How to Convert Between JPG and PNG: When to Use Which

JPG and PNG are the two most common image formats on the web. They look the same to most people, but they work very differently under the hood, and using the wrong one can mean unnecessarily large files, unexpected quality loss, missing transparency, or print jobs that come out the wrong colour. Knowing when to convert in each direction (and when to reach past both for WebP or AVIF) turns a routine task into a small but consequential decision.

A short history of JPG and PNG

JPEG (Joint Photographic Experts Group) was standardised in 1992 and became the dominant photo format almost overnight, the bandwidth savings over uncompressed bitmaps were enormous, and the patent landscape was favourable enough for browsers to embrace it. PNG (Portable Network Graphics) arrived in 1996 specifically as a free, lossless, web-friendly replacement for GIF, which at the time was encumbered by Unisys's LZW patent. PNG added 24-bit colour, alpha transparency, gamma correction, and a streaming-friendly chunked structure. GIF's patent eventually expired in 2004, but by then PNG had already won the lossless niche.

Two decades later, WebP (Google, 2010) and AVIF (Alliance for Open Media, 2019) appeared as universal replacements that handled both lossy and lossless cases in smaller files. Browser support reached over 97% for WebP and over 92% for AVIF by 2024, so most modern teams default to those for new content. JPG and PNG remain ubiquitous because billions of existing assets, third-party APIs, and email clients still treat them as the lowest common denominator.

The key difference

JPG (JPEG) uses lossy compression. It makes files small by discarding image data that your eye is unlikely to notice: high-frequency detail, subtle colour gradients in saturated areas, and information in regions the human visual system pays less attention to. Great for photos, bad for sharp graphics.

PNG uses lossless compression. It preserves every single pixel exactly using DEFLATE (the same algorithm as ZIP), so files are larger but pixel-perfect. Great for screenshots, logos, and anything with text, sharp edges, or transparency.

The mismatch is the source of most format-choice mistakes: a 4 MB JPEG of a wireframe diagram, an 8 MB PNG of a holiday photo, and the resulting page that loads in twenty seconds when it should load in two.

When to convert JPG to PNG

• **You need transparency, JPG does not support transparent backgrounds. If you need to place an image on a coloured or textured background without a visible white box, convert to PNG.
• **You are editing the image repeatedly, each time you save a JPG, it recompresses and loses a tiny bit more quality. Convert to PNG first, edit as many times as you need, then save back to JPG only when you are finished.
• **The image has text or sharp lines, JPG compression creates visible artefacts around sharp edges (the famous "ringing" halos). PNG keeps text crisp and lines clean.
• **You are layering it in a design tool, Figma, Sketch, and PowerPoint render PNGs more cleanly than JPGs when composited over backgrounds.
• **You need a screenshot for documentation, screenshots always look better as PNG; the UI elements have sharp edges that JPEG mangles.
• **The image is a graph, diagram, or QR code, anything with large flat-colour regions and hard borders is what PNG was designed for.

When to convert PNG to JPG

• **Photos and realistic images, a PNG photo can be 3-5x larger than the same image as a high-quality JPG, with no visible difference to the eye.
• **You need to reduce file size, sending photos via email or uploading to a website is much faster with JPG. A 6 MB PNG often becomes a 600 KB JPG with no perceptible loss.
• **The image does not need transparency, if it will always be on a white or solid background, JPG is smaller and perfectly fine.
• **You are sending to a printer, many print services still expect JPG for photographic content; PNG is fine but not always recommended.
• **You are uploading to a platform with a size cap, profile pictures on most platforms compress to JPG anyway, so converting first lets you control the quality.

How to convert

JPG to PNG:

1. Upload your JPG files, drag and drop or click to browse. The converter accepts JPEG, JPG, and JPE extensions.
2. Click "Convert to PNG" to process. Conversion runs in the browser; nothing is uploaded.
3. Download your lossless PNG images. The resulting files are larger but contain every pixel from the source.

PNG to JPG:

1. Upload your PNG files.
2. Adjust the quality slider if needed (higher quality = larger file). 85-92 is the sweet spot for most photos.
3. Choose how to handle transparency (transparent pixels become white, black, or a colour you pick).
4. Download your compressed JPG images.

The whole flow runs client-side: the file is read with FileReader, decoded by the browser, drawn onto a canvas, and re-encoded via canvas.toBlob. Even sensitive screenshots stay on your machine.

Quick reference

Format comparison with the modern alternatives

JPG and PNG are not the only options. Two newer formats handle most of the same cases with smaller files.

If your audience is on modern browsers, exporting once to AVIF and once to WebP (with JPG/PNG as fallback) is the current best practice for web images.

Common pitfalls

• **Converting JPG to PNG to "improve quality", if quality was already lost during JPEG compression, converting to PNG will not bring it back. It just makes the file larger and looks the same.
• **Saving photos as PNG by default, a 12 MP photo as PNG can hit 20 MB; the same image at JPEG quality 88 is under 2 MB and visually identical.
• **Ignoring transparency when converting to JPG, transparent pixels become a solid colour (usually white). For logos with transparent backgrounds, keep them as PNG or WebP.
• **Re-encoding JPGs repeatedly, each save adds compression artefacts. Edit in a lossless format (PNG, TIFF) and export to JPG only at the end.
• **Forgetting EXIF data, JPEGs from cameras carry EXIF with GPS, device model, and timestamp. PNG converters may or may not strip this. If privacy matters, verify with a sample image after conversion.
• **Wrong colour profile, dropping an Adobe RGB JPEG to sRGB PNG without conversion can shift colours visibly. Most browser converters assume sRGB; for wide-gamut sources, convert in a photo editor first.
• **CMYK JPEGs misinterpreted, CMYK is used in print workflows. Browsers (and most web converters) expect RGB; a CMYK JPEG can come out greyscale or with reversed colours. Use a desktop tool for print assets.
• **PNG with alpha on a JPEG-only site, social-media platforms that recompress to JPG will fill transparent pixels with whatever they choose, often black on dark themes.
• **Comparing formats by looking at the header byte, a .jpg file with a PNG signature in the first 8 bytes is a misnamed PNG, the extension does not reflect the content. Use a hex dump or file command to confirm.
• **Forgetting that PNG quality is binary, PNG has no quality slider. You cannot "save a PNG at 80%". The only knobs are bit depth, palette size (PNG-8 vs PNG-24), and pre-filter choice.

Alternative tools and libraries

A web converter is the fastest path for one or a few images. For batches or scripted work, command-line tools and libraries take over.

For automating product photo pipelines, sharp or vips are usually the right tools. For a quick one-off conversion, the browser tool wins on convenience and privacy.

Privacy and the converter

The JPG and PNG converters run entirely in your browser. The file you select is read with the FileReader API, decoded by the browser's image pipeline, drawn onto an offscreen canvas, and re-encoded via canvas.toBlob. Nothing is uploaded, nothing is logged, and nothing is shared. For sensitive material, screenshots of internal dashboards, ID scans, draft contracts as image proofs, that local-only flow is the difference between trusting a stranger's server and trusting no one. Even ordinary photos often carry EXIF metadata (GPS coordinates, device serial number, timestamp) that you may not want a third party to see; the Canvas-based pipeline strips most EXIF by default, and the lack of upload means it never leaves the page either way. For a task as routine as converting between two formats, the privacy default should be: nothing leaves the page, nothing is stored, nothing is shared.