Pentax K-S2 Exposure

Saturation & Hue Accuracy
Very high mean saturation, with about average hue accuracy.

Saturation. The Pentax K-S2's default image tone setting of "Bright" pushes most colors by quite a bit at base ISO, especially blues, greens, dark reds and purples. Mean saturation at ISO 100 is 119.8% or 19.8% oversaturated. That's about 10% higher than most other brands at default settings. Overall, colors are very bright and punchy, a trait we've come to expect from Pentax, and mean saturation remains higher than average throughout the ISO range. You can of course always select a different image tone preset and/or turn down settings such as saturation and contrast to suit your own tastes. 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. Caucasian skin tones from the Pentax K-S2 were a touch yellow using Manual white balance in our test shots, however Auto white balance produced a slightly more pinkish, "healthier" appearance. Good results here. 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 Pentax K-S2's mean "delta-C" color error of 5.51 after correction for saturation at ISO 100 is about average for a DSLR these days. Most noticeable were moderate shifts in orange toward yellow and cyan toward blue, with minor shifts and some reds, yellows, and greens. (The cyan to blue shift is very common among the digital cameras we test; we think it's a deliberate choice by camera engineers to produce better-looking sky colors.) Hue accuracy does degrade slightly at higher ISOs, but not as much as some cameras. Hue is "what color" the color is.

Exposure and White Balance

Indoors, incandescent lighting
Very warm results with Auto white balance, but good color with Incandescent and Manual white balance settings.

The Pentax K-S2's Auto white balance had a difficult time with the warm color of the household incandescent bulbs used in this shot, producing a very warm image with a strong orange tint, even with "Strong Correction" enabled by default. (There is also a "Subtle Correction" Auto WB correction setting, however we did not test that option.) Results with the Incandescent setting are actually pretty good, though, just slightly on the warm side. The Manual setting produced the most accurate color balance, though just a touch cool.

* The Pentax K-S2 may have a slight compatibility issue with our Sigma 70mm f/2.8 reference lens, resulting in shots with brighter than normal exposures, so we won't comment on exposure accuracy for lab shots using this lens such as the above images. However our gallery shots taken with Pentax glass also shows inconsistent exposures.

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 bright, slightly cool colors with high contrast.

The Pentax K-S2 handled tough outdoor lighting under harsh sunlight fairly well, producing very bright though slightly cool colors. Default contrast is on the high side (as most users prefer), resulting in quite a few clipped highlights in the mannequins's shirt and some of the flowers, though shadows contained good detail, with only the very deepest shadows a little noisy. Skintones were just a touch warm and yellow using Manual white balance, so we preferred Auto white balance for our "Sunlit" Portrait shot here. Our Far-field shot was well exposed at 0 EV, again with punchy, slightly cool color. Only a few highlights were clipped at default exposure (mostly specular highlights) and very few shadows were lost. Details in the shadows are quite good, but deep shadows contain a moderate amount of luma noise, though chroma noise is well-controlled. Good results overall here.

* The Pentax K-S2 may have a slight compatibility issue with our Sigma 70mm f/2.8 reference lens, resulting in shots with brighter than normal exposures, so we won't comment on exposure accuracy for lab shots using this lens such as the above left Portrait shot (the Far-field shot on the right was taken with a Pentax 35mm f/2.8 Macro Limited lens).

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

Resolution
~2,500 lines of strong detail from JPEGs, about the same from converted RAW files.

Our laboratory resolution chart reveals sharp, distinct line patterns down to about 2,500 lines per picture height in the horizontal direction, and to about the same 2,500 lph in the vertical direction in best quality JPEGs, though some aliasing in the form of moiré patterns can be seen as early as 2,100 lines per picture height. (These shots were taken with the AA Filter Simulation set to off for maximum resolution.) Complete extinction of the pattern didn't occur until just past 3,000 lines in both directions. We weren't able to resolve more with an Adobe Camera Raw conversion, though complete extinction of the pattern was extended to about 3,800 lines, and aliasing artifacts were much lower before the resolution limits. 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.

