Graphic design notes #3: Vectors

by Katya


A question I get asked a lot when requesting logo files is “what format do you want it in?” often followed by “is a jpeg OK?”.

I admit that jpeg files are very handy – compressed and easy to view for everybody – but what I really like is a vector file, an eps, with all its smooth lines and scaling potential.

The difference is mathematical. A vector is a description of a shape defined by geometrical primitives such as points, lines and curves. This makes it great for printing as it can be scaled up to any size without losing crispness. It also means that the file size is very low. Bitmaps however, including jpegs, are descriptions of a picture made up of coloured blocks, the number of blocks being determined by resolution, making it much less efficient and flexible.


Animation depicting the construction of a Bézier curve from six points. Sam Derbyshire

A vector can be rasterised into a bitmap file and saved at any resolution, which makes it the ideal ‘master’ logo file format. You can’t do the reverse – convert a vector file from a bitmap – unless you painstakingly redraw it or trace it in a program like Illustrator.

I generally answer the logo file format question with “an eps, please” but there is still potential for confusion. In this context an eps (Encapsulated PostScript) should be a file created in Illustrator containing vector graphics. But because it’s also technically possible to save a bitmap file, for example a jpeg, as an eps containing no vector information at all, that is quite often what I get.

A better option is to save a vector as a pdf (portable file format) that will ‘carry’ a vector file and yet still allow it to be editable as a vector file (while displaying it as a bitmap file on screen).

I’m still grateful to Dennis Crompton who took the trouble to explain this to me when I worked in the Architectural Association print studio. Looking back, I’m amazed that I hadn’t encountered this basic knowledge either as a student or later as a junior graphic designer.

I like vectors because they are clever and compact, they need more processing power to read but are tiny to store. A small shape or letterform can be made up of hundreds of Bézier curves containing complicated mathematical formulas that I couldn’t even begin to comprehend and yet the end result is simplicity itself.