Why do some DSLRs have fewer megapixels than some pocket cameras?

Question

Some point and shoot cameras like the Olympus mju range have more megapixel capabilities than many DSLRs. Why is this? Is this because they have larger sensors or more dense ones? What are the trade-offs that are made to deliver such high density?

Answer

Pocket cameras have significantly smaller sensors than DSLRs, usually in the range of 5mm across as opposed to 22mm across. I'm not familiar with the Olympus mu range however I've seen 12 and 14 megapixel compacts.

These have more megapixels than DSLRs produced a few years ago, however it is mostly done for marketing purposes. The lenses in pocket cameras often wont have the resolving power to justify 14 megapixels, and if they did the limited light gathering ability of small pixels means aggressive noise reduction is used, smearing out any fine details.

There are reasons to produce DSLRs with lower megapixel counts, usually for speed of shooting for example the 10 megapixel Canon 1D mkIII or the 12 megapixel Nikon D3s. In any case these cameras will consistently beat a 14 megapixel compact in terms of resolution / noise, so there is no advantage to compacts when it comes to megapixels.

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