JPG vs JPEG vs PNG: Differences and Which Format to Use

JPEG is the name of a committee, not a file. The Joint Photographic Experts Group, working under ISO and the ITU, published its compression standard in 1992 as ISO/IEC 10918-1, also known as ITU-T T.81. The standard describes how to squeeze a photograph into fewer bytes; it never said what the file should be called. The obvious extension was .jpeg, and that is what Unix systems and early Macs used. The group still runs jpeg.org and now maintains newer formats such as JPEG 2000 and JPEG XL alongside the original.

Windows went another way because of MS-DOS. DOS file names followed the 8.3 rule: up to eight characters, a dot, and at most three characters of extension. A four-letter .jpeg simply could not exist on a FAT disk of that era, so Windows programs saved .jpg instead. Windows 95 lifted the limit with long file names, but by then .jpg was the habit of camera makers, scanner drivers and websites. The camera file system rule that digital cameras follow still writes names like DSC_0001.JPG, so most photos in the world carry the three-letter version.

Inside the file nothing differs. A .jpg and a .jpeg open in the same programs, use the same registered media type, image/jpeg, and contain identical bytes if you rename one into the other. The rarer .jpe and .jfif endings are the same format again. The spelling only matters when software checks the extension text instead of the contents, such as an upload form whose allow-list says jpg, png and nothing else. In that case rename the file or run it through JPEG to JPG, which re-saves it at quality 95 with the extension the form expects.

JPEG is lossy by design. The encoder converts the image from RGB into one brightness channel and two color channels, and usually stores the color channels at half resolution, because the eye is far less sensitive to color detail than to brightness. It then cuts the picture into 8 × 8 pixel blocks, describes each block as a sum of smooth wave patterns, and rounds away the fine patterns that matter least. The quality number in an export dialog controls how hard that rounding is. At 85 a photo looks unchanged on a screen; at 50 the savings continue, but the rounding starts to show.

PNG is lossless. It stores every pixel exactly and compresses with DEFLATE, the same algorithm used inside ZIP files, after a filter step that predicts each pixel from its neighbors. Compression works by finding repetition. A screenshot with a flat white background, a chart with five colors or a logo with crisp edges is full of repetition and packs into a small file. A photograph is not: sensor noise, grain and soft gradients mean almost no two neighboring pixels match, so a PNG of a photo stays several times larger than a JPEG of the same picture. The specification is published by the W3C.

This difference explains the artifacts you have seen. JPEG damage appears as blocky squares in smooth skies, color smearing along saturated red edges, and faint ripples, called ringing, around sharp text and lines. Saving a JPEG again after editing repeats the rounding and adds a little more damage each time, which is known as generation loss. PNG never adds artifacts of its own, but it cannot remove ones that are already there: a JPEG converted to PNG keeps every block and ripple, just stored perfectly. The JPG to PNG converter is for freezing a picture before editing, not for repairing it.

PNG can carry an alpha channel, a fourth value for every pixel that says how opaque it is, from 0 (invisible) to 255 (solid). That makes soft shadows, anti-aliased curves and cut-out product photos look right on any background, which is why logos, icons, stickers, overlays and interface graphics are usually PNG. PNG can also store a palette of up to 256 colors with transparency, often called PNG-8, which keeps simple icons especially small. JPEG has no alpha channel at all: every pixel in a JPEG is fully solid, and the format has no way to mark any area as see-through.

So when a PNG with transparency becomes a JPG, something has to fill the empty areas. Many programs pick white, some pick black, and a careless converter can leave odd dark fringes where semi-transparent edges were. If you need a JPG, choose the fill on purpose: convert PNG to JPG with Transparent areas set to white, black or a Custom colour that matches the page or slide where the image will appear. The reverse never works by conversion alone. A white background in a JPG stays white in the PNG; removing it is an editing job, done by selecting the background and deleting it.

File size is where the two formats separate most clearly, and the direction depends on the content. For photographs, JPEG at quality 80 to 90 is typically five to ten times smaller than PNG at the same pixel dimensions, with no difference you can see on a phone or laptop screen. For flat graphics the order can flip: a logo, chart or text screenshot often makes a smaller PNG than JPG, and the PNG stays perfectly sharp while the JPG grows ringing around every letter. The figures below are typical ranges, not measurements of one file; noise, detail and color count move them up or down.

