Meganpixels & Images Sizes

[DigitalDarkroom]

Hello.

Here's an odd newbie question for the technophiles. I'm still researching my first buy and reading up on alot of the technology, learning as much as I can. While checking out some of the announcements about the new Canon A-series cameras, I noticed something on this page:

http://www.imaging-resource.com/NEWS/1187582482.html

In the specs, where they show "Image Dimensions", they give mexapixel numbers. My question is, on lower size/quality images, does the camera still use (using the 12MP A650IS as an example) all 12 million pixels and then re-size the image, or does the camera only use, for example, 8 million pixels for a smaller image? And if it's the latter case, do they use a lens to refract the image down to just the 8 million adjacent pixels in the middle of the sensor, or do they use some pattern of non-adjacent pixels to make up the image?

[sla]

Hi
Maybe there are simply 2 different sensors?
But if there are the same sensors (hipotetically), the less megapixel camera would use part of the larger sensor (they write diagonal 1/2,5" vs 1/1,7")
Regards

P.S.
Less megapixels DOES NOT mean lower quality images!

[DigitalDarkroom]

Thanks for the reply, sla, but just to clarify, I was using one of the cameras on that page as an example, not comparing the two. Bad, coincidental choice of megapixel numbers on my part. Sorry.

Just about all the cameras I've read up on allow you to select a picture size (smaller pic size equals more pics on the card). I was just wondering how they get the smaller pic sizes -- capture the full size pic and re-size it (which seems like it would slow things down a bit) or in some way "crop" down the sensor to take a smaller pic in the first place.

[sla]

I'm not in the industry, but I am pretty sure cameras resize photos from full-size sensor. Cropping would require a different lens, wouldn't it?
For instance 640x480 from 4000x3000 - do you imagine how small part of sensor this is? This would reqiure a completely different lens to project the whole image on such small area.

[David Metsky]

Yes, since you're dealing with an optical lens then image falls on the entire CCD, and is then reduced. You can prove this by taking a shot at full resolution, changing the resolution size (note that the lens won't move) and taking a second shot. The image will cover the same area.

[BowerR64]

Go with the larger CCD, if you are deciding on 2 cameras each with a different size CCD go with the larger one. For the same megapixels the 1/1.8" CCD will take better pictures then the 1/1.25