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Background: I am using Illustrator to combine several raster images. I apply scaling and clipping masks to them. Next, I try - if possible - to avoid non-integer resampling steps during subsequent printing. I.e. if an image originally was e.g. 150 ppi and the publisher asks for 150 dpi, I aim for 150 (original dimensions) or 300 ppi (i.e. the size was downscaled by an integer factor of 2), since

  • (a) most times I am very close to such integer factors anyway, or
  • (b) picture dimensions need to be reduced to meet minuimum ppi/dpi without "upsampling".

Question: Is there a way to tell AI to scale image dimensions to meet a defined ppi (at least necessary in scenario b)?

E.g., an image which is 140 ppi should get slightly smaller to become 150 ppi (I am NOT looking for upsampling!). I know I can see the resolution via Document Info window / flyout embedded (or linked) images and manually calculate a scale factor (actual ppi / desired ppi), but I am looking for a solution that is automatic and has no rounding issues.

Question (optional part): Am I wrong to aim to avoid non-integer factors b/o quality issues in subsequent resampling steps where possible (scenario a)?

Edit for clarification: I am dealing with composite figures, where I need to fine-adjust the size (millimeters) of each individual subfigure (bitmaps, may be photographs, microscope images, MRI scans, ...). Subfigures are prepared at sufficient resolution that allow using them at integer multiples/fractions of original mm dimensions to meet publisher-desired ppi and to fit to the other subfigures. Once the subfigures are at an approximately useful size, I need to fine-tune widths/heighths to have them aligned in a tidy way. To this end, I prefer cropping (clipping mask) them since I was afraif of quality loss by resizing by non-integer factors. Since one needs to see how it looks like (how much I can crop, do sizes look balanced, ...) it is not useful to "calculate" the millimeter dimensions and do the rest in photoshop.

  • llustrator does not know how to upsample so theres no chance it will do so. – joojaa Sep 14 '14 at 20:39
  • @joojaa Sorry, but as I wrote I do not want to upsample, but scale dimension to meet a defined ppi. – Martin Sep 16 '14 at 20:09
  • Why are you doing this in illustrator to begin with? – DA01 Aug 11 '15 at 16:20
  • @DA01: Because the subfigures need to be aligned to a composite figure, see edit above. – Martin Aug 14 '15 at 20:28
  • I think you may be over-concerned about the 'non-integer' factor scaling. If this is all for print, it's likely not going to be a noticeable issue. In fact, the difference between 140 and 150ppi likely won't be noticeable on paper. If we're talking 100ppi vs 300ppi, then yes, that'd be noticeable. But I'm not sure you need to worry too much about a 50-or-so difference in ppi between images in the collage. – DA01 Aug 14 '15 at 20:33
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No.

Illustrator does not interpolate any raster image and does not store "effective" ppi settings either. There is no feature, tool, or method to ask Illustrator to read, interpret, or show the ppi of an embedded or linked raster image therefore there is no mechanism for Illustrator to doanything regarding ppi on a raster image.

You may have some luck by looking into the Rasterino plug in from AstuteGraphics.com. It offers some additional raster image features within Illustrator.

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Photoshop > Image Menu > Image Size

Then if you must use Illustrator for some reason, place the newly adjusted image into Illustrator.

  • Thanks for the suggestion. Probably I miss sth, but if I copy from AI and paste to PS (new/from clipboard/paste), I get very low resoulution images (76 ppi, was 173 ppi in AI). If I increae the ppi in PS/new/from clipboard dialogue, the image seems bigger, but looks as pixelated as before. I did not find an easy way to safe (as opposed to copy-paste) an individual raster image from AI to PS - there are many raster images, text and vector graphic parts in AI, so placing them on individual artboards for export is not really an option. – Martin Sep 16 '14 at 20:26
  • @Martin charing the ppi dose nothing to change the amount of pixels in the image. It just makes the existing pixels bigger or smaller. – DA01 Aug 11 '15 at 16:20
  • @DA01 You're probably confusing "size" with pixels. It seems like a print project and he probably meant the resolution and real size (eg. imperial units, metric units). Increasing resolution does change this output size and Illustrator doesn't update these dimensions unless it's specified; it was upsampling the image. – go-junta Aug 12 '15 at 3:41
  • @go-me afaik resizing images in illustrator doesn't resample them. (Though PS might when pasting into it) – DA01 Aug 12 '15 at 5:31
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"If I increase the ppi in PS/new/from clipboard dialogue, the image seems bigger, but looks as pixelated"

YES!

There is a way to force Illustrator to keep the original size and resolution of your images, the same way InDesign and QuarkXpress does it when an image is updated.

That is, you still need to fix your resolution in Photoshop. But when you'll update your images, they won't show "low quality" as you described in one of the comment; they will be resized according to the real dimension and resolution you specified in Photoshop.

Your clipping masks might need to be adjusted though.


1) Open Photoshop and change your resolution and size in the "Image Size" panel as you already did. Illustrator will prompt you to update your image when you open your file with that linked image.

2) Open your "Links" panel in Illustrator, select your image and go in the options of that panel.

3) Select the "Placement Options"; in the scroll down select "File dimensions."

Whenever an image resolution will change or the size of the original image, Adobe Illustrator will keep it at its original size.

How to preserve file dimensions in Illustrator

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