Raster and Vector Made Simple
Vector and raster are the two main graphics types in desktop publishing. If you don’t understand how they work, you also will not understand the difference between Illustrator and Photoshop, or the difference between a vector graphics application and a raster graphics application at large.
The definition of vector can be a bit confusing. Type it in a Google search or look for it in a dictionnary and if you understood totally what it means then hats off to you, because I don’t understand many of the things they say. There are also simple definitions which are incomplete. Others, when defining vector graphics, simply skip all the complicated stuff and simply say that they are composed of mathematically defined objects, they are scalable and that’s all they say.
What is a vector in simple words? Vector is like saying: I am going from Africa to the USA, the distance from where I am now to the USA is bla bla and I have to go a certain number of degrees North and a certain number of degrees West to get there. A vector is something that goes from point A and moves towards a certain direction until it reaches point B. So a vector graphic is composed of many of these things that once put all together make up an image.
Programs like Illustrator rightly see these different vector objects as different, and in a way you can say that vector programs are “smarter” than raster programs when talking about recognizing what each object is. Now why are vector graphics scalable without loss in quality? Because all you have to do is to say to a vector program that point B is further away than used to be, and how distant it is now, and with all the other data (for example how far North and West it has to go), the vector program is able to recreate the vector object. Only that now it’s bigger. It’s like saying that you made it to New York and now you can carry on to the next city.
Raster Graphics (AKA Bitmap)
Now that we got vectors out of the way somehwere up in New York, let’s talk about raster images. Raster images are composed of pixels, that is tiny “dots of light” which compose your image. Pixel stands for picture element. When you draw a red line with the paintbrush for example, Photoshop doesn’t see a line. It sees bunch of red “dots” one after the other. It doesn’t see any difference at all in those dots a part from the fact that the red dot is composed of a certain amount of red, blue and green, or a certain amount of cyan, magenta, yellow and black, etc.
Photoshop doesn’t know that a specific dot belongs to the image that you see as the car or to the image that you see as your dog. It doesn’t know that. That is why Photoshop has all of these selection tools and you always have to tell it: “Look, leave these dots alone and edit only these ones, would you?”. If Photoshop was a person and you’d said to him to leave alone the dog and only wash the car, he would likely go wash your shoe! Therefore you can say that Photoshop is less smart than Illustrator in this case. However if you said to Mr Photoshop to wash all the red objects, he would go wash your car, the street lights, the red line in your socks, etc.
Vector, Raster and Resolution
While vector graphics can be scaled without any problem, raster graphics, when scaled will loose quality. Because raster graphics are made of pixels, when you enlarge an image Photoshop (or any other raster program) will have to add pixels. They will have to be invented from nothing and the image can get fuzzy because of that. When you make a picture smaller you need to keep in mind that you are throwing away a bunch of pixels. Your picture will look allright when viewed in small size, but once you enlarge it again, Photoshop will not “rescue” the pixels you have previously thrown again, it will invent new pixels and your image won’t look as good as the original.
Based on the above, vector images are resolution independent, while raster images are resolution dependent.
September 14, 2005