Image resizing or compression: which should you choose?
Resizing changes width and height. Compression mainly reduces file weight.
Explanation
Resizing and compressing are not the same thing.
Resizing changes the visible size of the image: its width and height in pixels. For example, turning a 4000 × 3000 px photo into 1200 × 900 px.
Compressing reduces the file size, for example from 5 MB to 500 KB. The image can keep the same dimensions, but the file becomes lighter.
In most cases, resize first if the image is too large, then compress it if it is still too heavy.
Formula / method
If the image is too large in pixels: resize first.
If the dimensions are already correct but the file is too heavy: compress it.
Total pixels = width × height
Example:
4000 × 3000 = 12,000,000 pixels
1200 × 900 = 1,080,000 pixels
Resizing therefore greatly reduces the number of pixels before compression is even applied.
Concrete example
A 4000 × 3000 px photo weighing 5 MB can first be resized to 1200 × 900 px. Then JPG or WebP compression can reduce the final file size further.
Common mistake
Compressing a much-too-large image without changing its dimensions is rarely optimal. You keep too many unnecessary pixels.
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