You saved an image from a website and it's WebP, which your software won't open. You took a photo on your iPhone and an application portal rejected it as HEIC. You converted a logo to JPG and got an ugly white box around it. A simple screenshot is 3 MB because it's a PNG.
All of these come from one fact: each image format stores data differently, with its own strengths and weaknesses. Understand the basics and you'll pick the right format from the start. This guide explains the five most common formats in plain language, then gives you a quick decision table.
- JPG: for photos. Small and accepted everywhere, but no transparency and slight quality loss.
- PNG: for logos, graphics, screenshots and text. Perfectly sharp with transparency, but huge for photos.
- WebP: the modern web format. Usually smaller than both, with transparency — but some software and portals don't accept it.
- HEIC: iPhone's photo format. Great for storage, poor compatibility; convert to JPG to share.
- To convert between them: Convert image.
Two concepts before comparing
Lossy vs lossless
- Lossless: every pixel is stored exactly, just more efficiently. Open it and you get the identical image. Example: PNG.
- Lossy: detail the eye is unlikely to notice is discarded, shrinking the file a lot. Example: JPG. Push it hard and artefacts appear — blockiness and halos.
Transparency
The ability to make parts of an image see-through, so whatever's behind shows. Essential for logos and icons placed on different backgrounds. JPG doesn't support it and fills transparent areas with a colour, usually white.
JPG (JPEG)
Introduced in 1992, still the world's most common format for photos.
Strengths: - Very small files for photos and natural scenes. - Accepted by virtually every program, site, portal and device. - Adjustable quality to balance size and clarity.
Weaknesses: - Lossy: each re-save adds a little degradation. - No transparency. - Text and sharp lines get halos, especially at low quality.
Use it for: photos, scanned documents for uploads, portraits, and anywhere "JPG" is requested.
PNG
Created in the mid-1990s as an open alternative to GIF.
Strengths: - Lossless: the image exactly as it is. - Full, graded transparency. - Perfectly crisp text, lines and flat colours.
Weaknesses: - Very large for photos — often several times the JPG size of the same image.
Use it for: logos, icons, screenshots, charts, tables, and images you'll keep editing.
WebP
Developed by Google and announced in 2010; supported by every modern browser today.
Strengths: - Both lossy and lossless modes. - Transparency and animation. - Usually smaller: Google's data shows lossless WebP around 26% smaller than PNG, and lossy WebP 25–34% smaller than comparable JPEG.
Weaknesses: - Some older software won't open it. - Many government and university portals and application forms don't accept it yet. - Images saved from websites are often WebP, causing problems when you upload them elsewhere.
Use it for: website and online-store images, where size and load speed matter. For official uploads, convert with WebP to JPG.
HEIC (HEIF)
The default photo format on iPhone since iOS 11 in 2017.
Strengths: - High quality at noticeably smaller sizes than JPG. - Supports advanced features such as Live Photos and depth data.
Weaknesses: - Poor compatibility outside Apple devices: many sites and older Windows software can't open it. - Most portals won't accept it.
What to do: convert to JPG for sharing, or set the camera to Settings → Camera → Formats → Most Compatible so new photos save as JPG. iPhones also often convert to JPG automatically when uploading through a browser.
AVIF
The newest, released in 2019 by the Alliance for Open Media.
Strengths: excellent compression — often smaller than WebP at the same quality — plus transparency and wide colour.
Weaknesses: less support in software and tools than WebP, and slower to encode.
Use it for: performance-focused websites, with a JPG or WebP fallback for older browsers.
Full comparison
| Factor | JPG | PNG | WebP | HEIC | AVIF |
|---|---|---|---|---|---|
| Compression | Lossy | Lossless | Both | Mostly lossy | Both |
| Transparency | ❌ | ✅ | ✅ | ✅ | ✅ |
| Animation | ❌ | ❌ (APNG rarely) | ✅ | ✅ | ✅ |
| Photo file size | Small | Very large | Smaller | Smaller | Smallest |
| Text & graphics sharpness | Fair | Excellent | Excellent (lossless) | Good | Good |
| General compatibility | Excellent | Excellent | Very good | Poor | Fair |
| Accepted by official portals | Excellent | Good | Poor | Very poor | Very poor |
Quick decision table
| You want to… | Format |
|---|---|
| Upload a portrait or document to an official portal | JPG |
| Use a logo with a transparent background | PNG, or WebP on websites |
| Share a screenshot with text | PNG, or high-quality JPG if size matters |
| Show product photos in an online store | WebP, or AVIF with a fallback |
| Share a photo | JPG |
| Keep editing an image | PNG while working, then JPG or WebP to publish |
| Store phone photos in the least space | HEIC on Apple devices; JPG for compatibility |
| Put a chart in a presentation | PNG |
| Put images in a PDF | JPG for photos, PNG for graphics |
Converting between formats: what really happens
PNG → JPG: photos shrink a lot, but transparency becomes a solid background and text may lose some sharpness. Use PNG to JPG.
JPG → PNG: never improves quality — detail discarded by JPEG doesn't come back — and the file gets bigger. Only convert if you'll edit the image and want to avoid further loss with each save.
