5. Advanced stuff

First up: Anti-aliasing. You know how i said that pixel art should be devoid of automatic anti-aliasing, right? Well, now's the time to learn how to do it manually. Let's look at an example...



That's a pretty big difference, eh? You may notice that the intermediate colors aren't exactly grey, but don't worry about that, this is due to the palette i'm using. What's important is that you should always take the intermediate color between the two colors you need anti-aliased. Once you've picked your color, you should anti-alias "away" from the line, else it'll end up wrong. Personally, i don't use anti-aliasing a lot, but then again, that might be due to me having a fixed 256 color palette, so feel free to do it. The amount of anti-aliasing needed depends on how many pixels per "segment" of a line there is, but generally, it shouldn't be necessary to anti-alias more than 3 pixels away from the line.
Another example of anti-aliasing would be this:



See how much smoother the border gets? Like previously, i've anti-aliased "away" from the border, but only with one color, as the difference isn't as big as between black and white.

Right, now that we've got anti-aliasing out of the way, let's look at dithering. Dithering generally serves the same purpose as anti-aliasing, but without using additional colors. It doesn't produce a totally clean look like anti-aliasing does, but it's quite useful if you don't want to use a gagillion colors.
Before i start rambling about something unrelated, let me show you an example of the most basic dithering...



The checkerboard pattern. Basically, you make the border between two colors into a checkerboard of the two different colors. So simple, yet so effective. However, that if you can use anti-aliasing, do so. Dithering tends to produce a noisy look, which might not be what you're looking for. Due to me working with a limited palette, i often use dithering, because there's a lack of some intermediate colors in the palette.
When you move on to lines that aren't horizontal or vertical, things get a bit more complex, though. Lemme show you...



The border appears smoother, but also more blurred. This is because that dithering is actually closer to blurring than to anti-aliasing, but since anti-aliasing is a kind of blurring, i guess it's allright. =P
Another important detail to remember, is that you should only dither if there's room for it. If you're going to dither on both sides of a color block, it needs to be at least 3 pixels wide, and if you're only dithering on one side, it should be at least 2 pixels wide. This is because of the fact that the checkerboard pattern extends (at least) 1 pixel into the color block, and if two opposing checkerboards meet, shit looks weird.
Now, i'll show you how you can extend the dithering further, to allow smoother gradients and what not.



Notice the checkerboard in the middle, and then look at how i've extended it. You rarely need to dither more than the simple checkerboard, but if you do, now you know how to do that. ;)
Also, if you're faced with a line that has segments of two pixels, you need only to place a dithering-pixel at the corner of each segment, on both sides of the line. Generally, if you're faced with the choice of skipping a pixel or extending a segment, then do the former. I'm sure you'll figure it out. Especially with this example. ;)



Now for the last part about dithering: The circle. This also pretty much includes curved lines, because as previously mentioned, circles are composed of 4 curved lines. Let's see an example:



Again, the checkerboard pattern. It really is versatile, don't you think? :U

An example of how to use the above dithering in a circle will have to wait, due to me running out of time. So i guess that's it for today's lesson. =P