Image Sharpness of 2K vs HD fm Full Frame Sensor

[Rick LaLonde]

It occurred to me as I'm camera shopping that 1920 x 1080 taken on a full frame sensor will be blown up by fewer multiples than 2K taken on a super 35 sensor when thrown onto say a 60ft screen.

Am I missing something or would sharpness go to the HD full frame sensor all other factors being equal?

 

[Nick Morrison]

Rick, uncortunately there is no DIRECT corrolation btw sharpness at 1080 and sensor size. A perfect example is the BLACKMAGIC POCKET CINEMA, a s16 camera that generally shoots 1080 just as sharp as the Canon 5D, even though the latters sensor is 4x larger.

See this compsrison below:

And this one:

Truth is, there are MANY variables that decide sharpness - OLPFs, pixel counts, resolution (2k, 4k, etc) all have an impact on percieved sharpness. The Black Magic Pocket has NO OLPF (helping increase sharpness), whereas both the Canon 5D Mark II and III are known to have well thought out OLPFs, that while controlling moire, etc...do have an impact on resolution. The RED Dragon has more PIXELS than RED MX even at the same resolution (say 5k), helping Dragon look richer and sharper.

So..there are lots of factors that determine sharpness...when shooting digitally. Yes, when shooting FILM, a bigger negative generally meant more sharpness (ie IMAX or 4Perf..vs 16mm)...but that dynamic is now being played out more in resolution (6k, 5k, 4k, etc)....which are only loosely tied to sensor size (there are 4K cameras in many sensor sizes). Allthough, the HIGHEST resolution cameras do often have larger than s35 sensors (ie Arri 65 and Epic Dragon), truth is sensor size is still only one of numerous variables that determines sharpness.

Hope this helps.

 

[David Mullen ASC]

Other than the Sony A7S, which only has a 12MP sensor so that the entire full-frame pixels can be used for recording 4K video, most of the full-frame digital still cameras that shoot video have to employ pixel binning and other forms of decimation in order to reduce the number of pixels down to HD, which is only 2MP -- they don't do what a cinema camera like the Red Epic does, which is record all of the pixels in raw video and then convert to RGB and downsample to HD, if that's what you want. For example, even the Magic Lantern hack of the Canon 5D that allows raw recording only gives you HD resolution in raw, because the hack is allowing you to record the raw signal after the pixel binning (or whatever they are doing) needed to reduce 22MP down to 2MP.

So just because the camera has a full-frame sensor, doesn't necessarily mean you are getting the maximum resolution & benefits that comes from downsampling from 4K, 5K, 6K to 1080P.

The fact that some of these still cameras have a full-frame sensor is misleading if you are talking about which camera provides the sharpest 1080P image for projection on a large screen.

 

[Rick LaLonde]

David and Nick, thank you for clarifying - very helpful.

 

[Dunkan Wolf]

Bigger sensors allow for bigger higher quality pixels, but you can have fewer high quality pixels on a smaller sensor. This is the main reason why Alexa wasn't 4K. The 6K Arri 65mm maintains the same pixel pitch but on a bigger sensor.

Since a full frame DSLR generally doesn't have the power to process all data coming from the sensor (with A7s being the exception), they need to dump pixels in order to render the full frame image... either through lineskipping or pixel binning.

 

[Freya]

For example, even the Magic Lantern hack of the Canon 5D that allows raw recording only gives you HD resolution in raw, because the hack is allowing you to record the raw signal after the pixel binning (or whatever they are doing) needed to reduce 22MP down to 2MP.

You can also do a sensor crop as well as the downscaled live view but at the end of the day the problem is that the camera is only capable of going so fast and can thus only record a certain amount of data before it is maxed out so you have to make some kind of compromise whether it is windowing the sensor or recording the full sensor downscaled with all the artifacts from that. At least you have the choice.

Freya