My take on what's interesting and what's irritating.

Wednesday, May 10, 2006

Sensor Guide Number

I was trying to explain to a colleague that an 8MP point and shoot digital camera was no where near the image quality of an 8MP Digital SLR. Fact of the matter is that sensor size, noise filtering and in-camera processing don't register with most consumers. During this conversation, bells went off about an article I had read a few months back over at Luminous Landscape. In it, Michael Reichmann stated,
"More Megapixels aren't what most photographers need. We need better Megapixels, and the manufacturers seem to have realized this."
While the manufacturers know this, the general public still doesn't have a good, easy way to differentiate 8MP point and shoot garbage from 6MP high quality Digital SLR. It reminds me in a way of the MHz myth that Intel has only recently abandoned. There's more to performance than megahertz (or megapixels).

In the spirit of the flash Guide Number system, I'm proposing a similar system for digital cameras. While in no way perfect, this system at least gets the consumer in the right ballpark and lets them make more informed decisions about the image capture capability of any given camera.

It basically works like this:

Sensor Guide Number = Effective Sensor Megapixels * Sensor Diagnol (in mm)

The higher the Sensor Guide Number, the higher assumed image quality.

A quick comparison between apparent equals in terms of megapixels tells a different story when the Sensor GN is applied:

Canon EOS 20D 8.2MP; diag = 27.04mm; SGN = 221.74
Canon EOS 5D 12.7MP; diag = 43.27mm; SGN = 549.49
Nikon D200 10.0MP; diag = 28.40mm; SGN = 284.01
Pentax *ist DL2 6.0MP; diag = 28.26mm; SGN = 172.40
Pentax Optio A10 8.0MP; diag = 8.01mm; SGN = 64.04

As we can more clearly see, the 8MP Canon EOS20D and 8MP Pentax Optio A10 are not created equally. The 20D has a SGN of 222 while the Optio A10 has a SGN of 64. Even though both are 8MP cameras, the 20D SGN is 3.4x that of the Pentax. Even the two Pentax cameras - one a 6MP DSLR and one a 8MP Point and Shoot - show clear differences favoring the larger sensor size of the smaller MP digital SLR. A consumer might wonder why a 12.7MP digital camera with "50% more MP" than an 8MP point and shoot is so much more expensive. When you look at the SGN and understand it's 8.5x "better" then its a more realistic comparison of capability.

It would be easy to take this to the next level and have a Dollar Per Sensor Guide Number ($pSGN) metric where you can factor in the cost of the camera per SGN. The lower the $pSGN the better the "value" of the megapixels you are purchasing.

$pSGN = Price of Camera System / SGN

Continuing our 20D vs Optio A10 comparison, today's price at B&H Photo-Video lists a 20D with lens kit for $1129. The Optio A10 can be had for $299. The 20D has a $pSGN of $5.09 and the Pentax has a $pSGN of $4.67. Given the superior SGN of the 20D (3.4x of the Pentax), it's the better value. Whether or not you have >$1000 to spend on a digital SLR is another story!

I like that this method abstracts MP as the sole arbiter of camera quality, provides a way to compare disparate models and manufacturers and with the $pSGN value allows one to assess value.

This method is not without faults and doesn't encompass factors such as in-camera noise filtering or the quality of a given CMOS or CCD sensor, but it does provide a much more informed decision for the average consumer.

This same system could be used as a guide to consumers interested in translating "how much camera do I need to make 5x7 prints". If the answer is at least a GN of 50, then that makes a more informed decision as well.

What do you think? Let me know.


5/12/06 - Update - check out this post for another good analysis of the "MP myth".