Image Quality

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The capture and publication of the NOSSDAV 2005 conference presentations and discussions was an experiment to test the suitability of using RGB capture and record-to-disk technology to produce material for on-demand replay suitable for use in a digital library. Details about the capture technology and process and the publication of the material on the web are provided in the NOSSDAV 2205 Conference Presentation Capture paper we wrote.

I have looked again at the material we published in particular the slides, and I have to admit the higher bit rate material, that is the material coded with 512x384 images at 1200 Kbits/sec (Kbs), is harder to read than the lower bit rate material, that is the material coded with 384x256 images at 600 Kbs. This difference is true on both Windows and Macintosh computers no matter what image size was captured (i.e., native or scaled). I have created two examples taken from talks:

• Harrick Vin (Mac presentation; VGA display and capture)
• Chris Chambers (PC presentation; XGA display and capture)

I draw several conclusions from these examples and some ideas for further things with which to experiment.

1. Native capture and playback is best. I am beginning to think that the encoding at 600 Kbs might be the best one for most people. In other words, the 1200 Kbs material may be more trouble than it is worth.
2. I suppose it is not surprising that Quicktime playback quality is better on a Mac than on a Windows PC. If I am right about the post decoding filter being implemented on the Mac, I hope a future release of Quicktime for Windows includes the filter. As a content producer, I want the material to look as good as possible on all platforms.
3. I am curious if the material will look noticibly better if I encode the original source material using the two-pass H.264 encoder in Quicktime V7 Pro using native resolution. I didn't do this orignially because the time required to do the encoding was prohibative - as I recall 40X real-time for each file.
4. Lastly, images on the Mac are lighter due to the difference in gamma correction. I keep being reminded of this when I see images created for one platform or the other.