Image Format Converter

What Is an Image Format Converter?

An image format converter changes the container and encoding of a picture file — the same pixels expressed in a different structure. JPG stores them with lossy compression, PNG uses lossless compression with optional transparency, WebP applies a more efficient codec that beats both, and BMP keeps every pixel uncompressed. The visual content of the image remains the same; only how the data is packaged changes.

Every conversion here uses your browser's built-in Canvas API — the same engine that powers online image editing and game graphics. Your files are drawn to an off-screen canvas and re-encoded on the fly. Nothing is sent to a server, and nothing persists after you close the tab.

JPG vs PNG vs WebP vs BMP — When to Use Which

Choosing the right format often means cutting file size significantly without any perceptible quality difference. Here's a practical guide:

Real-World Use Cases

Converting to WebP for Faster Websites

Google's PageSpeed Insights and Lighthouse audits routinely flag JPG and PNG assets as opportunities to "Serve images in next-gen formats." A product photo saved as a 240 KB JPG can shrink to 150 KB as a WebP at equivalent visual quality — a 37% reduction. Multiply that by a page with 15 product images and you've saved over 1.3 MB per page load. That directly improves Largest Contentful Paint (LCP), a Core Web Vital that affects Google search ranking.

The workflow is simple: export your originals from Photoshop or Figma as high-quality JPGs, convert them here at quality 80–85%, then serve the WebP versions with a JPG fallback via the HTML <picture> element. All modern browsers (Chrome, Firefox, Safari 14+, Edge) support WebP natively.

PNG to JPG for Email and Social Media

Screenshot tools often save as PNG by default — lossless, but unnecessarily large for sharing. A full-screen screenshot at 2× retina resolution can be 4–6 MB as PNG, but only 400–800 KB as JPG at quality 85%. This matters for email attachments (many clients warn or block attachments over 5 MB), Slack file previews, and social media uploads where platforms re-compress anyway.

Note that if your PNG contains transparent areas — a logo on a transparent background, for instance — those transparent pixels will be filled with white when converting to JPG, since JPEG has no alpha channel. If you need the transparent background preserved, convert to WebP or keep it as PNG.

Converting Old BMP Files

Windows Paint, legacy medical imaging software, and certain industrial control systems save images as BMP — an uncompressed format from the early 1990s. A 1024×768 BMP can be 2.3 MB, while the same image as PNG is around 300 KB and as JPG around 80 KB. Converting old BMP archives to PNG or JPG makes them practical to share and store. For scanned documents with text and sharp edges, PNG preserves the crispness better than JPG; for photographs with gradients and color, JPG at quality 85+ is usually indistinguishable from the original BMP.

Choosing a Quality Setting for JPG and WebP

The quality slider controls the trade-off between file size and visual fidelity. Here's what each range means in practice:

• 90–100%: Near-lossless. Barely smaller than the original. Good for archival copies where quality must be preserved, or for source files you'll edit again later.
• 75–89%: The sweet spot for most web use. The human eye cannot reliably distinguish from 100% quality at normal viewing distances. Recommended for product photos, blog imagery, and profile pictures.
• 60–74%: Visibly smaller files. Slight compression artifacts may appear in areas of fine detail or sharp color transitions. Acceptable for thumbnails, low-resolution previews, or images displayed at very small sizes.
• Below 60%: Noticeable blocky artifacts. Useful only for very rough previews or when bandwidth is severely constrained. Most professional uses avoid this range.

PNG and BMP do not have a quality slider because they are lossless formats — every pixel is stored exactly as-is regardless of file size. The quality setting only affects JPG and WebP output.

