Hardware interpolation, is there any point?

Question

We've all seen digital cameras that advertise X megapixels, but when you look at the specs, it says the actual sensor is X/3, etc. Is there any value in this other than advertising hype? I can take a 3mpx image and blow it up to 20 in Photoshop, is the in-camera version any better? 3mpx is 3mpx no matter what you do with it, as far as I can tell. There's only so much image data there and you can't magically create more, right?

-Thx for the replies, guys. I was aware of the digital zoom issue. I'm specifically referring to cameras that claim to take '12 mpx' pictures yet the specs say the sensor is only 5mpx, for example. Same deal?

Answer 1

Thanks for the intro, OMG. This is the same thing that you are asking about, but some companies call it "interpolation" and others call it "digtial zoom," so the pictures are of interest for enrichment of OMG's answer.

Optical zoom is good and digital zoom sucks. Optical zoom is "real" zoom done with the camera lens. Digital zoom is really just a way to enlarge pixels and degrade the image. Ignore it completely when you are comparing cameras.

Here are three sample pictures taken with my Canon Powershot SD900, which is a 10.0 megapixel camera. All three pictures are taken with the optical zoom maxed out at 3X or 23.1 mm, which is the equivalent of 111.6 mm after calculating for the lens crop factor. There is no image processing at all done with any of these pictures. All were taken using the self-timer to (hopefully) eliminate camera shake as the camera sat on the top of my car. (Okay, I'll use a tripod next time, but I think they are pretty sharp images.) Please click on "View All Sizes" and then view each image at the largest size available, which should be 3648 x 2736 pixels. The first picture (3xOpticalFull) is the full frame image at 3x optical zoom, or 111 mm. The second picture (4xDigitalFull) is the result of zooming out the additional 4x in digital zoom, for an equivalent of 444 mm. The third picture (3xOpticalCrop) is actually a cropped version of the original image, maintaining the full pixel dimension. In other words, I accomplished the "digital zoom" entirely in the computer and not in the camera. If you compare the full-sized images, I think it is immediately obvious that the third picture is far superior in any aspect that you care to examine. I think it is much sharper (Check the tower and the antenna up near the top of the frame.), has better color, and less digital noise and artifact (Check the plain sky and the shadows on the building.). These images are all tagged "digital zoom."

3xOpticalFull: http://www.flickr.com/photos/7189769@N04/459603923/
4xDigitalFull: http://www.flickr.com/photos/7189769@N04/459603931/
3xOpticalCrop: http://www.flickr.com/photos/7189769@N04/459603939/

In other words, please ignore any claims of superiority based on "digital zoom" when you choose your camera. It is only "in camera cropping" and it is not anywhere near as good as "in computer cropping." Any attempts at cropping a digitally-zoomed picture will be a waste of time.

Answer 2

You're 100% right. In fact, if you're going to interpolate, Photoshop does a better job than the often rudimentary in-camera software.
Dr. Sam, another regular here, recently did his own tests for PC interpolation vs. in-camera interpolation (as a result of digital zoom). If he answers, he'll tell you the same. Unlike me however, Sam can back this up with sample images. Take the time to check them out. Heck, if he answers, just award him Best Answer and THEN check out the samples.