Sigma dp2 Quattro Exposure

Saturation & Hue Accuracy
Fairly typical saturation levels at low ISOs, but falls rapidly as sensitivity increases. About average hue accuracy that also falls with ISO.

Saturation. The Sigma dp2 Quattro produces images with colors that are a little more saturated than most cameras at ISO 100 and 200. Default saturation is 112.1% (or about 12% oversaturated) at base ISO, which is a bit higher than the typical 110% mean saturation we normally see. Dark red is pumped quite a bit, while purples and dark blues are boosted moderately. Most other colors are close to idea or just pushed a bit, though cyan is undersaturated. Mean saturation falls rapidly above ISO 400, though, reaching as low as 75.5% at ISO 6400, as it becomes more difficult to keep colors separated and noise under control. Most consumer digital cameras produce color that's more highly saturated (more intense) than found in the original subjects. This is simply because most people like their color a bit brighter than life.

Skin tones. The Sigma dp2 Quattro generally does a good job with Caucasian skin tones, but sometimes it renders them too yellow or with reddish or orange casts in shadow areas. The very high resolution and unique processing also tend to exaggerate fine features such as wrinkles and freckles which can lead to somewhat unflattering portraits at default settings. Where oversaturation is most problematic is on Caucasian skin tones, as it's very easy for these "memory colors" to be seen as too bright, too pink, too yellow, etc.

Hue. The Sigma dp2 Quattro shifts green and orange toward yellow, red toward orange and cyan toward blue, but most shifts in color are very minor; even the cyan to blue shift we normally see is quite small. Mean "delta-C" color error at base ISO is 5.98 after correction for saturation, which is about average, but color error increases dramatically above ISO 400 as the camera struggles with strong color pollution and noise. Hue is "what color" the color is.

Exposure and White Balance

Indoors, incandescent lighting
The Sigma dp2 Quattro's Manual white balance setting worked well indoors, but other settings produced moderate to strong color casts. Slightly higher than average exposure compensation required.

Indoors, under normal incandescent lighting, color balance is reddish with the Auto setting, and the Incandescent setting resulted in a strong orange cast. Manual white balance produced very good results, though. The Sigma dp2 Quattro required +0.7 EV exposure compensation, which is a bit higher than the +0.3 EV average amount required for this shot. (Our test lighting for this shot is a mixture of 60 and 100 watt household incandescent bulbs, a pretty yellow light source, but a very common one in typical home settings here in the U.S.)

Outdoors, daylight
Very good performance outdoors in bright daylight, with about average exposure accuracy.

The Sigma dp2 Quattro produced overly warm and yellow skintones with the Manual white balance in our "Sunlit" Portrait, so we preferred Auto white balance shot above left. Skin tones are pretty good if a little flat, though darker areas take on an orange or reddish tint. The dp2 Quattro required +0.7 EV compensation to keep facial tones bright on the mannequin, which is about average for this shot. And despite the bright appearance, relatively few highlights were clipped. Shadow detail is very good but noise in dark shadows is on the high side and grainy. The dp2 Quattro underexposed our Far-field shot slightly (perhaps by 1/4 f-stop), producing a slightly dim exposure, but with natural colors. The Sigma dp2 Quattro preserved all but the brightest specular highlights here, though it did generate some very dark shadows. Shadow detail is again actually very good, though a little noisy and grainy-looking.

See full set of test images with explanations
See thumbnails of all test and gallery images

Resolution
Extremely high resolution, about 3,100 to 3,200 lines of strong detail in "High" size files, about 3,300 to 3,400 lines of strong detail in "Super High" size files,

A "High" size SPP conversion of our laboratory resolution chart reveals sharp, distinct line patterns to about 3,100 lines per picture height in the horizontal direction, and to about 3,200 lines in the vertical direction. Some may argue for higher numbers, but individual lines begin to fade and merge with others at those resolutions. Complete extinction of the pattern doesn't occur before the limit of our chart (4,000 lines) in both directions. Interestingly, an SPP "Super High" (39MP) conversion of the same RAW file shows higher resolution particularly in the horizontal direction (about 3,400 lines), though detail is not as well-defined or crisp. Although there is no color moiré to be seen (as expected), there is still plenty of luminance moiré, and you can also see bright or dark individual pixels between some of the lines, a result of imperfect bad pixel substitution. Use these numbers to compare with other cameras of similar resolution, or use them to see just what higher resolution can mean in terms of potential detail.

