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DxOMark Mobile Report: Nokia's Lumia 925 scores nearly as high as 41MP Lumia 1020

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DxOMark Mobile Report: Nokia Lumia 925

At a quick glance the Nokia Lumia 925's camera specification appears to be identical to its predecessor's, the Lumia 920, but if you look again you'll see that there are a few small but potentially important differences. The lens gains an extra element with a now 6-element design, a dual-LED flash element is added and the camera also gains an ISO 3200 setting. According to Nokia the image processing has also been significantly improved, to offer both improved detail in good light and better quality in low light. (We recently pitted all three Lumia 900 series models — the 920, 925 and 928 — against one another in our Nokia smartphone shootout.)

The Lumia 925 is PureView branded but doesn't use the Lumia 1020's large sensor and pixel-binning algorithms. Instead it features a conventional 8.7 MP CMOS sensor, a F2.0 lens and optical image stabilization. Its aluminum-edge body comes with a polycarbonate back and integrated antenna. On the front you'll find a piece of curved Gorilla Glass 2. At 4.5 inches the screen itself is the same size as that of the Lumia 920 and 1020. The device also features wireless charging (with an accessory cover) and LTE connectivity.

With the introduction of the Lumia 1020 and its large 1/1.5-inch 41MP sensor the Lumia 925 has lost its status as Nokia's flagship smartphone but given its street price is currently almost $250 lower than the 1020's it can still be a compelling device for the price-conscious mobile photographer. Read on to find out how it performed in DxO's comprehensive studio tests.

Nokia Lumia 925 headline specification:

  • 8.7 MP CMOS sensor
  • F2.0 lens
  • Optical Image Stabilization
  • Windows Phone 8
  • 4.5" AMOLED screen, 1280x768 pixels resolution
  • 1.5 GHz Dual-core Snapdragon processor
  • 1GB RAM
  • 16GB internal memory
  • 2000 mAh battery
  • Wireless charging via accessory cover
  • LTE

Summary

With a DxOMark Mobile score of 73 the Nokia Lumia 925 finds itself on the 6th position on DxO's smartphone ranking. It scored just one point less than its bigger brother, the Lumia 1020, and is trailing four points behind the current top-rated camera phone, the Nokia 808.  

The DxOMark team report that the Nokia Lumia 925 captures images with "good overall exposure" and that "in extreme low light conditions, exposure stays good when other camera phones fail". The image output shows "very low noise levels with no chroma component" and the flash performance is very good, with "good exposure, color, white balance, texture and noise". 

On the downside: Images show "noticeable color shading with indoor lighting and sometimes outdoor, low-contrast details is badly preserved, especially in low light and in low light conditions, exposure time is too long which may cause motion blur." The 925 occasionally also struggles with white balance which "is sometimes blueish outdoors or with fluorescent lighting."

In video mode, DxOMark's engineers reported that the Nokia Lumia 925 offers "good texture reproduction" and that the "video stabilization is reliable in both bright and low light". On the downside there are "instabilities in white balance when changes occur in light conditions or scene content, unpleasant sudden corrections in video stabilization during walking motion and visible color fringing".

Still Photography

Color, Exposure and Contrast

The DxOMark team found that the Nokia Lumia 925's images show "good overall exposure and -pleasant colors outdoors". "In extreme low light, the exposure stays good thanks to longer exposure time". However, there is also "strong color shading with some illuminants (e.g. fluorescent lightings), the white balance is sometimes blueish outdoors" and shows "some variation with indoor lighting".

Overall DxOMark awarded the Nokia Lumia 925 scores of:

  • 4.5 out of 5 for Exposure
  • 3.0 out of 5 for White Balance accuracy
  • 2.5 out of 5 for Color shading in low light*
  • 3.5 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 Nokia Lumia 925 image output shows "very low noise levels, even in low light conditions, thanks to longer exposure time and no chroma noise". On the other hand "low-contrast detail is badly preserved, especially in low light and in low light conditions, exposure time is too long (1/4s compared to 1/15s for other camera phones at 10 lux), which can cause motion blur".

