ppi

Find the PPI (pixels per inch) of an image.

Example

var PPI = require('ppi');
var parse = require('exif2');
var exif = parse('./photo.png');

var ppi = PPI(exif);

API

ppi(exif)

Determine the PPI of an image. If it cannot find the PPI, ppi returns false.

Support

Parsing exif data is not trivial. There are many different formats and lots of pictures (especially those from the internet) do not have enough data to determine the PPI.

This library is a test-driven approach to determining the PPI on a variety of pictures. Right now this library tests the following image sources:

ppi(exif)
  should find ppi of:
    ✓ retina screenshot from mac
    ✓ photo from an iphone 4
    ✓ photo from an iphone 5s
    ✓ photo from an ipad 3
    ✓ photo from an samsung s3
    ✓ photo from a camera (leica)
    ✓ screenshot from windows
  should not find ppi of:
    ✓ old photo from the internet
    ✓ screenshot from ubuntu
    ✓ screenshot from ipad 3
    ✓ screenshot from iphone 5s

To test a photo from your device simply add it to test/images, run the tests with make test, then inspect the exif data inside test/exif. Hopefully there will be enough data to determine the PPI.

TODO

Depending on what kind of computer the screenshot was taken on the PPI will change:

• Non-retina mac: 72 ppi
• Retina mac: 144 ppi
• Windows: 96 ppi
• Linux: 96 ppi (?)

We can provide sensible defaults for images that we know are taken on a specific computer

Test

make test

License

(The MIT License)

Copyright (c) 2012 Matthew Mueller <mattmuelle@gmail.com>

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