Tugela said:
There is a physical limit on how quickly mechanical devices such as iris blades can work, so at very high frame rates they will have to be kept stopped down. Most modern Canon DSLRs can image at 60 fps or more, but there is absolutely no way their iris blades can flex at that rate. DSLR focusing works in a different way, and has far fewer focusing elements, so the overhead on the processor is lower. Accurate focusing requires shallow depths of field, and at 20 fps with a full sensor read (which the Canon processors can't handle) when you need to keep the aperture stopped down you are not going to have enough time to calculate the focus point at small apertures. That is the price you pay for very high frame rates. Canon would have the same problem if they shot at those frame rates. At that speed focusing would have to be handled like video focusing, which does not happen every frame but rather happens dynamically over a number of frames and is independent of the frame rate itself. You need the aperture stopped down for that since you are monitoring trends over time and using that to control focusing. Which is fine for video but obviously would less optimal for stills where you would want focus on every frame. That is where the compromise comes in, it is to enable those high frame rates where the data that is used for focus calculation is less optimal. In situations where you have enough data (wider apertures/lower dof) you can focus at those frame rates. The Sony is behaving more like a video camera at those high frame rates, something the Canon can't do unless it also behaves like a video camera (in which case it will experience the exact same problem).
In any case it is academic since I doubt there is any lens that can focus fast enough at that frame rate. No matter what camera you have it is going to be an approximation.
The hardware for 4K is there in the latest Digic, it just isn't implemented due to the processor overheating. The Digic 7 and the DV5 are the same processors for the most part, just like all of the earlier processors came in families. They don't redesign the processor separately for video or stills, the core logic is the same, you just have areas enabled/disabled to optimize performance for a particular application. Likewise the DV6 will be the same as the Digic 8, when it is eventually used. The DV6 implementations appear to have fans as well, so we may still not get hardware 4K in Digic 8, if the thermal envelope is not yet controlled enough.
It seems that there is confusion in your statement about how still and video cameras process images they take.
There are 3 sets of core functionalities in both still and video cameras:
1. A/D performed usually by external circuitry to get the image/video signal in.
2. Core ARM based functions that don't change regularly. These include Connectivity (USB, HDMI, SD/CF Cards), sensor (Wifi, GPS, tilt/level), display (LCD back and top, OVF/EVF), actuators (shutter, focus, lens drives, buttons, etc.)
3. Image/Video processing using CPU and GPU, that includes: audio processing (in and out), image/video processing (compression), and DRAM/buffer management.
Depending on how the sensor array processing is performed (4:2:0, 4:2:2, etc. also number of bits for color 8, 10, etc.) and how much of this is pushed off the CPU/GPU to the sensor chip itself the image/video processing may vary. The image/video processing is done within the CPU/GPU using the stored processing software. The processing itself depends on how much data you want to move, how much processing you need (e.g. noise, color profile, edge smoothing, aberration correction, etc.) and how much compression you want to apply to the data before packaging it and sending to the SD/CF cards.
Therefore, there is no fundamental difference between the way the image and video is processed and everything is done with a combination of software and hardware.
Canon's technology encompasses all three areas. The focus in between frames is a technology that Canon has developed and is included in all newer version of its DIGIC processors.
Heat management is part of the design process. There is no dedicated ventilation mechanism for the CPU. If the whole circuitry produces so much heat, fan is added, e.g. in XF series.
Some other companies concentrate mostly on the third set of functionalities and for some heat management is an after thought.
