So when does the compression begin... After pressing record?

S

Stab

Well-known member
Im sure people have thought about this before but it came to my mind as well:

It is well known that the Canons DSLRs' video quality is greatly compressed and therefore loses quality. But when is that compression applied by the camera? As soon as you hit the record button? Or even when you switch to live view?

If it is only after pressing record, couldnt this be avoided by some kind of hdmi recording device? So you dont record on the camera, just send its' signal to an external recording device / software?
 
Well, there are two things that apply to make the video the way it is:
1) the way it's scanned off the sensor (and the attendant moire and chroma contamination and jaggy aliasing that comes with it) and
2) the way it's compressed and stored on the memory card.

The actual h.264 compression takes place when you're recording it to the card. But the rest of it happens as the sensor is being scanned, and there's pretty much no escape from that. You can see how much better it could look if you were sampling just a small patch, when you go into the 5x or 10x super-zoom focusing mode. When you're sampling a tiny patch, it looks great. But when you try to sample the entire width and height of the sensor, that's where the problems come in, and those would be apparent on any HDMI recording device as well.
 
Ah thanks Barry.

So its not the compression that is mainly responsible for the aliasing and loss of detail but simply the sensor-read out...
Hmm, but how much 'damage' does the h.264 compression actually?
 
Right, the aliasing is caused by the way the stills-camera sensor is read for video purposes. h.264 can be a great codec, although the implementation in the DSLR isn't all that good. "damage" from the h.264 would be any codec compression artifacts, or the chroma subsampling down to 4:2:0.
 
I'm sure this would take some extreme hacking and electronics skills, but, I wonder if there is a way to somehow record straight of the sensor through to some mass flash storage.
 
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