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My 4Mp P&S can record at 4 different resolutions:

2304 x 1728 (4Mp)
1600 x 1200 (~2Mp)
1280 x 960 (~1.4Mp)
640 x 480 (~0.3Mp)

Presumably the size of the sensor approximates to the highest resolution.

How are the lower resolutions obtained? ie at 1600x1200 are 50% of the
pixels discarded or is a smaller area of the sensor used?

Before anyone mentions it - Yes - I always use the highest resolution
and minimum compression!

Tony M

"Tony M" <> wrote in message
news:ddo819$91g$...
> My 4Mp P&S can record at 4 different resolutions:
>
> 2304 x 1728 (4Mp)
> 1600 x 1200 (~2Mp)
> 1280 x 960 (~1.4Mp)
> 640 x 480 (~0.3Mp)
>
> Presumably the size of the sensor approximates to the highest resolution.
>
> How are the lower resolutions obtained? ie at 1600x1200 are 50% of the
> pixels discarded or is a smaller area of the sensor used?
Perhaps your camera just discards the unwanted pixels. Perhaps it uses some
kind of interpolation schem to reduce the resolution. Perhaps it uses some
other method, but it would be very unlikely to reduce the are of the sensor
(that operation is called digital zoom).
Jim
>
> Before anyone mentions it - Yes - I always use the highest resolution and
> minimum compression!
>
> Tony M

Tony M <> wrote:
: My 4Mp P&S can record at 4 different resolutions:

: 2304 x 1728 (4Mp)
: 1600 x 1200 (~2Mp)
: 1280 x 960 (~1.4Mp)
: 640 x 480 (~0.3Mp)

: Presumably the size of the sensor approximates to the highest resolution.

: How are the lower resolutions obtained? ie at 1600x1200 are 50% of the
: pixels discarded or is a smaller area of the sensor used?

: Before anyone mentions it - Yes - I always use the highest resolution
: and minimum compression!

: Tony M

The image area remains the same for all modes. So the reduction in
resolution either is a reduction of pixels read or a mathematical
averaging of several pixels into a single one, or some other software
reduction. But the overall area of the sensor that is capturing the image
remains constant. So an image of an object that exactly fills the image at
one resolution will still exactly fill the image at all the resolutions. A
reduction in the area would give the effect of zooming in (digital zoom).

Randy

==========
Randy Berbaum
Champaign, IL

Tony M wrote:
> My 4Mp P&S can record at 4 different resolutions:
>
> 2304 x 1728 (4Mp)
> 1600 x 1200 (~2Mp)
> 1280 x 960 (~1.4Mp)
> 640 x 480 (~0.3Mp)
>
> Presumably the size of the sensor approximates to the highest resolution.
>
> How are the lower resolutions obtained? ie at 1600x1200 are 50% of the
> pixels discarded or is a smaller area of the sensor used?
>
> Before anyone mentions it - Yes - I always use the highest resolution
> and minimum compression!
>
> Tony M


No, the pixel values are not discarded, they are averaged. While the
process is more complicated than this, here is at least an approximation
of the process. Lets say we are downsampling by a factor of two
linearly, i.e, a 4X reduction in total pixels. Start at the top left.
The first two leftmost pixels in the top row and the second row are
averaged. This average value is assigned to the top left pixel of the
new, downsampled array.