Bitmap fonts are fonts composed of bitmaps. A bitmap is an array of binary bits--ones and zeros. The computer displays these as black and white pixels on a black and white screen, for example. "Raster" refers to any grid-like array of dots or pixels.

So-called pixel fonts are outline fonts that simulate the appearance of bitmap fonts. Outline fonts are by nature scalable, but pixel fonts are intended to be used only at sizes in which their outlines exactly align with the pixel grid of the computer display.

"Raster" is just the German word for grid.

Thanks Mark! that was a clear and informative.
but i thought outline fonts are vectorized and therefore do not have any problem if scaled to any size. in case of pixel fonts the fonts lose their clarity at sizes other than designed for. why are they outline if it is faster to work with bitmaps especially if their function is to serve as bitmaps?

Modern operating systems and applications don't support bitmap fonts the way they used to, and in some cases not at all. Outline-based pixel fonts are a work-around.

then again, why does one need to use pixel fonts in sizes that they are designed for?outline fonts shudn't have scaling problems, right?

Because this happens:

The first line shows what this font is supposed to look like at 14 pt. The second font shows the same font at 18 pt. (This is a "pixel" outline font.)

Bitmap fonts (pixelfont or "hard") continue to flourish exactly because outline fonts do have rasterization problems. Essentially, outline fonts are a convenience, and are mismatched to the way they end up being rendered. In print the resolution is simply high enough that you don't notice the problem. But it's there.

Furthermore, scalable fonts promote ignorance with respect to optical scaling.

hhp

Mark and hrant, I don't quite understand what you are relating. An outlined (vector) font should scale up perfectly. I don't see that with Mark's showing. That looks exactly like a pixel font enlarged in a non-vector program.

Any program that does not understand vector will create a fuzzy image. Therefore, create the image in a vector-based program first. Then convert to the pixel-based program. In that way, you can not go wrong.