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03-17-2009, 02:32 PM   #91
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QuoteOriginally posted by jay Quote
Holy smokes! Look at all these people that don't know what they're talking about!

It all started with this:



It's understandable -- this can be very confusing, because there's two different pictures going on

Many of us understand the particle model. A pixel is a square light-sensitive detector. Obviously, the larger the pixel is, the more light it can collect, which means that for a given exposure, a larger sensor means a brighter image.

In this model, light falling on a sensor is like rain falling into a rain gauge. The bigger the gauge, the more water you get.

But by looking at the electromagnetic wave model -- which is equally valid -- things aren't as simple. Light oscilates at different wavelengths, and each pixel is an antenna. The size of the photosite determines the transfer characteristics. When I say "transfer characteristics," I don't mean a simple linear model showing that as the sensor gets bigger or smaller, light is easier or harder to collect. It's not that simple.

In general, all things being equal, when you increase the pixel density of a sensor, you're shrinking each photosite, which redueces the amount of light, and increases the noise of the photo.

And, to add insult to injury, more megapixels doesn't mean sharper images. There's really no correlation at all once you hit the dozen-or-so megapixel mark on a APS-C sensor. At that point, the transfer characteristics of the photosite becomes less intuitive.

There's other issues, too, when we're talking about image quality and sensors "outresolving lenses" (always a loaded statement to make). Sampling has to do a lot with what I was talking at previously, and I don't have time to explaiin it here, however, there was a great article on LL:

Do Sensors “Outresolve” Lenses?

Check it out.
Except that that's not what I was talking about.

Smaller pixels collect less light. Common sense, like the title of this topic.

This degrades performance on the pixel level. This is what we see in numerous tests that lead people to declare things like "the Canon 40D has better image quality than the Canon 50D due to its lower pixel density." Because honestly, the pixel-for-pixel crops from the 40D do look nicer.

But that's not the same as having superior imaging characteristics overall. Once you zoom out and look at the whole picture, or equal-area crops, the noise is about the same (except finer grained) and you get more resolution from those 15 megapixels. Maybe less than you would hope, but whether that's due to a particularly strong AA filter in one and a weaker one in the other or something else is up in the air and there's really nothing to test it against so far.

03-17-2009, 05:57 PM   #92
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QuoteOriginally posted by falconeye Quote
In order to bring some fun to this thread, let me show a detail from a bee's wing.
that gallery is insane!!!! Photomicrography, Charles Krebs, Gallery 1
03-17-2009, 08:33 PM   #93
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QuoteOriginally posted by er1kksen Quote
Except that that's not what I was talking about.

Smaller pixels collect less light. Common sense, like the title of this topic.

This degrades performance on the pixel level. This is what we see in numerous tests that lead people to declare things like "the Canon 40D has better image quality than the Canon 50D due to its lower pixel density." Because honestly, the pixel-for-pixel crops from the 40D do look nicer.

But that's not the same as having superior imaging characteristics overall. Once you zoom out and look at the whole picture, or equal-area crops, the noise is about the same (except finer grained) and you get more resolution from those 15 megapixels. Maybe less than you would hope, but whether that's due to a particularly strong AA filter in one and a weaker one in the other or something else is up in the air and there's really nothing to test it against so far.
some more food for thought......
Trade-offs between high speed and image quality versus high resolution - Page 2 - Open Photography Forums
A Panasonic FZ50 with it's pixels binned down to 1DmkII size has slightly less shot noise at all levels, and 60% of the read noise, for up to 0.7 stops more DR at the output pixel level (I don't believe you need to bin to get the benefit, though).

I really don't see how people can believe that small pixels are bad. It's a long way down past 8 microns where you will start losing photons, even with current technology. Canon's 1.3 and 1.0 sensors give good images because of their size; not because of the size of the pixels.


Followed with:
Trade-offs between high speed and image quality versus high resolution - Page 2 - Open Photography Forums
Traditional noise statistics lie in the real world, where noise has width and height, in addition to the depth that is measured as standard deviation. Look at this graphic, both at normal monitor distance, and from across the room:


Then follow this thread down the rabbit hole.......
First, the theory. . .: Open Talk Forum: Digital Photography Review


only to end up here:
So for the case of 100 MP or more on an APS-C sensor, one will still produce the same print image quality as your 6 MP sensor at ISO 1600, but will have something about twice better than the print image quality of the FZ50 at ISO 100 at 25 MP or about the resolution limit of most lenses one would use with it. That's about 4000 X 6000 pixels!!!

So more to the point of the OP, more MP isn't necessarily bad, only when accompanied by too much processing including NR, saturation and contrast boosts, and sharpening that can't be reversed and can't be downsampled properly. Now those are bad!


I am aware that there is no theory that explains why the readout noise or black level noise varies as the inverse square root of the photosite size, but observations made by comparing different cameras with different sizes of photosites with about the same technology form a trend that seems to hold that there is approximately such a relationship. I'm sure the exact explanation for the relationship is very complex, but the observations speak for themselves: black level readout noise expressed in electrons always is smaller for smaller photosites by about the relationship of the inverse square root of the size of the photosites.



BTW: that last thread is almost 2 years old and the same discussion goes on and on.........

Last edited by jeffkrol; 03-17-2009 at 08:40 PM.
03-18-2009, 05:31 AM   #94
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QuoteOriginally posted by m8o Quote
QuoteOriginally posted by falconeye Quote
In order to bring some fun to this thread, let me show a detail from a bee's wing.
that gallery is insane!!!! Photomicrography, Charles Krebs, Gallery 1
I absolutely agree.
Just to make sure I haven't got mistaken ... the bee's wing photography was mine, not krebsmicro's

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