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Lien28851630299c
New Participant
March 13, 2023
Answered

DPI/PPI Indesign

  • March 13, 2023
  • 4 replies
  • 8114 views

Hi

 

For a project I should create a banner of at least 150 DPI. I have been working in Indesign for a while, but don't know how or where to adjust it. I know you can't adjust the DPI, but you can adjust the PPI.

I have already been told that the photos can be edited in Photoshop to get the correct resolution.In addition, the difference between actual and effective PPI is still a mystery to me.

 

Who can clarify these issues for me?

Thanks in advance!

 

This topic has been closed for replies.
Correct answer James Gifford—NitroPress

It's crucial to understand the difference between PPI and DPI. Even a lot of pros — and printers — are soggy in their understanding.

 

DPI, dots per inch, applies only to print. It's the usually the number of ink dots per inch, sometimes confused with the linescreen (LPI, Lines Per Inch, the effective resolution of the print image, usually much less than the DPI).

 

Everything digital is PPI, Pixels Per Inch, and PPI is something of a phantom number at that. No digital image file has an actual PPI (or DPI). Images have pixel dimensions — 1000 x 1600, for example — and any PPI associated with them comes from one of two sources: an arbitrary value assigned to a field by apps like Photoshop, and an effective value from being placed at a particular size in an app like InDesign.

 

That is, you can take that image and assign it a PPI of 200, but it's only a convenience figure used to load and interpret the image as being a specific layout or print size. You can open it in Photoshop and assign it a PPI of anything between 10 and 10,000, and it won't change the image or file a whit, except for that field and how apps automatically interpret it. But when you lay it into an InDesign layout, the intended print size will set the effective PPI regardless of that field value. If you place that image at 2 print inches wide, it will be effectively 500 PPI; at 3 inches, 333 PPI, and so forth.

 

You usually want your images to be about double your final DPI. So for your project, any element that is not vector — type, InDesign graphics, most things you would import from Illustrator — must be at least 300 effective PPI. You can lay in some tiny web graphic and scale it up to a foot across, so that it has an effective PPI of about 33, and the output process will upscale it to 150 DPI, but it will be a blur. So if you have a raster graphic you want to print at ten inches across, it should be 10 x 300 or at least 3000 pixels across in the layout.

 

InDesign has a variety of info panels and such that will show effective PPI, as just described. Learn to rely on those, not the arbitrary PPI value embedded in an image file or other phantom values. And learn to keep an eye on the actual pixel size of images to the exclusion of all other references. (Especially the completely meaningless designations like "a 2K image" or "a six inch image.")

 

Ask away if that doesn't make it clear.

 

4 replies

Dave Creamer of IDEAS
Dave Creamer of IDEAS
Community Expert
March 15, 2023

IMO, the use/misuse of the terms won't change until the scanner software on multi-function printers change the term. I just purchased a new Canon MFP and the software still says "dpi". 

 

David Creamer: Community Expert (ACI and ACE 1995-2023)
    Dave Creamer of IDEAS
    Dave Creamer of IDEAS
    Community Expert
    March 15, 2023

    Here is an old PDF that I wrote about the different resolution terminology. Some parts might be out of date but most if it is still good info.

    David Creamer: Community Expert (ACI and ACE 1995-2023)
    leo.r
    leo.r
    Community Expert
    March 14, 2023

    in addition to all the detailed replies you received, just wanted to mention that in your case DPI is interchangebale with PPI. "DPI" is just historically established term to refer to image resolution (regardless of the way this acronym is deciphered). it's like people still can use the word "filming" when recording video - while there's no actual film anymore.

    rob day
    rob day
    Community Expert
    March 14, 2023

    "DPI" is just historically established term to refer to image resolution

     

    Ancient history—Adobe removed the confusing DPI term in the early versions of Photoshop. The Image Size dialog from PS2 in 1994:

     

     

    Now DPI is reserved for printer resolution references—from InDesign’s Print>Printer...>Print Settings:

     

     

