How to convert PNG to JPG on iPhone
This is the conversion people reach for when a PNG is too big to email or a form rejects it. It works — but it is a one-way, lossy step, and if your PNG has transparency, you need to decide what colour replaces it.
The two formats
PNG is lossless. It stores every pixel exactly, supports a full 8-bit alpha channel, and compresses with DEFLATE. It is excellent for screenshots, logos, UI, line art and anything with hard edges — and inefficient for photographs, where its refusal to discard anything makes files enormous.
JPG is lossy. It converts the image to a frequency representation, discards the high-frequency detail your eye is least sensitive to, and quantises the rest. On a photograph this is nearly free — you can throw away 90% of the bytes and struggle to see a difference. On text, screenshots and flat graphics it is ugly, because the artefacts cluster exactly where the hard edges are.
Transparency will be destroyed. JPG has no alpha channel — it cannot represent a transparent pixel at all. Convexy detects that your PNG has alpha and flattens it onto a solid background, white by default. You can set a different background colour in Options. If your logo was designed to sit on a dark page, a white flatten will look broken, and no amount of editing afterwards will bring the transparency back.
When PNG to JPG is the right call
- The PNG is really a photograph. Screenshots of photos, camera images someone saved as PNG, exports from tools that default to PNG. Here JPG can cut the size by 80–95% with no visible loss. This is the best case, and it is common.
- An upload form or old system rejects PNG. Some legacy portals only take JPG.
- You need to email or message it and the PNG is too heavy.
When it is a mistake
- The image has transparency you still need. Convert to WebP instead — it keeps the alpha channel and still gets small.
- It is text, a screenshot, a chart or line art. JPG will put visible ringing and mosquito noise around every letter and edge. A flat-colour graphic often compresses better as PNG anyway, so you would be making it uglier for no gain — occasionally even for a bigger file.
- It is a working file you will keep editing. Every JPG save re-quantises. Do the edits, export JPG once at the end.
Quality setting: Convexy's quality slider maps directly to the JPEG encoder's quality parameter and defaults high — visually transparent on photographic content. Pushing it far down produces obvious 8x8 blocking. There is no honest “compress with no loss” setting for JPG; the format's entire mechanism is loss.
It runs on the device
Convexy uses Apple's ImageIO frameworks locally, so the image is never uploaded and there is no account or server in the loop. That is worth caring about here specifically, because PNGs are so often screenshots — of bank statements, of private messages, of internal dashboards. Those are exactly the files you should not be posting into a random web converter.
Metadata (EXIF, GPS, IPTC, TIFF) is stripped by default. Turn that off in Options if you need the tags preserved.
How to do it
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Pick the PNG
Tap Browse files, choose from Photos, or share the image into Convexy from another app. Pick several at once to run them as a batch.
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Choose JPG
Convexy offers only the formats a PNG can actually become. Tap JPG.
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Set a background colour if the PNG is transparent
JPG cannot store transparency. Convexy flattens alpha onto white by default; if the image is meant to sit on a coloured or dark background, set that colour in Options first so the edges composite correctly.
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Choose a quality
Leave it high for anything you might print or crop later. Lower it if you are optimising for an email attachment or a message.
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Convert, then check the size
The result screen shows the before and after sizes. On a photographic PNG the drop is usually dramatic. Save to Photos or Files, rename it, or share it on.
Common questions
Does converting PNG to JPG reduce quality?
Yes. JPG is a lossy codec — it permanently discards image information to get smaller, and that step cannot be undone. On a photograph, at a high quality setting, the loss is essentially invisible. On text, screenshots or flat graphics it is visible: you will see halos and noise around sharp edges. Match the format to the content.
What happens to transparency when I convert PNG to JPG?
It is flattened. JPG has no alpha channel, so every transparent or semi-transparent pixel must be composited onto something solid. Convexy uses white unless you choose another background colour in Options. There is no way to preserve transparency in a JPG — if you need it, use PNG, WebP or AVIF.
Why did my PNG get bigger when I converted it to JPG?
Rare, but real: it happens with flat-colour images — logos, simple diagrams, screenshots of plain UI. PNG's lossless compression is extremely efficient on large areas of identical colour, while JPG spends bytes encoding frequency detail that isn't there. If your image is graphics rather than photography, PNG is likely the better format already.
Can I convert the JPG back to PNG to undo it?
No. You can create a PNG from the JPG, and it will be lossless from that point on, but it cannot resurrect detail JPG threw away or transparency that was flattened. You just get a bigger file containing the same damaged pixels. The lossy step is permanent — keep the original PNG.
Which quality setting should I use?
The default high setting is right for almost everything. Use lower values only when a specific size limit forces your hand, and check the result — JPG degrades gracefully until it suddenly doesn't, and the point where blocking becomes obvious depends heavily on the image.
Does the app upload my screenshots anywhere?
No. Convexy has no server and makes no network calls for conversion — it uses the imaging frameworks already in iOS. You can put the phone in Airplane Mode and every conversion still works, which is a good way to verify the claim rather than trust it.