What is the PNG format?

1What is a PNG file?

PNG stands for Portable Network Graphics. It was born in the mid-1990s as a free format to replace GIF, whose compression algorithm was subject to patents at the time. It quickly became the standard format for web graphics and today it is a W3C recommendation and an ISO/IEC standard.

Its main feature is that it keeps every pixel exactly as is: what you save is what you get back, with no degradation. It also supports high-quality transparency with soft edges, something GIF could only handle with all-or-nothing transparency.

2How does PNG's lossless compression work?

PNG first applies filters that predict each pixel's value from its neighbors and store only the difference. It then compresses the result with Deflate, the same algorithm used in ZIP files. When there are large areas of solid color or repeating patterns, as in an interface or a logo, the result is very small.

In a photograph, however, there are almost no identical areas and the natural noise makes it hard to compress, so a PNG can be several times bigger than a JPG that looks similar. That is the reason it isn't recommended for photos meant for the web.

3Transparency and color depth in PNG

PNG can store palette images with up to 256 colors, grayscale, or 24-bit true color, and optionally add an alpha channel that says how transparent each pixel is. It also supports 16 bits per channel, useful in professional work. Palette PNGs are smaller, although they can show banding in gradients.

The alpha channel lets you place a logo over any background with clean edges. If you convert it to JPG, the transparency disappears and is filled with a color, usually white or black. Keep that in mind before converting.

4PNG vs. JPG, WebP and GIF

Choose PNG for logos, icons, screenshots, diagrams and any image with text, sharp edges or a need for transparency. Choose JPG for photos when file size matters more than exact fidelity. WebP offers a lossless mode that is usually smaller than PNG, with transparency, and it works in current browsers. GIF is left for simple animations and, otherwise, PNG outperforms it.

A practical test: if you see smudges around the text when exporting to JPG, your image calls for PNG. If the PNG of a photo weighs several megabytes, it should probably be a JPG or WebP.

5Common PNG problems and how to fix them

The main one is file size, especially with high-resolution screenshots and photos. With “Compress image” you can reduce it; with “Resize image” you lower the pixel count; and reducing the number of colors can save quite a bit on simple graphics. Another common problem is a PNG with a transparent background that shows up with a black background in some viewers, which isn't an error in the file but in how the viewer displays the alpha channel.

If you need to send screenshots as a document, “Images to PDF” gathers them into a PDF, and if the destination requires JPG, convert it knowing you will lose the transparency.

6Practical tips and privacy

Save your master logo files as PNG or in a vector format such as SVG, and export lighter versions for the web. For screenshots with personal data, remember that hiding it with a semi-transparent box is not safe; use an opaque fill or “Pixelate” at a strong enough level. Screenshots can include names, emails or numbers you don't want to share.

All the image tools in Rayo PDF GO process your files on your device, without uploading them, which matters when screenshots contain account details, chats or documents.

One last practical detail: when you upload a PNG to a social network or a portal, the platform may recompress it to JPG and replace the transparency with a background. If the final result matters, export the right version yourself, with the background you want, and check it before posting.

7How to get the most out of PNG in Rayo PDF GO

A frequent use is gathering screenshots into a report: “Images to PDF” places them in order in a single document, which you can then compress or protect. If a PNG is too big for a portal, “Compress image” and “Resize image” slim it down, and “Crop image” removes extra margins.

In the other direction, “PDF to images” converts the pages of a PDF into PNG, which keeps text sharp and is useful for presentations or for publishing a page. If the PNG has personal data, “Pixelate” helps hide it before you share it.