Sony Xperia Z1 review: A smartphone with a camera-sized sensor
DxOMark Mobile Report: Sony Xperia Z1
With a DxOMark Mobile score of 76 the Sony Xperia Z1 takes the number two spot in the DxO smartphone rankings, just above the Apple iPhone 5s and the Samsung Galaxy S4. With a score of 77 only the Nokia 808 has done better so far.
The DxOMark team reports that the Xperia Z1 images show "good overall exposure, excellent detail preservation outdoors, pleasant colors and low noise levels in all situations. Noise is pleasant (no chroma component) with a very small grain size." The autofocus was found to be "fast and precise in most situations." The Z1's also performed well when using its flash, with "precise autofocus, good exposure, good color rendering and white balance and good detail preservation."
On the downside: "Slight color shading is sometimes noticeable" and "excessive exposure times in low light under 20 lux can be a source of motion blur." Images show "strong ringing" (halos around high-contrast edges) and "low-contrast detail is slightly smeared in low light conditions."
In video mode the Xperia Z1 displayed a good overall performance, with "good noise reduction especially in low-light conditions." However, the "autofocus lacks stability and a residual high frequency motion is visible in indoor conditions for walking movements."
Color, Exposure and Contrast
The DxOMark team found that the Sony Xperia Z1 images show "good overall exposure, nice colors in all situations and stable white balance."
However, the Xperia Z1 also displayed "very slight color shading, sometimes noticeable both indoors and outdoors" and "in extreme low light, exposure time is too long (1/10s under 20 lux when other camera phones do not use longer exposure than 1/15s)".
Overall DxOMark awarded the Sony Xperia Z1 scores of:
- 4.4 out of 5 for Exposure
- 4.3 out of 5 for White Balance accuracy
- 3.5 out of 5 for Color shading in low light*
- 3.8 out of 5 for Color shading in bright light*
- 3.0 out of 5 for Color Rendering in low light
- 4.5 out of 5 for Color Rendering in bright light
*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.
Noise and Details
DxOMark's engineers reported that the Sony Xperia Z1 image output shows "very low noise levels with a small grain size, even in low light conditions, and very good detail preservation. Outdoors, more details are visible than with other current 8MP mobile cameras. Most noise is luminance noise."
On the downside "low-contrast detail is slightly smoothed out compared to the edges and noise levels are not constant in the image: edges are noisier than areas of plain color; image corners are noisier than the center."
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.
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 and Detail Perceptual scoring
- Texture (bright light): 4.8 out of 5
- Texture (low light): 3.0 out of 5
- Noise (bright light): 3.8 out of 5
- Noise (low light) 3.8 out of 5
Phone cameras, like entry-level compact cameras, tend to suffer from artifacts such as sharpening halos, color fringing, vignetting (shading) and distortion, which can have an impact on the visual appeal of the end result. DxOMark engineers measure and analyze a range of artifacts. Their findings after testing the Sony Xperia Z1 are shown below:
- Strong ringing noticeable near edges
- Slight color fringing sometimes visible
- Sharpness 4.0 out of 5
- Color fringing 4.0 out of 5
- Ringing center 15.3%
- Ringing corner 8.6%
- Max geometric distortion -0.3%
- Luminance shading 30.8%
Distortion and Chromatic Aberrations
DxOMark also tests autofocus accuracy and reliability by measuring how much the acutance -- 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 dependent 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 Sony Xperia Z1 is much better, especially in low light, than its predecessor, the Xperia Z. The overall score is 72/100 in bright light and 73/100 in low light.
- Fast and reactive autofocus
- Good overall repeatability and precision.
- Occasionally pictures are completely out of focus in outdoor conditions
DxOMark scored the Sony Xperia Z1 84/100 overall for its flash performance.
- Good flash performance: precise autofocus, good exposure, good color rendering and white balance, good detail preservation
- Slight change of white balance in presence of tungsten lighting
- Some noise noticeable
Overall DxOMark Mobile score for Photo: 77 / 100
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 Sony Xperia Z1's overall video performance to be good, with good noise reduction in low light and the autofocus exposure was the best of any device which the lab has tested to date. However, some instability of the autofocus was also observed.
- Good overall video performance
- Good noise reduction, especially in low-light conditions
- Autofocus lacks stability
- A residual high frequency motion is visible in indoor conditions for walking movements
Overall DxOMark Mobile score for Video: 74 / 100
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