DxOMark Mobile Report: OnePlus 2
Like its predecessor the OnePlus 2 offers the specification of a high-end phone at a budget price point. The camera's 13MP resolution isn't anything out of the ordinary these days, but optical image stabilization and a laser-assisted AF system are usually only found on expensive top-end models. Images are captured through an F2.0 lens with six elements, and in low light a dual-LED flash helps get skin tones right. The OnePlus 2 is capable of 4K video and can record 720p slow-motion footage at 120 frames per second. For image viewing and composition there is a 5.5-inch 1080p LCD and the Android operating system is powered by a Qualcomm Snapdragon 810 processor and 3 or 4GB of RAM.
With a DxOMark Mobile score of 76, the OnePlus 2 performs on the same level as Apple's iPhone 5s or the Sony Xperia Z1 and occupies a joint 22nd place in the DxOMark smartphone rankings. The DxOMark testers liked 'very good detail and fine luminance noise in outdoor images' and 'good detail preservation in low light'. They also noted the 'fast and accurate autofocus in bright light' and 'good exposure, detail preservation and color accuracy' in flash mode.
On the downside, 'pictures are slightly under-exposed', especially in high-contrast scenes which can result in clipped shadow areas. The testers also found the 'yellow cast under tungsten light' was too strong and the AF did not work accurately in trigger mode. There is also 'color shading in all light conditions' and 'visible color fringing and ringing'.
In video mode the DxO team noted 'low noise in bright light' but criticized 'frequent unnecessary refocusing and focus failure, color non-uniformities' and jerkiness due to low frame rates in low light. 'Exposure transition is not smooth' and 'image shake is very noticeable' in indoor recordings. The testers also noted a pink cast under low tungsten light.
Color, Exposure and Contrast
The DxOMark team found that the OnePlus 2 images showed 'good white balance in outdoor conditions but 'pictures were slightly under-exposed, especially in high-contrast scenes', with clipped shadow areas, 'color shading is visible' and the usual 'yellow cast under tungsten light is too strong'.
Overall DxOMark awarded the OnePlus 2 scores of:
- 4.3 out of 5 for Exposure
- 4.6 out of 5 for White Balance accuracy
- 3.5 out of 5 for Color shading in low light*
- 4.1 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 OnePlus 2 images show 'very good detail and fine luminance noise in outdoor conditions and good detail preservation in low light'. However, they also found 'visible noise in areas of plain color in low light'.
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 (such as fine foliage, hair or 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's 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 edges are sharp and if fine details are visible. In-camera processing means that 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 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 the 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): 3.6 out of 5
- Noise (bright light): 4.0 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 OnePlus 2 are shown below:
- Strong color fringing
- Visible ringing
- Slight difference of horizontal field of view in consecutive shots
- Sharpness 4.2 out of 5
- Color fringing 3.5 out of 5
- Ringing center 8.6%
- Ringing corner 5.4%
- Max geometric distortion -0.2%
- Luminance shading 24.4%
Distortion and Chromatic Aberrations
DxOMark also tests autofocus accuracy and reliability by measuring how much the acutance - or 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 setting, the OnePlus 2 performs well in bright light but drops off noticeably in lower light. The overall score is 80/100 in bright light and 66/100 in low light.
- Accurate and repeatable in Auto mode
- Fast in bright light, especially in macro position
- Inaccurate in trigger mode
The OnePlus 2 offers a dual-tone LED flash for better color balance. DxOMark scored the camera 90/100 overall for its flash performance.
- Good exposure, detail preservation and color accuracy
- Good flash uniformity
- Slight green cast when shooting only with flash, yellow cast when flash is mixed with Tungsten light
Overall DxOMark Mobile Score for Photo: 80 / 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. Overall, DxOMark found the OnePlus 2 video footage to have low noise levels in bright light but also show some problems, including focus failures, jerky motion in low light and abrupt exposure transition.
- Low noise in bright light
- Frequent unnecessary refocusing and focus failures
- Color non-uniformities
- Jerky footage due to low frame rates in low light
- Exposure transition is not smooth
- No roll correction and visible image shake when recording indoors
- Pink cast under low tungsten light
Overall DxOMark Mobile Score for Video: 67 / 100
DXOMark Image Quality Assessment
The OnePlus 2 achieves the same DxOMark Mobile score as Apple's iPhone 5s or the Sony Xperia Z1, taking a joint 22nd place in the DxOMark smartphone rankings. The testers like its good detail and finely grained noise in bright light, and noted good detail retention in dimmer conditions.
However, they often found high-contrast pictures to be underexposed and images shot under tungsten light to show a strong yellow cast. Color casts are noticeable in all light conditions as are color fringing and sharpening artifacts around edges.
In video mode the DxO team liked low noise levels in bright light but found several problems, including unnecessary refocusing, jerky motion and poor stabilization. For a more detailed analysis, visit www.dxomark.com.
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