Quick answer

Image resizing changes an image's width and height. Resampling may add or remove pixels, while changing only its displayed or print dimensions can leave the underlying pixel grid unchanged.

Original example

Make a 1600 by 900 image smaller

Reducing a 1600 by 900 image to 800 by 450 keeps its 16:9 proportions while using one quarter as many pixel positions. Stretching it to 800 by 600 instead changes its shape to 4:3.

Resizing and resampling

Resampling creates a new pixel grid. Downsampling removes pixels; upsampling estimates new ones. Neither process can guarantee detail that was absent from the original.

To avoid distortion, keep width and height linked by the original aspect ratio unless a shape change is intentional.

Common misunderstandings

  • Making pixel dimensions larger does not automatically create genuine new detail.
  • Resizing and cropping are different: cropping removes part of the picture.

Related answers

Sources

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