What Is Image Resolution?
The real amount of detail in an image, counted in pixels — and why it's a different thing from megapixels, DPI, and how big the picture looks on screen.
Resolution is how many pixels an image contains — its width times its height. A 4000 × 3000 photo holds twelve million pixels; that's its resolution, and it's a measure of how much real detail is in the file. It is not how big the picture looks on your screen, and it is not the same thing as DPI. Getting those three apart clears up most of the confusion around the word.
Pixels, and then megapixels
An image is a grid of coloured squares called pixels. Count them across and down, multiply, and you have the resolution. Divide that total by a million and you have megapixels — the number cameras advertise. A 4000 × 3000 image is 12,000,000 pixels, or 12 megapixels. That's all "12MP" means: the size of the grid.
Resolution is not DPI
This is the trap. Resolution is the fixed number of pixels in the file. DPI is a separate label that tells a printer how tightly to pack those pixels onto paper — it changes the print size, never the amount of detail. The same 12MP file can print as a crisp postcard or a soft poster depending on DPI, but it always contains exactly twelve million pixels. Changing DPI never adds a single one.
More pixels means more detail — and a bigger file
Higher resolution genuinely holds more detail, which is why it also weighs more: twice the width and twice the height is four times the pixels. That's the first thing to check when you're wondering why an image is so big — a photo several thousand pixels wide shown in a small web column is storing detail nobody will ever see. Bringing the resolution down to what's actually displayed, with Resize Image or Resize by Percentage, is usually the biggest single saving available.
The one thing resolution can't do: come back
Detail that was never captured can't be added later. Enlarging a low-resolution image doesn't invent the missing pixels — the software just guesses at them by averaging neighbours, which is why an upscaled photo looks soft or blocky. Our guide on resizing properly covers this: you can shrink a big image cleanly, but you can't meaningfully grow a small one. Start from the highest resolution you have, and only ever scale down.
Cropping trades resolution for framing — every pixel you crop away is resolution you no longer have, so a heavy crop of a modest photo can leave you short. Crop Image is worth doing deliberately for that reason.
How much resolution do you actually need?
- On screen: match the pixel width to where it's shown. A full-width web banner might want ~2000px; a thumbnail wants a few hundred. Beyond that you're just adding weight.
- In print: work backwards from the size and DPI. Roughly, inches × 300 = pixels per side. A sharp 8 × 10 inch print wants around 2400 × 3000 pixels — see the DPI guide for the arithmetic.
FAQ
Is a higher-megapixel photo always better?
It holds more detail and prints larger, but it's also a bigger file, and past what your screen or print size can show, the extra pixels do nothing but add weight. More is only better up to the point you actually use it.
What's the difference between resolution and DPI?
Resolution is how many pixels the file contains. DPI is an instruction about how large to print them. One is stored detail; the other is a print setting that adds no detail.
Can I increase an image's resolution?
Not in the sense that matters. You can enlarge the pixel dimensions, but the software has to invent the new pixels by guessing, so no real detail is added — it just looks softer. Always start from the largest original you have.