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

Sharpness & Detail
Very sharp images with excellent detail, though with moderate edge-enhancement on high-contrast subjects. Minor noise suppression visible at base ISO.

Sharpness. The Pentax K-S2 produces very sharp images with excellent detail at default settings. Images are slightly oversharpened as edge enhancement artifacts are visible on high-contrast subjects such as the sharpening halos around the lettering and border in our Mas Portell bottle label above left, but overall crispness is still quite pleasing. Edge enhancement creates the illusion of sharpness by enhancing color and tonal differences right at the edge of a rapid transition in color or tone.

Detail. The crop above right shows only minor detail loss due to noise suppression. Individual strands are still distinguishable even in the lighter shadows, though they begin to merge as shadows deepen, and in places where the tone and color of adjacent strands is very close. Still, very good performance here, though false colors in the hair are noticeable. Some individual strands of hair also show aliasing in the form of "jaggies", however the K-S2's selectable AA filter should help prevent those from occurring when enabled (AA Filter Simulation was off by default). 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.

Anti-aliasing Filter Simulator
During the exposure, the Pentax K-S2's anti-shake actuator can oscillate the sensor assembly microscopically in either a linear (Type 1) or circular (Type 2) motion, simulating the effects of an anti-aliasing (or optical low-pass) filter. To see the effect on image sharpness and alias artifacts, roll over the links in the table below to compare the crops in our Resolution target at base ISO:

As you can see when mousing over the links above, AA Filter Simulation Type 1 blurs fine detail slightly, while Type 2 offers a slightly stronger effect, almost eliminating the aliasing artifacts and moiré that can be seen in the center of the starburst crop on the left, as well as in the fine line pattern crop on the right. It really is quite amazing to have on-demand anti-aliasing filtering like this, and the K-S2 even offers an AA bracketing mode allowing you to capture images with all 3 settings with one press of the shutter button..Keep in mind that even AA Type 2 may not avoid all aliasing artifacts, though. That will depend on multiple factors such as the subject matter, sharpness of lens, aperture setting, etc.

RAW vs In-Camera JPEGs
As noted above, the Pentax K-S2 does a great job at capturing lots of fine detail in its JPEGs, but more detail can often be obtained from carefully processing RAW files, while at the same time reducing sharpening artifacts. Take a look below, to see what we mean:

In the table above, we compare an in-camera JPEG taken at base ISO using default noise reduction and sharpening (on the left) to the matching RAW file converted with Adobe Camera Raw 9.1 using default noise reduction with some strong but tight unsharp masking applied in Photoshop (200%, radius of 0.3 pixels, and a threshold of 0).

As is usually the case, Adobe Camera Raw delivers finer detail than the camera's processing as well as smaller sharpening halos with the settings we used, and its default noise reduction does better with our difficult red-leaf swatch, even resolving some of its thread pattern which the camera blurred away as noise. ACR also did a better job with color, rendering the pink fabric closer to reality instead of the more magenta interpretation of the camera. The ACR conversion does however show more noise compared to the camera's cleaner JPEG, though of course you can always adjust noise reduction to your likely. Overall, though, the Pentax K-S2 does a very good job with its JPEGs at base ISO, but as is usually the case you can extract even more detail with fewer sharpening artifacts and more accurate color with a good RAW converter.

ISO & Noise Performance
Excellent handling of noise versus detail in JPEGs to ISO 3200.

The Pentax K-S2's images are pretty clean and very detailed from ISO 100 through 400, with just a touch of luminance noise becoming more visible in the shadows and darker midtones as ISO increases, however there are false colors in the mannequin's hair that are likely due to the AA filter being off by default, rather than chroma noise. There's a slight drop in fine detail at ISO 800 and then again at ISO 1600 thanks to stronger noise reduction, though detail is still excellent. At ISO 3200, there's a larger drop in image quality with increased blurring and more visible noise "grain" particularly in the shadows, but detail is still quite good. ISO 6400 shows stronger luminance and chrominance noise, though the noise "grain" remains fairly tight and there's still a fair amount usable detail left. Chroma blotching is more noticeable in the hair and shadows, though. Image quality at ISO 12,800 and above falls off quickly, though, with much stronger blurring and much less detail than at lower sensitivity levels. Chroma noise in the form of yellow and purple blotches becomes an issue at ISOs 25,600 and 51,200, and overall color balance shifts toward yellow/green, particularly at the highest ISO.

