What I thought worked didn't, and the internet hasn't helped either. Mac desktop, using Pages word processor and Adobe Acrobat.

Do I need to use Photoshop (which I have access to at the library) or something else? Is there a simple way to accomplish fixing the dpi while also cropping and resizing to match how they already are in the document? I've inserted all the photos already but the dpi changed as I edited them in Photos and/or Pages.

I have 286 photos which need to be 300 dpi minimum and 600 dpi maximum in the PDF document as submitted to the printer. The photos vary from cell phone photos that claim 72 dpi all the way to 600 dpi.

I can change the dpi just fine in Preview and it recalculates a new file size. but then when inserting the photos into the document the dpi changes. Tons of wasted hours there thinking it was going to work!

There are 3 very specific issue, depending if the original dpi is lower or higher than the new value.

1) The dpi is lower than 300, and I need to fix that without changing the image data (not adding interpolated new pixels). Basically, increase the dpi by a factor, e.g. 2x, and let the image dimensions (height and width) decrease by the same factor, e.g. half as high and half as wide. So, same number of pixels just crammed closer together.

2) The dpi is higher than 600, and it needs to be reduced without changing the size of the image. e.g. if it is at 1000 dpi then reduce that by a factor of 2 down to 500 dpi, but keep the height and width the same. So, strip out half the pixels.

3) The dpi is in the acceptable range of 300 to 600, but resize the image smaller to put it in the document without changing the dpi. e.g. take a 4x5 inch image which is at 600 dpi and resize it to some random smaller dimensions and strip out enough pixels to keep the dpi at 600 rather than the dpi increasing.


Thanks for any help.

Sounds like your publisher’s pre-flight software discovered all this.
Photoshop will enable you to standardize this. You’ll have to do them one by one. At least I would, for consistency.
If you use shortcuts (Command-Option-I for image size; change the dpi FIRST, then the width and height; Command S to save - or Command-Shift-S to Save As a new copy in a different folder; Command W to close that individual photo) then you can move quickly through them all.

You could set this up as a Batch process to do them all, however, they will all be the same size when done. And that’s not cool.

I have only used Adobe InDesign in my four-color print work - your Pages software will probably notice the change to all the photos you made when you open your book project; you will need to re-import or scale each photo/box in the book so the composition matches what you had before, etc.

It has been 4 years since I did CMYK print work, so my recollection of the process may not be exact. Hopefully, I made sense.

My email is in my profile, if you need more detailed help. Good luck.

Professional software for professional results.

You will need to open each photo, check the attributes and go from there.

They want to be 300dpi at size. You can remove pixel information but not add pixel information.

In other words, you can reduce a large low resolution photo down, but not inflate a small photo.

Do not strip out the icc information the camera assigned.

Thank you both very much.

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When you get to the next step of transmitting the PDF to your publisher, be aware some email programs compress files. This may decrease the DPI when the publisher opens the email to view your file.

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