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

Started Jun 6, 2009 | Discussions thread
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ejmartin Veteran Member • Posts: 6,274
Re: Pixel density - can the playing field be leveled???

briander wrote:

I will try to ask my question as simply as possible. If two camera's
have the same size sensor, and one is a 10 MP, and the other is a 15
MP, and I lower the resolution on the 15 MP to 10, can I expect the
same picture quality for a noise perspective? Of course, this is
putting all of the other camera functions (noise reduction, etc)
aside.

This issue was studied around the time of (and in response to) Phil's blog post from last Fall, which spouts a lot of misinformation. Relevant posts are

http://forums.dpreview.com/forums/read.asp?forum=1018&message=30211624
http://forums.dpreview.com/forums/read.asp?forum=1000&message=31708796

Noise has two major sources, photon shot noise and electronic noise incurred in reading the sensor. Photon noise is purely an issue of the statistics of counting, as is explained here:

http://forums.dpreview.com/forums/read.asp?forum=1019&message=31922352
http://forums.dpreview.com/forums/read.asp?forum=1019&message=31922793

Smaller pixels mean smaller samples of the image, so noise per sample relative to sample size goes up. However aggregating samples to the same size by downsampling recovers the sampling statistics of the larger pixel sensor.

Read noise is more complicated. If the two 10/15MP cameras under discussion are the 40D and 50D, then read noise went down enough between the two that the 50D is has a slight advantage.

I am tired of reading "if this company would have resisted the
megapixal war, this would be a great camera". What the hell does
that mean?

Can I lower the resolution to get the same reduction in noise, that
the lower res camera has?
--

I would put it differently: does a higher MP camera have the same noise at the same spatial frequency (ie scale in the image) as a lower MP camera? The answer is yes unless their read noises are wildly different (when normalized to the same scale). Phrased this way, no resampling need be done, since image scale and spatial frequency are defined without resampling the image -- it's just that the image scale which is the pixel level of the lower resolution camera, is somewhat coarser than pixel level of the higher resolution camera, and one needs to take this into account in making comparisons. DPR does not do this, and it is a major flaw in their testing protocol; it makes many of their noise comparisons meaningless (unless comparing cameras of equal resolution). For a proper testing methodology, go to DxOmark.com.

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