4K generates a lot of heat on the sensor and related ADC's etc - they are converting / reading far more data than 1080p is.
The ADCs are on the sensor, the task is to remove the heat from the sensor and place it elsewhere which reduces artifacts caused by high thermal concentrations (banding & such), the DSPs being one and memory being an other heat producers, then the global removal of the heat - ie the spreading of the heat out is a big problem on a small camera.
But this is obviously ONLY an issue for small body cams NOT cams in general, once again NX1 ! Canon does NOT offer 4kHD on any DLSR but the 1DC !
Larger sensors due to the density of heat producing parts are the issue, since only a 8mp-12mp sensor is needed for 4kHD then higher mp Still sensors (18-36mp) and sizes are the issue.
Video specific sensors are smaller than 35mm or APS-C making it easier to dissipate that heat due to the physical size.
since larger sensors have larger wiring structures, this increases the resistance and also the thermal conditions on the sensor itself - combine that with the image processing and compression - which with h.265 is significant.
Not a wiring issue, the wiring just brings the data off the sensor to the other pertinent componenets (DSP memory, etc), and the larger the piece of the processing performed on the sensor the more heat produced there, then the associated processing (DSPs and ancillary circuitry) next produces big heat.
So yes small bodies have a hard time dissipating heat (with current tech solutions), but then the iphone does 4kHD does it not?
Panasonic states that there is no way right now that 4K will come to their smaller Gx series bodies because of thermal conditions. canon stated with the 1DC that internally they had to shunt more heat away from the camera itself to support 4k.
Of course that is with current or 3 yr old tech, but small sizes 'cluster' the heat and w/o active effort the heat will limit the size of 4kHD cams.
Tablets have the same issue, especially the i5,i7 tablets, they solve it via heat pipes and small fans, fans not likely in cams but heat pipes could be used - but of course making the cam just that much larger.
The only obvious solution is reduce the heat at the source via smaller chip topology (how Intel has done it) and smarter/clever heat management
....
is canon working on 4k? I'm sure they will - but they will probably also really wait until TI supports it natively in their DSP's and processors before they implement. it's not in DiGiC 6, it may be possible in DiGiC 7.
I suspect Canon submits specs to TI and TI responds with can or can not meet the spec, TI may have topology size issues (still too large). Samsung who I believe can make their own DSPs solved it, so can Canon but maybe not via TI (Texas Instruments) DSPs.
TI will support H.265 either when someone pays them or they think the market demands it - Canon apparently has not demanded or payed for it, yet, nor has TI produced for Canon a sufficient single DSP for advanced cam uses.
I do not know if TI are the leaders in DSPs of the type needed for a power limited applications - maybe.
I am certain that many chip firms are either soon to deliver or working ferociously to produce H.265 solutions - either single chip or multiple chips - as many/all those 4kHD non cam devices need them.
But NX1 has solved it, and somehow so can Canon !! Maybe just in DSLRs for now maybe not, we shall see yes? That is their tech hurtle to leap over !
