The question almost everyone asks is “how small can I make this?” It is the wrong question. The useful one is “how small can I make this before anyone notices?” — and the answer is usually far smaller than people expect.

Most photographs shed 80 to 90 per cent of their file size before a difference becomes visible at normal viewing size. An 8 MB camera JPEG lands somewhere near 1 MB. The picture looks the same. The page loads in a fifth of the time.

What “losing quality” actually means

Two different things get called quality loss, and conflating them is where most confusion starts.

The first is resolution — how many pixels you have. Throw those away and detail is gone permanently. That is resizing, and it is a separate operation with separate consequences. We wrote about the difference between resizing and compressing because the two words get used interchangeably and they should not be.

The second is compression artefacts — the blockiness, banding and mushy edges that appear when an encoder is told to be aggressive. Your pixel count is untouched. The pixels are simply described less precisely.

Compressing an image well means spending your budget on the second, never the first.

Lossless is not a marketing word

Lossless compression rebuilds the file with a more efficient encoder and throws away nothing. Decode the result and you get the original pixels back, bit for bit. Typical savings run 20 to 30 per cent — modest, but genuinely free.

Use it when the image is going to be edited again later, when it is going into an archive, or when you simply cannot justify the risk. A master file you will re-export from is a good candidate. A hero image on a landing page is not — you are leaving most of the saving on the table for a guarantee nobody will ever check.

The four levels, and what each is for

  • Lossless — nothing discarded. Masters, archives, anything you will edit again.
  • High — a conservative cut. Print-adjacent work, portfolio images, photographs where texture is the subject.
  • Balanced — the default, and the right answer for most web work. Around a tenth of the original with no visible difference at normal viewing size.
  • Smallest — for thumbnails, email attachments and anything where the file size limit is the constraint you are actually solving for.

You can also set a target file size and let the software find the quality level that hits it. That is the setting to reach for when someone has told you “under 500 KB” and you do not care how it gets there.

Judge it with your own eyes, not a number

Quality percentages are not comparable between encoders and they are not comparable between images. Quality 80 on a portrait and quality 80 on a screenshot of a spreadsheet produce completely different amounts of damage. Trust the preview instead.

When you check, view at 100 per cent, not fit-to-window — a downscaled preview hides exactly the artefacts you are looking for. And check the places compression fails first:

  • Smooth gradients — skies, studio backdrops, out-of-focus areas. Banding shows here before anywhere else.
  • Fine repeating detail — foliage, hair, fabric weave, crowds, brickwork.
  • Hard edges against flat colour — text, logos, UI screenshots.

If those four areas hold up, the rest of the image is fine.

Where lossy compression is the wrong tool

Screenshots, diagrams, logos and anything with text in it are the classic failure case. JPEG-style compression works by discarding high-frequency detail, and a hard black edge against white is nothing but high-frequency detail. You get a grey halo around every letter.

For that material, stay lossless, or move to a format built for flat colour. Our format guide covers which one to pick, and there is a longer piece on why WebP and AVIF beat JPEG for most web work.

Do it once, for everything

Compressing images one at a time is how the habit dies. The moment it is forty files it stops happening, and the folder ships at full weight.

Point the app at a folder instead and every image inside is handled with the same settings, subfolders included. There is a step-by-step walkthrough in compressing a whole folder without losing quality. The four-step guide on the home page covers the short version.

A workflow that holds up

  • Keep your originals. Compress into a separate output folder so the masters stay untouched.
  • Start at Balanced. Move to High only when the preview tells you to, not out of caution.
  • Check one representative image per batch, not all forty. Same camera and same lighting means the same result.
  • Compress last, after any cropping or colour work. Every re-encode costs a little more.

That last one matters more than people think. Each save through a lossy encoder compounds on the one before, so a file edited and re-exported five times has been through five rounds of damage. Do your editing, then compress once on the way out.

SqueezeImages is a free desktop app that does all of this offline — nothing is uploaded, and there is no account to make. Download it here, or read the answers to the usual questions first.