There are, essentially, two types of graphic files in today's digital world: the bitmap and the vector image. Each format has its own array of sub-formats, which all differ from each other in some manner, but share the same overall principals. Furthermore, bitmap and vector images each have their own advantages and disadvantages. The following is intended as a brief explanation of how the two types of images vary, paying special attention to benefits and drawbacks as well as the practical applications of these formats.

Also, please note that this page is not intended as a "How To" guide or a tutorial for graphical construction or manipulation. Its sole purpose is to explain the fundamental differences between bitmap and vector images.

Bitmap images are, for all intents and purposes, static. They are comprised of hundreds, and more often thousands, of tiny coloured 'dots' commonly called pixels. Each pixel has a fixed position within the makeup of the bitmap, and when these pixels are displayed together on a computer screen, they form and image. Below is small section of a bitmap which has been significantly enlarged. Each of the coloured squares represents a single pixel.

Bitmap images are, with a few exceptions, the standard for internet graphics, as well as Windows icons and backgrounds. Bitmaps are also the standard format for images captured by scanners and digital cameras.

Vector images differ from bitmaps at the most basic and fundamental level. Rather than being comprised of pixels, the vector image is made up of various "objects," a term which essentially means lines and shapes. These objects are defined mathematically by a set of algorithms or formulas, which allow them to be redrawn over and over. This is not to say that using vector images requires any great mathematical skill, as the mathematics are handled almost entirely "behind the scenes," by whatever software is using the image. It does, however, translate into an entirely different kind of functionality.

Whereas the bitmap is static, the vector image is dynamic. It is not restricted by size or shape. It can easily be shrunk or enlarged, widened or compressed.

Most forms of "clipart" are vector-based.

The following sub-sections of this article will each focus on one graphics related issue and explain how bitmap images compare against vector images, further demonstrating the strengths and weaknesses of each type of image. Typically, the vector image is strong where the bitmap image is weak, and vice-versa.

Photo-Realism

Because it is comprised of small pixels, the bitmap is the most suitable format for photo-realistic images or images with high amounts of fine detail. Because each pixel can represent any one of the more than 16 million different colours that can be displayed by most computer monitors, the bitmap image is able to imitate the subtle colour variations of a photograph.

Take for instance, this bitmap image of the beautiful Elora Gorge.

Notice the fine detail of the image. The viewer is able to see all of the subtle colour variations within both the trees and rocks, giving the image a highly realistic appearance.

The vector image, on the other hand, does not possess the same kinds of photo-realistic capabilities. Because it is comprised of larger objects the vector image cannot achieve the kind of fine detail that is necessary for photo-realism. Instead, vector images tend to have a more cartoon-like appearance, like this clip-art image of a palm tree, downloaded from the Microsoft website.

Thus, since photo-realism is unachievable when using vector images, the bitmap is the standard format for working with digital or scanned photographs.

Scalability

When it comes to being able to make an image larger or smaller without any loss in quality, the vector image is undoubtedly the superior format. Because the vector image is comprised of mathematically defined objects, rather than by a pre-ordered pattern of pixels, its size can be easily manipulated with little to no loss in the quality of the image. The objects within the image are simply re-rendered at a greater or smaller scale, providing consistently smooth edges at any size.

Bitmaps, on the other hand, are more difficult to scale, because changing the size of a bitmap requires a complete rearrangement of the pixels. Many graphics programs do an excellent job of reducing bitmaps, but enlargements always result in a loss of quality. An enlarged bitmap is likely to appear blurry, or even "pixelated," meaning that the different pixels of the image have become visible, as in this expanded portion of the Elora Gorge picture shown above.

Shape

A bitmap always has four straight edges. It cannot be elliptical, triangular or any other shape other than a rectangle. This obviously presents certain difficulties when attempting to lay one non-rectangular image over another, or when publishing an image to the internet when the background of the image is not the same as the background of the website. Certain efforts have been made to rectify this problem, such as the transparency option available to GIF bitmaps, but for the most part, the rectangular nature of the image remains a disadvantage to bitmaps.

The vector image, on the other hand, is much more versatile. It can be any shape, from simple geometric forms to many of the most complicated and most abstract forms imaginable. This eliminates the problem of having a rectangular background around a non-rectangular image.

Conversions

Converting from one bitmap format to another bitmap format is generally a very simple process, which can generally be achieved through a simple "Save As" command. For example, if a file is in .bmp format, to change it to .jpg format, simply select the "Save As" command from the "File" menu, select JPEG (or equivalent) from the "Save as type" selector, rename the file if desired, and click the save button. The software will make all the conversions itself.

Converting between vector types generally involves a similar process, although there is a more frequent loss of quality during vector type conversions than during bitmap type conversions.

Converting from vector to bitmap is also a simple process which generally yields excellent results. However, converting from bitmap to vector is more difficult as pixels have to be converted into algorithms. There are some applications, such as Corel Trace, that will attempt these types of conversions, but quality is nearly always lost during this process.

File Size

While file size does not affect the quality of the image, it is still a concern, especially when images are being transferred over the internet or carried on floppy disks. Unfortunately, it is impossible to say that either vector or bitmap images are smaller than other, as their size is dependent on certain variable factors.

For Bitmap images, the most important determinant for file size is the proportions of the image itself. The larger the image, the more pixels it contains and, thus, the larger the file size. Size is also affected by format. Different formats have different properties, and save information in different ways. For example, the GIF image type only allows for 256 colours to be displayed within an image, helping to reduce the overall size of the file. JPEGs, on the other hand, use all 16 million available colours, but use compression algorithms (which are different from vector algorithms) to reduce the overall size of the file.

The size of vector graphics files is not dependent on the size of the image, but on its complexity. The more objects there are in a vector, the more algorithms it will need to contain in order to render those objects, and the larger the file will become. This means that a large image comprised of a few objects will have a smaller file size than a small image comprised of numerous objects. Take, for instance, the two images below.

If these were vectors (they have been converted to bitmaps for display on the internet), the image on the right would have a much larger file size than that of the image on the left, because the image on the right is more complex. Yet as normal bitmap images, they have identical file sizes.

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