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I have a project I'm creating in Adobe Illustrator where I've been bringing in raster images and doing a "High-Fidelity" image trace to make them scalable and easy to manipulate. I've had some photos I brought in to the illustration that would look better as-is, but they aren't 300dpi. Most are 72dpi. For those who have seen results in print production, is a 72dpi photo saved in a 300 dpi CMYK file going to look shoddy, or will the quality be manageable. The photos don't have to look entirely life-like, but close.

I'd include specific examples, but I'd prefer not to for my client's sake.

  • To my knowledge there is no such thing as a 300dpi Illustrator file. Perhaps you mean that you set the raster effects quality to 300dpi. Placed or linked images are not resampled (until export or print/plate time). A 3000 pixel square image is 300 dpi @ 1 inch, and is 72 dpi @ 3 inches. DPI without inches or pixels is meaningless, it is merely a scaling factor. If I asked you how far it was from you house to the nearest town and you said 60mph that would be absurd. So it is with dpi. – Yorik Oct 22 '15 at 17:28
  • You can get a rough proof of the quality by printing it out yourself at 100% final size. If you don't have a suitable printer, try a service. You can place a cropped version on a standard sheet, centering the the image on the portion you are most interested in . – Yorik Oct 22 '15 at 17:32
  • Pardon me, I did mean that my raster effects are set to that value. Thanks! The canvas I'm working with is 71" by 42" and the largest image in the design is 54" by 45". Thanks! – Nicko Oct 22 '15 at 17:59
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A 72dpi (at actual size) file placed into illustrator, then said illustrator file saved out at 300dpi (at actual size) won't really improve the quality of the original 72dpi photo. It will still be, in essence, a 72dpi photo "embedded" into a 300dpi photo.

None of that is technically accurate, but hopefully explains the concept. You just can't magically make lower-resolution raster files better by resaving them at a higher resolution.

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I've been bringing in raster images and doing a "High-Fidelity" image trace

If you've traced the placed images, they are no longer raster and PPI is no longer an issue. Tracing results in vector objects which are resolution independent.

If you do not trace a placed 72ppi image in Illustrator, it outputs as a 72ppi image. Illustrator does not miraculously increase the PPI of placed raster images. The only way to increase the effective PPI within Illustrator is to scale (reduce) the placed raster image by a factor of 4 or more. This essentially "squishes" the existing pixels into a more dense area increasing the effective PPI. But be aware, Illustrator does not do any raster image interpolation.

  • I apologize for the confusion, I had been doing image tracing, but wanted to avoid it for a more realistic look if possible. I figured Illustrator wouldn't automatically increase my image quality, but I was wondering what happened to the images. Thanks for the help! – Nicko Oct 22 '15 at 18:11
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I've been in the print industry for fifteen years or so, and here's what I have to say:

If you zoom in to about 125% on the image at full size and it looks okay, it'll print okay. If it looks bad, then it will print badly.

The most useful tools for judging quality are your own eyes.

As the others have stated, changing a 72ppi image to a 300ppi image doesn't make the image better. That doesn't stop people from doing it all the time, though, and it'd be funny if it didn't just clog up our hard-drives and make our programs run slower.

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Picture will be saves as EFFECTIVE D/PPI (lookup up under 'links' panel or upper bar while selecting the picture)

To elaborate: It depends whether your picture is placed in its original size or in an up/down scaled size.

  • And just to make sure, if your picture is traced it means its not longer as bitmap, but as vector. Traced appearance quality is of course not as good as bitmap. – Yar Oct 22 '15 at 17:23

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