I recall looking at a paper ad about SLR cameras and it appeared to me that Canon is selling its Digital Rebel camera with 10.1 Mega Pixels while the EOS 30D has only 8.2 Mega Pixels. The semi professional 30D is sold with less pixels than the consumer version! This is evidence that amateur photographers are made to believe that “more is better” completely ignoring physics and facts about digital imaging.

I guess it’s more important sitting next to your friend who owns a lousy 8.2 MP camera that one can now brag that my camera is 23% bigger, better, etc. This, however, completely ignores the fact that the resolution of the camera is not 23% better. There are only 23% more pixels. The resolution, which accounts for sharpness and acuity of an image, is determined by the number of pixels in a row or column of the sensor while mega pixels are calculated by multiplying these two numbers. This makes the difference because if you want to double the sharpness of an image based on the pixels used you need 4 times the pixels.

Let’s do some math here to explain this fact. Both cameras contain a 3:2 format sensor.

EOS 30D: 3,504 x 2,336 = 8,185,344 px

EOS XTi: 3,888 x 2,592 = 10,077,696 px

Dividing the total pixel numbers leads to

10,077,696 / 8,185,344 = 1.2312

which shows the 23% increase in pixels I mentioned above.

To get the increase in resolution we need to either divide the number of pixels in a row or in a column, which leads to 1.1096. That’s only an 11% increase in resolution. Why is that so? Because we are working in a two dimensional space which leads to the square root. Take the square root out of 1.2312 and you get 1.1096.

Let’s consider one is buying this camera because the desire is to create prints larger than 8 x 10. With the pixel difference you can now go and print a 8.9 x 11 at the same resolution. I doubt that this is explained to customers when they buy such a camera. And if you print 4 x 6 this increase in pixels does not make a difference at all. Well, at least they can go home and say: mine has more than yours and thus must be better.

Often there is an argument that more pixels are good because this allows for cropping without loosing resolution. Applying the math from above only 10% cropping is possible without loosing resolution. I don’t know if that improvement really helps anyone.

Another issue often overlooked when talking about more pixels is the noise or grain. More pixels on the same size sensor mean smaller pixels. Smaller pixels are equivalent to more noise or grain. The noise goes up by 23% because statistically you have 23% more pixels which in turn reduces the likelyhood of a pixel being hit by a photon by 23%. That brings up the noise. From my point of view noise is much worse to deal with in an image than cropping and resolution problems. It’s really hard to reduce noise without reducing the acuity or sharpness of an image.

In terms of printing the 8.2 MP camera allows for a 11 x 17 print at a resolution of 206 dpi while the 10 MP camera brings this to 228 dpi. I doubt that anyone would notice the difference.

This entry was posted on Sunday, September 7th, 2008 at 9:25 am and is filed under Photography. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.