DxOMark Mobile Report: Blackberry Z10

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.

Texture acutance is good and pretty much identical for daylight and tungsten light sources.

In terms of texture acutance the Blackberry Z10 compares well to the competition. In low light it is only beaten by Nokia's 808 with PureView technology, in bright light it is on the level with Apple's iPhone 5. The Nokia leads this competition at all light levels but the Blackberry is the best among the devices with conventional imaging technology.

Visual Noise

Noise and 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 Blackberry Z10 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 analyse a range of artifacts. Their findings after testing the Blackberry Z10 are shown below:

Pros:

• n/a

Cons 

• Slight loss of sharpness in image corners
• Strong color fringing
• Slight ringing

Perceptual scores

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

Measured findings

• Ringing center: 14.1%
• Ringing corner 6.1%
• Max geometric distortion -0.29%
• Luminance shading 26%

Distortion and Chromatic Aberrations

The graph shows the magnification from center to edge (with the center normalized to 1). The Blackberry Z10 shows a slight complex distortion which you are not going to notice this in normal photography.

Lateral chromatic abberations minimal; chromatic abberation this small are not seen by most observers.

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%). Using the 8MP equivalent condition the Blackberry Z10 results are decent but not quite up there with the very best. The overall score is 75/100 in bright light and 64/100 in low light.

Pros: 

• Autofocus is accurate and repeatable in bright light conditions
• Good sharpness levels even in low light

Cons: 

• Autofocus is slow

Autofocus repeatability - average acutance difference with best focus: low light 5.0%, bright light 6.5%

DxOMark scored the Blackberry Z10 62/100 overall for its flash performance, deducting points for occasional white balance issues in mixed light.

Pros: 

• Good detail preservation, exposure and color rendering
• Stable autofocus with flash

Cons: 

• Strong noise
• White balance is slightly blue with no light and turns red when flash is mixed with tungsten lighting
• Color shading when mixed with tungsten light source

Overall DxOMark Mobile score for Photo: 67 / 100

---

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. DxOMark found the Blackberry Z10's exposure and color reproduction to be good. However, the white balance is unreliable in tungsten light and image stabilization performance is under par.

Pros: 

• Reactive autofocus with some tracking abilities

Cons: 

• Visible color non uniformities
• Perfectible texture reproduction
• Perfectible video stabilization

Overall DxOMark Mobile score for Video: 66 / 100