On 1080i sources, vs weave/motion adaptive deinterlacing? What artifacts are telltale to bob interpolation?

And does bob interpolation leave 1080i effectively inferior to 720p?

Bob (scan line interpolation for de-interlacing) results in a slight blurring of vertical detail. By definition it must.

There are no ghost images or echoes. It's just that top and bottom edges of objects are not as crisp as they could be. Occasionally horizontal edges may shimmer or flicker, whether you want to call this an artifact is a subjective decision. The word "bob" came about because some stationary subject matter seemed to vibrate, or bob, up and down very slightly (by one scan line).

Correctly in the bob method, when an odd field is being processed, all the odd scan line positions have original material in them and the even scan line positions are interpolated. And vice versa.

So for example scan line 11 on the screen will have real scan line 11 content in it half the time and have a blend of scan lines 10 and 12 (that's what interpolation is) in it half the time. Scan line 12 will have real scan line 12 content in it half the time and a blend of scan lines 11 and 13 in it half the time.

Motion adaptive de-interlacing tries to identify areas with "stationary" subject matter and do weave instead of bob in those locations. This preserves all the vertical resolution. Moving subject matter is still "bobbed".

There are cruder methods too, for example use only the odd fields, interpolating the even scan line positions all the time, and use those bobbed frame twice instead of process the even fields. This effectively "downrezzes" 1080i to 540p in terms of resolution.

The most dramatic demonstration of 540p bob-only deinterlacing, outlined in Merson's article (http://hometheatermag.com/hookmeup/0506halfrez/), involves a standard test pattern--available on a test-HD disc--that presents flashing alternately B&W full-screen images instead of accurately 'stacked' horizontal B&W lines. The deinterlacing is alternately using black, then white, TV fields (half-frames) to create 1080 images. -- John