDF. Maybe there is a setting to turn that off. It would likely be in your print settings (if you're "printing" to PDF) as your method of export. Otherwise, some default settings for export to PDF.

Another thing to look for, if the export process is controlled by Photoshop/InDesign are the settings for image compression in the PDF. Be sure not to allow it to make the PDF smaller or size down the image file. That could also be happening. (And I do think that compressing images for a JPEG is default behavior or PDFs tend to get huge. Most users aren't photographers seeking the best image quality... they want that compromise in image quality in exchange for a smaller file.