Texture Acutance

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 increases with light levels and is slightly better under low tungsten light than daylight balanced sources. 
In terms of texture acutance the Nokia Lumia 925 is on a similar level as the Samsung Galaxy S4 and iPhone 5s in low light but cannot quite keep up with the S4 at 100 and 700 Lux. The Lumia 1020 with its large sensor and downsampling technology is a notch above the competition at all light levels.

Edge Acutance

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."
The Lumia 925's ability to retain fine texture in images decreases very slightly from very low light (20 Lux, for example, a floodlit building at night ) to 100 Lux (very dark overcast day) and then increases significantly at 700 Lux (outdoors on an overcast day). 
In terms of edge acutance the Nokia Lumia 925 trails slightly behind the competition in all but the brightest conditions. 

Visual Noise

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.

Visual noise levels are low and remain almost unchanged across the Lux scale. Most of the measured noise is luminance grain as chroma noise is being eliminated by noise reduction.
The Nokia Lumia 925's noise levels are very similar to the Samsung Galaxy S4 and Nokia Lumia 1020. Apple's iPhone 5s is significantly noisier at low and medium light levels. 

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 Nokia Lumia 925 were:

Natural scene

  • Texture (bright light): 4.3 out of 5
  • Texture (low light): 3.5 out of 5
  • Noise (bright light): 4.0 out of 5
  • Noise (low light) 3.8 out of 5
Bright light sample shot
100% crop
Low-contrast detail is smeared but noise levels are low.
Low light (20 Lux) studio shot
100% crop
Low-contrast detail is lost through noise reduction but noise is very well controlled.
At low light there is some visible luminance noise (grain) but no chroma noise.

Artifacts

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 Nokia Lumia 925 are shown below:

Cons 

  • Slight fringing sometimes noticeable

Perceptual scores

  • Sharpness 3.0 out of 5
  • Color fringing 3.5 out of 5

Measured findings

  • Ringing center: 9.0%
  • Ringing corner 6.2%
  • Max geometric distortion -0.2%
  • Luminance shading 21.1%

Distortion and Chromatic Aberrations

The graph shows the magnification from center to edge (with the center normalized to 1). The Nokia Lumia 925 shows a slight pincushion distortion, which you are not going to notice in normal photography.
The Lumia 925 shows some chromatic abberations that can be noticeable under close inspection of images.

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%). The overall score for the 925 is 79/100 in bright light and 65/100 in low light.

Pros: 

  • Fast AF both in low and bright light
  • Good repeatability when taking pictures using the physical shutter button

Cons: 

  • Some AF errors when using the touch screen to focus
  • Overshooting in all situations
Autofocus repeatability - average acutance difference with best focus: low light 7.79%, bright light 6.63%

Flash

DxOMark scored the Nokia Lumia 925 72/100 overall for its flash performance, deducting points for strong corner shading. 

Pros: 

  • Good overall behavior with flash: good exposure, color rendering, white balance, texture preservation and noise levels

Cons: 

  • Strong loss of light in image corners

Overall DxOMark Mobile score for Photo: 75 / 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 Nokia Lumia 925 to produce good texture and offer efficient image stabilization in video mode. However, the white balance can be unreliable when the light changes, the OIS can overcorrect when walking while recording and there is some visible color fringing in the video footage. 

Pros: 

  • Good texture reproduction
  • Video stabilization is reliable in both bright and low light.

Cons: 

  • Instabilities in white balance when changes occur in light conditions or scene content
  • Unpleasant corrections in video stabilization during walking motion
  • Visible color fringing

Overall DxOMark Mobile score for Video: 69 / 100

DXOMark Mobile Score
73

DXOMark Image Quality Assessment

After the launch of the Lumia 1020 the 925 might not be Nokia's flagship smartphone anymore but at an almost $250 USD savings compared to the 1020 means it can still be a great alternative for cash-conscious mobile photographers.

The Nokia Lumia 925 captures images with good exposure, even in very low light, and low noise levels across the ISO range. Flash performance is also very good. 

On the downside images can show color casts under artificial light and low-contrast detail is lost through noise reduction, even in bright light. Extremely slow shutter speeds in low light also increase the risk of image blur through camera shake. 

