image resolution in smartphones and laptop
Based on your comment:


  I mean that the image is captured using say, for example, the 5
  megapixels camera of the smartphone, and displayed on its screen
  having a certain dpi value. What happens if the same 5 megapixels
  image is displayed on another smartphone having different screen size
  and different dpi?


If you display an image (taken by whichever device, with whatever megapixel camera) on two different displays with two different DPI or PPIs, then it will seem smaller on the high PPI screen and larger on the low DPI screen.

This is very easy to see. Lets say the image has 2000V x 3000H pixels. And display this image on a screen with 200 PPI. Then it will take 15 inches horizontally and 10 inches vertically. On the other hand, if you display it on a second device with 100 PPI, then it will take 30 inches horizontally and 20 inches vertically, hence enlarged by 4 times. Lets conclude :


  Everything else being the same except the screen PPIs; a given image displays larger on a low PPI screen
  and smaller on the high PPI.