Steven White |
April 19th, 2007 09:53 AM |
Quote:
Originally Posted by Harm Millaard
(Post 663001)
NOT if you are playing back from tape, then HDMI is nothing more than fire wire, just a digital connection to transfer 4:2:0 at 1440x1080.
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I don't think this is quite correct.
HDMI is not a digital data connection like Firewire. Via Firewire you are essentially copying bit-for-bit the data on the miniDV tape encoded in the HDV codec.
HDMI is a digital display connection, and so it is broadcasting uncompressed (or, if playing back from a tape, "de-compressed") footage at the specified 1920x1080 4:2:2 rate. This means that in-camera the video is being decoded from 1440x1080 4:2:0 and up-sampled to 1920x1080 4:2:2. There's no more actual information there, but there is some additional synthesized information. Depending on 4:2:0 artefact reduction circuitry used in the 4:2:2 upsample, there could actually be a boost (or a decrease) in quality attained this way that is hardware specific.
When capturing via HDMI live, you are bypassing the HDV compression and colour decimation to the degree that this is possible out the ass-end of the DSP. If the colour and gamma correction done in the DSP outputs only to 1440x1080 4:2:0 before sending it the MPEG-2 algorithm, you are only saving on the HDV artefacts and GOP structure. Still, uncompressed 1440x1080 4:2:0 is much better than the MPEG-2 followup.
From what I've read, there is evidence that processing is done at full 1920x1080 4:2:2, and that what is broadcast on HDMI live is indeed significantly higher quality than the HDV output. I believe this applies to all the HDV cameras with an HDMI output, but someone would have to do careful case-by-case testing to be sure.
-Steve
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