Doug Pardee Offline Image Upload: Off
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As to the Digic not being the bottleneck for higher frame rates…
I confess that I was primarily thinking of the 5D, which is the camera that I hear the most complaints about frame rate about.
But I'm not smart enough to just leave it at that, so I'm going to go ahead and address the 1-series 
The burst performance of the camera is pretty much uncoupled from the throughput of the Digic chip. What matters is if there's room in the buffer and how fast the buffer can be loaded with sensor data. I presume that there are limits in the Digic II as to the fastest memories that it can deal with, and the size of those memories, but I'd be disappointed if it was already "maxed out" in those regards just a couple of years after it was introduced.
But let's look at the throughput of the Digic chip anyway. It can process JPEGs faster than it can process Raw files. Both involve the same amount of data coming in from the buffer, JPEG files (almost certainly!) require a lot more internal processing than Raw files do, and yet on a 1D mark II N the buffer fills up with [about] 20 Raw files or 40 JPEGs. The bottleneck would therefore seem to be in writing to the flash card, where JPEG files are a fraction (1/2 or less) of the size of Raw files.
In fact, according to Rob Galbraith's flash speed tests, the best that the 1D2N can achieve on the CF slot is somewhere around 7 MB/sec (7-1/2 for Raw, 6-1/2 for JPEG). The SD slot is a bit faster, up to 8-1/2 MB/sec for Raw. For Raw files around 8 MB in size, the maximum sustained frame rate is therefore about 1 fps. For JPEG files around 3 MB in size, the maximum sustained frame rate is about 2.5 fps.
So the maximum throughput of the entire system is bottlenecked by the write to flash memory. The peak frame rate is determined by the shutter, the sensor readout, and the speed of the buffer. The maximum burst size is primarily controlled by the size of the buffer, although the system throughput affects it a bit.
But wait… the SanDisk Extreme III cards are rated at 20 MB/sec while the camera is only writing them at 7-8 MB/sec. It appears that there should be some room for substantial improvement in efficiency here, and that would seem to indeed be dependent on the Digic chip. Furthermore, the new SanDisk Extreme IV cards are rated at 40 MB/sec. If the (a?) new Digic chip is able to come close to using that 40 MB/sec speed, the throughput could go up to where it significantly increases burst size—perhaps even providing unlimited 8.5 fps burst for JPEGs.
Edited on Dec 06, 2006 at 11:16 PM
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