Go Back   Steve's Digicams Forums > Digicam Help > General Discussion

Reply
 
Thread Tools Search this Thread
Old Dec 3, 2006, 8:38 PM   #1
Senior Member
 
Join Date: Aug 2006
Posts: 268
Default

Say for example that I have a 10 MP camera, yet I set it to take 6 MP photos, what happens to make the resulting image 6 MP? It seems to be a fact that if you have two sensors that are the same size, yet one has more MPs then the other, the one with less MPs (larger photo sensors) will have less noise. I doubt it, but will lowering the resolution from 10 MP to 6 MP lower noise? And, again, what exactly does happen in the camera when you do this? Does it always take a 10 MP image, but alters it in post processing?
Contriver is offline   Reply With Quote
Sponsored Links
Old Dec 3, 2006, 10:36 PM   #2
Senior Member
 
Join Date: Dec 2002
Posts: 5,803
Default

This is a very camera dependent answer, so if you're thinking about
specific models then you should probably ask someone who owns (or has tested) them.

The answer is that it might have less noise, but that is probably because it reduced the resolution by post processing the image. Most of the time, that will average the pixels with the noise with surounding pixels that don't have noise and the resulting "average" has less noise in it.

The reason a 6MP sensor might have less noise than a 10MP sensor (and I'll say later why that is some times an incorrect assumption) is that the sensors are physically different. The photosites (the actual thing on the sensor that detects/measures the light) are larger on the 6MP sensor and therefor get more light into them.

But a 10MP sensor is probably newer and therefor probably has better noise reduction tech in its design - and the surounding circuits could be better as well. So if you have two sensors of the same age and same physical size then the 10MP sensor will *probably* have more noise, it isn't guarrentied.

Eric
eric s is offline   Reply With Quote
Old Dec 3, 2006, 10:51 PM   #3
Administrator
 
Join Date: Jun 2003
Location: Savannah, GA (USA)
Posts: 22,378
Default

It's taking it at full resolution and downsizing it in the camera. As for noise, you do tend to get less visible noise if you downsize an image to a smaller size, since you're averaging more pixels together. But, that doesn't mean that you'll have lower visible noise compared to a lower resolution camera with larger photosites.

The larger photosites will be generating a stronger signal to begin with, so you'll have less pixels that are generating a signal that's below the noise floor (since the larger surface area for each pixel gathers more light and each pixel will generate a stronger signal). With smaller photosites, you'll have a weaker signal from each photosite, with more photosites that are not generating a signal above the noise floor of the sensor. So, those noisy pixels get averaged into the values from the others.

I remember looking at a lot of photos a few years back comparing the DiMAGE A1 and A2 models, right after the A2 was introduced. Someone did just that (downsized images from both cameras and compared them at the same size). The A1 image still had lower noise levels at equivalent ISO speeds.

I saw a lot of Sony and Nikon owners gripe after upgrading when the 8MP 2/3" sensor came out, too. The photos had higher visible noise compared to images from their older cameras using a 5MP 2/3" CCD, even when downsized.

Now, you still have to take each camera on a case by case basis. Progress is being made in sensor design (lower inherent noise from electronics with better signal/noise ratios, more sophisticated microlens designs to help amplify the light hitting each photosites, more sophisticated image processing to reduce the appearance of noise, etc.). But, all things being equal (and they never are), you're better off with larger photosites from a noise perspective.

If you are thinking about downsizing on a routine basis, you'd probably get better results by using shooting a full resolution image, then using noise reduction software before downsizing. As an added bonus, you'd still have a full resolution photo if needed for larger print sizes. Storage is cheap. Buy a larger memory card versus shooting in a lower resolution mode. ;-)

JimC is offline   Reply With Quote
Old Dec 4, 2006, 6:28 AM   #4
Senior Member
 
BillDrew's Avatar
 
Join Date: Jun 2002
Location: Hay River Township, WI
Posts: 2,512
Default

JimC wrote:
Quote:
...
If you are thinking about downsizing on a routine basis, you'd probably get better results by using shooting a full resolution image, then using noise reduction software before downsizing. As an added bonus, you'd still have a full resolution photo if needed for larger print sizes. Storage is cheap. Buy a larger memory card versus shooting in a lower resolution mode. ;-)
I agree with Jim. The only reason I can think of to shoot at less than the best resolution is to get a longer burst - and that is not true of all cameras.

Downsizing from 10 to 6 Mpixels should increase the signal/noise ratio by about 29 percent [sqrt (10/6)] which isn't enough to be real noticable. As eric points out, using newer technology could have a much bigger effect.
BillDrew is offline   Reply With Quote
Old Dec 4, 2006, 1:39 PM   #5
Senior Member
 
Join Date: Aug 2006
Posts: 268
Default

Thanks for the information guys! So, let me ask you this...is it correct to say that, regardless of the manufacture,everyimage sensor of the same size and same MP has the same sized photosites? In other words, does every 1/2.5 sensor that produces 8 MP resolution have the same sized photosites?
Contriver is offline   Reply With Quote
Old Dec 4, 2006, 1:45 PM   #6
Administrator
 
Join Date: Jun 2003
Location: Savannah, GA (USA)
Posts: 22,378
Default

Not necessarily, as the spacing could be different between them. But, the differences in photosite size are probably going to be relatively insignificant.

You'd probably see more differences between them in other areas (how advanced the sensor electronics are, microlens design, image processing algorithms and more). The size of the photosites is only one factor out of many when comparing cameras.

JimC is offline   Reply With Quote
 
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -5. The time now is 11:22 PM.