Martin Reed’s question (Talk page – 14Dec2001) raised the subject of technical issues involved in transferring an image to different media. One of the most fundamental is the use of bitmap or vector graphics.

Bitmap or vector?

If you want to display a drawing on a computer, or by printing it, it must be prepared appropriately for the medium. Bitmap and vector are the two fundamental ways of storing images. As a reader you won’t care which you are looking at, as long as the preparation has been done properly. If you are the cartoonist, graphic designer, commissioner or printer there are some significant differences that will affect what you can do with the image and how you should treat it.

What is a bitmap image?

Image of an apple showing increasing grid size, and a reduction in image quality.

To draw a bitmap image you start with a rectangular grid made up of pixels. The pixels are little empty boxes that together form the “canvas” or “paper”. To draw an image, you colour in the boxes, and that’s it.  If the boxes are very small (in image 1 they are so small you can’t see them with the naked eye), the image looks great – with beautiful smooth curves. If you use bigger boxes, that are big enought to be noticable, the image will pixellate. That is, the edges of the boxes will become noticeable andcurves inthe image will appear jagged. The larger the boxes inthe grid, the worse the image.

A bitmap image is stored as a list of the pixels, and where they occur in the grid, with a description of what colour (hue, intensity etc.) is in each one. To reproduce the drawing the computer will re-draw the grid using all the information stored in each pixel.

What is a vector image?

A vector image is a completely different beast. There is no grid.  When you draw a vector image on a computer, the computer works out what you are drawing (the colour) and where you are drawing it (the coordinates in space) and stores that information as a set of formulae. Every time the image is displayed the computer takes the all the formulae, calculates where everything should be, and redraws it. Image 1 could be a bitmap image drawn at an appropriate scale for the position it is to be printed, or a vector image reproduced at any size.

I drew the small vector image shown here by hand,  like I would on paper. I’ve shown it deconstructed in the second diagram. Each of the parts of the image shown is a separate object and I can easily move, delete or manipulate any of those objects to change the picture.

So why would you care?

It depends who you are. If you are the consumer, the person reading the cartoon, as long as it looks OK you won’t care. If you are the commissioner of the cartoon, the artist, the graphic designer or the printer, it can matter a lot.  A bitmap image will display as the artist intended (i.e. clearly and with no jagged edges), at the size for which it was created.  If you try and scale it up too much it will pixellate, i.e. the individual pixels will become visible and spoil the image. A vector image will reproduce accurately and smoothly at any size.  When the computer recreates the image using the stored formulae, the artist or graphic designer can tell it how big to draw the image. For ease of use and flexibility in graphic design vector is hard to beat.

If you are the cartoonist the decision whether to use bitmap or vector is a big thing.  I’ve been involved in some emotive arguments about this question. The arguments largely come down to the aesthetics of drawing and the ease of creating an image. Bitmap software packages (like Adobe Photoshop, and Corel Painter) can more closely emulate drawing and painting as you would using pen and ink, watercolour or oil paints.

Vector packages (such as Adobe Illustrator and Corel Draw) are getting much closer to emulating the drawing-on-paper feeling, but they’re not as good, yet.  Where they really score is the ease with which you can manipulate and scale an image. In a vector image everything you draw (every line, curve, shape… everything) is an object that can be pulled, pushed, distorted, flipped etc. It’s a different way of working, but it’s enjoyable, and there is scope for getting different effects than you can with conventional media. I use vector graphics (Adobe Illustrator) almost exclusively for my work.

Bitmap and vector are equally valid methods for storing and displaying images, which you choose depends on how you like to work and what you want to do with the resulting image.

There is a lot more to this subject. For example you can turn bitmap images to vector and vice versa with varying degrees of success. You can also use either technology to incorporate a drawing on paper into the computer. I’ll blog some more about this in the future, but if anyone’s particularly interested let me know and I’ll do it sooner rather than later.