What is Vector Art?

Among the most frequent questions people ask are:

• What is Vector Art?
• Can I convert a .BMP, .GIF or .JPG to vector?
• I converted a Photoshop® file to .EPS, why can't I use this as vector art?

To answer these questions, you need to know a little bit about what "vector art" is, and what the other forms of imagery a computer uses are comprised of.

What is Vector Art?

There are two different kinds of art used by computers. The two types are "Bitmap" art, and "Vector" art. Bitmap art includes almost every file type there is: .BMP, .GIF, .JPG or .JPEG, .PCX - the list is enormous. Vector file formats include .EPS and the files created and manipulated by professional drawing software products such as Arts & Letters Express®, Adobe Illustrator®, and Corel Draw®.

The difference between these types of art lies in how an image is stored within the art files themselves. Bitmap files consist of a series of numbers that represent coordinates within the image area's grid, and the color for each pixel in the grid area. The image to the right will help illustrate the concept of a Bitmap file. The image at the top represents the actual bitmap image as you would see it on your computer screen. The lower representation shows how this image would be "understood" by your computer.

To store this image, the computer creates a gridwork of the image area. It stores information about the file by identifying each pixel and it's color. (Pixels are the tiny dots on your computer screen that light up to create everything you see on your screen.) In our example, the pixel at coordinate (1,1) is colored black, the pixel at coordinate (1,2) is colored medium gray, the pixel at coordinate (1,3) is colored medium gray, and so on.

For this example, let's suppose that the file format in which we will store this bitmap consists of ordered sets of 3 numbers. The first two numbers represent the coordinates and the third number represents the color. If the number that represents "Black" is "0" and the number that represents "medium gray" is "64", then the data in the file might look something like this:

(1,1,0), (1,2,64), (1,3,64)...

That's all there is to a bitmap file. A series of numbers representing pixels and their colors.

Vector files are nothing like that. A vector file contains the information for creating lines. It contains a starting point and an ending point for each line. With those coordinates, it also stores a vector equation for each coordinate. A vector equation indicates both direction and velocity. Using these coordinates and vectors, the computer can draw a line from point A to point B with any proper curve automatically created.

The file for the vector illustration to the right would contain coordinates within the drawing area for points "A" and "B" along with other supporting information. Each line or series of lines grouped together become objects in a vector file, so if the coordinates for point "A" were (12,1) and the coordinates for point "B" were (15,102), the file for the above vector illustration might look like this:

{Begin Object - Open Shape} {line color = 0} {12,1,(vector equation)} {15,102,(vector equation)} {End Object}

Because information for every possible pixel within the image area does not get stored within the file, the vector file is dramatically smaller than a bitmap file of the same drawing. Vector files only contain lines, but if multiple lines join up to create a closed area, additional commands can be included to tell the computer to fill that area with a color. By combining multiple lines and creating multiple objects, discernable images begin to appear.

Vector images have a number of advantages over bitmap images, including:

• If you try to enlarge a bitmap image, your computer can only enlarge the size of the squares making up the image area. That is why bitmap images get jagged as you enlarge them. Vector images remain smooth because your computer merely re-computes the coordinates of the points and adjusts the vector equation constants.
   
• Each set of lines in a vector image represent separate and distinct objects. Every object can be re-edited at any time. For example, let's say you created a vector art file with a circle in the background. You could open the drawing file at any time - even days later - and change the circle to a square.
   
• If you had a very large picture - such as a poster on your wall - the vector file might only take up a few kilobytes of space on your computer, while the same image in a medium resolution bitmap format might not fit on a CD-ROM!

Can I convert a .BMP, .GIF or .JPG to vector?

In this example: 1. The vector artist starts with a bitmap image of a logo. 2. A geometric vector object is added to approximate the shape. 3. New lines are added to the geometric shape to approximate the bitmap shape. 4. Finished recreating the bitmap shape. 5. Bitmap is removed, leaving the vector version of the object.

Vector images can easily be converted to bitmap images. To make this conversion, your computer need only go through the steps of displaying the vector image on your screen while recording which pixels are used, and in which colors. But there is no "Conversion" process for transforming bitmap files into vector files. There is no "line" or "object" information in the bitmap file. To create a vector image from a bitmap file is a difficult process. Most vector software products have an "Autotrace" feature that attempts to create vector information from bitmap images. These functions examine the bitmap for areas of a solid color, and attempt to create a series of vector lines to approximate their boundaries. These functions rarely produce results that the graphics professional would find useful, as most bitmaps contain occasional ragged pixels and the function tries to faithfully re-create the ragged edge. The result is a vector object with misshapen sides and far to many lines in the object.

Alternately, most vector artists attempt to manually recreate bitmap art as vector files. To "redraw" a bitmap, the bitmap file is displayed within the vector art software, and the artist uses geometric shapes to recreate the shapes he sees in the bitmap. (see example at right)

I converted a Photoshop® file to .EPS, why can't I use this as vector art?

Because vector art images use lines to create images, photographs can't normally be "vectorized." However, a vector file can contain a bitmap object inside the file. For example, let's say that the artist recreating the logo in the example above decides to save his file at step 3 and complete the work later. The bitmap object is on his drawing surface when the file gets saved, so the computer needs to add information to the file saying that there is a bitmap on the drawing board. But the bitmap isn't a vector object, so how is this information stored? The information for recreating the bitmap is stored in the vector file as an object in a bitmap format - not a vector format. The vector file for this portion might look like this - note the bitmap coordinate sets inside the vector file:

{Begin Object - Bitmap} {(1,1,0), (1,2,64), (1,3,64)...} {End Bitmap Object}

It helps to think of a vector file as an envelope. The envelope can contain many different objects, and you can edit the objects inside one by one, remove objects, or add more objects to the envelope. Each object in the envelope can only be edited by the rules for that type of object, however. That is why many products that create bitmap art objects, such as Photoshop® can save a file in a vector format, but all that is really happening is that the software creates a vector envelope and places the bitmap object in the envelope. There is still no vector art inside.