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.

[Gamerprinter]

Then of course, the exception to the rule, there's me and Xara.

Since Xara, though primarily a vector application has some hybrid raster operations built within it. I (as I always say) use Xara almost exclusively.

The question would be when do I use raster? Sometimes a texture is not condusive to my goals, so I image edit in PS or GIMP. I clean up images, alter colors, use cloner brushes to fix details. If I use 3D objects, which are rasterized before using them further, I do the fixes in PS/GIMP.

I almost never bring a map back into PS/GIMP to finish it. All compositing, texture filling, not to mention grids and labels are all done in vector.

I don't think I would ever totally create a map in GIMP - not my aesthetic or preferred method of operation.

I would like to learn to create bump maps better in GIMP, then I'd finish my maps by doing that - but that's the only thing I can think of to use GIMP as my final step in creating a map.

GP

[Redrobes]

Hmm ok better talk about texture mapping then. This is where you take a raster image and apply it into a vector space which is usually a 3D polygon for 3D models but it can also be a vector 2D area too.

What its essentially doing is resampling the raster texture but its not doing it with fixed scaling, the scaling is selected per pixel based on the vector shape so you can texture map a rectangular photo onto a circular disk for example. You can control the circle shape in a vector way and the image inside is a raster photo conforming to the shape of the circle.

I believe this is what Xara does and is what my ViewingDale does which allow both apps to scale up stuff using photo textures in a kind of vector way. In my opinion tho texture mapping is more of a raster process than a vector one. If you conform a low res photo into a shape and make that shape big then you will get the pixels showing up. If the photo was truly vectorized, which Xara can do very well too, then it would scale up perfectly but as said earlier it has to limit the colors and vectorize the bands within that photo instead of the full range of colors. So theres several options available but its just worth familiarizing yourself with all the options.