Conventional digital cameras use
monochrome sensors
You might be surprised to learn that
the sensors in most digital cameras
on the market, apart from Sigma's
SD and DP series, are basically
monochrome. Because monochrome
sensors do not capture color data, a
color filter with a mosaic of pixels for
the three primary colors — red, blue
and green (RGB) — is mounted on top
so that color data can be represented.
But each light-sensing photodiode
has a one-color filter, which means
that each pixel can only capture one
color, and data for the other two
colors is discarded.
Until this stage, of course, as in
the Autochrome process, the RGB
color “particles”, or pixels, are
recorded unmodified, forming the
photo. A color interpolation process
known as demosaicing is therefore
performed in the latter stage of the
image processing, and this restores
the colors lost by individual pixels.
This interpolation process basically
consists of guessing the missing
colors from the neighboring pixels,
and adding them back in.
Post-processing the image
leads to a loss of detail
Having been continuously improved
over an extended period, this image-
processing method has matured
to a certain extent, so the color
interpolation is now performed
fairly accurately. But because colors
are interpolated from neighboring
pixels, the subtle color nuances of the
original subject are lost.
Conventional digital cameras using
color filter arrays also generate
color artifacts – colors not found
in the original subject – during the
demosaicing processing. This is
due to the action of the color filter
(generally a Bayer filter), which tries
to regulate the color distribution if
the subject contains too much detail
(high-frequency areas).
A conventional digital camera using
a Bayer color filter has yet another
filter, known as an optical low-pass
filter, interposed between the lens
and the sensor, in order to suppress
color artifacts. The optical low-pass
filter acts on the images resolved at
a high level by the imaging lens, its
job being to eliminate any detailed
elements likely to generate color
artifacts (high-frequency areas above
a certain level), immediately before
they reach the sensor. So it can
effectively suppress the generation
of color artifacts, but the downside is
that it naturally reduces the resolution
of the image.
The Foveon X3® captures the
very feeling in the air.
Images produced by Sigma's SD
and DP series cameras have what's
been called an “emotional quality”.
This phrase expresses the distinctive
image-quality you only get with the
Foveon X3® direct image sensor.
In terms of clarity and fine detail, it
goes far beyond the capabilities of
conventional digital cameras. This
level of image quality reproduces the
scene you shot, right down to the
feeling in the air. It's only possible in
a vertical color-capture system that
does not require color interpolation,
and an image-processing system
that does not require an optical
low-pass filter.
A conventional image-sensor, on
the other hand, fudges the colors,
and even cuts out high-frequency
areas. To compensate, the sharpness
processing is ramped up to give
some overall nuancing and a general
impression of high resolution. This
explains the tendency to generate
images that, as a whole, have an
unnatural feel. The colors can be
adjusted to some extent in post-
processing, but the detailed data
previously lost cannot be recovered.
No wonder the images produced by
conventional digital cameras, despite
their emphasized edges and clever
nuancing, look so unnatural, so subtly
wrong, It's all about basic principles.
A sensor that discards none of the
original light and color. And adds
none either.
The DP1x's Foveon X3® direct image
sensor utilizes the special features of
silicon, which is penetrated to different
depths by different wavelengths of
light, to successfully achieve full-
color capture for the first time ever in
a single-chip configuration. No color
filter is required. Like modern color
film cameras, it uses a method that
captures all the colors vertically.
Because it does not need color
interpolation or a low-pass filter, the
X3 image sensor produces images
that are sharp right from the start.
Therefore, sharpness processing in the
latter stages of the image processing
– creating edges and emphasizing
contours – can be reduced to a
minimum. This is why reviewers have
evaluated the images captured by
the X3 image sensor as having a truly
nuanced, sharp feel, and praised them
as very natural and demonstrating
superior image quality.
The Foveon X3® direct image sensor
reproduces pure, rich data and
nothing else. The image quality it
delivers is breathtaking. You really
need to see it for yourself.
The Fine Art of Capturing Detail
09