In video mode the Lumia 925 captures good detail and offers very efficient image stabilization but the white balance can struggle when light conditions change, there is visible color fringing and the OIS has a tendency to overcorrect when you walk while recording a video. For a more detailed analysis, visit www.dxomark.com.

Photo Mobile Score 75   Video Mobile Score 79
Exposure and Contrast 88   Exposure and Contrast 79
Color 76   Color 76
Autofocus 72   Autofocus 62
Texture 61   Texture 78
Noise 84   Noise 59
Photo Artifacts 83   Video Artifacts 68
Flash 72   Stabilization 60

Comments

Total comments: 22
keeponkeepingon
By keeponkeepingon (10 months ago)

"the 8.7MP smartphone just scored nearly as well as Nokia's 41MP flagship phone"

DXOMark resizes everything to 8mp before testing so yeah, surprise surprise when everything is shrunk to the same size it all looks the same.

Continually disappointed that dpreview continues to publicize DXOMarks whacked mobile tests, especially without a disclaimer as to how they jimmy the images before testing to iphone size.

0 upvotes
peevee1
By peevee1 (10 months ago)

"the 8.7MP smartphone just scored nearly as well as Nokia's 41MP flagship phone in DxOMark's extensive imaging tests"

Probably says more about DxOMark's test than about the cameras. After all, the sensor in 1020 is about 4 times the size, not only in resolution.

0 upvotes
dpfan32
By dpfan32 (10 months ago)

Contrast of many 925 is very poor.
Especially bright objects are smeared and sharpness decreases a lot. Setting exposure compensation down does not help much, darker areas then disappear in a blurry mess as well.

You have to do heavy post processing: lighten shadows and massively lower the lights. Increasing sharpness, contrast and saturation is makes the picture look finally right.

0 upvotes
wansai
By wansai (10 months ago)

I really like the 925 but it'd be really cool if it could get raw support. There's potential to do much better than the in camera processing.

I am already happy a phone actually gives me night shooting capability but it's maddening how they process it.

0 upvotes
Michael Ma
By Michael Ma (10 months ago)

This can't be right. Tim Cook said the iPhone 5s camera was good as a DSLR. This can only mean the Galaxy S4 is better than a DSLR.

7 upvotes
fuego6
By fuego6 (10 months ago)

sigh.. windows phone... oh Nokia... what could have been!

2 upvotes
Infms
By Infms (10 months ago)

Try it before you knock it... incredibly stable and slick OS.

3 upvotes
Pavel Sokolov
By Pavel Sokolov (10 months ago)

with WP since htc mozart, lumia 800 and now 925 - really good os. bauhaus know the right things in design (metro is bauhaus style).

1 upvote
yabokkie
By yabokkie (10 months ago)

pixel count doesn't necessarily affect image quality
(well it should be well known since D3 and D3X)

1 upvote
OneMoreComment
By OneMoreComment (10 months ago)

Totally agree, it never did, but it works perfectly as an advertisment nothing more.

1 upvote
dpfan32
By dpfan32 (10 months ago)

Hmmm but real world performance is lightyears worse than 1020 ... strange ...

Or maybe the had a much much better unit than dpreview here:

http://connect.dpreview.com/post/6074844014/nokia-lumia-smartphone-camera-shootout-lumia920-lumia925-lumia928?page=2

LOL

Comment edited 2 minutes after posting
0 upvotes
bigley Ling
By bigley Ling (10 months ago)

yup that is posible, maybe DXO and Connect both ned multiple test units to make fair comparisons. There seems to be such variations in quality between handsets it is not funny!

0 upvotes
oduis
By oduis (10 months ago)

As a 925 owner, I must say that the DXO Mark Mobile score does not reflect reality at all. The problem is probably that the DXO Mark take way too few camera attributes into account.

The 1020 has a much bigger sensor, so it allows a narrower depth of field. This makes a big difference in composing images (and that’s why people buy full and mid format cameras). DXO does not measure that.

The 1020 uses its much higher resolution to have digital 3x zoom, versus no zoom on my 925. Not taken into account at all by DXO Mark Mobile.

