DxOMark Mobile Report: Samsung Galaxy S4 lab tests look outstanding
Lars Rehm | Published: May 22, 2013 at 22:18:49 UTC33
DxOMark Mobile Report: Samsung Galaxy S4
We covered Samsung's new superphone, the Galaxy S4, at its launch, tried some of its new camera features and also had a good look at its image capturing capabilities in our recent Smartphone Super Shootout. Thanks to our partners at DxOMark we can now also get a better idea what the Samsung's image output means in numbers and graphs. DxO's imaging experts have analyzed 14 aspects of mobile imaging including detailed image quality assessment, flash performance, autofocus reliability and more to calculate a final score. This report will be integrated into our full review once it is finished but for now read on to find out how the Samsung Galaxy S4's camera performed in the DxO lab tests. For DxO's own report, head to the Galaxy S4 page on DxOMark.com.
Samsung Galaxy S4 Headline features:
With a DxOMark Mobile score of 75 the Samsung Galaxy S4 is ranked number two in the DxO smartphone rankings, between Nokia's 808 and the Apple iPhone 5. The DxOMark team report that the Samsung Galaxy S4 captures images with "impressive detail preservation in bright light conditions," "good auto-exposure even with difficult outdoor situations" and "good image quality with the flash." Images also showed "pleasant and rich colors in all lighting conditions" and the "autofocus is fast and accurate in both auto and trigger mode."
On the downside: DxOMark observed "important loss of detail in low light due to noise reduction," "strong ringing" and "slight color shading under low tungsten light."
In video mode, Galaxy S4 cannot quite repeat the impressive stills image performance. DxOMark's engineers reported that the Samsung produced video with "good colors and good texture reproduction" but the report also found the S4 video showed "visible aliasing and staircase effect" and "strong noise in low-light conditions." Testers also found the video stabilization disappointing and that "in low light conditions the AF can trigger without any change in focus distance."
The DxOMark team found that the Samsung Galaxy S4 images show "good auto-exposure, even with difficult outdoor situations," "pleasant and rich colors in all lighting situations" and "good color shading correction in most situations although a slight error was noticed in low tungsten light."
The only downside in terms of color, exposure and contrast found by DxO testers is a tendency to clip highlights in contrasty scenes. DxOMark scored the Samsung Galaxy S4 at 83/100 for color in bright light and 77/100 in low light.
Overall DxOMark awarded the Samsung Galaxy S4 scores of:
*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 Samsung Galaxy S4 image output shows "impressive detail preservation in bright light conditions," with the 13MP sensor showing significant improvement over the best 8MP devices. The DxO testers also found that "noise levels remain acceptable even in low light conditions without chromatic components in flat areas."
However, on the downside "noise reduction is too strong, causing significant loss of detail in low light" and "in low light edges may either be sharp with chroma noise or slightly blurry depending on background." As the image stablization is of the digital variant, it "raises ISO values which significantly increases noise levels."
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.
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.
Edge acutance is a measure of the sharpness of the edges in images captured by the phone's camera, and again we're only looking at the most demanding of the three viewing conditions that DxOMark reports on, "8MP equivalent."
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
DxOMark engineers don't just point camera phones at charts, they also take and analyze scores of real-world shots and score them accordingly. Their findings for the Samsung Galaxy S4 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 analyze a range of artifacts. Their findings after testing the Samsung Galaxy S4 are shown below:
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 Samsung Galaxy S4 results are excellent in good light and still very good in lower light. The overall score is 87/100 in bright light and 74/100 in low light.
DxOMark scored the Samsung Galaxy S4 82/100 overall for its flash performance.
Overall DxOMark Mobile score for Photo: 79 / 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 Samsung Galaxy S4's video to have good texture reproduction. However, there is visible aliasing and the digital video stabilization is not very efficient.
Overall DxOMark Mobile score for Video: 68 / 100