Bitmap vs. Vector Graphics

A designer has asked you for your company logo, and you send him or her your logo file only to find out that it is not in the right format.  Have you heard that before?  What the designer is referring to is what they call, a “Vector” file.  So what is a vector file, why is it so important, and how do you get one? 

Digital images are pretty much divided into two categories: Bitmap (sometimes referred to as Raster images) and Vector graphics. 

Bitmap Images

Bitmap graphics are images that are made up of bits of an image, known as pixels.  Photographs, pictures that are scanned in by a scanner, or screen captures are all bitmaps.  If you have a bitmap image that is 300 pixels by 200 pixels, then that image would consist of 60,000 individual pixels.  On your monitor, this image would appear to be a little over 4″ x 2.5″ because most monitors display 72 pixels-per-inch.

To the left you see an image and to the right a 250 percent enlargement of the top of one of the mountains. As you can see the image consists of hundreds of rows and columns of small elements that all have their own color. One such element is called a pixel – short for picture element. The human eye is not capable of seeing each individual pixel so we perceive a picture with smooth gradations.

Bitmaps can be large in file size, especially for medium-high quality printing.  To print at a decent quality, most images should print at 300dpi (dots-per-inch or, pixels per inch).  So to print an 8″x10″ image, your image should be at least 2400 x 3000 pixels large. And an image like that could easily take up 40mb of disk space.  Back in 1988, that would’ve taken up an entire hard drive, but I digress.

File formats that are used for bitmap data

Bitmap data can be saved in a wide variety of file formats. Among these are:

• BMP: an outdated and limited file format that is not suitable for use in prepress.
• EPS: a flexible file format that can contain both bitmap and vector data. It is gradually being replaced by PDF.
• GIF: mainly used for internet graphics
• JPEG: or rather the JFIF file format, which is mainly used for internet graphics
• PDF: versatile file format that can contain just about any type of data including complete pages,it is not yet widely used to exchange just images
• PICT: file format that can contain both bitmap and vector data but that is mainly used on Macintosh computers and is not very suitable for prepress.
• PSD: the native file format of Adobe Photoshop (which can also contain vector data such as clipping paths)
• TIFF: a popular and versatile bitmap file format

Vector Graphics

Vector graphics are images that are completely described using mathematical definitions. The image below shows the principle. To the left you see the image itself and to the right you see the actual lines that make up the drawing.

Each individual line is made up of either a vast collection of points with lines interconnecting all of them or just a few control points that are connected using so called bezier curves. It is this latter method that generates the best results and that is used by most drawing programs.

This drawing demonstrates the two principles. To the left a circle is formed by connecting a number of points using straight lines. To the right, you see the same circle that is now drawn using 4 points (nodes) only.

Characteristics of vector drawings

Vector drawings are usually pretty small files because they only contain data about the bezier curves that form the drawing. The EPS file format that is often used to store vector drawings includes a bitmap preview image along the bezier data. The file size of this preview image is usually larger than the actual bezier data themselves.

Vector drawings can usually be scaled (resized larger or smaller) without any loss in quality. This makes them ideal for company logo’s, maps or other objects that have to be resized frequently. Please note that not all vector drawings can be scaled as much as you like:

• Drawings containing trapping information can only be scaled up to 20 percent larger or smaller.
• Thin lines may disappear if a vector drawing is reduced too much.
• Small errors in a drawing may become visible as soon as it is enlarged too much.

File formats that are used for vector data

Bitmap data can be saved in a wide variety of file formats. Among these are:

• EPS: the most popular file format to exchange vector drawings although EPS-files can also contain bitmap data.
• PDF: versatile file format that can contain just about any type of data including complete pages, not yet widely used to exchange just images
• AI: This is actually an Adobe Illustrator source file.  Usually, only the original designer has this file.
• CDR: This is a CorelDraw source file, another professional illustrating program.

So Why do you Need that Vector File of your Logo?

A designer may ask you for your logo or other artwork in vector format so that they can fully work with it in their design and layout program.  For example, they will most likely have to resize it, and they may want to integrate it with other elements, and/or maintain a transparent background.  They may also want to match any spot or CMYK colors that the logo has embedded in it.  Finally, the logo becomes completely editable in vector format, so the designer may want to copy styles, colors or objects for consistency of the entire piece, and vector files allow for that flexibility.

What About Bitmaps?  My Designer says it’s not big enough?

Remember that when you’re looking at your bitmap on your computer monitor, you’re seeing it at 72 dpi (dot-per-inch).  That same picture when printed, will print at 300-350 dpi.  So a picture that looks 4-inches big on your monitor will only print at less than 1-inch big on a printer… that is unless you enlarge it, which significantly reduces the quality. 

So if you’re designer is printing a brochure for you, and needs a picture that is 3-inches big, then you need to provide the designer with a 900-1000 pixel wide image to maintain quality resolution.

Can I convert a Bitmap file to a Vector Graphic?

Absolutely – in most cases.  Photographs are harder and more involved than line art, but it can be done with some amazing results.  Graphics will less than 20 colors and fairly simple lines are the easiest to convert.  There are tracing programs out there that do a good job, but I’ve found that manual augmentation of the curves after tracing produces the best results.

Recap

So there you have it.  Vector Files are mathematical representations of lines, colors, and curves, and are mandatory when working with logos, and line-art.  The most popular format is EPS, although PDF is accepted too.

 Bitmaps are primarily used for photos and scanned images.  It’s important to have a big enough bitmap size for printing (300-350 pixels for every inch) to maintain good image quality.

Finally, if you don’t have a vector file of your logo, a professional designer can trace it for you and create a vector file.