As both a professional printer of laser and inkjet labels and a full-service graphic design firm, we often are asked to enlarge images so that the client can use them elsewhere. Usually, we receive business logos and photographs. Unfortunately, many times, enlargement of the image is not possible because doing so would only result in a poorer quality image.
Explaining the reason why a photo cannot be enlarged can sometimes get complicated because of the terms being used. However, when you know what these terms mean, things become much clearer.
A vector image uses lines, shapes and curves when creating an image. This structure makes it easy for a computer to enlarge the vector image, because there are far fewer points in a vector image to be connected by the computer than there are in a raster image, which can contain thousands of pixels. The computer also stores colour information according to the points in the image. This means that should the image increase in scale, the computer knows where in the image to place certain colours and doesn’t guess like it is forced to with a raster image.
The file size of a vector image is typically far smaller than its raster counterpart because there is simply less information stored within the image. The same is true of colour; the vector image needs only to store points and colour information, which allows it to be more scalable but smaller in size.
In fact, a vector image is infinitely scalable. So even if you make a vector image incredibly small or incredibly large, it will never lose any of its quality. It is for this reason that many logos are stored in vector format; they can be scaled to any size for all manner of digital or printed media, from stamp to billboard, while retaining their quality.
Flexibility in Editing
The vector image also allows for editing, regardless of where you may be in the process of doing so. A rasterised image contains layers, all of which must be merged or ‘flattened’ before the image can be saved. Should you need to go back and do more editing, you will not be able to do so with a raster image. But with a vector image, design aspects can be changed at will, and independently of each other.
A raster image can use millions of dots of colour, or pixels if you are referring to print media or digital media respectively. These dots or pixels combine to create the image. One incredibly common form of raster image is the photograph. The megapixels of today’s digital camera refer to the number of dots contained in every image. The higher the number of dots, the better the quality of the image.
Raster images need to store individual colour information for each and every dot or pixel. As a result, the file size of a raster image can be enormous. Not only that, but each piece of information uses memory, making it impossible to send over email or other means. This is why many raster images are compressed into formats like .png and .jpg.
Unfortunately, raster images cannot be enlarged, as they quickly lose quality and become distorted or ‘pixelated’. The number of dots in a raster image do not change; as a result, the space between them becomes larger as the image gets larger.
For all its flaws, the raster image’s quality is second-to-none. They are usually far more detailed than a vector graphic.
The next time you hear your professional printer speak about vector and raster images, you will have a better idea of what makes each image type unique.