What is a vector image?

A vector image stores a picture as a set of mathematical instructions rather than a grid of coloured dots. Instead of recording millions of individual pixels, it records shapes: start at this point, curve to that one, fill the enclosed area with this colour. Because the shapes are described rather than sampled, the picture can be redrawn at any size and stays perfectly sharp.

That single property, scaling without loss, is why logos, icons, road signs, fonts and cutting patterns are all vector artwork, and why a printer will refuse the PNG you sent and ask for something else.

Vector and raster, side by side

Every image file is one or the other. Raster stores pixels; vector stores shapes. Nearly everything else follows from that difference.

	Vector	Raster
Stores	Shapes, points and curves	A fixed grid of coloured pixels
Enlarging it	Stays perfectly sharp at any size	Blurs or shows visible blocks
File size depends on	How many shapes there are	How many pixels there are
Editing	Move points, recolour individual shapes	Repaint pixels
Best for	Logos, icons, type, diagrams, line art	Photographs and anything with continuous tone
Common formats	SVG, AI, EPS, PDF	PNG, JPG, WebP, GIF, TIFF
Print and cutting	Accepted, and usually required	Often rejected

A concrete example

Picture a black circle, 100 pixels across, saved two ways.

As a raster file, it is 10,000 pixels, each storing a colour. The computer knows nothing about a circle; it only knows that certain squares are black. Blow it up to 1,000 pixels across and there is no extra information to draw with, so each original pixel becomes a visible ten-by-ten block.

As a vector file, it is one instruction: a circle, centred here, with this radius, filled black. Ask for it at 1,000 pixels and the software simply draws a bigger circle. Ask for it on a billboard and it draws a much bigger circle. The instruction never runs out of detail, because it never contained detail in the first place, only a description.

Which formats are vector?

SVG is the open standard, maintained by the W3C. It is plain text, opens in every browser, and is the usual choice for the web. You can read one in a text editor.
AI is Adobe Illustrator's own format. Excellent inside Adobe software, awkward outside it.
EPS is older, widely accepted in print, and still what many suppliers ask for by name.
PDF is the confusing one. A PDF can contain vector artwork, raster images, or both. A PDF exported from Illustrator is usually vector; a PDF made by scanning a page is raster inside a vector wrapper.

PNG, JPG, WebP, GIF, BMP and TIFF are all raster. PNG in particular gets mistaken for a vector format because it supports transparency and looks crisp, but it stores pixels like any other raster file.

How to tell what you actually have

Three checks, in order of speed.

Zoom in. Open the file in a browser and press Ctrl and plus, or Command and plus, until you are past 500 per cent. A vector stays crisp. A raster breaks into blocks.
Try to select one shape. Open it in Figma, Illustrator or Inkscape. In a vector you can click an individual shape and change its fill colour. In a raster there is one object and nothing to select inside it.
Read the file. If it is an SVG, open it in a text editor. Genuine vector artwork contains<path>, <circle> or <polygon> elements with coordinates.

That third check matters more than it sounds, because some online converters produce an SVG that simply contains your original bitmap embedded whole. It has the right extension and none of the benefits, and it is the usual reason a print shop rejects a file that you were told was a vector. There is a fuller walkthrough inis my SVG a real vector?

Why suppliers insist on vector artwork

Scale. The same file works on a business card and on the side of a building, with no separate versions and no quality decision to make.
Colour separation. Screen printing and spot-colour work need each colour as its own shape. In a raster image the colours are just adjacent pixels with no boundary a machine can act on.
Cut paths. Vinyl cutters, laser cutters, CNC routers and embroidery machines all follow a line. A vector supplies that line directly.
Editability. Changing one colour in a vector logo takes a click. In a raster it takes a designer.

Getting a vector when you only have a PNG

The information is not in the file, so it has to be reconstructed. That process is called tracing or vectorizing: software finds the boundaries between areas of colour and fits curves along them, producing genuine shapes.

How well it works depends entirely on the original. Logos, wordmarks, icons, signatures and line drawings trace well, because they are built from flat colour with clear edges. Photographs do not, because there are no flat areas to find, and the result is a posterised approximation of hundreds of shapes.

You can try it here without signing up for anything. Drop an image and the tool traces it in your browser, and the Paths overlay draws every outline and anchor point over the result so you can see the geometry rather than take it on trust. Converting uploads nothing.

A note on the word "vector"

The term is borrowed from mathematics, where a vector is a quantity with direction and magnitude, which is roughly what a line segment in a drawing is. It is unrelated to the other common uses of the word, such as a disease vector in medicine or an attack vector in security. In graphics it means only one thing: artwork described as shapes.

Common questions

What is a vector image in simple terms?

A picture stored as a set of instructions rather than a grid of dots. Instead of recording the colour of millions of individual pixels, a vector file records shapes: start at this point, curve to that one, fill the enclosed area with this colour. Because the shapes are described mathematically, the picture can be drawn at any size without ever losing sharpness.

What is the difference between a vector image and a raster image?

A raster image is a fixed grid of coloured pixels, so it has one true size and blurs when enlarged. A vector image is a set of shape instructions with no fixed size, so it is redrawn perfectly at whatever size you ask for. Photographs are raster; logos and icons are usually vector.

Which file formats are vector?

SVG, AI, EPS and, in most cases, PDF. SVG is the open standard used on the web. AI is Adobe Illustrator's own format. EPS is older and still common in print. PDF can hold either vector or raster content, or both, which is why a PDF is not automatically a vector file.

Is a PNG a vector image?

No. PNG is a raster format, as are JPG, GIF, WebP, BMP and TIFF. PNG supports transparency and lossless compression, which makes it a good raster format, but it still stores a fixed grid of pixels and still blurs when enlarged.

How can I tell whether a file I was given is a vector?

Open it and zoom in past 500 per cent. A vector stays perfectly crisp; a raster breaks into blocks. If the file is an SVG, you can also open it in a text editor: a real vector contains path elements with coordinates, while a fake one contains an image tag followed by a long block of encoded data.

Why do printers and sign makers insist on vector files?

Three reasons. The artwork can be scaled to any size, from a business card to a vehicle wrap, with no loss. Individual colours can be separated for screen printing or spot colours. And cutting machines need a path to follow, which a grid of pixels cannot provide.

Can a photograph be a vector image?

Not usefully. Vector formats describe areas of flat colour, and a photograph is continuous tone with no flat areas. Converting one produces a posterised approximation made of hundreds or thousands of shapes, usually larger than the original photo and much harder to edit.

How do I turn a raster image into a vector?

By tracing it, which means using software to detect the edges between colours and fit curves along them. The result is a genuine vector, though its quality depends entirely on how clean the edges in the original were. Logos and line art trace well; photographs do not.

Are vector files always smaller?

For simple artwork, usually much smaller, because a logo may only need a few hundred coordinates. For complex artwork with thousands of shapes a vector can be larger than the raster version. The size depends on how many shapes there are, not on the dimensions of the image.

What software opens vector files?

Adobe Illustrator, Inkscape (free), Affinity Designer, CorelDRAW, Figma and Sketch all open vector formats. SVG files additionally open in every web browser and in any text editor, since they are plain text.