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When getting an InDesign file ready for print I knwo that images should be: 1. CMYK 2. at least 300 dpi 3.preferably .tiffs

But if the files are less than 300dpi but due to the size of the images on the page the 'effective dpi' is more than 300. Is that ok to send to print? Or do I still have to convert to 300 pdi which would make the effective dpi much greater? dpi vs effective dpi

Thanks

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    The DPI set in the file itself doesn’t matter at all. It’s only a hint to tell you how big the image will be at a certain density. Effective DPI is all that matters. – Janus Bahs Jacquet Oct 23 '17 at 10:20
  • Just some opinions on the "3 rules": 1. In most cases images should be edited and placed as RGB and converted to the right CMYK profile when exporting. Converting to CMYK should be done as the last thing. If you edit images in CMYK they may no longer confine to the color profile. 2. 300 ppi is good for images seen at "normal reading distance" (which is most cases). Longer distances require less. 3. @joojaa says this isn't a requirement any more. In my experience it is 99.99% true. In 7 years of making press plates I've had 1 "unknown error" where the fix was to use tif instead of psd. – Wolff Oct 23 '17 at 16:14
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The printer does not really care about what the metadata of the image said before you scaled it in the page layout software. THis is what the original designer wished. You, the pagesetter, are by no means bound by that decission.

Your override is now for all intents and purposes the new PPI in your final document (unless say your pdf export setting is instructed to resample the images beyond sertain size). So only effective PPI counts.

But other than that the guidelines you lay out in 2 is just a guideline you can easily live with less, and number 3 is not really a requirement in a modern workflow.

  • Keep in mind that the pixels per inch / resolution / dimensions required for printing depends very much on the halftone screen frequency, film/plate maximum resolution, and even the paper stock and press type. This used to be understood by everyone, back when Adobe's manuals and many books explained the details of color printing and digital images. Nobody learns the fundamentals anymore, and lazy people say "images should be 300 DPI." That's wrong on many levels, including that "DPI" ONLY applies to output devices that make "dots," and therefore have resolutions that are expressed in DPI. – user8356 Oct 24 '17 at 17:47
  • @user8356 We actually had to build a printer in Uni, that did the normal shape rasterisation and stochastic screens also, and compare the results. The thing is days have changed. There are so many different imaging devices that work differently these days that probably its not worth going into that anymore unless your an engineer like me. As for PPI vs DP its kindof a attempt to separate concerns. Still they are interchangeable in many literature's. But 300 is like the magic 72 they can means a serious explanation or they can just mean i didnt want to think about it. – joojaa Oct 24 '17 at 18:34

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