Originally posted by BarryE A larger PW will fill up to max with received photons, slower than smaller PWs
Actually not. As the well capacity increase, the light sensitive exposed area also increases by the same amount. That's why for a given set of aperture and iso sensitivity, the exposure time is roughly the same regardless what the sensor size is. So, adding up signals coming from two adjacent pixel or having a double sized pixel is roughly the same, except a few percent of sensitive area lost for the additional insulation area and additional interconnects needed with smaller pixels. It's also possible to increase DR by adding up well capacity but then departing from standardized ISO values (what Nikon are doing basically). Now, keeping actual ISO constant to its standardized values, by having one large pixel instead of several adjacent smaller pixels, the gain in DR versus pixel merging is only a few percents. On the other hand, having small pixels and combining them by matrix configuration or software has the advantage of having a single techo plateform (lower NRE) and for the final camera product design, the flexibility to chose the tradeoff between better resolution or better efficiency (slightly better noise, or DR). Furthermore, having more smaller pixel, eliminate the need of optical anti-alias filter, and even after decimation, contains slightly more image information then an equivalent lower pixel count would contain.
Originally posted by BarryE This may be limited by processor speeds and what else it has to do.
Regarding processing speed, image processors have embedded specialized DSP hardware computing blocks, hence some standard operations such as JPEG compression can be performed by hardware instead of going through a sequential machine. Typically, digital decimation is easy to implement in a pipelined FIR (Finite Impulse Response) filter fashion, so basically, there is not computing time involved, only data latency added, and since the amount of data is reduced after the decimation filter. In your current DSLR, you actually have this already implemented, for instance on the K-3, you can select JPEG 24Mpixels, 14Mpixels, 2Mpixels, and you'll see that you can even achieve a larger number of shots in burst mode.
---------- Post added 23-07-15 at 13:00 ----------
Originally posted by Rondec I don't know the answer, but photon wells are not necessarily related to pixel size. The D7200 has significantly better dynamic range throughout its range than even the old 16 megapixel Sony sensors did, despite having 24 megapixels in an APS-C camera. The D810 once again has better dynamic range up to iso 3200 than other cameras out there right now.
Given the same sensor techno, more dynamic range with same pixel size, is achieved via a decrease of sensitivity (=different min ISO setting).
---------- Post added 23-07-15 at 13:04 ----------
Originally posted by falconeye There are technical reasons why a high pixel count facilitates a high dynamic range.
Actually, the larger the pixel the lower the noise and the better the DR (thermal noise = K*T/C). So, increasing pixel count on same sensor area actually decreases DR. In order to counter this issue, adding extra cap in the signal path helps reduce noise , increase DR, but at the same time decreases cell sensitivity. In order to achieve more DR, D810 used lower ISO, but then the user need a tripod or image stabilization more often...
---------- Post added 23-07-15 at 13:18 ----------