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ethank59616381
Known Participant
May 30, 2020
Answered

Does anyone know how PPI is calculated?

  • May 30, 2020
  • 5 replies
  • 2567 views

Hi,

 

I'm hoping to make a script that takes an image say at 200DPI and converts it to 300DPI, while also keeping the PPI above 300.

 

Does anyone know A. how to do this, and B. how it's calculated? 

This topic has been closed for replies.
Correct answer rob day

It‘s a waste of time—upsampling simply adds pixels via an interpolation algorithm, it doesn’t add any detail quality, or information to the image.

 

300ppi is a rule-of-thumb for generally acceptable quality when the output is to a 150LPI halftone screen.  To get true 300ppi resolution it has to be captured by the camera or scanning input device.

 

InDesign’s scripting resolution properties are read only, so if you do think upsampling will have some beneficial affect, the script will have to upsample from Photoshop. Photoshop also uses ppi—there is no image dpi property in either app.

 

5 replies

Sheena Kaul
Community Manager
Sheena KaulCommunity Manager
Community Manager
June 12, 2020

Hi there, 

 

I hope your issue has been resolved. But if the issue still persists, please let us know so that we can assist you.

 

If any of the above-mentioned solutions have worked for you, kindly mark the answer correct. 

 

Regards,

Sheena

T
Test Screen Name
Legend
May 31, 2020

Increasing ppi is rather like trying to turn chicken soup back into chicken. You can’t get there from here. Or rather you can, but your chicken won’t be very convincing. 

    rob day
    Community Expert
    rob dayCommunity Expert
    Community Expert
    May 30, 2020

    With Adobe applications, and the scripting API, image resolution is always referred to as PPI, not DPI.

     

    DPI is sometimes confused with PPI, but DPI is a measure of an output device’s resolution—a platemaker or imagesetter might have a resolution of 2400 DPI. The high imagesetter resloution is needed to draw the halftone (LPI) or stocastic screen, which the press or printer outputs. A 150 LPI haftone screen would need a print device with least 2400 DPI in order to draw the 150LPI halftone screen correctly.

     

    As Frans suggests your script would need to open the image into Photoshop in order to increase its actual PPI resolution. LPI and DPI resolutions are controlled by the print driver and are not a property of a placed image or the document.

     

    Images placed in InDesign have an .actualPpi and .effectivePpi JavaScript read only property—.actualPpi is the resolution of the image at 100%, and .effectivePpi is the scaled resoultion. If an image with an Actual Resolution of 300 PPI is scaled by 50%, its Effective Resolution would be 600 PPI—the pixels are 50% smaller, so the output resolution is twice as high.

     

    In your first post’s screen capture the last column is showing Actual PPI and the middle column is showing the Effective or scaled PPI

      Randy Hagan
      Community Expert
      Randy HaganCommunity Expert
      Community Expert
      May 30, 2020

      A couple of questions:

       

      1) Do you need effective resolution to bump up from 200 ppi to 3000 ppi because you're enlarging the pixel image to 15 times it's original size? If so, I'd suggest that you give up even trying and find a higher-resolution original because you're built to lose big if you even try to do this.

       

      2) DPI is a print-output measurement for an output device. How does your 200ppi original image print at its original size?

       

      Please let us know the answers to these questions and we can try to help you from there.

       

      Randy

       

      Update: After this posted, your original resolution bump read from 200-300ppi. I could've sworn I saw 3000 in the question before I posted my response. Did you edit it?

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      ethank59616381Author
      Known Participant
      May 31, 2020

      Nope, didn't edit it.

       

      Basically, I need all images for print ready output at 300DPI - when I bring up the DPI, the PPI (naturally) goes down. I then am taking images into photoshop, upscaling them 120%, and that is what works best. Sometimes, I have to go to photoshop again and upscale it another 110% or something. It's frustrating and time consuming, so I'm trying to find a good work around

      rob day
      Community Expert
      rob dayCommunity ExpertCorrect answer
      Community Expert
      May 31, 2020

      It‘s a waste of time—upsampling simply adds pixels via an interpolation algorithm, it doesn’t add any detail quality, or information to the image.

       

      300ppi is a rule-of-thumb for generally acceptable quality when the output is to a 150LPI halftone screen.  To get true 300ppi resolution it has to be captured by the camera or scanning input device.

       

      InDesign’s scripting resolution properties are read only, so if you do think upsampling will have some beneficial affect, the script will have to upsample from Photoshop. Photoshop also uses ppi—there is no image dpi property in either app.

       

      Frans v.d. Geest
      Community Expert
      Frans v.d. GeestCommunity Expert
      Community Expert
      May 30, 2020

      You can not just 'convert' an image to a higher ppi, you must upscale it in Photoshop with all the risk for quality! You can resize to height and widht to get a higher ppi, but the image proportions will then be smaller. That said, is your question more about  using a script and reading the actual ppi or the effective ppi? That is not clear in your question...

      E
      ethank59616381Author
      Known Participant
      May 31, 2020

      If you see my response to Andy below, it's basically just a frustrating process of going fron Indesign to photoshop over and over that i'm attempting to remedy.

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