THE ARTICLE · 11 MIN
Image and file formats come with a lot of folklore. Some of the rules were true once, some are true in one program, and some were never true at all.
This page takes twelve common beliefs about JPEG, PNG, HEIC, WebP, AVIF and PDF files. Each one is set against format specifications, official documentation and published tests. The short answers are in the summary table, and the evidence for each is below.
Where one of the site’s free tools fits, a section ends with a link to it. The image converters linked here run in your browser and do not upload your files, as each tool’s own page explains.
The claims, one by one
1. “A JPEG loses quality every time you open it”
Doesn't hold up Opening a JPEG to look at it does not change it; the loss comes when a JPEG is saved again.
The loss itself is real. JPEG’s usual mode throws detail away to make files small. MDN’s guide to image formats calls JPEG the most widely used lossy compression format for still images.
A 2013 Library of Congress post on personal digital archiving explains when that loss happens. Each new save compresses the picture again, and after multiple rounds of changes and re-compression, the post says, you would begin to see the image degrade. If you don’t intend to change a JPEG, the same post says you can archive it as it is.
The guide Lossy vs. lossless compression explains the difference in plain words.
2. “Images for the web must be 72 dpi”
Doesn't hold up On a screen, an image’s size comes from its pixel dimensions and the page’s layout.
It’s easy to see why dpi seems to matter: image files can store a value for it. But by default, MDN explains, browsers assume one device pixel equals one CSS pixel. In that case an image’s natural, or intrinsic, size is simply its pixel height and width.
MDN adds that an image’s intrinsic size and resolution can be explicitly set in its EXIF data, details about the image stored inside the file. So a browser can use stored resolution information in some cases. Neither case makes 72 dpi a rule for the web.
The dpi value describes physical size, which is what matters on paper. The PNG specification stores it as pixels per unit, which give the intended pixel size or aspect ratio for display of the image. For what printers ask for, see our business card basics page.
The site’s free image resizer reduces an image’s pixel width in your browser, which is what changes its size on screen.
3. “PNG is always better quality than JPEG”
Partly PNG keeps every pixel exactly as it was given, but that doesn’t make it the better choice for every picture.
The W3C specification describes PNG as a format for lossless, portable, well-compressed storage of images. Lossless means the original data can be rebuilt exactly, bit for bit, which JPEG’s usual mode does not allow.
Whether it is better still depends on the picture. MDN recommends lossless encoding for screenshots, diagrams, logos and line art, where blurring around text is very visible. Photographs, it says, can usually take lossy compression, because the lost detail is harder to see.
A PNG is also only as good as the pixels handed to it. Tools such as pngquant offer lossy compression of PNG images by first reducing the picture to a palette.
A palette is a list of colours that each pixel points to, and in the PNG specification it holds from 1 to 256 entries. The result is still a PNG, but colours were merged before it was written.
The site’s image format benchmark encodes your own picture as JPG and WebP at several quality settings, plus one lossless PNG, in your browser, and reports the real file sizes.
4. “Converting a JPEG to PNG restores the lost quality”
Doesn't hold up A PNG made from a JPEG is an exact copy of the JPEG’s pixels, artefacts included. It can’t add back detail the JPEG already threw away.
The idea makes sense at first glance, because PNG is lossless. But lossless only means nothing more is lost: it keeps what it is given. The Library of Congress post says of compression loss that once that digital information is lost, you can never get it back.
The site’s JPG to PNG converter says the same on its own page. The guide How to convert JPG to PNG without losing quality covers when converting still makes sense.
5. “HEIC only works on Apple devices”
Doesn't hold up Android can read HEIC files too, and so can Windows with Microsoft’s extensions, though most web browsers can’t.
The link to Apple is real. HEIC files use HEIF, and Apple’s devices took up HEIF when iOS 11 and macOS High Sierra introduced support for it. Apple itself calls it an industry-standard format.
Apple says HEIF and HEVC offer better compression than JPEG and H.264, using less storage while preserving the same visual quality.
Other systems read HEIC too:
- Android’s table of supported media formats lists HEIF (.heic, .heif) decoding from Android 8.0.
- On Windows, Microsoft’s HEIF Image Extension lets Windows read and write HEIF files. Its Microsoft Store page adds that the HEVC Video Extensions must also be installed to view images in HEIF files with the .heic, .hif or .heif extensions.
