Re: NASA's Mars probe: NO cmos, NO Bayer
- From: Mark Sieving <mark_sieving@xxxxxxxxx>
- Date: Thu, 29 May 2008 12:25:38 -0700 (PDT)
On May 28, 3:58 am, Colin_D <nos...@xxxxxxxxxxx> wrote:
Voodoo Thunder Pig wrote:
RichA wrote:
from Amateur Photography magazine;
The camera has a double Gauss lens system, a design commonly used in
35mm cameras,' explains the space agency.
'Images are recorded by a charge-coupled device (CCD) similar to those
in consumer digital cameras. The instrument includes sets of red,
green and blue light-emitting diodes (LEDs) for illuminating the
target area.'
Nasa claims that the camera can focus down to 11mm and record images
at a resolution of '23 microns per pixel' at the closest focusing
distance - allowing the camera to show details 'much finer than the
width of a human hair'.
This means tri-colour imaging through three different filters onto a
monochrome CCD.
Nice try, Captain Obvious, but that's not what it means. It means the light
sources providethe three colors, and no filters are necessary.
I doubt that. What about ambient light? and the shots shown on the box
go out to infinity at the top of the vertical pan. Some leds!
There are five cameras all together on Phoenix, though "imager" is
probably a better term, since these devices bear only a passing
resemblance to consumer cameras. The description above is of the
Robotic Arm Camera (RAC), which as the name suggests, is mounted on
the spacecraft's robotic arm, and is used for closeup imaging. In
ambient light, the RAC will produce monochrome images. The LED lights
are required to produce color images.
The panoramic shots are made with the Surface Stereo Imager (SSI),
which is mounted on a mast extending above the spacecraft. This
imager has two sensors and two lens systems, to produce the stereo
images. Each sensor has a filter wheel containing twelve separate
filters, including a red filter and a blue filter (see
http://www.met.tamu.edu/mars/SSI_filter.html for details on the
filters). By combining images using two different filters, a false
color image can be produced, but the colors produced are not really
what the human eye would perceive.
The article says the sensor is similar to consumer digital cameras.
That means a Bayer matrix.
The Bayer matrix is not actually a part of the sensor on consumer
cameras, but it's a filter array lying on top of the sensor. The
imagers on Phoenix don't use a Bayer filter; they use other filtering
mechanisms. The imagers are magnificent for their purpose, but you
probably wouldn't be happy with the colors if you used them to take
pictures of your kids.
.
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