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In InDesign, I used the preflight panel to mark pics with resolution lesser than 300dpi to light up as errors.

In the process, it also selected some vectors. Does it mean that vectors' resolution also needs to be taken care of?

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  • No. Vectors have no resolution, because they have no pixels.
    – Billy Kerr
    May 23, 2017 at 20:11
  • @BillyKerr Yup I know that.. But why do you think that InDesign highlighted a few vectors too. It dint highlight all the vectors in the document. Also, the vectors shown included both .ai and .eps too
    – Polisetty
    May 23, 2017 at 20:29
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    AI and EPS files can contain raster images.
    – Billy Kerr
    May 23, 2017 at 21:43

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While it is true that vectors have no resolution because they have not yet been rasterized, it is possible that there are rasterized textures stored in the file as a component. One can make a perfectly valid SVG that only contains a JPEG image encoded as base-64 for example. This would be a vector file in name, but not in spirit. Less extreme examples would be drop-shadow effects and the like that are "baked in" rather than calculated. These are quite often used and can be poor quality when scaled.

So it is plausible any preflight software might flag such a file for some arbitrary threshold for effective resolution.

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  • So the only solution would be to check how it does in print?
    – Polisetty
    May 23, 2017 at 20:33
  • Yeah, pretty much. Bear in mind that 300ppi is a rule of thumb: for mathematical reasons, you are trying to provide twice as much resolution as the halftone line screens for printing, which is typically in the range of 100 to 150 lpi. And this is for reading material at arms length. For a large banner etc. the reading length is farther, and the required LPI/ppi drops. Beyond that, I once placed a stock image that we purchased for use at 2 inches as 8x10 full bleed and I forgot to replace it with the bigger version. I only noticed a year later when looking at the file. Printed fine.
    – Yorik
    May 23, 2017 at 20:40
  • You can also cheat a little on resolution if you don't have small repeating patterns. Screen doors and brick walls may show moire, but even gradations like shadows may not. You can do a low-cost proof by enlarging it to the size you want, then cropping to, say 6x6 on any areas you have any doubt about.
    – Yorik
    May 23, 2017 at 20:43

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