Color Resolution

Mouse over the links to compare how the Foveon Quattro sensor compares to a Bayer sensor of similar size and resolution.

The above two sets of crops compare the Sigma dp2 Quattro's ability to resolve our green/black and red/blue star burst patterns to that from the Samsung N30 which uses a Bayer (RGBR) filter of roughly the same size and pixel count. The green/black pattern is the best-case for a Bayer sensor while the red/blue is the worse-case primary color combination, since there is only one red and one blue filter for every four photosites (the other two are green). We chose the Samsung NX30 because the images it produces are roughly the same dimensions as the dp2 Quattro in pixels (~20 megapixels) and like the Sigma, it also does not have an optical low-pass filter. Note that both images are RAW conversions.

As you can see, the Sigma dp2 Quattro clearly out-resolves the Samsung NX30 in both cases, as it's able to resolve the "spokes" of the star burst much closer to the center of the target (where they get closer and closer but never touch), though poor bad pixel substitution and well as stronger aliasing artifacts and false detail such as straight horizontal and vertical lines are visible in the Sigma's red/blue crop.

See full set of test images with explanations
See thumbnails of all test and gallery images

Sharpness & Detail
Excellent sharpness and great detail overall, with fairly minor edge-enhancement artifacts visible around high-contrast subjects. Low levels of noise suppression generally leaves excellent detail at base ISO.

Sharpness. The Sigma dp2 Quattro captures incredibly sharp, detailed images. Some minor sharpening halos are visible around high-contrast subjects such as the text and border in the crop above left (taken from a RAW file converted with SPP at default settings), but sharpening is too high in camera JPEGs at default settings, with noticeable sharpening halos. Edge enhancement creates the illusion of sharpness by enhancing colors and tones right at the edge of a rapid transition in color or tone.

Detail. The crop above right shows relatively minor noise suppression in the darkest areas of the mannequin's hair, as most individual strands of hair are well defined except in very low contrast areas. Some very fine-grained luminance noise is visible, however this is preferable to the smudging we often see, and there is almost no chroma noise to speak of. You can however see aliasing in the form of "jaggies" if you look closely at individual strands of hair. This is because Foveon sensors do not have an anti-aliasing filter and the camera's lens is quite sharp. Noise-suppression systems in digital cameras tend to flatten-out detail in areas of subtle contrast. The effects can often be seen in shots of human hair, where the individual strands are lost and an almost "watercolor" look appears.

RAW vs In-Camera JPEGs
The Sigma dp2 Quattro produces very sharp, detailed in-camera JPEGs, but lets compare to a RAW file at base ISO converted with Sigma's Photo Pro v6.0.6 (Adobe Camera Raw, the converter we usually use, does not support the Sigma Quattro series yet.)

As you can see, the RAW conversion via Sigma Photo Pro version 6.0.6 (the latest as of time of writing) is similar to the camera running the latest firmware (version 1.02) in many respects, but there are a number of significant differences. Most noticeable is the improved rendering of our red-leaf swatch, revealing more detail than the camera JPEG (though many cameras still do a better job at low ISOs). Another difference is in amount of contrast and sharpening applied, as the camera appears to apply higher contrast and sharpen more aggressively than the software using default setting, though the camera does a little better in some respects, such as in the pink fabric and the more even rendering of fine horizontal lines. There are also slight differences in micro contrast, reduced color bleeding, as well as a reduction in certain artifacts especially at higher ISOs.

For example, check out the improvement in color rendition at ISO 1600 and above:

ISO & Noise Performance
Good image quality at low ISOs, but the dp2 Quattro is not a good high ISO performer.

