Not Your Everyday Banana

by Bart Arondson

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I've been given an image (I'm guessing straight from a camera) and it's currently at at 240 pixels per inch. It's been a while since I did much Photoshop; I have three questions for two requirements:

  1. Back in the day the web used 72dpi images because that's all screens worked at. Is 72dpi still the most appropriate resolution for the web?
  2. I need to use the image in a phone application. I know phone devices have higher DPIs than 72 but do you need to feed them a high-DPI image to begin with, or will a massive 72dpi image work properly?

BONUS QUESTION

  1. How do I resize an image from 240dpi to 72dpi while maintaining detail? i.e. I don't want to go from a 240px * 240px at 240dpi to 72px * 72px at 72dpi.
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marked as duplicate by Michael Clark, MikeW, mattdm, Paul Cezanne, Philip Kendall Apr 23 at 12:52

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

    
Current web applications are pretty much "ppi agnostic". The application will resize the image to fit the screen or the space on the screen it is willing to give to the image. See also: photo.stackexchange.com/q/39072/15871 and photo.stackexchange.com/questions/11182/…. –  Michael Clark Apr 23 at 1:49
    
For the difference between DPI and PPI see: photo.stackexchange.com/questions/1715/… –  Michael Clark Apr 23 at 1:50
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1 Answer 1

If your image is 240px * 240px at 240dpi, and you change the resolution in photoshop to 72dpi, the image is still 240px * 240px and the quality isn't changed. It is just a reference for if the image is to be printed.

If you're using an image onscreen you can ignore the dpi, it will only ever display the number of pixels.

I've found the best way to export an image is if you have Photoshop, you can use File > Save For Web, and it has all sorts of presets for the main web graphic formats: png, gif and jpg, you can experiment with these and display 2-up or 4-up to compare different formats or compare with the original.

For use on the phone app, you only really need to know the resolution of the phone, ie the number of pixels across by the number of pixels high. For the best display on that phone, set the pixels across and the pixels high to as close to that as possible before exporting

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