Re: How many pixels?
- From: Aaron <nghy@xxxxxxxxxxx>
- Date: 21 May 2006 21:52:02 -0500
I have worked with the Zeiss Axiocam and several other digital cameras
including the Leica 5 megapixell dedicated microscope camera. the
Nikon Coolpix 990, Coolpix 5000, and the polaroid DMC 1e..
Film images, especailly those taken with very fine grain film do not
show evidence of aliasing errors and they provide a gradations of
color, tone and intensity.
The digital dectectors have areas around each photosensitive element
that are not light sensitive. This fundamental fact of geometry under
lies aliasing errors and limits information about gradations in color,
tone and intensity.. The missing information must be mathematicallly
interpolated. To reduce the aliasing errors the image sharpness must
be reduced and another layer of interpolation is introduced with the
anti-aliasing routines used by many to restore the sharpness . To
obtain color information, the photosensitive elements must be masked
with Bayer color filters. Unless the camera is of the three chip
design, the infromation must be interpolated to create the proper
colors for each pixel. The real benefit of the single ccd design with
all of the interpolation is that the image can be captured in a very
exposure in "real time" The drawbacks of this single chip design is
that the image contains a lot of "false" or "approximate" information
For this reason the colors are often unusually simpler and the images
artifically "sharp". Photographically this may be appealing but as a
system to record scientific inlformaition is is lacking.
The advantage of the piezoelectric displacement of the detector in the
Axiocam and similar designs is that information can be measured for
three different color masks and points between the photosensitive
elements that would not be recorded were the ccd not moved. The
amount of interpolated information is far less. Actually the Axiocam
megapixel resoluti0on reported is a truer statement of its
perfomance than the high end DSLR cameras which use single Bayer
filters and stationary detectors. The results produced by the Axiocm
are closer to the best film cameras.
The main drawback of the Axiocam design is the time it takes to
repeat exposures at various locations and with different color
filters. This design is not suited to moving specimen.. It also
means the system must be free from any vibrations or movement.
The images taken with the Axiocam are characterized by accurate color
and shading variations which are very important for scientific
imaging. .
Aaron.
On 18 May 2006 14:27:43 -0700, nigelvl@xxxxxxxxx wrote:
It is important to note that the Zeiss table refers to a camera which.
uses a pixel jiggling interface - this means that you do NOT get 12.5
Megapixels effectively! All you are doing is shifting the CCD in
increments to increase the "so-called" pixels. Do the same with an RGB
filter and a 4Megapixel camera and the result is actually much better
spatial resolution.
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