Size matters more than it seems. Gmail caps attachments at 25 MB per message and Outlook.com at 20 MB, so five PNG photos from a phone can fail where five JPGs pass easily. Many government and exam portals limit uploads to a few hundred kilobytes or less. Web pages load every byte over mobile data, and oversized PNG photos are a common reason a page feels slow. When a JPG is still too big for a portal, lowering quality step by step usually gets there with less visible change than shrinking the dimensions; the guide to reducing image size in KB walks through both approaches.

Decide by content, not by habit. If the image is a photograph or looks like one, with continuous tones and soft gradients, JPG wins on size with no visible cost. If it contains sharp text, flat color, thin lines or areas that must be transparent, PNG keeps it clean, and often smaller too. Mixed images, such as a photo with a caption printed across it, lean toward JPG at a higher quality of 90 or above, unless the text is small enough that ringing would hurt readability. A screenshot of a photo is still a photo for this purpose.

Also think about what happens to the file next. An image you will edit several more times is safer as PNG, because each JPG save adds loss. An image going to a form, a marketplace listing or a print lab is usually best as a high-quality JPG. For your own website, both are now often beaten by newer formats: WebP and AVIF give photos smaller files than JPG and still support transparency, and every current browser displays them. The comparison of AVIF, HEIC and WebP covers when those are worth adopting and when compatibility still favors JPG.

JPG is the format almost every upload form accepts. Passport and visa systems, exam and job portals, insurance claims, school applications and marketplace listings usually list JPG or JPEG first, often with a kilobyte cap and fixed pixel dimensions. The U.S. Department of State's online passport renewal, for example, asks for the photo as a JPEG file. PNG support on such forms is common but far from universal, and WebP, HEIC and AVIF are often refused outright. If a form lists only JPG, a PNG photo or screenshot has to be converted, not renamed, because many portals check the actual file contents.

Some places want PNG instead. App Store Connect expects a 1024 × 1024 px PNG app icon, Google Play asks for a 512 × 512 px PNG icon, and print-on-demand shops that put designs on shirts and mugs typically want PNG with a transparent background so the fabric color shows through. Favicon generators, sticker apps and presentation templates often prefer PNG for the same reason. In these cases a JPG is either rejected or looks wrong, with a white box drawn around the design where the background should have disappeared.

Printers sit in the middle. Consumer photo labs and drugstore kiosks accept JPG everywhere and PNG at many but not all counters, and a JPG saved at quality 90 or higher prints identically to a PNG at normal sizes. What matters more for print is resolution, around 300 pixels per inch at the final size, and color. Commercial printers work in CMYK, which JPEG can store and PNG cannot, so offset print shops usually ask for PDF, TIFF or high-quality JPG rather than PNG. When in doubt, send the printer a JPG at quality 95.

Converting is a one-way trade, so do it in the right direction and keep the original. PNG to JPG is the common move for forms and email: transparency is filled with a solid color, file size usually drops sharply for photos, and fine edges soften a little. JPG to PNG is the move before editing or when a rule demands PNG: nothing improves and the file gets bigger, but no further loss is added. JPEG to JPG changes nothing about the image at all; it fixes the extension for software that is picky about spelling.

All three run in a browser. On UltKit you drop up to 20 files, each up to 95 MB, pick the target format and press Convert to JPG or Convert to PNG; nothing is installed, no account is needed, and files are deleted 30 minutes after processing. On your own computer, Paint on Windows and Preview on a Mac can save one image at a time as JPEG or PNG, though neither gives much control over the background color that replaces transparency. Phones generally need an app or a website for either direction.

A few settings decide the result. For photos going to JPG, a Quality between 80 and 90 balances size and look; use 95 for prints or images with text. Tick Strip metadata only when privacy or size matters, since the date taken and camera model can be useful later. If the output still exceeds a portal limit, compress after converting rather than guessing a low quality during it, so you can see the file size you actually reach. A size-focused tool such as compress image lowers quality until the file fits.