Why Your PNG Is Ten Times Bigger Than the Same Photo as a JPG
Export a photo as a PNG and you may find it is ten times the size of the JPG version, with no visible difference between them. That is not a bug or a bad setting. It is the two formats doing exactly what they were designed to do.
PNG Looks for Repetition. Photographs Have None.
PNG compresses using DEFLATE, the same algorithm that powers ZIP files. DEFLATE is a lossless compressor, which means it must be able to reconstruct the original data exactly, bit for bit. It achieves size reduction purely by finding and encoding repetition.
That works brilliantly on certain kinds of image. A screenshot of a settings panel is mostly flat grey, with long runs of identical pixels and patterns that repeat. DEFLATE finds all of it and the file collapses to a fraction of its raw size.
Now consider a photograph of a beach. Adjacent pixels in the sky differ by a shade or two. Sand is thousands of subtly different browns. Sensor noise means even a flat wall is not really flat. There is almost no exact repetition anywhere in the frame, so DEFLATE has very little to work with. The file stays enormous, because there was never anything to remove.
JPEG Solves a Different Problem Entirely
JPEG does not attempt to be lossless, which frees it to use a completely different strategy. Rather than looking for repetition, it looks for detail your eye is unlikely to miss — and throws that away.
It divides the image into eight-by-eight pixel blocks and converts each block from pixel values into frequency information: how much fine texture there is, how much broad tone. Human vision is far more sensitive to broad tonal shifts than to very fine texture, so JPEG keeps the low frequencies faithfully and discards much of the high-frequency detail.
For a photograph this is close to a free lunch. The discarded detail is largely noise and micro-texture nobody was looking at, and the file shrinks by an order of magnitude. This is why JPEG has dominated photography for three decades.
PNG asks how can I store all of this using fewer bits. JPEG asks which of this does the viewer not need. Those are different questions, and they produce wildly different results depending on what is in the picture.
Where the Advantage Flips
None of this makes PNG the loser. Change the content and the ranking reverses completely.
Give JPEG a screenshot full of text and it performs badly. Text is nothing but hard edges, which in frequency terms is exactly the high-frequency detail JPEG is designed to discard. The result is visible fringing and smearing around every letter — and because the image was mostly flat colour to begin with, the file barely shrinks. You get a worse-looking image at roughly the same size.
PNG handles that same screenshot effortlessly, storing every letterform exactly and compressing the flat background aggressively.
| Content | As PNG | As JPG (85%) | Which wins |
|---|---|---|---|
| 12 MP photograph | ~8 MB | ~900 KB | JPG, decisively |
| UI screenshot | ~320 KB | ~290 KB | PNG — JPG adds fringing |
| Logo, flat colour | ~40 KB | ~85 KB | PNG, on both size and quality |
| Line drawing | ~60 KB | ~140 KB | PNG, on both |
| Photo with text overlay | Large | Small but smeared | Depends on priority |
Figures are typical rather than exact — actual results vary with the specific image.
A Simple Test for Which Format You Need
You rarely need to think about compression algorithms. One question sorts almost every case correctly.
Did this image come out of a camera, or out of a piece of software?
Camera output — photographs, anything with continuous tone and natural texture — belongs in JPEG or WebP. Software output — screenshots, logos, diagrams, charts, anything with flat colour and hard edges — belongs in PNG or lossless WebP.
The awkward middle case is a photograph with text laid over it, such as a social media graphic. There is no perfect answer; you are choosing between smeared text and a large file. In practice, WebP handles this hybrid case better than either JPEG or PNG, which is one of the strongest arguments for using it where you can.
If You Are Stuck With a Large PNG
Sometimes you have a PNG that is too big and you cannot simply switch formats. A few things genuinely help, in rough order of effectiveness.
- Reduce the pixel dimensions. This is by far the biggest lever, and the one most people never touch. Halving the width and height removes three quarters of the pixels.
- Convert to lossless WebP. Identical pixels, no quality change at all, and typically 25 to 30 percent smaller than PNG.
- Reduce the colour palette if the image genuinely uses few colours. An 8-bit PNG with 256 colours is dramatically smaller than a full-colour one, and for flat graphics the difference is often invisible.
- Strip metadata. Minor, but free.
- Accept lossy compression if the content is actually photographic — in which case the file should probably not have been a PNG in the first place.
What will not help is running the PNG through a compressor and expecting JPEG-scale savings. Lossless is lossless. If the image is a photograph, no amount of optimisation will bridge that gap, because the information is genuinely there and PNG is obliged to keep all of it.
Frequently Asked Questions
Is PNG a bad format?
Not at all — it is an excellent format for the content it was designed for. PNG is lossless and supports full transparency, which makes it ideal for logos, icons, screenshots and graphics. It only looks inefficient when used for photographs, which is a job it was never intended to do.
Why does my screenshot barely shrink when I convert it to JPG?
Because PNG already compressed it very effectively. Screenshots are largely flat colour and repeated patterns, which is exactly what DEFLATE excels at, so the file is already close to its minimum size. JPEG has little left to remove, and what it does remove shows up as fringing around text. Screenshots should stay as PNG.
Will compressing a PNG reduce quality?
No. PNG compression is lossless by definition, so optimising a PNG never changes a single pixel. That is also why the savings are modest — usually 10 to 30 percent. Anything advertising dramatic PNG size reductions is either reducing the colour palette or converting to a lossy format.
What is the smallest lossless option available?
Lossless WebP. It stores identical pixel data to PNG with no quality change whatsoever, but uses a more capable compression scheme and typically produces files 25 to 30 percent smaller. The only downside is compatibility: some older software and most email clients still do not read WebP reliably.
Should I just use WebP for everything?
For anything served on a website, largely yes — it handles both photographic and graphic content well and has universal browser support. Outside the browser it is a different story: email clients, print services and older desktop software frequently reject it, so keep JPG or PNG copies for anything you send to people.