Short answer
Compressing lowers quality to shrink the file while keeping the same pixel dimensions. Resizing reduces the pixel dimensions themselves. For an upload limit, resize first — halving the width and height removes about 75% of the pixels — then compress only as much as you still need.
Compressing vs Resizing, side by side
| Aspect | Compressing | Resizing |
|---|---|---|
| Changes pixel dimensions | No | Yes |
| Effect on file size | Moderate | Large |
| Visible on a small screen | Artefacts if pushed far | Nothing, if still large enough |
| Printing at original size | Fine | Loses detail |
| Reversible | No | No |
| Best for a KB upload limit | Second step | First step |
Why resizing does more
File size scales with the number of pixels, and pixel count scales with the square of the dimensions. Halving both width and height leaves a quarter of the pixels — a much bigger reduction than any realistic quality setting will give you.
A 4000×3000 photo from a phone is 12 megapixels. Displayed at 800 pixels wide on a web page, more than 96% of those pixels are thrown away by the browser anyway. Resizing before upload simply does that discarding deliberately, at no visible cost.
When compression is the right lever
When the dimensions are already correct — a photo sized to an exact specification, or an image that will be printed — compression is the only tool left. Lower the quality in small steps and compare, rather than jumping straight to the minimum.
Most photographs hold up well down to around quality 70. Below that, artefacts start appearing in flat areas like skies before they show anywhere else.
The order that actually works
Government portals and job applications frequently specify both a pixel size and a KB range, and people fail them by attacking only one. Set the dimensions first, because that is where most of the size goes, then reduce quality until the file lands inside the range.
Never resize upwards to satisfy a minimum dimension. Enlarging invents detail that does not exist, produces a larger file, and looks worse than the original.
Frequently Asked Questions
Which one should I use to meet a 200 KB upload limit?
Both, in that order. Resize to the dimensions the form asks for, then compress until the file is under the limit. Attempting it with compression alone usually means pushing quality so low the image becomes visibly damaged.
Does compressing an image change its dimensions?
No. Compression keeps the same width and height and reduces the data used to describe each pixel. The image looks identical at a glance and only degrades under close inspection.
Can I get quality back after compressing?
No. Both compression and resizing permanently discard information — there is nothing to restore from. Always keep the original file and work on a copy.
Try it yourself
Terms used here
- Lossy vs lossless
- DPI — Dots Per Inch
- Aspect ratio
Related comparisons
- WebP vs AVIF — AVIF for the smallest files; WebP when you need guaranteed support everywhere.
- JPG vs PNG — JPG for photographs. PNG for screenshots, logos and anything needing transparency.