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Magic Lantern Forum

Developing Magic Lantern => Reverse Engineering => Topic started by: miyake on September 05, 2012, 08:54:46 AM

Title: High ISO needs more HW resource
Post by: miyake on September 05, 2012, 08:54:46 AM
Is this a well known things?
I just understand it.

CBR 3.0 + ISO3200 = recording stop immediately
CBR 2.6 + ISO3200 = recording stop immediately
CBR 2.4 + ISO3200 = sometime recording stop
CBR 1.0 + ISO 3200 = no problem

CBR 3.0 + ISO200 = no problem
Then push ISO button and ISO change dynamically, will recording stop when we changed to over ISO 1600
Title: Re: High ISO needs more HW resource
Post by: a1ex on September 05, 2012, 09:05:35 AM
The noise is considered detail and requires higher bitrate.
Title: Re: High ISO needs more HW resource
Post by: nanomad on September 05, 2012, 09:15:01 AM
Right
A simple test is to compare the bitrate of ml vs Canon iso 500. On dark scenes I found Canon to be more noisy and with a higher bitrate
Title: Re: High ISO needs more HW resource
Post by: miyake on September 05, 2012, 03:15:48 PM
Thank you for your explaining.
Anyway, CBR is not Constant bitrate. We can't set maximum bitrate for CBR. right?
Title: Re: High ISO needs more HW resource
Post by: a1ex on September 05, 2012, 03:23:10 PM
CBR is maximum bitrate (not per frame, but with some kind of averaging). I think the process goes like this:

- record frame 1 with some fixed QScale
- see what frame size it got
- compute QScale for frame 2, according to CBR factor and other settings
- record frame 2 with this QScale
- repeat
Title: Re: High ISO needs more HW resource
Post by: miyake on September 05, 2012, 06:01:36 PM
I see. Thanx!
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