Apple iPhone 5 Camera Review
DxOMark Mobile Report: Apple iPhone 5
No real surprises in the report from DxOMark's engineers, with the iPhone 5 putting in a decent performance but offering little advantage over its predecessor, reflected in the fact that the new model scored exactly the same as the 4S, with a DxOMark Mobile score of 74.
"The iPhone 5 achieves the same mobile score as the iPhone 4S. A score of 74 is very good, but falls short of the best cellphone camera that we have tested, the Nokia 808 PureView, which scores 81. The iPhone 5's strengths are good color and exposure in most lighting conditions, good detail, even in poor light, and accurate and reliable (if a little slow) autofocus in everyday use".
Where the iPhone 5 isn't so strong is under artificial light, where "it tends to give yellowish results" and when shooting with bright light sources at or near the edges of the frame, where lens flare can be a concern. Another thing that might cause problems, is the fact that "the iPhone 5's live view image only shows 88% of the actual vertical image area, which makes accurate framing rather difficult".
In video mode, DxOMark's engineers reported that the iPhone 5 gives "good detail in outdoor, bright conditions, and offers effective stabilization". As with stills, video footage shows "good, accurate colors, except in low artificial lighting where things go a little yellow". They did find some aspects of the iPhone 5's video mode frustrating, including the fact that "image stabilization can't compensate for walking motion if you're filming while moving, and autofocus is not continuous during shooting". Finally, "..in poor light, video footage from the iPhone 5 is quite noisy, and exposure can become unreliable too".
Color, Exposure and Contrast
The DxOMark team found the iPhone 5 to produce "very pleasant and vivid colors in studio conditions", and that it offered "good exposure for most scene types (above 20 Lux)". The iPhone definitely came out better in bright, natural light than in very dim conditions (especially when shooting under artificial light), offering "accurate white balance on natural images", but showing "slight color shading with some indoor illuminants". Because of this DxOMark scored the iPhone 5 at 84/100 for Color in bright light and 76/100 in low light. Overall though a good performance, with exposure and contast scoring a very respectable 88/100.
Overall DxOMark awarded the iPhone 5, based on both measured and perceptual analysis, scores of
- 4.5 out of 5 for Exposure,
- 4.5 out of 5 for White Balance accuracy
- 4.0 out of 5 for Color shading*
- 3.0 out of 5 for Color Rendering in low light, and
- 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. The iPhone 5 didn't exhibit significant shading in anything but the very lowest light conditions (20 Lux).
Noise and Details
DxOMark's engineers reported that the iPhone 5 captures images with "nice details in outdoor pictures", but that in low light conditions the images show "moderate loss of details". In low light they also criticize the fact that "smooth contrast gradations show some staircase effects" and that the noise has "a large grain shape". They noted that Apple has changed the denoising algorithm that controls the compromise between noise and texture, compared to iPhone 4S - see below.
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 & Detail Perceptual scoring
- 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
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 iPhone 5 are shown below:
- No ringing (halos)
- Noticeable flare in some outdoor and indoor pictures.
- Noticeable moiré in some pictures.
- Loss of sharpness in the corners.
- Sharpness 3.5 out of 5
- Color fringing 3.5 out of 5
- Ringing center: 9.6%
- Ringing corner 2.1%
- Max geometric distortion 0.39%
- Luminance shading 8%
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%). Even using the 8MP equiv. condition the iPhone 5 did pretty well, earning an overall score of 74/100 in bright light and 69/100 in low light.
- Accurate and repeatable autofocus in low light and bright light conditions.
- Automatic face detection.
- Autofocus is sometimes slow.
- Unnecessary refocusing.
DxOMark scored the iPhone 5 70/100 overall for its flash performance, docking points for its lack of power (which means noisy images), autofocus errors (when using flash in very low light) and occasional white balance issues, summarizing the performance as offering "Fair detail preservation but strong residual noise (flash is not powerful enough)"
- Good white balance.
- Good flash uniformity.
- A reddish cast is noticeable in low light tungsten plus flash illumination, .
- Autofocus is not always accurate when using the flash.
- Strong noise (flash is not powerful enough).
Overall DxOMark Mobile score for Photo: 74
DxOMark engineers put phone cameras through a similarly gruelling 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 iPhone to produce good results with plenty of detail, with effective stabilization and accurate color. They were less impressed with the lowlight performance when there is a visible "loss of texture", and noted the auto exposure jumping around as lighting conditions changed. They also complained about clipped highlights and poor image stabilization in low light and the fact that there is no continuous autofocus, adding that "Lens breathing is visible and unpleasant" when manual focus is triggered.
- Nice details in bright light conditions.
- Good video stabilization in outdoor conditions.
- Good colors.
- The stabilization has low performances in indoor conditions for walking movements.
- Autofocus only works when manually triggered. Visible focus overshoot.
- Strong noise in low light and dark areas with an unpleasant chrominance component.
- Exposure oscillations during scene illumination changes and clipped highlights.
- Highlights are easily clipped
- Some strange and unpleasant oscillations in exposure have been noticed.
Overall DxOMark Mobile score for video: 70 / 100
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