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PDF only with JPG photo is 7 times larger than original

Graphic Design Asked on December 31, 2021

I start a file in Illustrator with these settings:

Illustrator file settings

I save the file with these settings (no PDF compatible file):

Illustrator save settings

The AI file weighs 1.1 MB.

I place a JPG picture from a DSLR camera which weighs 4.4 MB, rescaled to A4 size. I save it and it still weighs 1.1 MB.

I save it as PDF with the standard settings, except that I uncheck "Keep Illustrator editing capabilities":

PDF save settings 1

PDF save settings 2

The PDF now weighs 33.1 MB.

I would expect the PDF file to simply embed the JPG image with coordinates and thus be only be marginally larger than the photo, or maybe a bit more for thumbnails. Instead, the PDF is more than 7 times larger than the original.

Why is the PDF so large?

One Answer

Yo do not have a JPG file anymore.

When you embed a photo inside a document, you do not have a JPG file anymore, you have a document with a photo inside. And this image is now subject to the new file's compression rules.


The abrupt change in the file size of the PDF is most likely due to two things:

You do not have an RGB file anymore. You are converting it to CMYK which has, not only more channels but compresses less efficient than an RGB file. You could even use some JPG compression but this compresses every channel separately, versus the way a standard RGB file is compressed, where a luminescence channel and two chroma channels are used.

You are not using a JPG compression, but a lossless ZIP one. But even this one would only apply on similar grounds if you maintain an RGB file.


Keep in mind that you are NOT saving a PDF, you are exporting a file to PDF. The difference is that a saving tries to keep the data as it is as possible, including some effects that are reloaded and re-rendered, while an export makes a series of processes, like converting files, resampling, merging layers, antialiasing, converting vector effects to raster, among other things, depending on the target format and the configuration.

Answered by Rafael on December 31, 2021

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