I need a video switcher as well as would like to ability to tune each input. My 720p TV does the whole 1080i-->throw away half the resolution-->upconvert 540p (BOB) thing and figure I may as well buy a unit that corrects this also. I found a 196 page thread on the VP30 which probably has my answer, but wow!!

So which weaves or just plain deinterlaces 1080i and scales to 720p? VisionHDP or VP20/30w/ABT102D?

The vp30 (with or without abt102) does that too (bob deinterlacing) on 1080i sources. I think the HDP does proper per-pixel deinterlacing on 1080i, like the vp50.

The vp30 (with or without abt102) does that too (bob deinterlacing) on 1080i sources. I think the HDP does proper per-pixel deinterlacing on 1080i, like the vp50.


Good point, I updated my question!

The VP30 does something called field scaling which does not throw away 1/2 the resolution. While it's not as good as properly deinterlacing a 1080i source, it's a lot better than most implement bob. Here's a link (http://www.avsforum.com/avs-vb/showthread.php?p=8532660&highlight=That+s+a+misunderstanding+of+how#post8532660) that gives a nice explanation.

The VP30 does something called field scaling which does not throw away 1/2 the resolution. While it's not as good as properly deinterlacing a 1080i source, it's a lot better than bob/weave.The VP30's field scaling is bob, plain and simple. It's a well-implemented bob, but it's still bob.

- Dale Adams

Thanks for the link, but I do not know if I fully understand this.


From what I gather fro JoshZ, since I will output 720p, the VP20/30 will

1. take each 1080i field (which is two 540 line fields)
2. scale each of the 540 lines fields to:
a. two 720 line fields (combined for 1440p internally)
or
b. two 360 line fields (combined for 720p)

3. offset both newly scaled fields
4. create a new interpolated 720, or 360 (I dunno) line field that fits between the two offset fields
5. I now have either:
a. Three 720 line fields
or
b. Three 360 line fields

6. So internally I am combine these three fields to form:
a. 2160p
or
b. 1080p

7. Scale the above to 720p Output resolution and I have a near perfect, non-stair stepped image on my display. If this is my understanding from that Link, then I can see where a 1080p ouput would benefit from this method. I may not see it on my 720p set.

Am I way off? Seems it may be easier to offset both 540 fields, interpolate a third 540 line field, take the triple combined 1620p field and scale it to match the output resolution. I am so confused!!!!!!!!!

wow, can't believe JoshZ got that one so wrong.

Each individual field is directly scaled to the output frame resolution, taking into account the vertical shift between even and odd fields. That essentially combines bob deinterlacing and scaling into a single operation. If you re-read Josh's post you'll see that this is exactly what he says - i.e., his post is completely correct and is in agreement with what I wrote above.

Alternatively, you could first vertically scale a field by 2X (again, taking into account the vertical offset between even and odd fields), which is a bob deinterlacing operation, and then scale the result to the desired output resolution. However, you can combine both of these into a single scaling operation and get the same result, which is what the VP30 does with a 1080i signal.

- Dale Adams

The VP30's field scaling is bob, plain and simple. It's a well-implemented bob, but it's still bob.

- Dale Adams


I stand corrected :o, original post edited

Thanks for the link, but I do not know if I fully understand this.


From what I gather fro JoshZ, since I will output 720p, the VP20/30 will

1. take each 1080i field (which is two 540 line fields)
2. scale each of the 540 lines fields to:
a. two 720 line fields (combined for 1440p internally)
or
b. two 360 line fields (combined for 720p)
c. two 720 line frames

3. offset both newly scaled fields
offset one of them

That's about it.

Each individual field is directly scaled to the output frame resolution, taking into account the vertical shift between even and odd fields. That essentially combines bob deinterlacing and scaling into a single operation. If you re-read Josh's post you'll see that this is exactly what he says - i.e., his post is completely correct and is in agreement with what I wrote above.

Alternatively, you could first vertically scale a field by 2X (again, taking into account the vertical offset between even and odd fields), which is a bob deinterlacing operation, and then scale the result to the desired output resolution. However, you can combine both of these into a single scaling operation and get the same result, which is what the VP30 does with a 1080i signal.

- Dale Adams


He still claims that it is superior to bobbing, and that's simply not the case. It is simply a slightly more sophisticated bobbing algorithm, but it is bobbing nonetheless.

The use of "540p" to describe bobbing is just for illustrative purposes, yet he seems to have taken it for gospel.

540 refers to the fact that instead of applying inverse telecine to film sources which would yield individual frames with 1080 unique lines, you take one field of 540 unique lines only and apply an algorithm to interpolate the "missing" lines - the algorithm can look at the other field for that, but doesn't have to.

So for every displayed frame using this bobbing or field interpolation method, you effectively use only 540 source lines, even though you output them at 1080 lines (due to interpolation).

Correctly, "bob", when it takes the odd field, puts the original scan lines in the odd positions and interpolates the even scan lines and when it takes the even field, puts the scan lines in the even positions and interpolates the odd scan lines. This is another way of saying "taking into account the vertical offset..." The result is better than pure 540p although it still fails a test consisting of alternating black and white scan lines.

Inferior methods may do such things as always put the incoming scan lines in the odd positions and interpolate for the even positions (two field bob without stagger), or even more simply, use the odd scan lines only, always interpolate the even scan lines, and output that frame twice (one field bob). The two methods described here yield no more than 540p quality.

All of these methods can insert the original scan lines into frames of fewer than 1080 lines, say, 720 or 768 lines, leaving fewer positions needing interpolation. The offsetting (or stagger) occurs simultaneously with the scaling by inserting the original scan lines into the finished frame differently for incoming odd fields compared with for even fields. For scaling 1080i to 720p, etc. just one finished frame is completed for each incoming field. There is no need to deal with 360, 1440, etc. scan lines at a time.

Video hints:
http://members.aol.com/ajaynejr/viddoubl.htm