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Old Feb 9, 2010, 6:23 AM   #1
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Hello all,

New to the forum. Just wondering if anyone can help answer this question:

Does setting a lower pixel count help improve the images from a camera with a sensor that's clearly too small to handle the maximum amount? That is, if you use only 6MP on a small 12MP camera, will that aid in noise reduction? And, if that's the case, do cameras' processors generally recognize that there's a lower MP count and accordingly perform less noise reduction/smearing? Or are you somehow stuck with those noisy and/or soft images regardless?

My own tests were inconclusive in this regard (I'm not a very experienced photographer), and it will definitely make a difference in what camera I decide on.

Thanks in advance!
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Old Feb 9, 2010, 7:14 AM   #2
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Downsampling (reducing the resolution of an image) will average out the noise, but it will also average out the detail.

Noise happens at the pixel level, so reducing the resolution means that an image will be less noisy, so you can and probably should turn off the noise reduction.
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Old Feb 9, 2010, 7:14 AM   #3
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No, there is no point in reducing the number of pixels captured. Or buying a camera with less pixels.

http://dxomark.com/index.php/eng/Insights/More-pixels-offsets-noise!

http://dxomark.com/index.php/eng/Ins...tion-over-time
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Old Feb 9, 2010, 7:20 AM   #4
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Quote:
Originally Posted by peripatetic View Post
No, there is no point in reducing the number of pixels captured.
I agree that higher resolution image sensors produce less noticeable noise, but that's not what the OP is talking about. Sarrr is talking about the effects of downsampling.
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Old Feb 9, 2010, 7:34 AM   #5
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Just read the original post again. The question is working from a false premise; that a sensor can be too small to cope with the amount of Mp. When the question contains a false premise the best thing is not to respond as if the premise were true.

The answer is don't muck about. Keep your camera on its highest resolution and don't pixel peep at 100% magnification. When you make your prints they will be the better for it.
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Old Feb 9, 2010, 8:05 AM   #6
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But you answered a question that wasn't asked.

Sarrr asked if downsampling reduces noise. And, while it does, it also reduces detail. So downsampling in the camera is a way to avoid noise, but downsampling in the printer (or other output device) is a better place to do it.
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Old Feb 9, 2010, 11:58 PM   #7
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Thanks very much to both of you.

The reason I asked this is that my recent Canon SX200 purchase was a big disappointment, with overeager noise reduction technology that can't be turned off and a bad auto mode, besides, that ruined a lot of my pictures. I've always used comparatively low-MP cameras in the past and never had this problem, so I began to think these problems were at least partially symptomatic of too many pixels on too small a sensor. But I guess the problem is in the camera itself. And if downsampling produces an equal effect regardless of whether it's done via a low-MP setting or downsizing after the fact (something I didn't realize before), then it obviously makes far more sense to do the latter--thanks, TCav, for that helpful advice.

Those studies are interesting, as well, peripatetic. If accurate, they dispel everything I've read about the purported problems with the recent high-MP compact cameras.

Thanks again--this all clarifies a lot.
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Old Feb 10, 2010, 3:16 AM   #8
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I think there is a lot of misinformation, and the relationship between the increase in Mp and the sensor noise is very poorly understood.

Obviously it seems noisier at 100% view, because that is very much zoomed in on lower Mp sensors. Downsampling, as TCav says, reduces both noise and resolution.

Now it is not necessarily the case that all higher-Mp sensors will be equal to the lower Mp sensors when normalised for a particular print size. It may be that with some of the current designs down at the 2-micron pixel sizes they have gone further than the technology really supports.

But it is also certainly true that it is not necessarily the case that increased noise is a function of increasing the Mp count. If you study the DXOMark results it seems pretty clear that the sensors of a given size have not really been improving in their overall quality as rapidly as one might think. In the last 5 years or so they seem to have been able to squeeze out maybe 5-10 DXOMark improvements, or about 1/3 to 2/3 of a stop. During that time pixel counts have gone up by about 300% on average. And there is essentially no difference between cameras like the 40D and 50D even though the forums unanimously declared that the 50D had a noisier sensor because of the increased resolution.

Consider that the DXOMark scores for the Canons: 20D, 30D, 40D, 50D, 7D are respectively 62.2, 59.5, 63.5, 62.9, 64.9. A DXOMark score of 15 = 1 stop. The sensors have increased their Mp count - which is useful in good light, but are otherwise effectively unchanged in efficiency.

It really seems that the most important factor in overall IQ by some distance is still the size of the sensor.

The Canon S90 and G11 though do seem to be punching way above their weight i.t.o. what you would expect from their sensor size (which is a lot bigger than most P&S cameras but even so.)

So in order to get what you are probably looking for you are going to need to think about the eternal compromise between portability and overall IQ. Currently the Canon S90 and G11, as well as the M4/3 cameras are very much hitting the sweet spot there.
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Old Feb 10, 2010, 7:14 PM   #9
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Here is what I did after a suggestion from peripatetic.

Setup a controlled scene with my 7D. Shot that scene in manual mode at 1600 ISO. One shot was with the camera set at Medium (8mp) and a second at Large (12mp). Now viewing each at 100% you get the immediate impression that the 8mp is sharper but its simply because your viewing at less magnification. Noise seemed less on the 8mp. I then left the 8mp at 100% view and changed the view of the 12mp to 66.7%, which appeared to match the 8mp exactly as far as view size. In this case, after viewing fine details the 12mp seemed to look less noisy and had finer detail in some areas.

Not sure if this is a fair comparison but it does tell me that leaving the camera on Large will have advantages even though at 100% you might think different.
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Old Feb 10, 2010, 7:43 PM   #10
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I agree. I am dead set against discarding data. ... in any form.

Always shoot at the highest resolution you can, at the lowest ISO setting you can.

Downsampling an image (in the output device) that has already been downsampled (in the camera) reduces image quality more than downsampling an image (in the output device) that was recorded at the full resolution of the camera.

Statistically, it's known as a mean of the means [See http://en.wikipedia.org/wiki/Weighted_mean#Example ] and distorts the actual data, which, in this case, would be the image.
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