How is the OMD so fast

Started Jan 7, 2013 | Discussions thread
OniMirage Contributing Member • Posts: 990
Re: Good tracking requires PDAF.

Paul De Bra wrote:

Your expectation that CDAF will somehow be able to track in the future is somewhat unrealistic. The fundamental difference in property is that with CDAF when a subject goes out of focus the image does not have any information whether the subject is coming closer or moving further away. This could be done with clever motion analysis but from a single image captured by the sensor you cannot know this. With PDAF when a subject goes out of focus the sensor can detect whether it is out of focus because the subject is too close or because it is too far away. It works like with the "two halves" in older MF dslrs: the two halves of the focus point move away in one way when you focus closer and the other way when you focus further away, and with PDAF this info is used. So PDAF knows in which direction focus needs to be adjusted and CDAF does not know and has to try one way and if the image becomes more blurred then try the other way... The info for selecting the right direction just isn't there in the image. An image sequence is needed and clever processing to detect the direction of motion. We need a serious gain in on-board processing power to achieve that.

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Both systems are reactive. If the image becomes out of focus the PDAF system may know where to go but it's still lagging by reacting to an out of focus subject. CDAF in its current form unfortunately focuses to infinity and back and doesn't know if the image is getting worse until it comes back the other way. Developers need to find a way to determine if the subject is getting worse by going so far it needs to stop and go the other way. Continuous CDAF actually works this way right now. Alternatively they could do it another way, by using an infrared depth sensor which would be superior to either PDAF or CDAF in tracking capability. Considering the size of the sensor in a m4/3 camera the depth range available would be pretty extreme if they could incorporate that type of system.

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