PNG vs JPG: which to use

Two ways of making a file smaller

An uncompressed full colour image stores three bytes for every pixel, so an A4 page at 2480 by 3508 pixels would be roughly 26 megabytes before any compression. Both formats shrink that, in opposite ways. PNG, which the W3C first released as a Recommendation in October 1996 and which later became ISO/IEC 15948, uses lossless compression: it finds repetition in the data, such as runs of the same colour, and stores it more efficiently, so the decoded image is identical to the original. JPEG, standardised as ISO/IEC 10918 and described by the JPEG committee as still the most dominant still image format, uses lossy compression based on a discrete cosine transform. It throws away fine variations the eye is least sensitive to, and the quality setting decides how much.

What each is good at

Lossless compression works brilliantly on images with large flat areas and hard edges, such as a flyer that is mostly type on a solid background, a logo, a chart or a screenshot. Those files stay crisp and often compress well. It works poorly on photographs, where almost every pixel differs slightly from its neighbour, so a photographic PNG can be several times larger than a good JPG that looks the same. Lossy compression is the reverse. It handles the gradual tones of a photograph efficiently, but around sharp edges, particularly dark text on a light background, it leaves faint ringing and small blocks, the artefacts people notice as a dirty look. MDN's image format guide sums it up: prefer PNG when precise reproduction or transparency is needed.

PNG and JPG for print

Most print shops prefer PDF, but many accept high resolution PNG and JPG uploads for single page jobs. For print, the pixel count matters far more than the format, so a file must have enough pixels for the finished size either way. A JPG saved at a high quality setting is effectively indistinguishable from the original for a photograph led flyer, while a text heavy design is safer as PNG. One practical difference catches people out: the PNG specification has no CMYK colour type, so a PNG is always RGB or greyscale, while JPG can carry CMYK. Shops that require CMYK files will convert an RGB PNG themselves or ask for a different file, so check before uploading.

Common mistakes

The most common is saving a flyer full of text as a low quality JPG to meet an upload limit, which softens every letter. The second is repeatedly opening, editing and resaving the same JPG, because each save recompresses the already compressed image and the artefacts build up; keep a lossless master and export a JPG last. The third is exporting photographs as PNG and then struggling with email attachment limits. The fourth is expecting a JPG to keep a transparent background, which it cannot; the transparent area turns white or black. The fifth is converting a JPG to PNG to improve it, which only preserves the damage already done at a larger size.

PNG and JPG from the flyer builder

The flyer builder exports PDF, PNG and JPG, and the two image formats behave differently from the PDF in two ways. They export only the page currently selected, not every page, and every file comes out at exactly twice the canvas size: an Instagram post at 2160 by 2160 pixels, a story at 2160 by 3840 and an A4 page at 2480 by 3508. JPG exports are written at quality 95, high enough that a photograph stays visually very close to the canvas at a fraction of the PNG size. All exports are RGB. The practical rule is PNG for pages that are mostly type, flat colour or a QR code, JPG for pages led by one large photograph, and PDF when a flyer has several pages that must stay together in order.

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