You have a photo. The upload box says “JPEG or PNG, max 100KB.” Or maybe it says nothing about format at all — just a size limit. You stare at your file: it’s a PNG, 4.2MB. Should you convert it? To what? And does the format even matter when you’re squeezing it down to 100KB?
It matters more than most people think. Pick the wrong format and you’ll either get a blurry mess or a file that still won’t fit. Here’s how to choose, with the least theory and the most practical advice.
The short answer
| Situation | Use this |
|---|---|
| A photo (face, scenery, anything from a camera) | JPEG |
| Text, screenshots, logos, signatures, line art | PNG |
| The site says “image only” and you control the page (your own blog) | WebP |
| An exam portal or government form that names a format | Whatever it names |
That’s the whole decision in four lines. The rest of this article is the “why,” so you can stop second-guessing yourself.
JPEG: the format for real photos
JPEG (or JPG — same thing, different file extension) is built for photographs. It compresses by throwing away details your eyes barely notice: subtle color gradients, fine noise in shadows. A 3MB phone photo becomes 200KB and still looks like the same photo.
That trade-off has two consequences:
- JPEG is lossy. Every time you save a JPEG on top of a JPEG, quality drops a little. This rarely matters in practice — you’re uploading once, not editing and re-saving ten times.
- JPEG has no transparency. There’s no such thing as a transparent JPEG. If you need a transparent background, JPEG is out.
For upload forms, JPEG is the default correct choice for any photograph: ID photos, passport photos, scanned documents photographed with a phone, anything with continuous tones.
Rule of thumb: if the image came from a camera, it’s a JPEG situation.
PNG: the format for sharp edges
PNG compresses without losing a single pixel — it’s lossless. That’s great for screenshots, text documents, diagrams, logos, and signatures, where every edge needs to stay crisp. A JPEG version of a signature at the same file size would show ugly smudges around the lines; PNG keeps them razor-sharp.
The catch: for photographs, PNG files are enormous. A photo saved as PNG can easily be 5–10× the size of the same photo as JPEG. When a portal demands a photo under 100KB, a PNG will fight you every step of the way.
Rule of thumb: if the image is mostly flat colors, text, or sharp lines, use PNG. If it’s a photo, don’t.
WebP: the format portals don’t ask for (yet)
WebP is Google’s format, launched in 2010, and it does both jobs reasonably well: lossy compression that’s 25–35% smaller than JPEG at the same visual quality, and lossless mode that beats PNG for many images. Every modern browser supports it now.
So why isn’t everyone using it? Two reasons. First, many upload systems — especially government and exam portals — validate the file extension or the file’s magic bytes and reject anything that isn’t JPEG or PNG. A technically superior WebP gets bounced at the door. Second, some older desktop software still opens WebP reluctantly.
Use WebP where you control the destination: your own website, a blog, anywhere page speed matters. Our take: don’t upload WebP to a form unless the form explicitly lists it as accepted. The few kilobytes you save aren’t worth a rejection.
What exam and government portals actually check
From experience with Indian exam portals (UPSC, SSC, banking exams, university admissions), here’s what the upload validator typically checks, in order:
- File extension —
.jpg,.jpeg, or.png, depending on the instructions. - File size — the KB limit. This is the one that rejects most people.
- Image dimensions — some portals require a minimum or maximum pixel size (e.g., photo between 200×230 and 300×360 px).
Notably, most portals do not check whether a file labeled .jpg is “really” a high-quality JPEG. They check the bytes against the size limit and move on. So the winning move is: pick the format the portal names, then compress to a bit under the size limit.
One more practical note: if the portal says “JPEG” and your file is a PNG, convert first, then compress. Converting a 4MB PNG to JPEG alone often cuts it to 1–2MB — the compression step then has much less work to do, and the result looks better at the same final KB.
Converting and compressing without installing anything
You don’t need Photoshop or a sketchy “free converter” site for any of this. The flow is:
- Open Compress Image to Exact KB — it runs entirely in your browser, so your photo never gets uploaded to a server.
- Drop in your image (JPEG, PNG, or WebP — it accepts all three).
- Pick your target size: 20, 50, 100, 200, 500 KB, or a custom number.
- Download the result.
The tool outputs JPEG by default, which is the right choice for photos. If you’re compressing a signature or a scanned document with lots of text, keep it as PNG — sharp edges matter more than file size there, and the tool preserves your original format when you need it to. One tip from the previous article: always target a few KB under the portal’s stated max, because portals sometimes measure size slightly differently.
FAQ
Can I just rename a .png file to .jpg?
No — renaming changes the label, not the content. The file is still PNG data inside. Some upload validators check the actual file signature and will reject it; others will accept it but display it wrong. Convert properly instead of renaming.
Is WebP better than JPEG for uploads?
Technically, yes — smaller files at the same quality. Practically, for form uploads, no — too many portals only accept JPEG or PNG. Save WebP for your own website.
Why does my JPEG look blocky after compression?
Those squares are compression artifacts: the encoder grouped similar pixels into blocks to save space. It happens when you push a JPEG much smaller than its content allows. Fix: start from a smaller original (resize to ~1200px wide first), or accept a slightly larger KB target.
PNG or JPEG for a scanned signature?
PNG. Signatures are black lines on white — exactly what PNG does well. A JPEG signature at the same size will have gray smudges around the strokes. Keep PNG and let the size limit decide how far you compress.
Does converting PNG → JPEG lose quality?
Yes, a little — JPEG is lossy. But for a photo being uploaded to a portal at 100KB, the difference between “original PNG → JPEG at 100KB” and “camera JPEG → 100KB” is invisible. Don’t let perfect be the enemy of submitted.
Need to hit an exact KB target for a form? Compress Image to Exact KB does it in your browser in about 30 seconds — no upload, no sign-up, no watermark.