PNG to JPG Converter — Convert PNG to JPEG Online

What this converter does, and the trade it makes

This tool re-encodes a PNG as a JPEG entirely inside your browser. It decodes the PNG to pixels, fills a canvas with your chosen background colour, draws the image on top, and saves the result through the browser's built-in JPEG encoder at the quality you pick. Nothing is uploaded and no server touches your file. The honest headline is that this is a lossy trade: PNG is lossless, JPEG is not, so the conversion throws away some detail to make the file smaller. For a photograph that trade is almost always worth it; for a screenshot of text or a sharp-edged logo it usually is not, and the section below explains why.

Two facts drive everything else. First, JPEG has no alpha channel, so any transparent pixel must be given a solid colour before it can be saved. Second, JPEG compresses in a way that suits smooth photographic tones and struggles with hard edges. Get those two ideas straight and the tool's behaviour, and its limits, stop being surprising.

Why transparency has to be flattened

A PNG can store a per-pixel alpha value from 0 to 255, where 0 is fully see-through, 128 is 50% opaque, and 255 is solid. JPEG stores only red, green, and blue, 8 bits each, no alpha at all, so the moment you convert, every transparent pixel needs a real colour. The tool solves this by flattening: it paints the whole canvas with a matte colour first, then composites the PNG over it, so a pixel at alpha 128 blends 50/50 with that background instead of turning black. We verified the order directly: a transparent-cornered PNG converted with a white matte reads pure white, 255, 255, 255, in the corner afterward, not the 0, 0, 0 you would get if the fill were skipped.

This is why the background choice matters. White is the safe default for artwork meant for a light page, but a logo designed to sit on a dark site will look wrong flattened onto white, ringed by a pale halo. For those, pick black or a custom colour that matches where the image will live. If you actually need the transparency kept, JPEG is the wrong target entirely; stay with PNG or use WebP, both of which carry an alpha channel.

How JPEG compression actually shrinks the file

JPEG's size win comes from a specific pipeline. It converts the image from red, green, blue into luminance and 2 colour-difference channels, then usually halves the resolution of the colour channels because the eye is far more sensitive to brightness than to hue. It splits the picture into blocks of 8×8 pixels, runs a Discrete Cosine Transform, or DCT, on each to turn 64 pixels into 64 frequency coefficients, and then quantises those coefficients against an 8×8 table, rounding away the high-frequency detail the eye barely registers. The quality slider is really a quantisation dial: at 100% almost nothing is discarded and the file stays large, while at 50% the quantiser is aggressive and the file shrinks 5 to 10×. The 85 to 92% band is the usual sweet spot, cutting size 70 to 90% while keeping artifacts below what most people notice.

That same block structure is why hard edges suffer. A crisp line between 2 flat colours is packed with high-frequency energy, exactly what quantisation throws out, so it comes back fringed with faint ripples called ringing, visible within roughly 8 pixels of the edge. On a photo you never see it; on a screenshot of black, 0, 0, 0, text on white, 255, 255, 255, you do.

When to convert, and when not to

Convert to JPEG when the source is photographic and does not need transparency: a camera photo saved as PNG, a rendered scene, a gradient-heavy background with thousands of distinct colours. These shrink dramatically, often to 10 or 20% of the PNG size, with no visible loss at a sensible quality. Keep PNG when the image is a logo, an icon, a screenshot of text, a diagram, or anything with sharp edges and few colours, because PNG's lossless compression already stores those under 8 colours efficiently and JPEG will both blur the edges and, on a small flat graphic, sometimes produce a file 2× larger than the PNG you started with.

That last point is the one most converters hide. A tiny, flat, few-colour PNG can be smaller than its JPEG version, because PNG's palette compression beats JPEG on that kind of content. This tool shows the original size, the JPEG size, and the percent change for every file, and flags in red any file that grew, so you see the real result instead of assuming the output is always smaller.

Quality settings and file size in practice

A rough map helps. At quality 92%, a typical photo lands around 10 to 20% of the PNG size with no visible loss, the right choice for archiving or print. At 85%, you save a bit more, roughly 8 to 15%, with artifacts still hard to spot, ideal for most web images. Drop to 70% for thumbnails or previews where small size beats fidelity, and 50 to 60% only when size is critical and the image is small on screen; below 50 the 8×8 blocks themselves start to show. Because the encoder runs locally on your own hardware, a batch of 10 to 20 files converts in 1 to 2 seconds without any of them leaving your device, and the size readout lets you compare quality levels by eye and by byte before you commit to a download.

The numbers behind the two formats

A few fixed figures explain most of the behaviour above. PNG shipped in 1996, became ISO 15948 in 2004, stores 8 bits per channel for 24-bit colour plus an 8-bit alpha for 32-bit RGBA, and compresses losslessly with DEFLATE. JPEG shipped in 1992, is ISO 10918, keeps only 8 bits each for red, green, blue with no alpha, and compresses lossily. The DCT works on 8×8 blocks, so 64 pixels become 64 coefficients, and the colour channels are usually subsampled 4:2:0, cutting chroma resolution to 1/4. Take a 1920×1080 image: that is 2.07 million pixels, roughly 6.2 MB uncompressed at 3 bytes each. As a 24-bit PNG it might be 2 to 4 MB; at quality-92 JPEG, often 200 to 400 KB, a 5 to 20× reduction. A 512×512 photo, 786 KB uncompressed, drops to about 40 to 80 KB at 85%. But a 64×64 flat icon of 4 colours can be 1 KB as PNG and 2 KB as JPEG, the exact inversion the red flag catches.

Every fact in one place

• Transparency: PNG stores alpha 0 to 255; JPEG has none, so see-through pixels are flattened onto a matte colour.
• Compression: PNG is lossless DEFLATE; JPEG is lossy, using 8×8 blocks, a DCT into 64 coefficients, and 4:2:0 chroma subsampling.
• Quality: the slider is a quantiser from 1 to 100; this tool defaults to 92% and a white matte.
• Matte: white, black, or a custom colour, for artwork meant to sit on a dark background.
• File size: photos typically shrink 80 to 90%; flat graphics may shrink little or grow, which the red flag will tell you.
• Size readout: original size, JPG size, and percent change are shown per file, plus a batch total.
• Keep transparency: if you need it, stay with PNG or use WebP; JPEG cannot carry it.
• Privacy: 100% in-browser; no upload, no server.