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In the book HTML and CSS, I came across the following quote:

The web browsers on most desktop computers display images at a resolution of 72 pixels per inch (ppi).

So is it really useless to create an image larger than 72 ppi if the browser will only render it at 72 ppi? After all, the larger the file, the slower it is to load and don't want to slow load time for nothing.

My monitor has a resolution of 1680 x 1050 yet according to this book, when I open up Firefox and view images, they will only be viewed at 72 ppi.

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    For what it's worth, browsers have never had any ppi settings. It is the monitor which controls display.
    – Scott
    Aug 10, 2014 at 22:17
  • It's only a rough approximation to say that browsers are viewed at 72 ppi. The actual answer may be +- 50% of that number.
    – Jeff-Inventor ChromeOS
    Aug 11, 2014 at 0:12

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They don't in fact you'll be hard pressed to find a modern computer that does. Its a historical remnant. So today it just means screen resolution. (the value has to be something in many formats).

So is it really useless to create an image larger than 72 ppi if the browser will only render it at 72 ppi?

No the value never comes to play. Resolution can mean two things at the same time. It can mean the fidelity of the display device in physical units or it can means total number of imaging elements. PPI value does not change the size of your image file, just the amount of pixels matters, even for print.

See the resolution is your images pixel dimensions. PPI or DPI do not come into play. This info is a piece of metadata where you say I wish this to be displayed as so and so inches wide. However nearly every device will ignore you, in fact even desktop printers can and often do ignore you.

For web and computer imaging it simply does not matter at all, only pixel dimensions matter. Ignore the info (again for historical reasons its considered important, because few decades back all images in Photoshop was destined for print). If you find this confusing then i can tell you your not the only one.

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PPI is pixels per inch. That is a measure of pixel density, at 72 pixels/inch. Resolution is total amount of pixels at width x height, or 1680x1050.

Density = total pixels / total inches

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  • So is it really useless to create an image larger than 72 ppi if the browser will only render it at 72 ppi?
    – JohnMerlino
    Aug 10, 2014 at 21:21
  • I am quite sure that different computers have different pixel densities. I don't see why they would be capped at 72PPI.
    – TwoShorts
    Aug 10, 2014 at 21:23
  • So then why does the book say that browsers display images at resolution 72, if different computers have different pixel densities. Do browsers like firefox limit the resolution of images to 72 internally?
    – JohnMerlino
    Aug 10, 2014 at 21:30
  • frankschrader.us/2013/04/…
    – TwoShorts
    Aug 10, 2014 at 21:37
  • That website explains how 72dp became de-facto. It doesn't really matter though. Try running a test: make two identical webpages, but have one with 72ppi, and one with a different dpi and see what happens
    – TwoShorts
    Aug 10, 2014 at 21:39

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