Senseless megapixels part 2

For anyone interested in cameras and (to a lesser extent) photography, there is no website which offers the same amount of information, the same volume of forum traffic and the same meticulous reviews of equipment as http://www.dpreview.com/

I have followed it for many years and can recommend it highly. Recently, dpreview.com reviewed the very popular and highly acclaimed Canon G10 which proudly boasts a 14.7 million pixel sensor. They compared the results with those from the older, 10 megapixel Canon 1000D with the ISO sensitivity set to 1600. There were many pictures captured by both cameras for the purpose and this is ONE of them, examined close up at 1:1 (1 image pixel to 1 display pixel).

Now we all know that more pixels means bigger, better clearer pictures ....... right? When we look at the two images at the head of the article it is easy to conclude that the upper one must have been taken with the new 14.7 megapixel G10 while the lower one must have been taken with the older 10 megapixel 1000D. Right? ............ WRONG! In fact the lower picture was shot by the G10.

In every way, the upper image is superior and there is just no way to get around that simple fact. 10 megapixels absolutely beat the crap out of 14.7 megapixels. It is important to emphasise that every precaution was taken to make the comparison as fair as possible. It is also important to emphasise that this one illustration does not tell the whole story and interested folk should go to http://www.dpreview.com/reviews/canong10/ where the entire article makes interesting reading.

Say what we may, however, the small illustration above IS accurate and for all those who agree with me about the senseless marketing-department-driven megapixel race, the result is not in the least surprising. The central point I am trying to make is that the resolution specifications of a camera are but one small part of the story about how good a particular camera may be for your purpose.

All right then .... WHY does the image captured by the higher resolution camera look so bad?

To begin with, the most important specification for image sensors is NOT just how much resolution is available to them but how physically large they are as well. The sensor in the Canon 1000D (being a DSLR) enjoys a APS-C sensor approximately 5 times the size of the tiny G10 sensor. This means there are many many more "photo-sites" to the square millimetre in the G10's sensor than is the case with the 1000D's sensor. In other words, the "pixel density" of the 1000D sensor is very much lower than the G10's. Beyond a certain point, the lower the pixel density of a sensor, the less noise will be evident in one of its images and the better that detail will be retained in an image as the sensitivity increases. Put simply, "low pixel density, clear picture - high pixel density, muddy picture".

Don't get me wrong. At ISO 80, the G10 will produce an image which seems every bit as good as the 1000D. Unfortunately, as you strive to capture more and more ambitious images under less than optimal lighting conditions or as you try to freeze faster moving objects or as you attempt to increase depth of field, increased sensitivity is desirable, revealing the limitations of pixel dense sensors.

To make matters even worse, pixel dense sensors place greater resolution demands on lenses. The same lens will appear to resolve images less clearly with more densely populated sensors than it would with less densely populated ones.

These simple facts seem to be ignored by the camera manufacturers who appear to be betting on newcomer ignorance to carry the day. It is easier for purchasers to digest steadily higher numbers of pixels than to appreciate the issue of optimum pixel density.

Thus the senseless increase in megapixel specs carries on unchecked while (in all but the best possible lighting conditions) the pictures themselves get noisier and fuzzier. Ridiculous isn't it?

See my work at www.pbase.com/davidhobbs