Newton Developer Technical Information: Newton Programmer's Guide: 2.1 OS Addendum /

Chapter 6 - Drawing and Graphics 2.1 / About Drawing and Graphics in the Newton 2.1 OS

About Anti-Aliasing

When a black and white picture is reduced in size, the resulting image will often have a jagged look. This jagged effect is called aliasing. Anti-aliasing is a technique to overcome this effect, by rendering a reduced picture in gray tones.

For example, consider a picture that is being reduced to half its size. The four pixels at the top left corner of the picture are now going to be represented by a single pixel. These four pixels could look like those shown in Figure 6-3.

Figure 6-3 Four black and white pixels

If these pixels had been all black, it would make sense to render them with a single black pixel. But since these four pixels are not all black (or all white), rendering them as a single black or a single white pixel, creates a picture with a jagged, aliased, look. This can be overcome by rendering these four pixels as a single pixel in a tone of gray.

Support has been added to protoImageView to automatically anti-alias reduced black and white bitmaps. The built-in fax viewer, for example, uses protoImageView.

You may also anti-alias monochrome bitmaps with the new view method *GrayShrink. The *GrayShrink method was used to anti-alias the text on Figure 6-4.

Figure 6-4 The anti-aliasing effect on a bitmap that has been reduced by 50%