SENSOR SIZE AND RESOLUTION

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Wladyslaw Wojciechowski - 20 Nov 2006 06:01 GMT

Hello everybody!
Can anyone explain how it works when a camera has an 8 mpix sensor
and its owner decides to take a 1280x960 photo. In this case does
the sensor use all the 8 million pixels to create a smaller photo
or does it use only 1,22 pixels and which ones (from the center
of the sensor?
Regards!
Wlady :)

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Dave Martindale - 20 Nov 2006 07:09 GMT

> Hello everybody!
> Can anyone explain how it works when a camera has an 8 mpix sensor
> and its owner decides to take a 1280x960 photo. In this case does
> the sensor use all the 8 million pixels to create a smaller photo
> or does it use only 1,22 pixels and which ones (from the center
> of the sensor?

First, let's assume that the "digital zoom" feature is turned off. Then, yes,
the camera reads the entire 8 million pixels from the sensor. It can't just
read the central area of the sensor, because the field of view would be much
narrower. It can't skip some of the rows and columns either, because there
wouldn't be enough information to decode the colour properly, and you could
have fine detail that alternately appeared and disappeared.

So it reads all the pixels from the sensors, does the colour decoding, and
then mathematically reduces the image from 8 MP to 1.2 MP before saving it.

Now, if you use digital zoom, the picture gets a bit more complex. Digital
zoom does make the camera use a smaller central portion of the sensor. If you
were using 2X digital zoom, the camera would read only the centre 1/2 of the
width and 1/2 of the height of the full sensor, a total of 2 MP. This smaller
image would then be scaled to 1.2 MP and saved.

Dave

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Wladyslaw Wojciechowski - 20 Nov 2006 07:38 GMT

> First, let's assume that the "digital zoom" feature is turned off.
> Then, yes, the camera reads the entire 8 million pixels from the
[quoted text clipped - 16 lines]
>
> Dave

Dave, thanks for your quick reply.
Having in mind what you wrote above I wonder how it correlates with
the question of noise. As I wrote in some other thread some say
'if there is visible noise while taking photos at 8 mpix
just reduce the resolution to e.g. 6 mpixels and teh problem ends'.
Does it mean the mathematical reduction from 8 to 6 mpix makes noise
less visible as well?

Besides, does this mean that to avoid noise one should make 8mpix
photos only in perfect light conditions and when the light is poorer
switch to 6 or 4 or even 2 megapixels?

Regards,
Wlady

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David J Taylor - 20 Nov 2006 19:45 GMT

[]

> Dave, thanks for your quick reply.
> Having in mind what you wrote above I wonder how it correlates with
[quoted text clipped - 10 lines]
> Regards,
> Wlady

[David, not Dave here!]

Yes, by combining pixels to make a lower resolution image, you will reduce
noise, but using 6MP rather than 8MP I think you would be pressed to see
the difference. You can do the combining (and therefore noise reduction)
in post processing as well, so still take the image at 8MP, but reduce to
2MP in post processing.

Of course, by using fewer pixels, the image will not look as sharp, so you
may need to consider if your viewers would prefer a sharper but noisier
image to a more blurred bur more noise-free image. Different image styles
may suit different subjects better as well!

Cheers,
David

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