exporting from gimp to pdf while preserving full resolution

[sedmont]

Hi,

How can I know that when I export a gimp image to pdf, that the original gimp resolution is preserved in the pdf?  

I created gimp images measuring 6.88 inches by 10.5 inches at 300 x 300 ppi. 

After I export one of those images to pdf and open the pdf in Adobe Acrobat, and set Adobe to display at 300px/inch, the image on screen visually appears MUCH bigger than 6.88 inches by 10.5 inches.  Maybe 3 times larger on the screen than that. That seems to mean the resolution of the pdf is far down from the resolution of the original gimp image, right? Yet Adobe has a little box at the lower left of the screen saying the image is 6.88 inches by 10.5 inches. 

So has the resolution gone down in the pdf?  

Thanks for any assistance.

[sedmont]

Ok, having thought more about this, I am maybe starting to get it. Could still use help. 

I want to know how to check if the full resolution of a gimp image is preserved when I export to pdf. 

When Gimp says my image is 6.88 inches wide, I guess that refers to the printing size -- not to how big the monitor makes the image look. 

My monitor's own resolution is 141 px per inch. (15.6 inch monitor, 1920 x 1080 resolution).

So if I set the image resolution on a gimp image to 300 x 300 ppi, then when I view that on my monitor with Gimp at 100% zoom, an image that will print at 6.88 inches wide will appear on the monitor I suppose as (300/141) x 6.88 inches, which is about 14.6 inches visually on the monitor.  That is roughly what I do see on my monitor with Gimp at 100% zoom (the 6.88 inch image appears 14.45 inches wide visually on my monitor). But when I export that image to pdf and open it in Adobe Acrobat at 100% zoom, and set Acrobat to 300 px/inch, the image is 18 inches wide, not 14.6.  

Why is that?  Thanks for any assistance.

[PixLab]

Understanding resolution/Dpi/ppi https://www.gimp-forum.net/Thread-Image-size-in-Gimp

Having said that, I recently read (yesterday or before yesterday) that GIMP export to PDF at 72 (or 74?) pixels/inch, and it's hard-coded.
If definition in PDF is important for you, I would recomment to export as JPG or PNG or whatsoever, then use another software to make that image as a PDF with respect of resolution.

[sedmont]

Thanks, Pix lab, for that link on resolution and the other thoughts. 

I saw a comment somewhere about 72 dpi being hard coded for gimp pdf exports, but then I saw a reply from someone else who said he'd been exporting from Gimp to pdf quite a lot and that the export resolution is not hard coded to 72 dpi but follows what one has if one looks at Image > Print Size on Gimp. The replier thought the 72 limit the other individual experienced could have been due to a specific plug in for Mac OS or something. 

Anyway -- as to your suggestion of first exporting to JPG or PNG and then finding another software to convert the PNG to pdf, did you have some software in particular in mind?

[PixLab]

(02-18-2023, 02:34 AM)sedmont Wrote: Thanks, Pix lab, for that link on resolution and the other thoughts. 

I saw a comment somewhere about 72 dpi being hard coded for gimp pdf exports, but then I saw a reply from someone else who said he'd been exporting from Gimp to pdf quite a lot and that the export resolution is not hard coded to 72 dpi but follows what one has if one looks at Image > Print Size on Gimp. The replier thought the 72 limit the other individual experienced could have been due to a specific plug in for Mac OS or something. 

Anyway -- as to your suggestion of first exporting to JPG or PNG and then finding another software to convert the PNG to pdf, did you have some software in particular in mind?

Not a specialist of PDF here, thus sorry, I don't know a dedicated PDF software, but if I have to do PDF more "seriously" than I actually do (I use this format for quick export/email/and so, nothing "important") I think I would use LibreOffice Draw or LibreOffice Writer, their export to PDF seems to have very serious options.


Or Scribus https://www.scribus.net/

[rich2005]

(02-17-2023, 02:23 PM)sedmont Wrote: So has the resolution gone down in the pdf?  

No.

When you export an image to PDF in Gimp, all it does is embed that image in a PDF 'wrapper' The PDF only cares about the page size, which in Gimp comes from the ppi value.

You can have two seemingly identical PDF's . This one 3553x3949 pix @ 300 ppi print size about 300x330 mm
In a PDF viewer, again the size is about 300x330 mm but check the file size 9.0 MB Big image = big file size.

   

Then there is the same image, except now scaled down to 1185x1317 @ 100 ppi, print size still about 300x330
Now in the PDF viewer, page (paper) size still 300x330 but file size now 2.3 MB.

   

All Gimp has done is embed images. All the PDF sees is the paper size.

The smaller PDF will have worse quality in a viewer when zoomed in. When you open a PDF in Gimp the default ppi is 100. It is up to you to increase that value.

Truthfully, Gimp uses a very low internal compression for PDF, hence those large sizes. You can get smaller PDF sizes with other programs, for example: ImageMagick 4.5 MB <> Gimp 9.0 MB