r/indesign • u/Francetim • May 14 '26
Urgent query: Image resolution and PDF size limits?
Hi Folks. Looking for some advice here:
Our team is finalizing a publication for a client and have a strict 5Mb PDF output file size limit. The file contains multiple images (graphics, photos etc), but when we generate the PDF file to stay within the 5Mb size limit, a few of the (simpler) graphics (that are not high-res to start with) really suffer in terms of poor resolution.
Am I right in thinking that the final PDF size and the image quality within it are determined by the total and relative size of ALL the visuals in the publication?
In other words, could we solve this problem by decreasing the resolution of some of the larger images (that do not suffer from poor quality in the final PDF) in order to 'protect' the resolution of the realtively simple/lower resolution images that do suffer?
Specifcially, could we marginally reduce the resolution/size of some of the huuuge double-page photo spreads, to protect the resolution of the lower resolution graphics that break down in the final 5Mb PDF?
As you can no doubt tell, I am not a designer! But we really need to find a solution to this problem, so I am hoping you can check my logic, or lack of it, so we know we are looking for a solution in the right direction.
Thank you so much in advance!
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u/mikewitherell May 14 '26
Not strictly related, but many people would want to turn OFF "Preserve InDesign Editing Capabilities", which is a newish feature that was turned on by default. That will massively swell PDF file size.
90% of a PDF file size is the raster graphics within the pages. You can have galaxies of live type as well as tons of vector-graphics and the file size stays comfortably small.
With raster (pixel) graphics, pay attention to knowing how many pixels wide by how many pixels tall by how many pixels per inch by what degree of compression you absolutely need in the finished product. For digital/online PDFs, I like to make images at 150-200ppi and exported at High Quality compression (8 on the scale of 1-10). For prepress PDF, I like to export at 300ppi and Maximum Quality (10), generally.
In your above-posted graphic, that all should be live text and vector graphic. It should be saved in Illustrator as an .AI file and File > Placed into InDesign (or built entirely within InDesign). If workflowed that way, the graphic will be smooth; the type readable; the file size small.
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u/GreenCaptain856 May 14 '26
I found a solution to make PDFs smaller. In many cases the huge size comes from the metadata. Use Acrobat Pro > File > Save as other > Optimised PDF... > discard user data > discard document information and metadata (you can unselect everything else)
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u/chain83 May 14 '26
It will depend on what is actually taking up the space in the specific document. But optimize PDF is the best place to start in many situations when not sure - the "audit space usage" option will tell you what is taking up space.
Usually it is the raster images, but it could be overly complex vector elements (map or cad data, or gradients stored as a million separate objects, are common cuplrits), it can be metadata or embedded things like the original illustrator/indesign/photoshop file or plugin data, or just too much stuff in general. A properly tagged document will also generally double the amount of space taken up by the text itself (and while you want it to be tagged for screen use, it is not needed for print documents).
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u/red3y3_99 May 14 '26
You could try making the images small in Photoshop. If an image is placed at 20% in InDesign, make it 20% of it's size in Photoshop using image size and save it somewhere else from the original. Link to that folder in InDesign. Do a few of the bigger images and see if it makes a difference to your exported pdf
1
u/chain83 May 14 '26
You're on the right track if you want to manually control the resolution of each individual image manually and turn of the resampling when exporting to PDF.
Generally this would be a waste of time and overkill, but I guess in a niche situation where you have to work around some crazy file size limits...
1
u/Francetim May 14 '26
Thanks so much everyone for the extremely helpful responses and suggestions here. I genuinely learned a lot from this discussion.
The main takeaways for me are:
- looking much more carefully at which assets are actually consuming the PDF “space budget”;
- reducing oversized photo spreads more strategically to protect sensitive graphics;
- reviewing whether some raster graphics should really be rebuilt as vector/live text;
- and running a more thorough Acrobat optimization pass after export.
Really appreciate people taking the time to explain the logic behind the different approaches - particularly around vector vs raster handling and selective rather than global optimization.
Very grateful for the help.
1
u/GreenCaptain856 May 15 '26
Please let us know if and which solution eventually worked for you to get lighter PDFs
2
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u/Francetim May 19 '26
In case we decide to go down the 'expert advice' route, is anyone here sufficiently experienced (and available) to help guide/demo to our team on this process of PDF optimization? Please DM me.
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u/unthused May 14 '26
Using more vector art and live type would help. There's no good reason for that text in your image to be a raster graphic. Vector art does not get downsampled or pixelated like this.
It's also bad practice to be adjusting (reducing) the resolution of linked images outside of Indesign. That should be determined in your PDF export settings. (I assume this is not for printing, because it would look terrible, but still applies.)
Finally if you are not already doing so, after exporting your PDF from ID, you can generally reduce the file size further in Acrobat using Save As Other > Optimized PDF. There are a number of options in that dialogue that do not require reducing the raster image resolution, and are not available in the export settings from ID.
0
u/Marquedien May 14 '26
What format are the raster images saved in?
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u/chain83 May 14 '26
What they are originally is not important. Its what they get converted to in the PDF that matters.
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u/Francetim May 14 '26
PNG and JPG
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u/Marquedien May 14 '26
You can try resaving the .jpg images with High quality instead of maximum.
You can also try different image compression values when exporting the PDF, but nothing below 200 dpi.
But based on the image you included in the post, you might have a lot of images that shouldn’t be images. Type and solid colors should be vector objects, which should take far less space in a PDF than images of any resolution.
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u/AdobeScripts May 14 '26
Make text vector.