Nokia 808 PureView Review

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."

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.

	A detail of  target made of a 'dead leaves' pattern, designed to measure Texture Acutance. It is obtained by drawing random shapes that occlude each other in the plane, like dead leaves falling from a tree. The statistics of this model follow the distribution of the same statistics in natural images.
	In this example from a DSLR without edge enhancement sharpness seems equal on edge and on texture. Many details are visible in the texture.
	In this second example edges have been digitally enhanced, and the edge looks over-sharp, with visible processing halos ('ringing'). On the texture part, many details have disappeared.

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.

The Pureview 808 shows class-leading ability to retain fine texture even at 20 Lux (3.0 EV: very low light, such as a floodlit building at night); even better at 700 Lux (outdoors on an overcast day).

The Pureview 808 (green line) is the clear winner here, most noticeably in low light where its noise reduction algorithms do considerably less harm than any of the competitor models.

In these 100% crops you can clearly see what a remarkable job the 808 does at preserving texture even in very low light.

Edge Acutance

The 8MP Pureview mode produces consistently sharp edges in all lighting conditions,

The 808 uses very subtle sharpening compared to some competitors, but still offers very competitive edge acutance.

Visual Noise

Visual noise is remarkably low thanks to the innovative Pureview technology. This graph shows the results for daylight; those for tungsten light are almost identical.

Although there's not a lot of difference in bright light, in low light the Nokia 808 is the clear winner here, thanks to its groundbreaking 'PureView' technology.

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:

• Texture (bright light): 4.5 out of 5
• Texture (low light): 3.0 out of 5
• Noise (bright light): 3.5 out of 5
• Noise (low light) 2.8 out of 5

Bright light sample shot	"impressive detail preservation throughout most of the field"

Low light (20 Lux) studio shot	"noise level is extremely low in homogeneous parts"

100% crops at 20 Lux: "very slight loss of details (faces are slightly blurry)"

Artifacts

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:

Pros:

• Ringing level (halos) is negligible, extremely low compared to other camera phones, while sharpness and details are still excellent

Cons 

• Slight loss of sharpness in the corners
• Very slight color fringes (red and blue) due to lateral chromatic aberration, only visible at 100% viewing.

Perceptual scores

• Sharpness 4.0 out of 5
• Color fringing 4.2 out of 5

Measured findings

• Ringing center: 1.2%
• Ringing corner 0.4%
• Max geometric distortion 0.46%
• Luminance shading 20%

Distortion & Chromatic Aberrations

the graph shows the magnification from center to edge (with the center normalized to 1). The Pureview 808 shows slight pincushion distortion, with a maximum geometric distortion of 0.46%. You are not going to notice this in normal photography.

Very slight color fringes (red and blue) are noticeable in real world shots (lateral chromatic aberrations)

Autofocus

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.

Pros: 

• Good autofocus repeatability in bright light conditions
• In low light conditions, repeatability drops a little but the sharpness level stays acceptable.

Cons: 

• Autofocus is not very reliable at close range (macro mode) and is less reliable when triggering the AF by pressing the shutter button halfway than by touching the screen

Autofocus repeatability - average acutance difference with best focus: Low light 7.24%, Bright light 1.77%

Flash

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).

Pros: 

• good flash quality: good repeatability and good exposure
• Very stable white balance (even when mixed with another light source)

Cons: 

• Fall-off is a bit strong at the corners.  

Overall DxOMark Mobile score for Photo: 81

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Video Capture

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.

Pros: 

• Very good performance in bright light with pleasant colors
• Fine details in bright light

Cons: 

• Very noisy in low light
• Autofocus is not very reactive, and cannot reach macro in continuous mode
• Stabilization does not correct jello effect, and quality is very scene dependent

Overall DxOMark Mobile score for video: 68 / 100