All things being equal, is a 1-inch 20MP sensor basically the same as a 1/2.3" 12MP sensor?
If it is the same, does it then boil down to which camera has better mechanics; lens, mechanics, etc?
Related to the above question: Which one's better: Panasonic Lumix DMC-ZS50 (1/2.3" 12MP sensor), or Canon G9 X (1 inch 20MP sensor)?
Asking specifically about low-light and image quality. Zoom is not the issue here.
A 1" sensor has a surface area of about 116mm². A 1/2.3" sensor has an area of about 28mm². That's over 4× the light-gathering area. This is a huge advantage that is pretty much impossible to overcome — see Why does it seem like large sensors are necessary for good low-light performance?. Or also see the last part of this answer: Can a smaller sensor's "crop factor" be used to calculate the exact increase in depth of field?
Perhaps you are wondering about the density of pixels, with 20mp vs 12mp. Generally, either of these provide enough pixels to produce high-quality large prints, so the sheer number isn't really an issue. While it's theoretically true that larger-sized individual pixels can provide higher quality, at similar print sizes in the real world, this isn't a huge factor (see Do megapixels matter with modern sensor technology?) — and more importantly, any differences here are usually less important than generational differences in sensor technology, and completely dwarfed by differences in sensor size — there may be a 20% improvement or whatever, but that's nothing compared to the fourfold improvement from 4× the sensor size.
And of course in this case, the individual pixel size advantage goes to the larger sensor anyway.
But, I should stress that this is only going to be a big factor when looking for high technical quality in challenging conditions. In most circumstances, both of these cameras are capable of producing amazing photographs.
All things being equal, is a 1 Inch 20MP sensor basically the same as a 1/2.3" 12MP sensor?
Short answer : not the same. There's a significant difference.
Which sensor size is better depends on your needs.
I have an RX 100 Mk3 and it has a 1" sensor. That model has a lens with a relatively wide aperture so the combination does quite well in low light (but it also has a flash !).
I've considered the 1/2.3" Panasonic P&S models including the one your mention. They do provide more focal length range, which is something the small sensor allows in a compact that is not at all easy in a large sensor model.
As far as light gather goes, the smaller sensor ( it is approximately half the size in length and width and hence roughly one quarter the area of the 1" sensor ) it is not able to gather as much light. For design reasons the zoom range means you also have a narrower aperture so it gathers less light to start with. It's probably about a stop to two stops less capable.
They simply do different things.
Asking specifically about low-light and image quality. Zoom is not the issue here.
Consider the combination of aperture values and sensor size light gathering and make your own mind up.
But the sacrifice of focal length is significant. It does frustrate me sometimes that I'd stuck with a 24-70 equivalent and can't get the extra focal length range.
If you're particularly chasing low light performance I'd suggest a larger sensor, like the ones in the Sony NEX and A6xxx models with a compact kit 16-50 lens. These also give you the option of mounting a "proper" fast lens if you're willing to add some weight and bulk.
lary909, as far as your question goes, they are NOT same. A 12MP 1/2.3" camera would be equivalent to 8MP 1" Camera. A 20MP 1" Camera image quality is 5-6 times of a 12MP 1/23" Camera. For the image to be of same quality, the number of pixels (or mega pixels) required DECREASES as the image size INCREASES. Note that, here "quality" does not mean just the "resolution". "Quality" means better performance in low light, less noise in the image, higher contrast, sharper image, etc., which improve the overall look of the image.
