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DVDO CUE Detection and Correction

post #1 of 13
Thread Starter 
A number of video processors such as those from DVDO feature Chrome Upsampling Error Detection and Correction.

Is this an exact science that genuinely captures all visible instances of the error, or is is just a poor attempt to bolt the stable door after the horse has bolted?

Kind regards,

Ash
post #2 of 13
First of all, I'm not aware of any processors outside of those by DVDO which offer automatic CUE and ICP error detection. Many processors have manually controlled CUE filters (or even permanently-on filters), but I haven't seen any others which actually detect the presence of these errors and only then attempt to 'correct' them.

I put 'correct' in quotes, because in all cases that I know of the errors are not actually corrected, but rather the artifacts which result from those errors are filtered out. While in some cases it might be possible to actually correct the errors, you'd have to know exactly how the upconversion was performed in order to reverse the process and eliminate the error. This in general isn't known, so a more general filter-based approach is normally used.

This is typically done by a vertical chroma filter which reduces the vertical bandwidth of just the chroma signal, while leaving the luma signal intact. No such process is perfect, of course, but the end result is usually much better than having the artifacts there in the first place. In many cases the results are very close to not having the error in the first place. This depends to some extent on the severity of the error and how the chroma upsampling was actually done.

- Dale Adams
post #3 of 13
Quote:
Originally Posted by Dale Adams View Post

First of all, I'm not aware of any processors outside of those by DVDO which offer automatic CUE and ICP error detection. Many processors have manually controlled CUE filters (or even permanently-on filters), but I haven't seen any others which actually detect the presence of these errors and only then attempt to 'correct' them.

I've always wondered why that is the case. Does DVDO have a patent on CUE/ICP detection? Or are the other VP chip manufacturers just not clever enough?
post #4 of 13
Quote:
Originally Posted by madshi View Post

I've always wondered why that is the case. Does DVDO have a patent on CUE/ICP detection?

Silicon Image has a patent on one technique of doing this that I developed in the short period that I was there between DVDO and ABT. I'm not aware that they've done anything with it, though. (This is also the case with other patents from DVDO and those which I filed while I was there - i.e., as far as I'm aware, they're just sitting there gathering dust.) The current implementation in the iScans uses a different technique to do this. ABT has no granted patent on this.

Quote:


Or are the other VP chip manufacturers just not clever enough?

You'd have to ask the other VP chip manufacturers about that.

- Dale Adams
post #5 of 13
Thanks Dale.
post #6 of 13
(copied from another post)
I would be interested in finding out whether anyone has developed a process that actually corrected CUE as opposed to just detecting it or filtering it.

By "correcting" CUE I mean, out of every four scan lines, exchanging the chrominance between the second and third. The detection process is still needed, namely to find out which lines are first of a foursome. If first of a foursome changes from frame to frame every now and then, the process is more complex.
post #7 of 13
most scalers just resample chroma content every other line (essentially the same idea as Faroudja has been doing for ages), but since content is 4:0:0 or 4:2:0, this has no real adverse affect on content even when no CUE is present.
post #8 of 13
Quote:
Originally Posted by Allan Jayne View Post

(copied from another post)
I would be interested in finding out whether anyone has developed a process that actually corrected CUE as opposed to just detecting it or filtering it.

By "correcting" CUE I mean, out of every four scan lines, exchanging the chrominance between the second and third. The detection process is still needed, namely to find out which lines are first of a foursome. If first of a foursome changes from frame to frame every now and then, the process is more complex.

Exchanging chroma samples between the 2nd and 3rd lines won't necessarily correct a CUE problem. It would do this only in the case of simple chroma sample replication - i.e., when a given chroma sample is used unaltered for the 2 lines it's assumed to be located between. That's a pretty poor upconversion technique, though, and I would hope that it's not being commonly used. Of course I would hope that CUE doesn't happen either, so perhaps it's more common than I would like.

Assuming that a more proper interpolation or filtering is done based on the presumed position of the chroma sample relative to the luma samples being used, then all of the chroma values in the 4:2:2 output will be incorrectly calculated. None of them will be identical to the original 4:2:0 values and none of them will be correct. In addition, you'd need to know the exact method used to do the interpolation or filtering in order to be able to correct them. Even then, you may well find that reversing the filtering process to recover the original samples is not possible as information may have been lost in the upconversion.

Now, it may be that swapping certain chroma pairs in the upconverted 4:2:2 signal gives you a better-looking result than not doing the exchange at all, but they won't be the same as if the chroma upconversion was done correctly in the first place.

- Dale Adams
post #9 of 13
Dumb VP50 question:

None of my source components are known to output CUE...
Would I be better off to turn the Auto CUE Correction to off?
post #10 of 13
Quote:
Originally Posted by oink View Post

Dumb VP50 question:

None of my source components are known to output CUE...
Would I be better off to turn the Auto CUE Correction to off?

I'd recommend leaving it on. The reason for this is that you can still get CUE-like artifacts from video sources (what the Secrets folks dubbed ICP, for Interlaced Chroma Problem). The VP50's chroma artifact detection will detect ICP as well as CUE artifacts, and then automatically switch on the vertical chroma filter to reduce or eliminate these artifacts. By leaving the auto detect feature on, your sources without CUE will not be filtered for film-sourced material, but will have the filter switched on for video sources (i.e., when the VP50's deinterlacer is operation in motion-adaptive mode).

- Dale Adams
post #11 of 13
I was wondering what the CUE function does on my VP50, so I did a search and this thread came up.

No surprise, but all this is WAY over my head but I think I can pick it up is I knew the basics. Can someone give me the quick and dirty description of what CUE is and why I should care?

Thanks in advance.mike
post #12 of 13
Good explanation here:

http://www.hometheaterhifi.com/volum...ug-4-2001.html

Sadly this is one of those problems that keep coming back. Manufacturers keep making the same errors over and over - never learning.
post #13 of 13
the DVDO CUE filter for SD sources is amazing and I always leave it to auto so it will pick up and correct ICP as Dale mentioned

DVDO we need an exact spec'd filter only for HD sources

-Gary
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