The 1020 will get DNG raw support, which opens a whole world of highlight recovery, noise reduction fine tuning, precision in shadows etc. in Lightroom. The DXO Mark Mobile does not measure that.

So to sum up, DXO Mark Mobile looks scientific but is pretty useless to determine real world camera capabilities.

Comment edited 11 minutes after posting
3 upvotes
bigley Ling
By bigley Ling (10 months ago)

I think DXO analysis is designed to cater for the "full auto" user.

The full auto user will not be capturing DNG and post processing using a PC/MAC later.

Also a full auto user, may want more of an image sharp rather than having narrow DOF.

Lastly the full auto use would probably use the smartphone camera for instagram shots, where higher resolutions are not important.

They should make two DXO results, one for "full auto" users and another for "enthusiast smart phone photographers" I guess connect does look into features like zoom, quality of MP, sensor size, software features more in detail than DXO

0 upvotes
joe6pack
By joe6pack (10 months ago)

With a short focal length, you can't do much background blur except for subjects within 1 ft or so. I don't see much of an advantage here.

I would even argue that most people using smartphone camera want deep DOF with everything in focus. So what you claim advantage may actually be a disadvantage.

Comment edited 3 minutes after posting
0 upvotes
oduis
By oduis (10 months ago)

I'd say the opposite: Many smartphone snapshots are friends and family, and especially portraits benefit from lower DOF. I compared the 925 and 1020 in a shop, and the DOF difference is clearly visible.
I agree with Bigley that DXOMark should be more comprehensive and maybe differentiate between serious and simple users.

But DXO Mark Mobile is even not comprehensive enough to judge just simple full-auto users. For instance they do not take optical image stabilizations for still shots into account at all. A big practical plus for the Lumias in general, but not measured by DXO Mark.

And there are more holes in the DXO Mark Mobile like this.

0 upvotes
vv50
By vv50 (10 months ago)

the DXO Mobile protocol explains what their "reality" is - http://www.dxomark.com/Mobiles/How-we-test-smartphones-The-DxOMark-Mobile-protocol
Every website's objective criteria for measurement is subjective to everyone's interests. Only if you care about exactly the same things would you agree with the points they assign to devices.

1 upvote
oduis
By oduis (10 months ago)

Thanks for the Link, vv50.
The measurement description opens up even more big holes.

For instance they measure low light and bright light according to Lux values (so a fixed brightness). But the ISO value that the camera takes is largely depend on what the camera automatic decides for that scene and brightness of the lens. So the ISO values vary greatly, and ISO influences image quality a lot.
So if a camera automatic decides on lower ISO, resulting in higher motion blur on moving objects, it will get much better DXO Marks, but real world results will be unsharp.
That is why the DXO Mark for DLSRs always measures all curves by ISO, not by lux brightness.

So the DXO Mark Mobile test results are not comparable between cameras at all. But the fancy charts try to fool you into thinking so.

I could dig up many more holes ;-)

0 upvotes
bigley Ling
By bigley Ling (10 months ago)

It does bring back the point that DXO is really testing "full auto" on smart phones as dependant on how the automatic setting is programmed in relation to what is an acceptable minimum shutter speed in a low light test.

I believe DXO will have a hard time taking into account ISO as well since on some handsets the ISO cannot be set manually like the iPhone, hence possibly the simple set lux rates for measuring performance of camera optics.

Comment edited 6 minutes after posting
0 upvotes
oduis
By oduis (10 months ago)

If your measurements are seriously wrong by structure, then you cannot say “but I don’t know a correct way to measure it, so I present you the wrong values anyway”. Especially when you try to give yourself a scientific look.

And as outlined above, DXO Mark Mobile is full of flaws, even by reduced point-and-shoot standards. Could give you some more if you need ;-)

0 upvotes
bigley Ling
By bigley Ling (10 months ago)

there must have been a severe penalty taken by the 1020 to result in DXO score that is that close to the 925! We know the textural detail and xenon flash is superior on the 1020 vs the 925, so somehow the 1020 must have had some major issue to bring it's score that close to the 925.

0 upvotes
MistyFog
By MistyFog (10 months ago)

That is assuming the test or measurement is correctly done. :)

0 upvotes
Total comments: 22
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