WebP → JPG: for compatibility with software and portals. Size may grow slightly. Use WebP to JPG.
JPG/PNG → WebP: to shrink website images. Use Compress image with WebP output, or Convert image.
HEIC → JPG: for sharing and uploading. iPhones often do this automatically when sharing.
Renaming photo.webp to photo.jpg doesn't change the file's contents. Some programs open it anyway because they detect the real format, but strict portals will reject it or treat it as corrupt. Always use a real converter.
Images inside PDFs
When you turn images into a PDF with JPG to PDF, the format carries into the file: JPGs stay compressed and small, PNGs stay lossless and larger. So:
- For photographed documents and photos, use JPG before combining into a PDF.
- For screenshots and graphics, PNG keeps text sharper — watch the size.
When converting PDF pages to images, choose JPG for scanned pages and PNG for text. See How to convert PDF to images in high quality.
Other formats you may meet
| Format | What it is | What to do with it |
|---|---|---|
| GIF | Old format for simple animations, 256 colours max | Short animations; WebP or video is better today |
| BMP | Nearly uncompressed images, huge files | Convert to PNG or JPG |
| TIFF | Professional print, archive and scan format | Keep for archives; share a JPG copy |
| SVG | Vector graphics that scale infinitely | Logos and icons on websites |
| RAW (CR2, NEF, DNG…) | Raw camera data | For photographers; edit, then export JPG |
Format choice and website speed
If you run a website or store, image format directly affects load time — and load time affects visitors and search rankings:
- Use WebP for photos and products; usually smaller at the same quality.
- Resize to the displayed size: no point serving a 4000 px image in an 800 px slot.
- Set width and height in HTML to prevent layout shift while loading.
- Lazy-load (
loading="lazy") images below the fold. - Use SVG for logos and icons instead of PNG wherever possible.
Compress image lets you choose WebP output and a max width to prepare website images in one batch.
Try it yourself
- Take a photo and a screenshot with text.
- Convert each to JPG, PNG and WebP with Convert image.
- Compare sizes, then zoom each to 200%.
You'll usually see: the photo as PNG is far bigger with no visible gain, the screenshot as JPG shows halos around letters, and WebP is smallest in both cases.
Quality questions
Does re-saving a JPG reduce quality? Yes, slightly with each save below 100% quality. Work from a PNG or the original and save JPG at the end.
Is PNG always "higher quality"? It's lossless, but if the original was a JPG, converting to PNG won't restore what was lost.
Does WebP reduce quality? Lossy WebP works like JPG in principle, just more efficiently. Lossless WebP preserves everything, like PNG.
Social media and messaging: what happens to your images
Most platforms recompress whatever you upload, regardless of the original format:
- Messaging apps usually convert photos to compressed JPG and shrink their dimensions. Send as a "document" or "file" to keep the original.
- Social networks resize and recompress to their own sizes; uploading at their recommended dimensions avoids double resizing and softening.
- Email keeps your file exactly as attached, so choose the format before attaching.
Practical tip: for anything where quality matters — a portfolio piece, a document photo — share as a file, not as an inline photo.
Colour, bit depth and why some PNGs are huge
Two more factors explain surprising file sizes:
- Bit depth: most images use 8 bits per colour channel. Some PNGs from design tools or scanners use 16 bits — doubling the data for differences you can't see on a normal screen. Re-saving as 8-bit shrinks them.
- Colour count: PNG compresses flat-colour graphics (logos, UI screenshots) extremely well, but noisy photographic content barely compresses. That's why a PNG screenshot of a simple app screen can be small while a PNG photo is enormous.
For photos, these details don't matter — just use JPG or WebP.
A format checklist before you publish or upload
- Is it a photo? → JPG (or WebP on your own website).
- Does it need transparency? → PNG or WebP.
- Is it text or a diagram? → PNG.
- Is it for an official portal? → JPG, unless told otherwise.
- Is it from an iPhone? → Check it isn't HEIC.
- Is it from a website? → Check it isn't WebP if the destination is picky.
- Are the dimensions no larger than needed? → Resize with Resize image.
FAQ
Which format is best for portraits on application forms?
JPG — accepted almost everywhere. Check the required dimensions and size in How to reduce image size in KB.
Why do images saved from websites end up as WebP?
Modern sites serve WebP to load faster. If you need the image somewhere that doesn't accept WebP, convert it to JPG.
How do I keep a logo's transparency?
Save it as PNG or WebP, never JPG.
Why is my screenshot so big?
It's a lossless PNG. If you don't need perfect sharpness, convert to JPG at 80% and it shrinks dramatically.
Are WPPR's converters safe?
Yes. Conversion happens in your browser; images are never sent to a server. See our security page.
Can I convert several images at once?
Yes — select multiple images in Convert image and they're all converted with the same setting.
Bottom line
There's no single "best" format — only the right one for each use: JPG for photos and official uploads, PNG for logos, text and screenshots, WebP for websites, and HEIC for storage on Apple devices before converting to share. Remember that converting to a "better" format never restores lost quality.
Convert your images now with Convert image — free, and nothing is uploaded.