APub: How to stop upscaling images on export to PDF?

[k_au]

When I made a big banner at full size, some images I used did not have the required 60dpi at that size. But that's okay, it will be viewed from quite a distance. 

So I export the project to PDF and set the resolution of the PDF to 60dpi.
I would hope that things like transparencies are flattened using 60dpi resolution, and the images remain at their lower native resolution.

But in the end, all images are re-scaled up to 60dpi. 
That doesn't make sense to me, the upscaling is not really introducing better quality. It only increases the file size.

Is there a way to stop the upscaling while exporting?

Ideally, images should be downsampled to the final output dpi, but not upsampled. I have tried a lot of export options and never got that result.

[lacerto]

Obsolete.

[loukash]

6 hours ago, lacerto said:

the camera on the left has been cropped by using the Vector Crop Tool (creating a mask), while the camera on the right has been cropped by using a clipping rectangle

Interesting! Thanks for sharing.

6 hours ago, lacerto said:

upsampling should never happen automatically so I consider this a serious error in a page layout app

Agreed.

[thomaso]

7 hours ago, lacerto said:

and make sure that you export using a non PDF/X-based method, or if using a PDF/X based export method, use PDF/X-3 without forcing conversion of color spaces, or use PDF/X-4 (with which you can force conversion of color spaces).

Oh, this would be a change in V2 towards V1, below a V1 example with PDF 1.7.
(interesting that in V2 certain PDF/X versions + colour conversion can cause this upscaling. Personally I appreciate this feature in V1 because there is the clipping method for images that should not be affected)

[lacerto]

Obsolete.

[thomaso]

7 minutes ago, lacerto said:

What do you mean?

I understand that you experienced in V2 that the upsampling does not happen with a non-PDF-X export:

9 hours ago, lacerto said:

it does not do it when using PDF/X-4, or any non-PDF/X-based export method, even if forcing CMYK conversion. 

Accordingly I assumed you get different results in V1 vs. V2 with an export as PDF version 1.7 for instance.

[lacerto]

Obsolete.

[thomaso]

2 hours ago, lacerto said:

EDIT: Note that I have so far tested this only on Windows versions, so there might be differences between platforms.

33 minutes ago, lacerto said:

Yes, and the same is true with version 1 (1.10.6.665, Windows version tested). So versions 1 and 2 seem to behave otherwise identically

So there might indeed be a difference between Windows and mac at least in V1 since I do get the upsampling in V1 with a non-X-PDF version 1.7

 

[lacerto]

Obsolete.

[thomaso]

4 hours ago, lacerto said:

could not reproduce upsampling with non-PDF/X-based export methods

Ah, we referred to different situations. I still

had your initial note in mind about upscaling for images cropped with a nested vector object:

On 12/2/2023 at 7:35 AM, lacerto said:

The most likely cause for having -- inadvertently, but by (bad) design) -- upscaled placed images is using the Crop tool to crop images, since a masked image will be upscaled to document DPI (or to specified export DPI) when exported.

upsampling_v01_cropped.afpub

This appears to upscale in V1 for PDF version above PDF v1.4, e.g. PDF v1.7:  upsampling_v01-cropped_PDF1.7.pdf

While I can confirm for V1 that upsampling also happens for a not cropped image or pixel layer with export as PDF v1.4 (and thus with PDF/X-3, X-1, too).

[lacerto]

Obsolete.

[k_au]

Thank you all for checking and confirming this!
I made a bug report at 

More info on the issue:
the JPG images were just dragged onto the page and then resized to fit the large canvas. So no extra masking, nesting or cropping was done.
I couldn't check if it only happens with PDF/X yet.

[wonderings]

Why not just turn off all scaling to begin with? Go with the native resolution of the images you have. If they are bad to start they don't get better by upping the DPI anyways, so let them go to print with the highest DPI they have. The only time I adjust these settings is when I am trying to make a PDF that is suitable for email distribution. 

[lacerto]

Obsolete.

[k_au]

I've got to correct myself from above: This does not happen with JPGs (unless you crop them the wrong way apparently). It only shows up when transparency is involved with PNG, TIFF, WEBP -- but interestingly not with GIF files. My test files are attached to the bug report.

[k_au]

On 12/2/2023 at 4:47 PM, lacerto said:

Affinity apps convert images to CMYK when using PDF/X-3, no matter whether using the "Convert image color spaces" option or not (even if the images could stay in RGB color mode). This happens both in v1 and v2, and probably because PDF/X-3 does not allow live transparencies, and as Affinity apps do transparency flattening by rasterizing, Serif has obviously chosen to do CMYK conversion anyway (also for objects that do not contain transparencies). 

Has this been reported as a bug yet? I couldn't find something like this on the forum.
If it's not a bug, I would ask Serif to disable the "convert color spaces" option on PDF/X-3, like it is with X-1a, so that the result does not come as a surprise.
(It would be even better if the greyed-out box was still showing a check mark, since the conversion is active and can't be switched off)

[lacerto]

Obsolete.

[k_au]

OK, so I made a bug report to bring this some attention and maybe a clarification if it's a bug or a feature...