Vector vs. Raster - when to use which?

[Chgowiz]

This is a subject that I asked privately, but I thought it might be useful to other hobbyists. We have an embarassing rich set of tools to choose from, Inkscape, GIMP on the freeside, Campaign Cartographer, Dunjinni, etc. So much so, that it is confusing to know which to use when.

I've been learning GIMP for awhile now, but I see people talk about vector based tools. I was curious to learn the differences and uses between the two, and I have found there's not really a clear cut definition of when to use either raster or vector. From what I understand, it seems that if you want smooth lines, non-pixellated text, or the ability to scale, you use vector. If you want textures, fills and other effects, you use raster. I'm not sure that's the whole story.

So I'd like to ask you all - when do you use vector vs. raster and more importantly - why? In talking to rank beginners - what should they learn from each tool and when does it make sense to use each tool?

Thank you.

[Steel General]

I almost always use raster, mostly due to laziness more than anything else - but I'm sure others will be along and give you a more complete (and much better) answer.

[RobA]

I tend to bounce back and forth between the different tool types.

I use vector tools for shapes I want good control of, i.e. text labels, roads, rivers, icons, symbols.

I tend to bring these as vectors into my raster software then convert them at the scale I need and then rasterize them and add effects, like texturing, shadows, etc.

-Rob A>

[Redrobes]

Its all about the flexibility really. Ultimately everything (save the most extreme examples) gets rasterized but by using vector lines the rasterization process can be optimal at whatever scale it needs to be done at so you can use multiple scales and have one vector map.

Its neigh on impossible to vectorize a photo however. The best you can do is quantize the colors into bands and vectorize those bands. It can look alright but you can usually tell. If those colors are solid like a logo or a font then it can be better to vectorize them however.

If all of your raster icons, textures and other source bitmaps are a lot higher res than the highest final version of map you want to make then there is minimal loss of accuracy by using these high res sources to make a lower res map. Thats why having all the source textures nice and high res is important.

So on to convenience. Its much easier to modify a vector line than it is to modify a rasterized one. Theres other math things that are much easier on vector lines too - like ensuring that the ends of two lines are linked perfectly or ensuring that circles are really circular etc.

Finally, its pretty easy to raster a vector line optimally but its harder to vectorize a raster line. Well ok a line on its own isnt so hard but generally its harder to vectorize raster stuff than rasterize vector stuff so it can be a kind of one way process in many cases. So people might make initial stuff in vector, modify it and then raster it and do all the fills and bitmap stuff from there on. Knowing whats good about each is the key tho. I always advise that you should be familiar with one of each type of app.

[ravells]

I tend to start in vector for general shapes and fills etc and then port it over to a raster editor to add textures etc.

[Korash]

begining to learn both Gimp and Inkscape (and going slow due to time constraints ) and I have a question for you.

I have seen reference to "rasterising" a vector image a couple of times, and I can't figure out if that just means bringing it into a raster prog (ala Gimp) or there is something I need to do in Gimp in order to rasterise it.

some guidance would be helpfull here.

Thanks muchly

[Midgardsormr]

Well, I don't know about the Gimp, but in Photoshop, you can rasterize a vector layer by right-clicking on it and choosing "rasterize" or by going through the layers menu. Generally speaking, I don't rasterize something until I need to add effects to it. As was mentioned, it's a one-way street. Again, though, I don't know how Gimp handles imported vector work.

Now, choosing between starting in raster or vector, for me, depends on the kind of image I want to produce. For textured maps like Mennin's Hallow, raster is the way to go. I can't imagine trying to do something like that in Illustrator. For clean-looking images like that Wheel of Time map I did recently, vector is the tool of choice. Best of all, though, is a combination of both. HandsomeRob's atlas maps are done with a combination of the two--raster for the shaded relief, and vector for the linework.

[Redrobes]

A vector line is a math representation of a line with either two end points or one starting point and a direction - all just numbers.

Raster is a bunch of dots in a grid which have colors assigned to them to make up the image.

Rasterizing is where you go from something into a raster set of pixels. So what happens is that the app runs down the math line and colors in the dots. Its a little more complex than taking the closest and making it black on a white background for example as most measure the distances from the exact math line to the square pixel position and shade it darker the closer you are so it looks smoother and better.

So apps like say inkscape can export the math vector data to a raster version where it will do all that processing for you and leave you with a rastered bitmap - a rectangular set of pixels stored in a container like a JPG or a PNG.

Going the other way involves looking at the rectangular set of pixels and trying to best fit a line onto the darker pixels. Thats a more inexact science and different programs will give different results - some better than others.

[Wordman]

If you want textures, fills and other effects, you use raster.

Actually, most vector apps are just as capable of the first two of these as most raster applications; it's really the last one that is the big difference, as well as the "pixel tweaking" advantage of raster apps.

For textures, all you need to do is create a brush in a vector program and use it for fills. For example, take any 512x512 (rasterized) texture and make it a brush, and it will work just like a raster program (including the crappy scaling). You can also, however, create vector patterns that can be used as textures, which are a bit more flexible, but not by much. (They'll scale better, at least.)

For fills (gradients, etc), most raster and vector apps seem to be about the same. Vector apps might have a slight advantage of being able to follow paths with a fill, but this is pretty advanced, and not many apps can do this.

Most of the effects available in a raster app (which work by doing math on the pixels) simply aren't possible on most vector systems. Naturally, there are some effects that only work on vectors but, for most map work, these don't really matter. Some vector apps use a strange hybrid, where they "remember" a series of raster effects to apply to an object and, after the vectors are rendered to to a screen buffer, apply the raster effects. This isn't really the same, though, as altering the pixels directly.

[Chgowiz]

Thank you to all who've responded. What I have learned from this is that while I can do a great deal with one or the other, there are some options that I may consider in using both. It sounds like I just have to try them out and see what works.

Thanks!