Transparency and What Happens to It

Transparency (the alpha channel) is one of the most important format-specific behaviors to understand. Here's what happens in each conversion direction:

• PNG with transparency → WebP: Transparency is preserved. WebP supports alpha channels and this conversion is completely lossless for the transparent areas.
• PNG with transparency → JPG: Transparent areas are filled with white (the Canvas API default for JPEG output). If you need a different background color, consider using a dedicated image editor before converting.
• PNG with transparency → BMP: Transparent areas become white. BMP does not support alpha channels in its most common 24-bit variant.
• JPG → PNG: The resulting PNG has no transparency. It will be a visually identical image to the JPG but encoded losslessly. The file size will typically be larger than the original JPG.

If you're working with brand logos, UI components, or any image that requires a transparent background, always use PNG or WebP as your output format.

How to Serve WebP with a JPG Fallback

Because WebP is not supported by every email client or older browser, the safest deployment strategy is to provide a WebP version for browsers that support it and a JPG fallback for those that do not. The HTML <picture> element makes this straightforward:

<picture>
  <source srcset="hero.webp" type="image/webp">
  <img src="hero.jpg" alt="Hero image" loading="lazy" width="1200" height="630">
</picture>

The browser reads the <source> elements in order and uses the first one it supports. A WebP-capable browser picks the first source; a browser without WebP support falls through to the <img> tag. The loading="lazy" attribute defers loading until the image enters the viewport, which is an additional performance improvement.

In Next.js, the built-in <Image> component handles this automatically — it serves WebP to supporting browsers and falls back to the original format, with no additional markup needed. In plain HTML projects, the <picture> pattern above is the recommended approach.

File Size Expectations: What to Expect After Conversion

Conversion outcomes vary significantly depending on the source image content and the target format. Here's a practical guide to the typical size changes you can expect:

JPG → WebP (quality 80%): Expect 25–40% smaller output. A 500 KB product photo JPG typically becomes 300–375 KB as WebP at equivalent perceived quality. The gain is most pronounced on photos with gradients, skin tones, and complex textures.

PNG → JPG (quality 85%): Size reduction depends heavily on image content. A screenshot-style PNG with mostly flat colors may only shrink 10–20% because PNG's lossless compression already handles flat colors efficiently. A photographic PNG may shrink 50–70% when converted to JPG.

JPG → PNG: The PNG will almost always be larger than the original JPG, sometimes dramatically so. A 200 KB JPG photograph can become a 1–3 MB PNG because the lossless encoder has to faithfully represent every pixel, including the compression noise that JPEG introduced. Converting to PNG does not "restore" image quality — it just stops adding new compression artifacts.

BMP → any format: BMP files are dramatically oversized compared to every modern format. A 2 MB BMP photograph typically converts to 80–200 KB as JPG or 150–400 KB as PNG. Converting BMP archives to PNG or WebP is one of the highest-ROI compression wins available.

Common Mistakes to Avoid

A few pitfalls trip up even experienced users:

Re-converting a JPG to JPG: Every time you save a JPG, lossy compression runs again and introduces more artifacts on top of the ones already there. If you need to edit a JPG repeatedly, keep an original high-quality copy and always export from that, not from the previously compressed version.

Expecting JPG→PNG to improve quality: Converting a compressed JPG to PNG does not recover the detail that JPEG discarded. The PNG will be losslessly exact — it stores the JPG's already-compressed pixels without further loss, but the original detail is gone. PNG is not a way to "undegrade" a JPG.

Using low quality settings for source files: If you're converting images you plan to use as sources for further editing or re-conversion, set quality to 90% or higher. Low-quality settings bake in artifacts that compound with every subsequent conversion.

Forgetting browser support: WebP is supported by every modern browser as of 2020, but some internal tools, email clients, and legacy systems still expect JPG or PNG. Always verify that your target platform supports the format before deploying WebP images in a production environment.

Converting instead of resizing: Format conversion changes how pixels are encoded but does not change the number of pixels. A 4000×3000 image converted from JPG to WebP is still 12 megapixels. If you also need to reduce the image dimensions for a specific display size, resize the image first (using the Image Resizer), then convert the format. Resizing first reduces the number of pixels that need to be encoded, compounding the file size savings from format conversion.

Frequently Asked Questions