Where HEIC still runs into trouble is the web. In caniuse’s browser data, read on 5 October 2026, Safari from version 17 is the only browser listed as supporting HEIF images.
Apple also notes what happens when you share by AirDrop, Messages or email and the receiving device does not support the format. In that case, Apple says, the media might automatically be shared in a more compatible format, such as JPEG or H.264.
If a HEIC will not open somewhere, the site’s HEIC to JPG converter converts it inside your browser tab. The guide Why won’t HEIC open on Windows and Android? covers each platform.
6. “WebP is supported by every browser”
Partly Every current major browser displays WebP, with two gaps. MDN lists support in Chrome, Edge, Firefox, Opera and Safari.
Internet Explorer never supported it, according to caniuse’s data. And on a Mac, MDN notes, WebP support depends on both the Safari and macOS versions. You need Safari 14 or later, and macOS Big Sur (11) or later.
The site’s WebP to JPG converter turns a WebP into a JPG in your browser when something will not take a WebP.
7. “AVIF is always smaller than WebP”
Partly For lossy images AVIF usually comes out smaller than WebP, but one test of lossless images found the opposite.
MDN says AVIF generally compresses better than WebP: a median 50% compression against 30% for the same set of JPG files. It cites a 2020 comparison by Daniel Aleksandersen.
In that test of 600 images at the same measured visual quality, AVIF’s median file was 50.3% smaller than the reference JPEG and WebP’s 31.5% smaller. AVIF beat both JPEG and WebP on every image in the test.
Lossless images are a different story. Johannes Siipola tested 94 images in a 2021 blog post, mostly designs of websites, apps, logos and illustrations. He found lossless AVIF files noticeably larger than WebP or JPEG XL.
Both tests are from 2020 and 2021, so their exact figures are a snapshot of the encoders of the time.
The guide WebP vs. AVIF vs. JPG compares the three formats. The image format benchmark measures JPG, WebP and PNG (not AVIF) on your own files.
8. “PDFs can’t be edited”
Doesn't hold up PDFs can be edited, though how much depends on the program.
The belief has a point. Apple’s Preview on the Mac lets you add, delete and rearrange pages and mark a PDF up. But Apple’s guide says plainly that you can’t edit the text of a PDF in Preview.
Word goes further: Microsoft’s instructions say that to edit a PDF, you open it in Word. Word makes a copy of the PDF and converts its contents. This works best with PDFs that are mostly text, and lines and pages may break at different locations.
So what you can change depends on the tool: pages and notes in one, the text itself after a conversion in another.
The site’s organise PDF tool rotates, deletes and reorders pages in your browser, and split PDF pulls out the pages you list into a new file.
9. “Screenshots are always PNG”
Doesn't hold up Many screenshots are PNG, but not all. On supported Macs with macOS Tahoe 26 or later, Apple’s Screenshot app lets you choose the capture format. Standard dynamic range captures use PNG, and high dynamic range captures use HEIF.
The belief has a good reason behind it: PNG suits most screen content. MDN recommends lossless encoding for screenshots, because blurring around text is easy to see.
The site’s PNG to JPG converter converts a PNG screenshot in your browser, and its page explains why sharp text is often better left as PNG.
10. “Removing EXIF removes all identifying data”
Doesn't hold up EXIF is one store of hidden data in a photo, not the only one.
IPTC, which describes itself as the global standards body of the news media, tests what photo-sharing sites keep. Its tests check for embedded EXIF metadata, and for IPTC metadata in the formats IIM and XMP. So removing EXIF alone can leave the IIM and XMP fields in place.
A camera can also leave a trace in the pixels themselves. In a 2006 paper, three researchers described a way to use the pattern of noise from a camera’s sensor as a unique fingerprint for that camera.
They tested it on about 320 images taken with nine consumer digital cameras. They also studied how its error rates change after common processing such as JPEG compression.
And what a picture shows travels with it, whatever happens to the metadata.
The site’s EXIF remover writes a new file from the pixels alone, so no embedded metadata comes with it. It cannot change what the picture shows.
11. “Photos you post online always keep their location data”
Doesn't hold up Whether a posted photo keeps its location depends on the service and on your settings.
The worry is reasonable. When location is on, Apple explains, the camera’s coordinates are embedded into each photo and video. The people you share them with may be able to access the location metadata.
What happens next depends on where the photo goes. Some services remove metadata from the copies they show. Others pass the original file along.
