Raster vs Vector Images: When to Use Each Type
Every digital image falls into one of two categories: raster or vector. Raster images (JPG, PNG, WebP, BMP, TIFF) store a fixed grid of colored pixels. Vector images (SVG, AI, EPS) store mathematical descriptions of shapes and paths. This fundamental difference determines how each type scales, what content it handles best, and where it should be used.
Understanding the distinction is not just academic. Choosing the wrong type leads to blurry logos on retina displays, massive file sizes for simple icons, or impractical file formats for photographs.
Raster vs Vector: Core Differences
| Characteristic | Raster | Vector |
|---|---|---|
| What it stores | Pixel color values | Math shapes and paths |
| Scaling up | Blurry/pixelated | Perfect at any size |
| Scaling down | Smooth (anti-aliased) | Perfect at any size |
| Photo content | Natural fit | Impractical |
| Geometric graphics | Works but fixed resolution | Natural fit, resolution-free |
| File size (complex photo) | Moderate (efficient codecs) | Enormous (millions of paths) |
| File size (simple icon) | Large relative to content | Tiny (a few bytes to KB) |
| Editing approach | Pixel-by-pixel manipulation | Shape/path manipulation |
| Common formats | JPG, PNG, WebP, AVIF, TIFF, BMP | SVG, AI, EPS, PDF |
| Color complexity | Millions of unique values | Defined fills and strokes |
How Raster Images Work
A raster image is a grid of pixels, each with a specific color value. A 1920x1080 image contains 2,073,600 pixels. The image has a fixed resolution: displaying it at a larger size means stretching pixels, which produces blur or visible pixel squares.
Raster formats use various compression techniques to reduce file size. JPG uses lossy compression tuned for photographs. PNG uses lossless compression ideal for graphics. WebP and AVIF use modern codecs that outperform both. But all of them fundamentally store pixel data.
How Vector Images Work
A vector image stores shapes as mathematical equations. A circle is defined by a center point and radius. A rectangle by its corner coordinates. A curve by Bezier control points. The rendering software calculates the final pixels at whatever size and resolution is needed.
This means vector images have no fixed resolution. The same SVG file renders as a crisp 16x16 favicon, a sharp 300x300 sidebar icon, and a perfect 3000x3000 hero graphic. The math is simply recalculated at each target size.
The Content Test
The easiest way to decide between raster and vector is to ask: was this image created by a camera, or was it designed by a human?
Camera images (photographs, scans, screenshots) are inherently raster. They capture millions of unique pixel values that cannot be efficiently described as mathematical shapes. A photograph of a forest would require millions of vector paths to approximate, producing a file orders of magnitude larger than the raster original.
Designed images (logos, icons, diagrams, charts, illustrations with clean lines) are often created as vectors and converted to raster for delivery. These images have defined geometric shapes, limited color palettes, and clean edges that vector format handles naturally.
The Retina Display Challenge
Modern displays (retina, 4K, 5K) render at 2x, 3x, or even 4x the traditional pixel density. A raster icon designed at 48x48 pixels looks blurry on a 2x retina display because the icon's 48 pixels are stretched to fill 96 physical pixels.
The raster solution is to provide multiple sizes: 48x48 for 1x, 96x96 for 2x, 144x144 for 3x. This means maintaining three versions of every icon. The vector solution is to use SVG: one file that renders perfectly at every pixel density. This is why modern web design has shifted heavily toward SVG for icons and logos.
Hybrid Approaches
Modern web design often combines both types. SVG handles navigation icons, logos, and decorative elements. Raster formats (WebP, JPG) handle content images, hero photographs, and user-uploaded content. This combination minimizes total page weight while maximizing visual quality.
Some tools also allow embedding raster images within SVG files. An SVG infographic might have vector text and borders with an embedded raster photograph. This hybrid approach provides vector scaling for the geometric elements while keeping photographic content in its natural raster format.
Converting Between Types
Raster to vector (tracing) is imprecise. Software like Adobe Illustrator's Image Trace can approximate raster images as vector paths, but the result is always an approximation. Simple graphics with clean edges trace well. Photographs trace poorly, producing artistic but inaccurate interpretations.
Vector to raster (rasterization) is exact. You choose the target resolution and the software renders the vector shapes as pixels at that resolution. This is a common operation: SVG logos rasterized to PNG for platforms that require raster images, or SVG icons rasterized for email clients that do not support SVG.
Frequently Asked Questions
Can I convert a photo to SVG?
You can trace a photo to create an SVG approximation, but the result is an artistic interpretation, not a faithful reproduction. The SVG will be very large and will not match the original photograph. For photos, raster formats (JPG, WebP, AVIF) are the correct choice.
Is SVG always better than PNG for logos?
For web use, SVG is almost always better for logos: smaller files, infinite scaling, and CSS styling. PNG is preferred when you need a raster version for specific platforms (email clients, social media profile images) or when the logo includes photographic elements or complex effects that SVG handles poorly.
What about PDF? Is it raster or vector?
PDF is a container format that can hold both raster and vector content. A PDF exported from Illustrator contains vector data. A PDF created by scanning a document contains raster data. Many PDFs contain a mix of both: vector text and shapes with embedded raster photographs.