Subclasses of PixelConverter. These subclasses are specific to surface types where we can definitively calculate the conversions. Note that some conversions are lossy; that is, we cannot necessarily convert a value and then convert it back and wind up with the original value. For example, an rgb value that has an alpha != 1 cannot be converted to an Xrgb pixel without losing the information in the alpha component. The conversion strategies associated with the ThreeByte* and FourByte* surface types swap the components around due to the ordering used when the bytes are stored. The low order byte of a packed-byte pixel will be the first byte stored and the high order byte will be the last byte stored. For example, the ThreeByteBgr surface type is associated with an Xrgb conversion object because the three bytes are stored as follows: pixels[0] = b; // low order byte of an Xrgb pixel pixels[1] = g; pixels[2] = r; // high order byte of an Xrgb pixel