I identified the same issue with cycle time, but to me the biggest problem is the assumption of an accurate, sensitive, non-destructive-read sensor. They're assuming that they can charge a capacitor from a photodiode accurately, and also hook a voltage comparator (which is effectively the same as an ADC) to it constantly to get an accurate pulse to count.
Assuming you have an accurate sensor that can be read non-destructively, then none of this modulus stuff is necessary anyway. Read once to set the proper gain on the ADC, then read again to get the fine bits. That way you still get the "unbounded HDR", but you don't need an ADC for every single receptor site, and you don't waste space on the counter or comparator. Instead, all of that lives on the image processor where it's not going to cause heat noise.
That's such an incredibly enormous hand-wave to me that I feel I've got to be missing something. Why make it so complex with all the modulus stuff if we have a magic sensor?
And we haven't even gotten into issues like thermal noise... Who knows, it may be great, but right now it just looks like a press release :-)
Oh the 1/10,000,000th comes from assuming they need to reset 128 * 8000 times per second to merely equal current sensor performance before losing sensitivity to misc losses.
If they want one more bit of DR they need to cycle in half as much time, and so on. Similarly, if we generously assume they're only losing 50% efficiency to cycle time and real estate then double again.
Also don't forget that you actually need to cycle significantly faster than just 128 * 8000 times per second, since presumably you can't integrate light into the capacitor while you're also zeroing it. Whatever goes into the capacitor while it's draining is lost, because it drains to zero.
Seems like a better approach would be to add a "gain pixel" to traditional sensors.
So imagine you've got your Bayer grid (or a layout that functions similarly), one of the pixels in the grid gets read out first. That one sets the gain for the ADC for the surrounding pixels. The downside is your iteration couldn't be linear and the gain control would be a lot more complex, but you could do it with technology that actually exists, and you wouldn't lose half of your vertical resolution by doing it a whole line at a time like Magic Lantern's dual-ISO mode.
You'd have to do fancy processing around high-contrast edges, but what else is new.
All good points. (And my figure actually assumes 10x faster and no loss of time between clearing wells and capturing photons -- i.e. 90% of time is spent capturing photons and 10% is spent clearing the well with no downtime -- to be generous. And, again, just to equal current performance.)
The underlying idea is sound -- storing bits is a linear problem but storing photons is an exponential problem. Of course you're still going to have to dump exponential amounts of energy... (So forget the "unbounded" part.)
Yeah I was thinking that too. No matter how tiny a capacitor, you have (tens of) millions of them on the sensor, one per photoreceptor, and you're charging and discharging them 100k-10M times per second. That's a lot of energy being accumulated and dissipated right next to the photoreceptors. Thermal noise is gonna be nuts on a modulus sensor, too.
No system is ever unbounded, period, unless you live in a world of frictionless spherical cows. At some point you run into issues caused by accuracy, energy, capacity, etc.
Comments
I identified the same issue with cycle time, but to me the biggest problem is the assumption of an accurate, sensitive, non-destructive-read sensor. They're assuming that they can charge a capacitor from a photodiode accurately, and also hook a voltage comparator (which is effectively the same as an ADC) to it constantly to get an accurate pulse to count.
Assuming you have an accurate sensor that can be read non-destructively, then none of this modulus stuff is necessary anyway. Read once to set the proper gain on the ADC, then read again to get the fine bits. That way you still get the "unbounded HDR", but you don't need an ADC for every single receptor site, and you don't waste space on the counter or comparator. Instead, all of that lives on the image processor where it's not going to cause heat noise.
That's such an incredibly enormous hand-wave to me that I feel I've got to be missing something. Why make it so complex with all the modulus stuff if we have a magic sensor?
And we haven't even gotten into issues like thermal noise... Who knows, it may be great, but right now it just looks like a press release :-)
Oh the 1/10,000,000th comes from assuming they need to reset 128 * 8000 times per second to merely equal current sensor performance before losing sensitivity to misc losses.
If they want one more bit of DR they need to cycle in half as much time, and so on. Similarly, if we generously assume they're only losing 50% efficiency to cycle time and real estate then double again.
Also don't forget that you actually need to cycle significantly faster than just 128 * 8000 times per second, since presumably you can't integrate light into the capacitor while you're also zeroing it. Whatever goes into the capacitor while it's draining is lost, because it drains to zero.
Seems like a better approach would be to add a "gain pixel" to traditional sensors.
So imagine you've got your Bayer grid (or a layout that functions similarly), one of the pixels in the grid gets read out first. That one sets the gain for the ADC for the surrounding pixels. The downside is your iteration couldn't be linear and the gain control would be a lot more complex, but you could do it with technology that actually exists, and you wouldn't lose half of your vertical resolution by doing it a whole line at a time like Magic Lantern's dual-ISO mode.
You'd have to do fancy processing around high-contrast edges, but what else is new.
All good points. (And my figure actually assumes 10x faster and no loss of time between clearing wells and capturing photons -- i.e. 90% of time is spent capturing photons and 10% is spent clearing the well with no downtime -- to be generous. And, again, just to equal current performance.)
The underlying idea is sound -- storing bits is a linear problem but storing photons is an exponential problem. Of course you're still going to have to dump exponential amounts of energy... (So forget the "unbounded" part.)
Yeah I was thinking that too. No matter how tiny a capacitor, you have (tens of) millions of them on the sensor, one per photoreceptor, and you're charging and discharging them 100k-10M times per second. That's a lot of energy being accumulated and dissipated right next to the photoreceptors. Thermal noise is gonna be nuts on a modulus sensor, too.
No system is ever unbounded, period, unless you live in a world of frictionless spherical cows. At some point you run into issues caused by accuracy, energy, capacity, etc.
maybe that energy can be used to recharge the battery