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Topic: Calculating Image Resolution (Read 470 times) previous topic - next topic

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Calculating Image Resolution
I'm currently working on a large format poster job and was asked to calculate the resolutions of the placed images to report back to the customer how bad they are going to look. Most images are placed at 150% or higher into an InDesign file then output from there. Does anyone know a formula for figuring this out? I'm thinking something like: original resolution / scale maybe? Thanks!

  • Joe
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Re: Calculating Image Resolution
Reply #1
You might look at the 2nd calculator on this page:

http://auctionrepair.com/pixels.html
Mac OS 10.12 Sierra | Prinergy 7.5 | Adobe Creative Cloud 2017 | Two Luscher XPose 160 CTP units

Prepress: One who does precision guess work based on unreliable data provided by those of questionable knowledge.

Re: Calculating Image Resolution
Reply #2
That's close but not quite what I need. That calculator lats you input size in inches along with resolution returning pixels. Im' looking for the resolution.

I think if I take the original image resolution (which so far seems to be a consistent 300dpi) and divide that by the % I think I should get what I need. I think since I was asked to flag anything below an effective DPI of 150 I will only need to worry about images that were scaled more than 200%. Still, with 50+ files to go through I was hoping to find out a better way of checking this. 

I can run the final PDFs through the PitStop preflight action which will flag low res images but as far as I can see it doesn't report back actual resolutions... I could be missing something there though... Hmm...  :undecided:

Re: Calculating Image Resolution
Reply #3
InDesign's links panel will show the actual (original) vs. effective (placed size) PPI values:

So place a 300ppi original and scale to 50% size and the effective PPI value is 600ppi... Scale to 200% size and it is 150ppi.

Same for the built-in preflight report.

For LF inkjet work under normal "poster" viewing distances of at least 1-2 times the distance as the longest edge of the poster, you should be fine with 150ppi effective resolution, if not down to 100ppi.

  • Last Edit: August 30, 2017, 04:23:10 AM by swampymarsh

Re: Calculating Image Resolution
Reply #4
Thanks Swampy! I didn't realize InDesign actually reported that. I will look closer at both options when I have a bit more time.

As for the 150ppi resolution that's being asked for on this project, we have an in-house large format department so even with the information filtered through <shudder> sales, I'm fairly sure that is an acceptable resolution. This is an update from a project last year and they had some image quality issues due to effective resolution so they are being a bit more proactive this time around.

  • DigiCorn
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Re: Calculating Image Resolution
Reply #5
I set mine up so I can see it in the link panel. Bring up the Link window, and select options from the drop down to add it.

[edit] did the screenshot show up? having issues on my end.
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  • Joe
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Re: Calculating Image Resolution
Reply #6
I set mine up so I can see it in the link panel. Bring up the Link window, and select options from the drop down to add it.

[edit] did the screenshot show up? having issues on my end.

Yes it showed up.
Mac OS 10.12 Sierra | Prinergy 7.5 | Adobe Creative Cloud 2017 | Two Luscher XPose 160 CTP units

Prepress: One who does precision guess work based on unreliable data provided by those of questionable knowledge.

  • frailer
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Re: Calculating Image Resolution
Reply #7
Quote
For LF inkjet work under normal "poster" viewing distances of at least 1-2 times the distance as the longest edge of the poster, you should be fine with 150ppi effective resolution, if not down to 100ppi.



We had a CSR; one of his favourite expressions was: "It's only a fucking post-ah!" (East London accent). ;D

Funny the shit that stays in your head; not always welcome.
Fujifilm XMF/AdobeCC/PitStop Pro/Black Magic/ScreenPlateRite_Fujifilm ZP processless. 28" Komoris  |  Forgotten good guys: Dennis Ritchie, Burrell Smith, Bill Atkinson, Richard Stallman
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Too old for this.. but.. there's that question of income. And lack of it if I stop.
~~~~~~

Re: Calculating Image Resolution
Reply #8
https://github.com/jpobojewski/InDesign-Toolbox/blob/master/Export%20List%20of%20Graphics.jsx

Press the "raw" button and then copy, paste into a plain text editor or Adobe Extendscript Toolkit app and save as .js or jsx extension (not .txt). Install into your InDesign scripts panel and you can have all of the link info exported into a spreadsheet for easy viewing.

Also attached is a full featured binary script for InDesign.
  • Last Edit: August 31, 2017, 10:10:12 PM by swampymarsh