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Canon DSLR bit rate - a question...

Guy Ducker

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Dear all,


I hope this isn't too rookie a question for this site, but I'm trying to make a decision about a project which we will almost certainly want to shoot in black & white on a Canon DSLR, and I realise that it takes me to an essential question about how those cameras record data.


I've done tests shooting 10 seconds of footage in the Standard picture profile, the same in Technicolour CineStyle and in Monochrome. All three tests gave me pretty much the same size of file with the same data rate.


Here's the question:


Does this mean that I'm getting a more detailed image in Monochrome? It's not having to compress any colour information into the h.264 file, so is it filling up the space this leaves with a little bit more lovely detail? Or, because it's CBR, is it including a lot of blank useless colour information, causing the file to be the same size as a colour file?


Why do I need to know? Well, if we are actually getting a more detailed picture by dumping colour information at source, then we'll go for that. If however it makes not a blind bit of difference, then we might as well shoot in colour, to leave our options open.






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There are specific monochrome modes in h.264, but it's unlikely the encoder in the Canon DSLRs support them.


So, it depends very much on how the camera's implementation of the h.264 codec works, which you can't tell. The h.264 documents themselves specify the decoder, not the encoder. Any encoder which produces material that the standard decoder will read is acceptable, so you can't really tell what they're doing. Hardware codecs such as the one built into your camera are likely to be simpler than those written into computer software, because of the simpler hardware that's available on a camera.


That said:


Most h.264 codecs should assign very little data to the colour difference channels if there wasn't any information in them, and it should do that without needing to be specifically told to. So, yes, I would hope that you'd get better results recording black-and-white, if only fractionally.



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