February 27th, 2007
The final word on the 'megapixel myth'
There's been a lot of talk of the "megapixel myth" lately all started by David Pogue of the New York times declaring that megapixels are a "big fat lie". Fellow blogger David Berlind also did an entire series of blogs with his own sets of tests declaring "there's a good chance you'll never need more than 3 or 4 megapixels from your camera". I read the articles and blogs and I took a look at the methodologies described and I found some serious problems that affected the conclusions. Here's a list of issues and I'll explain each one. [Update 11:00 PM - Pogue responded in the talkback and I responded to him.]
- Computer down-sampling was used to render lower resolution images
- Lack of adequate test patterns for resolution testing
- Lossy compression JPEGs were used which adds artifacts
- Lens and motion factors not accounted for
- Not all image sensors are created equal
- Megapixels are a unit of area and not resolution
- Actual resolutions needed for printing
1: The first MAJOR issue is the use of computer down-sampling (or down-sizing) to generate lower resolution samples. Someone pointed that out to Pogue that it may invalidate the results but Pogue ignored it with the simple comment "I'm not entirely convinced". Now David Pogue is attempting to conduct a "scientific" experiment in order to prove his hypothesis that the digital camera industry is pushing the "big fat lie" of more megapixel yet Pogue sees no problem synthesizing the data and violating fundamental science principals. Now I understand Pogue is no scientist, but he reaches a massive audience and he has the responsibility to be accurate when he's making such bold and damning assertions about an industry. I'm going to explain why this completely invalidates his experiments.
Whenever you down-sample a computer image especially when you use a high quality algorithm provided by something like Photoshop, you are guaranteed to get improved image quality because all the noise, lack of focus, and slight motion blur in the image is averaged out and you're left with the purest of images that maximizes the effectiveness of every single pixel. If you took a 4500×3000 (13.5 megapixel) image from a high-end camera and down-sampled it to 2250×1500 ( 3.375 megapixel) image, I can guarantee you that the resulting 3.375 megapixel image will be vastly superior to any image captured from a native 4 megapixel image. Pogue simply assumes that a down-sampled image is the same as a lower resolution image captured with fewer megapixels. Not only is it an assumption, it's a really bad assumption and anyone who does the experiment or works with digital images a lot will know that the native 4 megapixel camera will invariably have noise and imperfections in the image. The down-sampled 3.375 megapixel image on the other hand will have far fewer imperfections because the noise happens at the 13.5 megapixel level and it's mostly averaged out to produce a very clean image at 3.375 megapixels. [Updated 11:00 PM - Pogue did capitulate and allowed a professional photographer to use cropping instead of down-sampling to come up with lower megapixels.]
[Next page - The concept of optical resolution]
George Ou is Technical Director of ZDNet. See his full profile and disclosure of his industry affiliations.
