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PNG
What is a PNG file?
Lossless raster format with transparency. The safe choice for screenshots, logos and line art.
What PNG is
PNG is a binary format, meaningful only to a program that knows it. It stores a grid of pixels, so enlarging it past its own resolution softens it. It is used for screenshots, line art and logos and the web.
The extension is .png, and the full name is Portable Network Graphics. Both matter less than what the file can hold, which is what the rest of this page is about.
Where PNG came from
PNG Development Group published it in 1996. The specification is ISO/IEC 15948.
A format that has been readable for that long is a format worth trusting with something you want back in ten years.
The specification is public
Anyone can implement it without asking permission or paying a licence, which is why it turns up in so many programs and why files written twenty years ago still open.
Nothing is thrown away
PNG stores its content exactly. Saving it again changes nothing, so it can be opened, edited and re-saved as often as you like without accumulating damage — which is what makes it a working format rather than a delivery one.
It can be transparent
PNG carries an alpha channel, so a logo keeps its soft edges over whatever sits behind it instead of arriving in a white box.
Colour it can describe
Up to 16 bits per channel. It can work in RGB, greyscale and an indexed palette.
More than eight bits per channel is what stops a gradient from stepping when it is edited, which is why it matters in a working file and rarely in a finished one.
What it does to protect itself
PNG carries a checksum, so a damaged file is detected rather than silently mis-read.
A checksum will not repair anything. It tells you the file is wrong, which is the difference between finding out now and finding out from whoever you sent it to.
What opens PNG
Adobe Photoshop, GIMP and Paint.NET read it, and so do most programs of the same kind.
If a file will not open, the format is rarely the problem — it is more often that the program predates it. Converting to something older is the reliable way past that, and it is what the rest of this site is for.
Opening it in a browser
Every current browser reads it.
That makes it a safe thing to put on a page or attach to a message without wondering what the other end has installed.
What it can carry besides the content
PNG can hold EXIF, XMP and ICC profiles.
Whether any of it survives a conversion depends entirely on the target, and the honest answer is usually "some of it".
It is a delivery format
PNG is meant to be handed over rather than worked in. Editing one is possible and rarely pleasant; the sane approach is to change the source and export again.
What goes wrong with it
The recurring complaints: the files are large for what they contain.
None of these is a reason to avoid the format. They are the things worth knowing before you are surprised by one, which is a different claim and a more useful one.
The facts, in one place
| Extension | .png |
|---|---|
| Media type | image/png |
| Published by | PNG Development Group |
| First published | 1996 |
| Specification | ISO/IEC 15948 |
Converting PNG to something else
Converting something else to PNG
Formats worth considering instead of PNG
Where these figures come from
The claims on this page are checkable, and these are the documents that settle them.