Image Converter Tools

Understanding Image Formats: Lossy vs. Lossless Compression

When converting and optimizing images for websites, digital media, or archiving, choosing the right file extension and compression level decides both file size and what the image survives. Formats fall into two categories:

How Modern Browsers Handle Offline Image Encoding

DuckConvert bypasses backend servers entirely by compiling native compression libraries (like Rust-based OxiPNG or C-based libwebp) into WebAssembly (WASM). This allows your browser to run heavy graphic processing algorithms at near-native speeds. For basic formats, we use the HTML5 Canvas 2D API to render, scale, crop, and output high-quality image blobs dynamically.

Turning a vector into pixels: what decides the output size

Converting an SVG is unlike every other conversion here, because an SVG has no pixels to begin with. It is a set of drawing instructions with no inherent resolution, so something has to decide how large the resulting bitmap should be — and the answer is not a setting you choose.

The SVG is handed to the browser’s own renderer, drawn once onto a canvas, and read back out. The canvas takes its dimensions from the image’s intrinsic size, which comes from the width and height attributes on the <svg> element itself.

That has a consequence worth knowing before you are surprised by it. Many SVGs exported for the web carry only a viewBox and no explicit width or height, precisely so they scale to whatever container they are dropped into. Such a file has no intrinsic size to read, and the browser substitutes a default — so a logo that looks razor sharp on a page because it is being drawn at 600 pixels wide can rasterise to something much smaller, and enlarging that result afterwards will look soft.

The fix is in the source file rather than the converter: add width and height attributes at the size you actually want, keeping the viewBox intact so the proportions stay correct, and convert again. It is a one-line edit in any text editor, and it is the difference between a crisp export and a blurry one.

Transparency survives, if the destination can hold it. An SVG with nothing behind the artwork converts to PNG or WebP with that area still empty, so the result drops onto a coloured page without a white box around it. JPEG has no alpha channel at all, so choosing it flattens the transparent area onto white — not a defect, just the format. If you want the background gone, PNG and WebP are the two that keep it.

This is also why the conversion only runs one way. Every other pair on this page is one grid of pixels re-encoded as another, and is reversible in the sense that you can convert back and get a comparable image. Rasterising a vector is a one-way step: nothing recovers the shapes from the pixels afterwards, so keep the SVG.