300 dpi/ppi standard and resampling

[kathleend82868475]

I was just asked to take over a coffee-table book design project for a client in Guatemala. The original designer sent me the packaged inDesign file a couple days ago, and I find that of the 170+ images (photographs) in the book, the vast majority have effective ppi at significantly less than 300. Most are in the 200 – 285 effective ppi range, but many are less than 200 effective ppi and a few are 91.

In my years doing book design, including a couple dozen coffee-table books for artists and photographers, I have stuck to the standard of 300 effective ppi on all images placed in an inDesign file. In the rare case when I haven’t had access to an original image that could meet that standard, I’ve used the PhotoShop Preserve Details resample function to boost an image to 300 effective ppi. However, I’ve never dared to do that with an image that was less than 290 effective ppi to start with, assuming a large boost would make the image look altered.

I brought up the resolution issue with the client in question and she’s confident that her printer in Guatemala will not require that the images in her book be 300 dpi (I’ve worked with this printing house before and yes, they do request on their spec sheet that images be 300 dpi, though I don’t know if they require it).

Bottom line to me is: if the resulting proofs look good to the client, so what if they’re not 300 dpi. It’s her book and her call.

But this experience makes me wonder how rock-solid that 300 dpi/ppi standard is and if I’ve been enforcing it with my clients too strictly all these years.

My questions:

*Is 300 effective ppi still the best? Has that standard changed while I’ve been buried in my work? Is there leeway in that?

*Am I being too cautious with my use of the PhotoShop Preserve Details function? Can I use it for images that need more of a boost – say, taking an image from 200 dpi to 300?

*And this is a wild card question: This client has included on her copyright page the statement “No AI has been used in the creation of this book.” (I imagine statements like these will become increasingly common.) But if I use the PhotoShop Preserve Details function on an image, isn’t that a form of AI?

[Robert at ID-Tasker · Accepted solution]

300 PPI is just an "round and easy to remember number".

The PPI depends on the LPI of the RIP - and usually is 1.5x to 2x of the LPI.

But like you've said - it's her book and her money, and if she likes what she sees...

[Dave Creamer of IDEAS · Accepted solution]

A more efficent PPI is 1.5 x the LPI (if I recall, it's technically 1.4, but rounded to 1.5). So a LPI of 150 would require a minimum PPI of 225. An image at 225 PPI is about half the size of the same image at 300 PPI.) I've used this method for decades--keeping in mind it's for offset printing. Rember, if your images come in at 225 PPI, they can't really be enlarged in the layout program.

Here is an old, but valid, PDF I wrote a while back: https://www.ideastraining.com/PDFs/UnderstandingResolution.pdf

[kathleend82868475]

Thank you for the PDF - that's helpful info for me. So I gather in all of this that unless a printer REQUIRES 300 effective ppi, I can relax on images over 225. Most of the images in this project meet that standard, but many do not, including the image she plans to use on the cover of the book (174 ppi). Given the distance between us, I won't see the proof when it's printed and will just go with what she decides. But can you tell me: Is there a point at which there's a noticeable difference in quality? The resolutions in this book are all over the map. If a 150 ppi image shares a spread with a 300 ppi image, will that difference be seen?

[Robert at ID-Tasker]

[...] If a 150 ppi image shares a spread with a 300 ppi image, will that difference be seen?

By @kathleend82868475

Probably. But it depends on what those images show, their size and location. 

[Dave Creamer of IDEAS · Accepted solution]

If you have lower-res images lower than 225 ppi at actual size in InDesign (check the effective resolution in InDesign), I would res them up in Photoshop before placing. Nothing is better than have enough resolution in the original, but res'ing up in Photoshop is better than running a low-res image.

[kathleend82868475]

Yes, all of the values I've given in this discussion are effective ppi at final printed size in the layout. There are currently two dozen images with effective ppi below 225 - I can res them up. Thanks for the advice on that.

[kathleend82868475]

Okay, I screwed up trying to mark this one as the correct answer, but you get my drift. Thanks for your help.

[Dave Creamer of IDEAS]

I unmarked it. You can try again. Glad we could help.