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Nokia 808 PureView Review
Barney Britton | Published: Oct 9, 2012 at 03:46:21 UTC27
DxOMark Mobile Report: Nokia Pureview 808
Note: all the observations are based on results obtained using the Pureview 8MPixel mode. DXOMark's engineers were highly impressed with the Nokia 808 Pureview, noting that "this smartphone camera is the best tested by our Lab so far with a Photo Mobile Score of 81." They noted that the 808 offers "very good detail preservation even in low light conditions," and boasts "excellent noise management in low light conditions, far ahead of its direct competitors at its release." On the downside they criticized the less than perfect autofocus when shooting at close range and occasional exposure errors when shooting under difficult lighting conditions (such as scenes with a high dynamic range or with backlit subjects). Video also produced "very good performance in bright light, with pleasant colors," but DxOMark reported "very noisy" results in low light and that the stabilization system was far from 100% reliable.
Color, Exposure and Contrast
The DxOMark team found the Pureview 808 to produce "pleasant colors in every conditions, less saturated than on most smartphones", with "hardly noticeable" color shading, but that they experienced occasional "Small exposure failures (over or under exposure in some difficult outdoor pictures." Overall DxOMark scored the Purview 78/100 for Exposure and Contrast, an excellent 82/100 for Color (in bright light) and 77/100 for Color in low light.
Drilling down a little into the detail, DxOMark awarded the Pureview 808, based on both measured and perceptual analysis, scores of:
DxOMark noted that in low light conditions (20 Lux, tungsten - equivalent to a very dimly lit interior) the 808 did produce a slight yellow cast, but that "Despite the color cast, colors are vivid and pleasant."
Outdoors, with good lighting condition they described colors as "pleasant, but the contrast is not maximized."
*Color Shading is the nasty habit cellphone cameras have of rendering different areas of the frame with different color shifts, resulting in pictures with, for example, pinkish centers and greenish corners. The Pureview 808 didn't exhibit significant shading in bright light, and only a little in the very lowest light conditions (20 Lux).
Noise and Details
DxOMark's engineers reported that the Pureview 808 captures images that show "Impressive detail preservation even in low light conditions with 100% crops", and that "Noise level is very well controlled even in low light conditions." Unusually they found almost nothing to complain about.
Texture Acutance is a way of measuring the ability of a camera to capture images that preserve fine details, particularly the kind of low contrast detail (textures such as fine foliage, hair, fur) that can be blurred away by noise reduction or obliterated by excessive sharpening.
Sharpness is an important part of the quality of an image, but while it is easy to look at an image and decide visually whether it's sharp or not, the objective measurement of sharpness is less straightforward.
An image can be defined as 'sharp' if its edges are sharp and if fine details are visible, but in-camera processing means it's possible to have one of these (sharp edges) but not the other (fine details). Conventional MTF measurements tell us how sharp an edge is, but have drawbacks when it comes to measuring fine detail preservation. Image processing algorithms can detect edges and enhance their sharpness, but they can also find homogeneous areas and smooth them out, to reduce noise.
Texture Acutance, on the other hand, can qualify sharpness in terms of preservation of fine details, without being fooled by edge enhancement algorithms.
At first sight, the images from these two cameras may appear equally sharp. A sharpness measurement on edges will indeed confirm this impression, and will even show that the second camera is sharper. But a closer examination of low contrasted textures shows that the first camera has a better preservation of fine details than the second. The purpose of the Texture Acutance measurement is to qualify this difference.
Note: Acutance is a single value metric calculated from a MTF result. Acutance is used to assess the sharpness of an image as viewed by the human visual system, and is dependent on the viewing conditions (size of image, size of screen or print, viewing distance). Only the values of texture acutance are given here. The measurements are expressed as a percentage of the theoretical maximum for the chosen viewing condition. The higher the score, the more details can be seen in an image.
For all DxOMark Mobile data presented on connect.dpreview.com we're showing only the '8MP equivalent' values, which gives us a level playing field for comparison between phone cameras with different megapixel values by normalizing all to 8MP, suitable for fairly large prints. DxOMark also offer this data for lower resolution use-cases (web and on-screen). For more information on DxOMark's testing methodology and Acutance measurements please visit the website at www.dxomark.com.
Edge acutance is a measure of the sharpness of the edges in images captured by the phone's camera, and again we're only looking at the most demanding of the three viewing conditions that DxOMark reports on, '8MP equivalent'.
Visual Noise is a value designed to assess the noise in an image as perceived by the human visual system, depending on the viewing condition (size of image, size of screen or print, viewing distance). The measurements have no units and can be simply viewed as a weighted average of noise standard deviation for each channel in the CIE L*a*b* color space. The lower the measurement, the less noise in the image.
Noise & Detail Perceptual scoring
DxOMark engineers don't just point camera phones at charts, they also take and analyse scores of real-world shots and score them accordingly. Their findings for the Nokia 808 PureView were:
Phone cameras, like entry-level compact cameras, tend to suffer from artifacts such as sharpening halos, color fringing, vignetting (shading) and distortion, which can impact on the visual appeal of the end result. DxOMark engineers measure and analyze a range of artifacts. Their findings after testing the Pureview 808 are shown below:
Distortion & Chromatic Aberrations
DxOMark also tests autofocus accuracy and reliability by measuring how much the accutance - sharpness - varies with each shot over a series of 30 exposures (defocusing then using the autofocus for each one). As with other tests these results are dependant on the viewing conditions (a little bit out of focus matters a lot less with a small web image than a full 8MP shot viewed at 100%). In bright light the Pureview 808 did a great job, offering good autofocus accuracy and repeatability and earning a respectable 81/100 score. In low light things were far less impressive, especially in macro mode, when DxOMark found autofocus reliablity to be poor enough to drop the score to 66/100.
DxOMark scored the Nokia 808 a high 81/100 overall for its flash performance, noting it offers "Very good flash quality: good repeatability and good exposure" and very reliable white balance. The only demerit is the fall-off (darkening of corners).
Overall DxOMark Mobile score for Photo: 81
DxOMark engineers put phone cameras through a similarly grueling set of video tests, and you can read their full findings on the DxOMark website here. We'll simply summarize for you. In bright light DxOMark found the Pureview 808 to produce good results with plenty of detail and "pleasant colors." They were less impressed with the lowlight performance when the results where found to be "very noisy" and the autofocus to leave much to be desired.
Overall DxOMark Mobile score for video: 68 / 100