Welcome to my journal!

 So what's this all about?

This is my journal where I expound about anything and everything that interests me at the time. It includes descriptions of my thinking and work in progress, rants, raves, and other random musings. The formatting is shamelessly borrowed from Avery Lee's VirtualDub site (imitation is the sincerest form of flattery!). My only hope for this page is that it won't bore you (too badly).

Note that I add new entries at the top, so if you are an infrequent visitor, you'll probably want to scroll down a little to get into the flow.

[All contents are Copyright (c) 2003, 2004 Donald A. Graft, All Rights Reserved.]

 5-31-2004: "Objective" Test for Deinterlacers

Recently, I was involved in some discussions about the idea of making an objective metric for deinterlacing. Initially, I was skeptical, but after running some tests, I find that it is not really such a silly idea, as long as certain caveats are borne in mind!

To test the idea, I started with Spirited Away and used force film with DGMPEGDec to get progressive frames. Yes, I know it is anime, and the tests should be repeated with various kinds of source material. But this is what I used initially. Then I used MultiDecimate to remove duplicates because often the animator duped frames in low-motion segments. So now I had a stream of progressive frames without dups. By doing selecteven() on this I created the reference AVI for comparisons.

Next, I made the fake interlaced AVI by:

assumefieldbased.assumetff.separatefields
selectevery(4,0,3)
weave

I applied various deinterlacers and compared the results to the reference. I'll give some results and then make some remarks.

Results

compare reference to reference: average PSNR 106.53 (thus the max)
no deinterlacer: 29.97
discard field and Lanczos resize: 39.15
KernelDeinterlace(threshold=7) 39.97
FieldDeinterlace(dthreshold=7,blend=false): 39.29
FieldDeinterlace(dthreshold=7,blend=true): 31.92
AlparySoft [area-based search 64]: 27.25 !
TomsMoComp(1,5,0): 41.41
TomsMoComp(1,5,1): 38.43

Remarks

1. Based purely on the above results with this one source clip, TMC with no vertical filter is the king. But this is misleading because 1) this clip has no static scenes and 2) the picture areas that are static have very little vertical detail at the spatial frequency of combing (anime has large flat areas). Some deinterlacers are specialized to not touch static areas, and their superiority in this regard will not show up with this particular source clip. So, it is very important to use a source clip that is similar to the kinds of videos you want to deinterlace. Also, TMC becomes worse than KD and FD even for this clip when the vertical filter is turned on, so it's easy to inadvertently throw away quality if you are not careful. Of course, TMC can emit some artifacts with the vertical filter off, so you have to decide which thing you prefer, better PSNR or fewer artifacts. I suspect that the advantage of TMC (without filter) for this clip derives mostly from its edge-based interpolation.

In the high-motion/low spatial frequency clips like the one used for this test, the advantage of FD and KD and the like is small compared to simple field discarding. That is not surprising, because there is no detail in the large flat areas to be lost by field discarding.

2. Just because a deinterlacer has a better PSNR, that doesn't mean it has fewer objectionable artifacts. This is something that can be assessed only subjectively by eye.

3. Blending generally reduces PSNR, but it is subjectively preferred in some cases.

4. AlparySoft is declared terrible by this metric. It is worse than just passing the combs through, as far as the metric is concerned. But of course subjectively it is better because the combs are at least removed. I suspect that the bad metric arises from a combination of poor motion compensation, non-existent post-processing for combs not due to linear motion, and the blending mode that it uses.

Conclusion

As long as the caveats above are respected, it does appear possible to obtain objective metrics for deinterlacers. It is extremely important, however, to ensure that your reference clip for the measurements is similar in nature to the clips you are interested in deinterlacing, and to assess the artifacts subjectively.

These tests should be repeated with other source types, such as natural film (not anime). But the tests presented are sufficient to show that, contrary to my earlier thinking, the idea of objective metrics can be useful. This is especially apparent in the results for AlparySoft, which really is a terrible deinterlacer.

Journal entries for 2003 can be found here.