filter to reverse anti-alias effects

Question

I have bitmaps of lines and text that have anti-alias applied to them. I want to develop a filter that removes tha anti-alias affect. I'm looking for ideas on how to go about doing that, so to start I need to understand how anti-alias algorithms work. Are there any good links, or even code out there?

Answer 1

I need to understand how anti-alias algorithms work

Anti-aliasing works by rendering the image at a higher resolution before it is down-sampled to the output resolution. In the down-sampling process the higher resolution pixels are averaged to create lower resolution pixels. This will create smoother color changes in the rendered image.

Consider this very simple example where a block outline is rendered on a white background.

It is then down-sampled to half the resolution in the process creating pixels having shades of gray:

Here is a more realistic demonstration of anti-aliasing used to render the letter S:

Answer 2

I am not familiar at all with C# programming, but I do have experience with graphics. The closest thing to an anti-anti-alias filter would be a sharpening filter (at least in practice, using Photoshop), usually applied multiple times, depending on the desired effect. The sharpening filter work best when there is great contrast already between the anti-aliased elements and the background, and even better if the background is one flat color, rather than a complex graphic.

If you have access to any advanced graphics editor, you could try a few tests, and if you're happy with the results you could start looking into sharpening filters.

Also, if you are working with grayscale bitmaps, an even better solution is to convert it to a B/W image - that will remove any anti-aliasing on it.

Hope this helps at least a bit :)