PDF made from photos is too big: shrink it, and avoid it next time

Shrink it now

1. Drop the PDF on the tool above.
2. Pick Email for a file that gets read on a screen, Web if the reader will zoom into the photos. If a form or a portal names a number, type it in Size target instead.
3. Press Compress and read the result: the size before and after, and the pages that changed most.
4. Open the result and look at 1 photo at full screen before you send it.

Here is what that does to our 20-photo test file, 1 photo of 4032 by 3024 pixels per A4 page:

The Email preset took about 15 seconds on a mid-range 2024 laptop. A size target goes further than the preset when it has to: on the same file, a 2 MB target gives 1.4 MB (photos at 96 dpi), and a 1 MB target gives 647 KB (72 dpi), about 32 KB a photo. Each is the best quality that fits under the number, and each search took under a minute. At 72 dpi each photo is about 790 by 590 pixels: enough to see what it shows, not enough to zoom into.

Why a PDF of photos gets so big

The math is simple. A 12 megapixel phone photo saved as a JPEG is a few MB; ours are 3 MB each. A PDF made from photos stores every photo whole, so the PDF weighs what the photos weigh, plus almost nothing. 20 photos make 60 MB before anything has gone wrong.

That is by design, at least on our JPG to PDF tool: it copies each photo’s picture data into the file unchanged, so the conversion costs no quality at all. The only thing it leaves out is the camera’s metadata (GPS location, device, time), and the result says how many photos it cleaned. The size problem only appears when the file has to travel: an email cap of 20 or 25 MB, or a portal that takes 2 MB.

And it is a lot of pixels for the job. A photo on an A4 page, seen at 110 dpi, needs about 1 megapixel. The camera gave it 12. Compression throws away the 11 nobody sees on a screen, and that is where the 96 percent comes from.

Photos of documents and photos of people are different

Photos of paper (receipts, forms, a page of notes) tolerate heavy compression. What matters is that the writing stays readable, so a size target that goes to 72 dpi is usually fine; zoom into the smallest print on the result to be sure. Grayscale is optional: on a scan of black-on-white paper it saves little once the file is compressed, but the pages print predictably.

Photos that are the point (a holiday album, a portfolio, a property listing) deserve the Web preset at least. Faces and fine textures are where softness shows first. If even Web is too big for the destination, split the album into parts or send a link instead of crushing it.

Screenshots behave differently

Screenshots are usually PNG, not JPEG, and our compressor treats them by what is in them. A picture with 64 colours or fewer (a simple diagram, a flat chart) is kept lossless, so its edges stay crisp; it shrinks mostly when it is placed on the page at more than the preset’s resolution. Most screenshots of real screens have more colours than that, because of smoothed text and photos in them, so they are re-encoded as JPEG like a photo. Small text in a screenshot is the first thing to go soft, so for screenshots of documents use Web, not Email, and check the smallest text.

Fix it at creation, next time

There is no shrink setting in our picture-to-PDF tool, on purpose: it keeps the pixels of your photos exactly as they are, so the PDF is never worse than the photos. The habit that works is 2 steps, both on your device:

1. Make the PDF from the original photos with JPG to PDF (or HEIC to PDF for iPhone photos, which are written as JPEG at quality 90).
2. Compress that fresh PDF once, at the preset or target the destination needs.

Keep the big PDF or the photos as your master copy, and send the small one. The pictures to PDF guide covers the making side: page size, order, margins, and mixed portrait and landscape photos.

On a phone, both steps work in the browser with no app; the guides for iPhone and Android cover the phone-specific corners, and the 1 MB guide covers the most common portal limit.

What compression cannot undo

Compressing a photo that was already compressed stacks the damage. Each JPEG pass throws away some detail, and a second pass on top of the first cannot bring it back; it only adds its own. Our compressor will not re-encode a photo unless the result is at least 10 percent smaller, so a second run usually returns the file unchanged, but a different tool may not be so careful. If a compressed PDF looks too soft, do not compress it again or try to sharpen it: go back to the original photos, make the PDF again, and compress once with a gentler preset.

The same applies to photos saved from a chat or an email: they may have been shrunk on the way, so a PDF made from them starts softer. For anything that matters, use the photos from the camera roll.