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I am a student. I am using InDesign to create a magazine that has lots of illustrations and artwork in it but I’m getting confused about ppi and effective ppi.

So for example, one image has actual ppi of 600, an effective ppi of 2059 x 600 and needs to be printed across and area that is 340mm x 112.367mm. The piece of artwork is a Muriel. On my screen in actual size it looks a little pixelated.

If anyone can help that would be amazing!!!

closed as unclear what you're asking by Scott, Ovaryraptor, GerardFalla, Danielillo, WELZ Mar 18 at 14:47

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effective ppi of 2059 x 600

That would indicate a size not ppi.

The general rule of thumb when using raster images in InDesign for print production is to ensure all image are at least 240ppi and are never enlarged in InDesign. More than 240PPI is never an issue.

240ppi is the bare minimum for commercial printing. 300ppi is commonly used because it's a nice round number and offers support for slightly denser line screens. It is best to use 300ppi as a minimum if you can. 240ppi is only if you must.

Most digital cameras will capture data at 240ppi. This can be acceptable with a line screen (LPI) of 150. 150LPI requires 225ppi as a minimum and is a very common line screen for most offset printing. However, 175LPI will require 265PPI for quality reproduction. Minimum PPI = 1.5 * LPI. Often you won't know the LPI. Therefore, using 300PPI as your minimum often allows the same image to be reproduced at a decent quality even if the line screen being used is higher quality.

In short.. aim for a minimum 300ppi and don't enlarge images within InDesign.

The "effective PPI" can be largely ignored in many instances. If your images meet the above statement, then any output should be sufficient for print production.


Effective PPI can be helpful if you are reducing raster images within InDesign. If you have a 72ppi raster image and reduce it to 25%, then the effective PPI becomes 288ppi - making it suitable at that 25% size for commercial printing.

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If you reduce a 300ppi image within InDesign to the same 25%, the effective PPI will jump to around 1200ppi. But that's not really a problem. There's rarely such a thing as "too much PPI".

Raster images should really never be enlarged within InDesign. If you do enlarge a raster image, you can keep an eye on the Effective PPI to assist in finding the "break point" of an enlargement - that point where the effective ppi drops below 240. As the raster image size increases the effective ppi will decrease.

For example, you can enlarge a 300ppi raster image within InDesign to 120% it's original size. The effective PPI will drop to around 250. This is still suitable for commercial printing. However, I'd stress that it's really always best to enlarge raster images with Photoshop if they need enlargement. Photoshop will do a much better job at interpolating pixels than InDesign will.


If all your raster images are...

  • 240ppi or better
  • placed into InDesign
  • not scaled (up or down) within InDesign

then all the images are fine.

  • Wow thank you Scott, that’s a really comprehensive answer. I’m completely at a loss with the ppi thing so this is really helpful. I’ll put my images through photoshop as I’m pretty sure I’ve enlarged most of them in InDesign so far and I’ll make sure they’re over 240ppi. – Holly Pearce Mar 14 at 0:26
  • Where does the 240 PPI number come from? I know, for example, 212PPI is one option (probably too low) but it comes using the square root of 2 (because the 45° rotation of the black screening) multiplied by the lineature used (150LPI in this case), etc. Or 266PPI being the double of 133LPI on uncoated paper... But, 240? – Rafael Mar 14 at 2:45
  • @Rafael Most digital cameras will capture at 240ppi. Assuming you need 1.5 times the line screen and most common offset printing will use 150LPI (225dpi), then 240 is the bare minimum - or don't down-sample RAW images. At a 175LPI 265 would be better. But, in my experience, the difference between 240 and 265 is negligible at most - and that's only if a line screen greater than 150 is being used. 300ppi is still best to use for everything. I'm not advocating targeting 240ppi specifically, only stating if one must, then 240 may be acceptable. – Scott Mar 14 at 7:16
  • I clarified in the answer a bit. – Scott Mar 14 at 7:22
  • Actually, you can have effective PPI of 2059×600. It is done by scaling the image (in this case horizontally) without constraining it, i.e. by holding Cmd/Ctrl without Shift while resizing. – exer2k Mar 15 at 23:31
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Part 1... analyzing your stuff

confused about ppi and effective ppi

I do not really understand "effective PPI"

Let's break the Acronym PPI

Pixels (Element that makes a digital picture) per (how many of the above) Inch (Physical unit)

effective ppi of 2059 x 600 (let me round numbers 2000x600)

Here is what you have it wrong. 2000 x 600 px, they are just pixels. No inches here.

When you want to print them on a physical object (a paper) then you need to have the physical unit.

600 PPI is too much but let's continue 600pixels every inch. So

2000/600 = 3.33 inches

600/600 = 1 inches

That is the size of your print.


Or let's do it backward.

2000 when printed at 10 inches = 2000/10 = 200PPI.


340 x 112 mm

When you define a physical unit to be printed, the original PPI marked goes out of the window.

cm to inches:

34 => 13.38

11.2 => 4.4

Pixels on those inches

2000/13.38 = 149 PPI

600/11.2 = 53 PPI

Yes, you have a mess. But if it is the only image you have...

...

Ideally, don't change the aspect ratio of an image... Do not squish or squash it.

Part 2, answering How to get the right resolution for printing artwork?

You do not get it out of thin air. You prepare all the assets with a quality control mentality.

  1. Shapes in vectors, in the right proportions.

  2. Good raster images, good size photographs, illustrations, etc.

  3. Keep a good PPI (Not "effective" do not add fancy adjectives here, just real PPI)

  4. This "good PPI" is, for now, 300PPI, Forget all other numbers for now. Leave other PPI numbers to the experts.

  5. If they are not 300... something is not right.

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