Here, we can see the Sigma dp2 Quattro does extremely well at ISO 100 and 200, with phenomenal detail and sharpness. You can however see some luminance noise in the shadows already at these low ISOs, but it's very fine-grained. Fine detail starts to take a hit at ISO 400, but it's still very good, though there is a minor color shift towards red. Image quality from ISO 800 and beyond goes downhill rather quickly, though. ISO 800 still shows pretty good detail and noise, while more prominent, is still fine-grained, but overall color shifts toward yellow and starts to desaturate. ISO 1600 shows quite a bit of luminance noise as well as some purple and green blotching as colors continue to desaturate. Some horizontal banding (pattern noise) can also be seen. Noise, desaturation and banding just get worse at ISO 3200 and 6400, making the inclusion of these ISOs questionable.

While high ISO performance has improved over the DP1 Merril we tested, the dp2 Quattro is still not a good high ISO performer for its sensor size. We recommend selecting the lowest ISO you can for best image quality.

A note about focus for this shot: We shoot this image at f/4 which doesn't provide very deep depth-of-field, but is more representative of the low light light levels. To insure that the hair detail we use for making critical judgements about camera noise processing and detail rendering is in sharp focus at the relatively wide aperture we're shooting at, the focus target at the center of the scene is on a movable stand. This lets us compensate for front- or back-focus by different camera bodies, even those that lack micro-focus adjustments. This does mean, though, that the focus target itself may appear soft or slightly out of focus for bodies that front- or back-focused with the reference lens. If you click to view the full-size image for one of these shots and notice that the focus target is fuzzy, you don't need to email and tell us about it; we already know it. :-) The focus target position will simply have been adjusted to insure that the rest of the scene is focused properly.

Extremes: Sunlit, dynamic range, and low light tests
Excellent detail but with limited dynamic range. Able to produce bright images in very low light, but autofocus really struggles.

Sunlight. The Sigma dp2 Quattro struggled with the harsh lighting of this test shot. We preferred the +0.7 EV exposure overall as +0.3 EV is a little too dim in the face while +1.0 EV is too bright. While relatively few highlights are clipped at +0.7 EV and shadows aren't crushed, noise in dark shadows is a little high and grainy, limiting useful dynamic range. We also noticed some colors tend to clip to white more abruptly than others when overexposed (such as the yellow flowers in the above shots) making detail in the highlights difficult if not impossible to recover.

Because digital cameras are more like slide film than negative film (in that they tend to have a more limited tonal range), we test them in the harshest situations to see how they handle scenes with bright highlights and dark shadows, as well as what kind of sensitivity they have in low light. The shot above is designed to mimic the very harsh, contrasty effect of direct noonday sunlight, a very tough challenge for most digital cameras. (You can read details of this test here. In actual shooting conditions, be sure to use fill flash in situations like the one shown here; it's better to shoot in open shade whenever possible.)

Tone Control
The Sigma dp2 Quattro offers a Tone Control setting with Off, Mild and Strong settings (in addition to contrast adjustment in +/- 5 steps).

As you can see from the thumbnails and histograms, Tone Control settings had a very subtle effect on our "Sunlit" Portrait, with only the "Strong" setting showing a slight reduction in highlights.

Here, you can see the same effect of the Tone Control settings on our Far-field scene.

Dynamic Range Analysis
We've recently switched to using DxO Labs' dynamic range test results from their DxOMark website. As technology advanced, the dynamic range of modern high-end cameras in some cases exceeded the range of the Stouffer T4110 density scale that we used for our own measurements. DxO's approach based on RAW data before demosaicing is also more revealing, because it measures the fundamental dynamic range of the sensor, irrespective of whatever processing is applied to JPEGs, or to RAW data by off-the-shelf conversion software.

However, since DxO does not support Foveon sensors, we're including our own analysis of best-case dynamic range at based ISO, for both in-camera JPEG and SPP processed RAW file.

A key parameter in a digital camera is its Dynamic Range, the range of brightness that can be faithfully recorded. At the upper end of the tonal scale, dynamic range is dictated by the point at which the RGB data "saturates" at values of 255, 255, 255. At the lower end of the tonal scale, dynamic range is determined by the point at which there ceases to be any useful difference between adjacent tonal steps. Note the use of the qualifier "useful" in there: While it's tempting to evaluate dynamic range as the maximum number of tonal steps that can be discerned at all, that measure of dynamic range has very little relevance to real-world photography. What we care about as photographers is how much detail we can pull out of the shadows before image noise becomes too objectionable. This, of course, is a very subjective matter, and will vary with the application and even the subject matter in question. (Noise will be much more visible in subjects with large areas of flat tints and subtle shading than it would in subjects with strong, highly contrasting surface texture.)

