Re: [libdc] Corrupted frames under OS X - libdc1394 2.0.1
Capture and control API for IIDC compliant cameras
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From: Damien D. <ddo...@is...> - 2008-02-28 01:33:48
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Hi Mark, David, On Wed, 2008-02-27 at 15:39 -0500, David Moore wrote: > On Wed, 2008-02-27 at 17:55 +0100, Mark wrote: > > Here are some more screenshots of corrupted frames. > > > > http://www.dvd-memories.de/1.jpg > > http://www.dvd-memories.de/2.jpg > > http://www.dvd-memories.de/3.jpg > > http://www.dvd-memories.de/4.jpg > > http://www.dvd-memories.de/5.jpg > > http://www.dvd-memories.de/6.jpg > > http://www.dvd-memories.de/7.jpg > > http://www.dvd-memories.de/8.jpg > > > > Frames 1, 3, and 7 are pretty typical of what happens when a packet is > dropped due to bus traffic. In the future, I hope to detect some of > these cases in libdc1394 and drop the corrupted frames instead of > passing them through to the application. Note that the dropped packet happens just after a little strip of "bad data" in the three images. Not sure what to do with that info yet ;) > Frames 2, 4, 5, 6, and 8 are much more unusual. It appears that a few > pixels are merely corrupted rather than missing. I haven't seen this > type of failure mode before. Assuming that the camera didn't actually > send the data already corrupted, the only cause I can think of would be > a software bug that overwrites some of the existing image data. It is > not possible for the image data to be corrupted on the bus, since there > are checksums to verify the integrity of each packet. > > If this is indeed some type of bug, it would have to be in the Mac OS > firewire stack, libdc1394, or your display application. On frame 8, the bad data line on the left shows more than just bad data: a small area around each white spot is completely black, without noise. This contrasts with the noisy black region of the building's window. Similar artefacts are present on other images too. oh wait, this is a JPG! That explains a lot ;) As you suggested before, can you post RAW data as PGM? It probably won't change much but I want to be sure. Another thing to try: use an interface card (cardbus, etc) with an external power supply and see what happens. The fact that there is a correlation between a heavy use of other PC's ressources (HDD, QT) and the appearance of bad data makes me thing that there may be EMI when using the integrated chipset. I have seen this before on cheap PCs ;) -- Damien 高原 Douxchamps Assistant Professor, Image Processing Laboratory, NAIST http://damien.douxchamps.net/ |