Supposed JPEG is characterised with 3 params: width (pixel), height (pixel) and bit depth (what is the metric?). And resolution is the characteristic for output devices, e.g. monitor, printer. Why? Resolution is "Dots Per Inch" or "Pixels Per Inch", lets say in another words: "Ratio of any Discret value to any Length metric".
As we can see from JPEG file properties it also has horizontal/vertical resolution. But how can we say resolution to something that does not have length metric? (It sounds funny for me "5 inches width JPEG file")
And another word to this is about user perception.
Let's assume we have JPEG image 1920px width and we look at this picture on the screen of monitor and iPhone:
- 24-inch wide-screen computer monitor: 1920 x 1200, 102.5 dpi
- iPhone 6 Plus: 1920 × 1080, 401 dpi
So width is the same 1920px each pixel of image goes exactly to each pixel of device. So if we choose distanse to look at these two screens with the same ratio of pixels per degree of vision (by choosing corresponding distance of sight) we would have exactly the same quality (~70 PPD).
So why can we talk about resolution of JPEG?
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