IPTC’s tests, published in 2019, show how differently services treat embedded metadata. They checked whether caption, creator, rights and other embedded fields survived, not location in particular.
Facebook’s saved copies had no XMP metadata, though a few rights-related fields were kept. Dropbox passed the original file through, and Flickr let people download the original. Services change how they handle files, so a 2019 test tells you what happened then, not what happens today.
Apple’s share sheet has a switch for this: tap Options, turn off Location, and Photos shows “Location Not Included”.
The guide Does converting an image remove its metadata? explains what a photo can carry.
12. “Compressing a PDF always lowers its quality”
Partly Compressors that shrink the pictures inside a PDF can lower its quality; ones that only rewrite the file’s structure do not.
The worry is fair for one kind of compressor, but not for the other. Some tools only rewrite a file’s structure: qpdf, an open-source PDF program and library, describes its work as structural changes that preserve a PDF’s content.
Other tools shrink the pictures inside. Ghostscript’s documentation warns that its PDFSETTINGS presets alter the input, and so may give a PDF of poorer quality. Its /screen preset selects low-resolution output.
So a compressor that resamples images to a lower resolution lowers their quality; one that only rewrites structure does not.
The site’s PDF compressor is the structural kind: its page says photos and scanned pages are “Not re-encoded, not reduced in resolution”.
Putting it to use
A few patterns run through all twelve.
- Loss happens on saving, not opening. Each lossy save is another round of compression, so fewer saves to JPEG means fewer rounds of loss. Keeping a lossless working copy while editing, and saving to JPEG once at the end, is one way to get there.
- Pixels decide size on screen; dpi is about paper. A dpi setting is a note about physical size; it does not change how many pixels a picture has.
- The right format depends on the content. Lossless suits text, line art and screenshots; lossy suits photographs, where the discarded detail is harder to see.
- Compatibility is about the receiver. HEIC, WebP and AVIF are well supported in some places and not in others. MDN still calls JPEG the most widely used lossy format for still images.
- Metadata travels unless something removes it. What a photo carries depends on the device’s settings and on every service it passes through.
How to use this
Most of these twelve come down to three questions worth asking before you convert, compress or share a file. Will this step save the picture again? Who, or what, will open it? And what is the file carrying besides the picture?
Sources
Formats and specifications
- W3C, Portable Network Graphics (PNG) Specification (Third Edition), W3C Recommendation, 24 June 2025.
- MDN Web Docs, “Image file type and format guide” , “Intrinsic size”, “EXIF” and “HTMLImageElement: naturalWidth”.
- Library of Congress, The Signal, “What People Are Asking About Personal Digital Archiving: Part 1”, June 2013.
- pngquant, project home page.
- JPEG committee, “JPEG 1 (ISO/IEC 10918)”.
HEIC, WebP and AVIF
- Apple Support, “Using HEIF or HEVC media on Apple devices”.
- Android Developers, “Supported media formats”.
- Microsoft Store, “HEIF Image Extension”.
- caniuse, “HEIF/HEIC image format” and “WebP image format”, read 5 October 2026.
- Daniel Aleksandersen, “Comparing AVIF vs WebP file sizes at the same DSSIM”, Ctrl Blog, 12 July 2020.
- Johannes Siipola, “What’s the best lossless image format? Comparing PNG, WebP, AVIF, and JPEG XL”, 27 July 2021.
- Microsoft Support, “Edit a PDF”.
- Apple, Preview User Guide, “Add, delete, or move PDF pages in Preview on Mac” and “Annotate a PDF in Preview on Mac”.
- qpdf documentation, “What is qpdf?”.
- Ghostscript documentation, “High Level Devices”, section on PDFSETTINGS.
Screenshots, metadata and location
- Apple Support, “Take a screenshot on Mac”.
- IPTC, “Social Media Sites Photo Metadata Test Results 2019”.
- J. Lukáš, J. Fridrich and M. Goljan, “Digital Camera Identification From Sensor Pattern Noise”, IEEE Transactions on Information Forensics and Security 1(2) (2006), doi:10.1109/TIFS.2006.873602.
- Apple, Personal Safety User Guide, “Manage location metadata in Photos”.
We read each specification and help page on 5 October 2026. For the 2006 camera-identification paper we read the abstract only. What each of this site’s tools does is taken from the tool’s own page on the same date.
Checked October 2026.
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