What makes most sense then, is to specify useful dynamic range in terms of the point at which image noise reaches some agreed-upon threshold. To this end, Imatest computes a number of different dynamic range measurements, based on a variety of image noise thresholds. The noise thresholds are specified in terms of f-stops of equivalent luminance variation in the final image file, and dynamic range is computed for noise thresholds of 1.0 (low image quality), 0.5 (medium image quality), 0.25 (medium-high image quality) and 0.1 (high image quality). For most photographers and most applications, the noise thresholds of 0.5 and 0.25 f-stops are probably the most relevant to the production of acceptable-quality finished images, but many noise-sensitive shooters will insist on the 0.1 f-stop limit for their most critical work. A full discussion of all the data Imatest produces is really beyond the scope of this review: Visit the Imatest website for details of what the program measures, how it performs its computations, and how to interpret its output.

JPEG. The graph at right (click for a larger version) was generated using Imatest's dynamic range analysis for an in-camera dp2 Quattro JPEG file with a nominally-exposed density step target (Stouffer 4110). At default settings and base ISO, the graph shows 12.8 f-stops of total dynamic range, but with only 4.67 f-stops at the "High" quality level. (Note that threshold used by DxOMark is equivalent to the Low quality level, which is 9.34 f-stops.) Total dynamic range is excellent, among the best we've tested for an APS-C camera, but the scores at higher quality levels are much lower than average. The Sigma's higher than average noise levels are mainly to blame for the low scores. Note though that this measurement has a margin of error of about 1/3 f-stop, so differences of less than 0.33 can be ignored.

RAW. It'll probably be some time before Adobe Camera Raw supports the dp2 Quattro and DxOMark may never test it, so we'll make an exception here and use Sigma's Photo Pro RAW conversion software to see if converted RAW files improve upon the JPEG dynamic range scores. The graph at right is from the same Stouffer 4110 stepchart image captured as a RAW (.X3F) file, processed with Sigma's SPP v6.0.6 software using default settings. The Sigma dp2 Quattro's RAW file produced the same total dynamic range as the JPEG (12.8 f-stops) however the score at the Low quality level increased 1.36 f-stops from 9.34 to 10.7, and the High quality level score increased about 1.6 f-stops from 4.67 to 6.25. While better than the in-camera JPEG results, these are still below average scores when compared to state-of-the-art Bayer-filtered APS-C or Four Thirds sensors. It's worth noting here is that Photo Pro's default noise reduction settings reduced overall noise relative to the levels in the in-camera JPEG (compare the noise plots in the graphs), which tends to boost the dynamic range numbers for the High Quality threshold.

Low Light. The Sigma dp2 Quattro struggled in our low light tests. The dp2 Quattro's slowest shutter speed of 30 seconds and relatively fast lens did allow it to capture bright images at the lowest light level we test at (1/16 foot-candle), even at ISO 100. But while noise is low at ISO 100, it's high and grainy at ISO 3200, and ISO 6400 is quite noisy. You can also see the saturation drop as ISO is increased we mentioned previously.

Auto white balance did a decent job here at ISO 100 and 1-foot candle, producing fairly neutral results, but at 1/16 foot-candle, there was a noticeable shift towards magenta. ISO 3200 and 6400 were just slightly cool, but any shifts in white balance were likely masked by the saturation drop.

There are quite a few hot or bright pixels at the higher ISOs, though a few of them can be seen at base ISO. Horizontal banding (pattern noise) can also be seen at ISO 3200 and especially 6400.

The Sigma dp2 Quattro's autofocus system really struggled in our low light test, only able to focus down to just above the 1 foot-candle level. That's possibly the worst performance we've seen from a camera with an APS-C-sized sensor. The dp2 Quattro was however able to focus in complete darkness with its built-in focus assist lamp enabled, but real-world performance will of course depend on subject distance and contrast.

