The Nokia 808 PureView is a Symbian
Belle powered smartphone, first
unveiled on 27 February 2012 at the Mobile
World Congress. It is the first smartphone to feature Nokia's PureView imaging
technology based on a new 41 megapixel oversampling 1/1.2" sensor and a high
resolution f/2.4 Zeiss all-aspherical 1-group
lens. See examples.
The 808 won the award for "Best New Mobile Handset, Device or
Tablet" at Mobile World Congress 2012.(...)
PureView Pro Camera
PureView Pro is an imaging technology used in the Nokia 808 PureView device. It is the combination of a 1/1.2" large,very high resolution 41Mpix with high performance Carl Zeiss optics. The large sensor enables pixel oversampling, which means the combination of many pixels into one perfect pixel. PureView imaging technology delivers high image quality, lossless zoom, and improved low light performance (see below). It dispenses with the usual scaling/interpolation model of digital zoom used in virtually all smartphones, as well as optical zoom used in most digital cameras, where a series of lens elements moves back and forth to vary the magnification and field of view. Instead, it will give around 3x lossless zoom for stills, and 4x zoom in full HD 1080p, for 720p HD video, 6x lossless zoom and for nHD (640x360) video, 12x zoom.
PureView
Pro specifications
§ 41 megapixel CMOS image
sensor, 1/1.2" image sensor
format with 7728 x 5368 pixels, pixel size: 1.4 microns.
§ On-chip image processor performing image scaling with oversampling,
giving lossless (digital) zoom:
3x for stills, 4x for full HD 1080p video with on-chip video processor performing image resolution processing with over 1 billion pixels
per second[4] enabling the use of all pixels for
improved image noise and dynamic
range
§ Carl Zeiss optics with F-number: f/2.4. Focal length: 8.02mm: 35mm equivalent
focal length: 26mm @ 16:9 and 28mm @ 4:3.Construction: 5 elements in 1 group.
All lens surfaces are aspherical, partly extreme aspheric,one
high refractive index, low-dispersion glass mold lens. Focus range: 15cm – Infinity
(throughout the zoom range).
§ Mechanical shutter with short shutter lag and ND8 (3 f-stops) neutral density filter
Resolution
processing image sensor
PureView Pro sensor has an active
area of 7728 x 5368 pixels, totaling over 41Mpix. Depending on the aspect ratio
chosen by the user, it will use 7728 x 4354 pixels for 16:9 images/videos, or
7152 x 5368 pixels for 4:3 images/videos. What happens next depends on the
settings and whether or not zoom is used. But to give an idea, the default
still image setting is 5Mpix at 16:9, and for video, 1080p at 30fps. Using
these settings, the zoom is around 3x for stills and 4x for video. Conventional
digital zoom tends to scale up images from a relatively low resolution,
resulting in poor image quality.
The image sensor is a new resolution processing image sensor,
which is capable not only of delivering parts of its pixels, but ofdown- or oversampling its resolution by having its own on-chip image processor, highly reducing
external processing needs anddata rates as
well as image noise (see noise
shaping) when lower resolutions (or HD
video) are needed. Additionally this provides very high image resolution. Images up to 38
megapixels can be taken at full resolution at 4:3 aspect ratio and 34
megapixels at 16:9 ratio. The PureView is a pixel oversampling technology used
by Nokia that converts an image taken at full resolution into 3, 5 or 8
megapixels to eliminate noise in the image.
Zeiss
1-group lens
The optic is a 1-group lens, which is based on a
shiftable fixed-focus lens:
identical to the highly regarded prime
lenses in mostZeiss Planar or Tessar optics, focus is achieved by varying the distance to
the image sensor (unit focusing lens). This construction
has the advantage that no movable focus group is needed. Considerable movable
(focus-range) lens groups need a minimum of one additional adaptive lens
element in both the moved group and the stationary group, increasing the number
of elements by at least two. This increases unwanted reflections as well as
overall tolerances and therefore decreases sharpness.
Any 1-group lens is additionally an aperture-less lens, further increasing
the freedom of lens element arrangement and allowing the designer to optimize
the lens to only one f-stop. The
lens consists of only 1 group with molded elements, which gives a highly
stable, precise mechanical alignment. The lenses are partly made of plastic,
which provides sufficient stability at this size and as a 1-group lens and has
the significant advantage of making it possible to use extreme aspheric shaped lens elements.
5 all-aspherical lens elements
are used, making it possible to increase border-sharpness and lower distortion and astigmatism.
The high refractive index, low-dispersion glass additionally helps reduce chromatic aberrations. The
disadvantage of a 1-group lens is that no aperture is possible; a neutral density filter with approximately ND8 (3 f-stops) is instead used. Although the
lens is named a Vario-Tessar, it
has almost nothing in common with the 4 element in 3 group, non-aspherical
original Tessar.
Due to the comparatively large image
sensor format of 1/1.2" and
the comparatively fast lens with f/2.4, the camera has a quite shallow depth of field of approximately f/8, equivalent to a
35mm full-frame or approximately f/5, equivalent to a APS-C DSLR with
the same angle of view (without zoom).
Zoom
Zoom with the PureView Pro works
in a manner only partly related to the digital
zoom principle. With no zoom, the
full area of the sensor corresponding to the aspect ratio is used. Although it
is only possible in this case to use the full resolution, pixel oversampling
can be used to combine many pixels to calculate a single pixel and reduce image
resolution. This will filter away visual noise from the image and greatly
reduce noise in low-light conditions.
The limit of the zoom is reached when the selected output
resolution becomes the same as the input resolution. That means once the area
of the sensor reaches 3072 x 1728, the zoom limit is reached. So the zoom is
always provides the true image resolution the user wants. The level of pixel
oversampling is highest when zoom is not used. It gradually decreases until the
maximum zoom is hit, where there is no oversampling. At this stage, PureView
Pro optics and pixels start behaving in a more conventional way. But because
only the center of the optics is used, the best optical performance is achieved
– including low distortion, no vignetting and highest levels of resolved
detail.
Autofocus
PureView Pro comes with improved autofocus also for video as the optics with the
larger image sensor provide a relatively shallow depth of field. PureView Pro
gives continuous auto focus in all shooting modes, close-up (Macro) focus, Face detection, Touch focus with easy manually selected focus
point and Hyperfocal distance focus for defined depth of field, for
extreme focus speed or when no reliable focus is possible due to darkness.
Video
Most smartphone manufacturers
crop off a section of the sensor to ease the processing load. In contrast, the on-chip oversampling image processor of
PureView Pro enables oversampling of all 38Mega-pixels even at the high data
rates of 1080p with 30 fps. Plus, it provides lossless
zooming capability, which is output resolution dependent. Full HD 1080p gives
4x zoom; 720p HD video, 6x lossless zoom; and for
nHD (640x360) video, 12x zoom. In addition, encoding is up to 25Mbps in 1080p H.264/MPEG-4 HD video format. The PureView Pro sensor
integrates a special video
processor that handles pixel scaling before sending the required number to
the main image processor.
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