Pixel density - can the playing field be leveled???

Started Jun 6, 2009 | Discussions thread
Cheburashka Regular Member • Posts: 297
How it's done.

bushi wrote:

...sorry, I am not naive english speaker

Please, don't apologize. Many people have the same affliction through no fault of their own. And, yes, I got your pun.

Absolutely. However, I do have a question for those that feel fewer and larger pixels will have a noise and DR advantage at higher ISOs: just how much of an advantage, in terms of stops, do you think 10 MP would have over 20 MP?

eek... 17.673, roughly. How possibly one could estimate this? I guess anything between 1-2 stops comparing to G10? If it brings to the table usable ISO 800 setting, maybe acceptable 1600, I am sold.

Well, see, that's what I'm getting at. There's no way that you would get an extra 1-2 stops on the G11 over the G10. Let me explain. Noise comes from two components, the light itself (photon noise), and the sensor and supporting hardware (read noise).

To improve the photon noise, you either need more light (that's how larger sensors get most of their noise advantage), or to collect that light more efficiently. So, the question is how to fit more light into fewer, but larger, pixels.

The microlens covering is 100% efficient for either the G10 or G11, so we're not going to improve on 100%. But, we could argue that the overall area of the larger pixels is greater than the overall area of the smaller pixels, because if the electronics between the pixels occupy the same area per pixel, rather than scaling with the pixel size, the larger pixels would be more efficient and thus be able to absorb more light. But for a one stop performance here, the pixels of the G11 would have to have double the area as the pixels of the G10.

So, let's say the G11 uses Sony's new idea of putting the transistors under the pixels, rather than between the pixels, so that there's no wasted space between the pixels. So, if the G11 had one stop over the G10 in that regard, that would imply that fully half of the sensor area on the G11 is devoted to electronics between pixels, and that's even if there were no gap between the G11 pixels! In other words, no dice.

The read noise, on the other hand, depends on the noise from the pixel and the noise from the supporting electronics. It doesn't make sense that a larger pixel could have less noise than a smaller pixel for the same level of technology, nor that the supporting electronics would be more efficient, either. In fact, a larger pixel would have more noise for a given technology. It's just that fewer pixels with less electronics could mean less overall read noise.

So, for the same technology, at best you're going to get the same pixel noise per pixel for the larger pixels, but since the electronic noise would be the same, the overall read noise would still be higher. But, to make it easy, let's say that the read noise per pixel is the same. How would the overall read noise compare for the sensors? Well, you'd need 1/4 as many larger pixels to gain a stop in read noise.

In other words, the difference in photon noise and read noise between 15 MP and 10 MP for a given technology is going to be a lot less than what you, and others, are hoping for. Of course, I keep saying "for a given technology". Sure, the G11 will likely have technological improvements. But what I'm saying is that those improvements could have been implemented in a 15 MP, or higher, sensor as well.

Now, I'd love to be proven wrong. But I haven't seen any convincing arguments that larger pixels can offer any substantial increase in noise or DR. But I've seen lots of tricks that reduce noise by destroying detail, such as clipping the blacks early, and lots of misinterpretations of noise performance that was a direct result of comparing images at the pixel level rather than at the same dimensions, or comparing in-camera jpgs where one camera had a much better jpg engine than the other (one has to wonder what role Digic 4 plays in this?).

P.S.: Steen says hi. He's a cool guy, and you seem to be a cool guy as well. Just something to keep in mind.

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cpw
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