     

    leo.r
    leo.r
    Community Expert
    March 15, 2023

    I believe that the actual acronym "ppi" was only introduced in the first Adobe CS

     

    Photoshop was making the distinction 10 years earlier—my capture from above is from 1994, Photoshop 2 (not CS2)


    quote
    By @rob day
    Photoshop was making the distinction 10 years earlier—my capture from above is from 1994, Photoshop 2 (not CS2)

     

    I'm talking about the actual acronym "ppi". It wasn't used in 1994. I don't remember seeing it before CS.

    rob day
    rob day
    Community Expert
    March 13, 2023

    Hi @Lien28851630299c , Also, Effective Resolution (or output resolution) is the Actual Resolution (or starting resolution) scaled. When you scale an image in InDesign its pixels are resized not resampled.

     

    Effective Resolution = (100/image scale) x Actual Resolution.

     

    Here the scale is 80% so the pixels are smaller — (100/80) x 150 = 188:

     

      James Gifford—NitroPress
      James Gifford—NitroPressCorrect answer
      Brainiac
      March 13, 2023

      It's crucial to understand the difference between PPI and DPI. Even a lot of pros — and printers — are soggy in their understanding.

       

      DPI, dots per inch, applies only to print. It's the usually the number of ink dots per inch, sometimes confused with the linescreen (LPI, Lines Per Inch, the effective resolution of the print image, usually much less than the DPI).

       

      Everything digital is PPI, Pixels Per Inch, and PPI is something of a phantom number at that. No digital image file has an actual PPI (or DPI). Images have pixel dimensions — 1000 x 1600, for example — and any PPI associated with them comes from one of two sources: an arbitrary value assigned to a field by apps like Photoshop, and an effective value from being placed at a particular size in an app like InDesign.

       

      That is, you can take that image and assign it a PPI of 200, but it's only a convenience figure used to load and interpret the image as being a specific layout or print size. You can open it in Photoshop and assign it a PPI of anything between 10 and 10,000, and it won't change the image or file a whit, except for that field and how apps automatically interpret it. But when you lay it into an InDesign layout, the intended print size will set the effective PPI regardless of that field value. If you place that image at 2 print inches wide, it will be effectively 500 PPI; at 3 inches, 333 PPI, and so forth.

       

      You usually want your images to be about double your final DPI. So for your project, any element that is not vector — type, InDesign graphics, most things you would import from Illustrator — must be at least 300 effective PPI. You can lay in some tiny web graphic and scale it up to a foot across, so that it has an effective PPI of about 33, and the output process will upscale it to 150 DPI, but it will be a blur. So if you have a raster graphic you want to print at ten inches across, it should be 10 x 300 or at least 3000 pixels across in the layout.

       

      InDesign has a variety of info panels and such that will show effective PPI, as just described. Learn to rely on those, not the arbitrary PPI value embedded in an image file or other phantom values. And learn to keep an eye on the actual pixel size of images to the exclusion of all other references. (Especially the completely meaningless designations like "a 2K image" or "a six inch image.")

       

      Ask away if that doesn't make it clear.

       

        L
        Lien28851630299cAuthor
        New Participant
        March 13, 2023

        Hi

        Thank you for your quick and comprehensive response. English is not my first language, so sorry if I ask something that you already tried to explain or that I misunderstood.

        If I understand correctly, I need to enlarge my images to the correct proportions? I created my document in the correct dimensions. Am I doing it correctly then?

        James Gifford—NitroPress
        James Gifford—NitroPress
        Brainiac
        March 13, 2023

        Your images will print at the size you have placed them within the layout, regardless of their native resolution. If your banner is one foot by four feet and you have a logo image placed at six inches by two feet, that's the size it will print.

         

        However, to have acceptable resolution at that print size, it should be at least 3600 pixels wide (24 x 150) and ideally should be twice that (7200 pixels across). Very big images are needed for most banner and large format printing, which is why it's best to use vector images that have effectively infinite resolution. For things like photos, it's best to use the highest-resolution images you can.

         

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