Vector vs raster: what's the actual difference?

A raster image is a grid of pixels, each one a fixed color, so the file only knows what color each tiny square was at the moment it was captured or drawn. A vector image is a set of mathematical instructions (a curve from point A to point B, filled with this color) that gets redrawn from scratch at whatever size you display it. That single distinction explains everything else: a raster image has a fixed pixel count and degrades when you stretch it past that; a vector image has no pixel count at all and can be rendered at any size with perfectly crisp edges, because the math is just recalculated at the new scale. JPG, PNG, GIF, and WebP are raster formats. SVG, AI, and EPS are vector formats.

Every comparison page says vector scales infinitely and raster gets blurry, but the mechanism is simple once you see it: a raster file bakes in a fixed number of pixels at creation time, so enlarging it means inventing new pixels between the ones that already exist (interpolation), which is why edges soften and blur. A vector file bakes in no pixels at all, just equations, so displaying it at 10px or 10,000px wide runs the exact same math at a different scale and produces an equally sharp result either way. This is also why vector files tend to be tiny for simple art (a logo might be a few kilobytes of path data) while a raster photo at the same visual size can run into megabytes, since it has to store a value for every single pixel.

A photograph has continuous, irregular variation in color and light across millions of pixels, which is exactly what pixels are built to store and exactly what vector math is bad at representing. Turning a photo into vector shapes means tracing every subtle gradient and texture as a separate colored path, and pixeltools' own PNG to SVG converter shows how badly that scales in practice: a flat, simple two-shape logo traces cleanly to just 3 vector paths, and a busier 40-shape logo still traces to a reasonable roughly 500 paths. But synthetic photo-like noise, standing in for a real photograph, exploded to 9,471+ paths at the same tracing settings. That's not a minor inefficiency, it's a fundamentally different kind of content trying to fit a format built for something else.

Based on that measured blowup, pixeltools' PNG to SVG tool hardcodes 900 vector paths as its own internal threshold: cross it, and the tool flags the input as photo-like and being traced poorly, rather than being genuine flat-color art. That number sits comfortably above a busy but legitimate flat-art case (a detailed badge or mascot logo) while staying far below the thousands of paths a real photo produces, so it catches the failure mode without punishing complex-but-real vector candidates. It's a concrete, working example of the exact mechanism behind the rule of thumb every comparison page repeats without ever showing why it's true.

Vectorizing flat art is close to instant, but vectorizing photo-like detail can take upwards of 15 seconds of uninterrupted computation, since the tracer has to work through thousands of tiny color regions instead of a handful of flat shapes. That's slow enough that pixeltools deliberately runs the actual tracing work inside a Web Worker, a background thread separate from the page's main thread, specifically so the browser tab doesn't freeze while it works. If tracing ran on the main thread, a photo-like input would lock up scrolling, clicks, and even the tool's own progress indicator for the full 15+ seconds. That engineering detail is itself evidence of how much harder photo-like content is for vector tracing than flat art.

Tools like an AI image upscaler or a resize tool exist because raster images have a fixed pixel count that stops matching the size you actually need, so something has to add or recalculate pixels to fill the gap. A true vector file has no such problem: since it's redrawn from math at display time, asking to make an SVG bigger is just changing a number, not a computation that can succeed or fail. That's why pixeltools' upscale and resize tools are raster-only concepts. There's nothing for them to do to a vector file, because the thing they solve (a pixel grid that's the wrong size) doesn't exist in vector format in the first place.

Use vector for anything that needs to scale cleanly across sizes with a small number of distinct colors and shapes: logos, icons, line-art illustrations, typography, and print materials that go from a business card to a billboard. Use raster for anything with continuous tonal variation: photographs, textured digital paintings, and screenshots. If you're not sure which you're holding, open the file: if zooming in reveals square pixels, it's raster; if the edges stay sharp at any zoom level, it's vector. When you need to go from one to the other, converting raster to vector only works well on flat-color source art, and converting vector to raster (exporting an SVG as a PNG) is straightforward and lossless at whatever resolution you choose.