I keep wondering what is going to happen in the future with dual-pixel technology. They have the ability to read both sides of the pixel seperately, I wonder how much work it would be to set the two sides to different ISO values, read them both, and combine the values for greatly expanded DR.
This would obviously require more computing power than just reading the sensor would, but comments out of Canon about the greater computational needs of future cameras ties in with this... I am really curious to see what happens with the 7D2..... It should be dual-pixel and dual processor (Digic6 or even 6+?) so it will be able to do a lot more computing than a 70D. The next year or so could be interesting.
They wouldn't need to bother with the dual-pixel approach with this patent. They simply read "the pixel" (regardless of whether it is a single photodiode, or two/four binned, whatever) with two different gain levels (different ISO settings, done simultaneously on different signals). This patent offers a much better way to solve the problem without resorting to "hackish" approaches like what ML did, or like what you suggest with reading one half the pixel at one ISO and the other half at another ISO (which wouldn't be nearly as good, since each half pixel is only getting half the light, so the half-reads would already be at a disadvantage large enough to completely eliminate any gains you might make with the dual-read process in the first place.)
Even better than simply reading half pixels at different ISO settings, this patent reads each pixel twice simultanesously at different gain levels, while also bringing the ADC on-die and column-parallelizing them, allowing them to run at a lower frequency, thus reducing their potential to add downstream noise. With column-parallel ADC, they could do what Sony Exmor does...per-column read tuning to eliminate vertical banding. It also brings in the benefit of shipping image data off the sensor in an error-correctable digital form, eliminating the chance that the data picks up even further noise as it travels along a high frequency bus and through a high frequency DIGIC chip. This patent would single-handedly solve a LOT of Canon's noise problems.
The only real difference between Canon's Dual-Scale CP-ADC patent and Exmor's is that Exmor uses digital CDS and digital amplification (basically, it is an entirely digital pipeline)...I see no mention of Canon's patent referring to digital data processing on-die. There are theoretically pros and cons to both digital and analog readout, so only time will tell (assuming Canon actually IMPLEMENTS this design sometime soon) whether Canon's approach produces results that are as good as Exmor or not. Sometimes it is easier, and more accurate/precise, to apply certain kinds of processing and filtering on an analog signal rather than digital bits.
Thank you for the explanation! I got the gist of it, but I still don't understand the basics: how is it possible to read the same pixel twice simultaneously? I thought you can't eat your cake and have it too ? I mean, wouldn't the signal become weaker if you split it?