How bright is this? The one foot-candle light level that this test begins at roughly corresponds to the brightness of typical city street-lighting at night. Cameras performing well at that level should be able to snap good-looking photos of street-lit scenes.

NOTE: This low light test is conducted with a stationary subject, and the camera mounted on a sturdy tripod. Most digital cameras will fail miserably when faced with a moving subject in dim lighting. (For example, a child's ballet recital or a holiday pageant in a gymnasium.) A useful trick is to just prop the camera on a convenient surface, and use its self-timer to release the shutter. This avoids any jiggling from your finger pressing the shutter button, and can work quite well when you don't have a tripod handy.

Coverage and Range
A powerful flash, but with narrow coverage.

Coverage. Flash coverage from the Sigma dp2 Quattro's optional EF-140S compact flash is quite narrow, leaving the corners our flash test image a little dim even at the relatively normal focal length of 45mm equivalent. Some of the corner fall-off is from the lens itself, though.

Manufacturer Specified Flash Test. The Sigma dp2 Quattro's optional EF-140S compact flash is rated at a Guide Number of 14 meters at ISO 100, which is actually pretty good. That works out to about 5.8 feet at f/8 and ISO 100 which may not seem like very much, but you would normally shoot flash shots at wider apertures. In the test shot above, the dp2 Quattro produced a reasonably bright target so we'd say Sigma's Guide Number rating is credible.

Print Quality

Good 30 x 40 inch prints and higher at ISO 100; a nice 11 x 14 at ISO 800; and a reasonably good 4 x 6 at ISO 1600.

ISO 100 yields results we'd expect from a Foveon sensor. The sharpness and detail here at base ISO is phenomenal for 30 x 40 inch prints and larger -- as large as you need until the resolution of the Foveon sensor runs out causing pixelation. The colors at base ISO are deep and rich, though perhaps just a bit boosted in the darker yellows and magentas from the in-camera JPEGs.

ISO 200 requires a reduction to 24 x 36 inch prints, which look quite good in all areas of our test target when printed except for our tricky red fabric swatch which quickly begins to lose all contrast detail (and this usually doesn't happen on cameras with sensors this large until you get somewhat higher in ISO).

ISO 400 prints begin to show why Foveon sensors are made to primarily be shot at or near base ISO. There's too much noise in the 24 x 36 inch prints to call good, and even the 20 x 30 inch prints show some noise in flatter areas of our target, and the red fabric swatch detail is now all but gone. Still, we can give the 20 x 30's our seal of approval here.

ISO 800 shots begin to take on a scorched look in certain areas when printed, and some colors begin to appear muted. Even the 13 x 19 inch print is too noisy and muted to make our good rating, but the 11 x 14 inch print does make the grade here.

ISO 1600 images are not very good when printed. Detail and color accuracy fade quickly, allowing for only a modest 4 x 6 inch print to pass the test here.

ISO 3200/6400 both yield prints that are too scorched and noisy to be usable and these settings are best avoided.

The Sigma dp series of cameras sporting Foveon sensors continue to draw much interest among enthusiast photographers looking for astounding resolution and clarity at base ISO, and yet they're clearly not the cameras to use if you need performance as ISO rises. The Quattro sensor has been designed to improve on high ISO performance from the previous sensor, but the improvement is negligible in printed images. Remaining at ISO 400 and below is your best bet with these cameras for good image quality, and remaining at base ISO can produce stunning images that can yield terrific large prints.

[Note that the above print quality analysis was made using in-camera JPEGs, but we also printed Sigma Photo Pro 6.0.6 RAW conversions made with default settings. While SPP generally did a better job than the camera at higher ISOs, there wasn't enough improvement to alter any of our maximum size recommendations for what we'd consider "good" quality prints.]

Testing hundreds of digital cameras, we've found that you can only tell just so much about a camera's image quality by viewing its images on-screen. Ultimately, there's no substitute for printing a lot of images and examining them closely. For this reason, we now routinely print sample images from the cameras we test on our Canon Pro9000 Mark II studio printer, and the Canon Pixma MP610 here in the office. (See the Canon Pixma Pro9000 Mark II review for details on that model.)