What is a bitmapped or raster image?
You see bitmapped images every day. Pictures taken with a digital camera or scanned are bitmaps. Most common bitmapped file formats are:
There are many, many more bitmapped file formats but these are the main ones you'll run into. There are also many, many programs that can read and edit bitmapped images. They may be called Image Editors or Image Processors, or Paint Programs.
A bitmapped image is called that because the image is made of squares- squares mapped to a grid. So an 800x600 bitmapped image is made of a grid of 480,000 (800x600) little squares. Each square is defined by 3 bytes for RGB and 4 bytes for CMYK, one byte for each color Red, Green, Blue, or Cyan, Magenta, Yellow, Black.
Here is a small image of me:
And here is a closeup of the eyes from that image: You can pretty clearly see the blocks that make up the image, can't you? If you save the smaller image to your computer and open it in your image editor, set View to 800% and you'll see the same blocks.
What is a vector image?
A vector image or vector drawing is made up of a mathematical description of start points and end points. IE, to draw a line rather than a bunch of blocks, a vector is drawn from an X,Y starting point to an X1,Y1 ending point.
To complicate things, many vector image formats also allow bitmapped images to be embedded within them. However, for this discussion we'll concentrate on vectors.
There are far fewer well supported vector file formats and programs that work with them. All vector editing programs can export in a variety of vector formats, and can convert to bitmapped images, but the bitmap is then just a bitmap and gives up all the advantages of vector.
I would say that, for the graphic artist, the big ones are AI, CDR, and PS/EPS.
You can think of a bitmapped image like someone handing you graph paper and telling you to black in certain squares to end up with something that resembles a line if you blur your vision and look from a distance. Then think of a vector image as someone handing you a blank piece of paper and a ruler and telling you to draw a line from a point 1 inch up and 1 inch over, to a point 6 inches up and 8 inches over. Which means you can get as close as you like, or blow it up as big as you like and it still looks like a line.
Ironically I must show you this in a bitmapped file. Here blown up close for the screen are three lines. One at 150dpi, another at 300dpi, and finally a vector line defined by two endpoints and the thickness.
And here to really illustrate it is an extreme closeup of the ends:
Vector images are even more flexible than that simple description, because also included is the thickness of the line, its color, coloration inside shapes defined by those lines, mathematically defined curves, circles, elipses, boxes, etc. Don't worry, you don't have to write down columns of numbers or calculate a bezier curve! The programs do that for you.
Here is a shape drawn by something called bezier curves. That means the line is defined by phantom control points that drag out the line between its endpoints, kind of like a hanging string.
Or by dragging the control points in different directions and distances, make more complex curves.
Enclosed shapes can also be drawn and filled with any color, pattern, gradient, or even with an image fitted inside. Shapes and lines can be combinations of straight lines and bezier curves.
It helps to think of the parts of a vector image as if they were cut out of paper and set on each other. So unlike a bitmapped image, you aren't painting over anything that is covered. You can still go back and move pieces around, relayer them, change size, fill, pattern, line thickness, color, whatever you want. Break them apart, use one as a template to cut pieces out of another, join pieces together, etc.
Here I took the circle and used it to trim the points off the 7 pointed star. You can see the endpoints of the lines making up the clipped star.
Vector is great for text, lines, shapes, simple fill patterns. Bitmap is great for photographic images. A vector-only image can be resized as large as you like! Since it is all mathematically defined points and curves, it looks good no matter how large you blow it up.
However: any included bitmapped fills or textures are under the same constraints as any bitmapped image. And vector will not do photographic quality images. Very high quality vector images can look as good as airbrushed art, though it takes a -lot- of work to do that.
And since you can import bitmapped images into CorelDraw and Adobe Illustrator, you get the best of both worlds! Put a photo of someone's grandkids in a sharp vector frame, add some sharp text (even fill text with an image), and you've just made a sharp looking Tshirt!
Sample logo with mixed solid and bitmapped fills. This was designed to be printed on an opaque transfer for a green Tshirt, trimmed along the thin black line. Notice the leather texture in the dark red and grey parts. Click on image for larger size
Tshirt print with vector text added. Text has neon red fill and white outline to enhance readability without simply making the text stark white. Click on image for larger size
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Thanks, Alien Steve Polymorph Digital Graphics