Overall, though, high ISO noise performance appears to be very good for a 20-megapixel APS-C camera. Note that these images were shot using the Pentax K-S2 "Auto" noise reduction setting. The Pentax K-S2 offers an unusually flexible amount of control over noise reduction applied to its JPEGs. In addition to "Auto", you can adjust how much NR is applied ("Off", "Low", "Medium" or "High") at all ISOs, or you can select "Custom" which allows you to choose from the same four options at each ISO sensitivity setting (in whole EV increments). Of course, the impact of noise and detail loss are highly dependent on the size the photos are printed at, and pixel-peeping on-screen has surprisingly little relationship to how the images look when printed: See the Print Quality section below for recommended maximum print sizes at each ISO.

A note about focus for this shot: We shoot this image at f/4, using one of three very sharp reference lenses (70mm Sigma f/2.8 macro for most cameras, 60mm f/2.8 Nikkor macro for Nikon bodies without a drive motor, and Olympus Zuiko 50mm f/2.0 for Four Thirds and Micro Four Thirds bodies). 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
High default contrast limits dynamic range in JPEGs. Good low-light performance, capable of capturing bright images in near darkness, but autofocus struggles in low light.

Sunlight:
The Pentax K-S2 struggled with the deliberately harsh lighting in the above test, thanks mostly to its high default contrast. The "-0.3 EV" exposure did the best job here, as the "-0.7 EV" exposure was a bit too dim in the face and the default "0 EV" exposure clipped too many highlights. Even at "-0.3 EV", a considerable number of highlights were blown in the mannequin's shirt and flowers, however very good detail was preserved in the shadows with relatively low levels of noise in all but the deepest shadows. Turning down the contrast or using one of the D-Range options will help in situations like this.

* The Pentax K-S2 may have a slight compatibility issue with our Sigma 70mm f/2.8 reference lens, resulting in shots with brighter than normal exposures, so we won't comment on exposure accuracy for lab shots using this lens such as the above images. However our gallery shots taken with Pentax glass also shows inconsistent exposures.

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.)

D-Range Settings
The Pentax K-S2 offers four Shadow Correction levels (Auto, Low, Medium and High, plus Off) as well as two Highlight Correction levels (Auto and On, plus Off). As the name implies, Shadow Correction works to raise shadow levels while attempting to keep highlights and midtones as they are, and inversely, Highlight Correction attempts to reduce highlights without darkening shadows and midtones. Both can be used simultaneously. See the images below to see their effect on our high-contrast "Sunlit" Portrait test shot.

Mouse over the links to see how the various settings for D-Range affects our "Sunlit" Portrait shot, and click on a link to get to the full-res image. (The effect can be a little subtle in shots like those above, so we decided to use a mouse-over to better show how each setting compares to Off.)

Shadow Correction. Above, we see a gradual lightening of shadows and midtones as the Shadow Correction setting is increased, with almost no impact to highlights, and the Auto setting produced results identical to Low. If you look closely at the shadow detail, you will notice an increase in noise as the setting is turned higher, but that's to be expected and noise levels are still pretty low. The camera reports an ISO of 100 for all four settings of Shadow Correction.

Highlight Correction. Highlight Correction works as expected when highlights are blown, toning them down to protect nearly all of them while keeping shadows and midtones roughly the same. Do be aware that Highlight Correction requires at least ISO 200 to be enabled, so noise is a little higher than base ISO. Sorry, we neglected to take an Auto lab shot.

Here are the results of the available D-Range settings with our Far-field shot. Again, we see a lightening of shadows as the Shadow Correction setting is increased, and a slight reduction in highlights with Highlight Correction On (Auto HC decided no highlight correction was required, as very few were clipped).

HDR Capture
The Pentax K-S2 also has a High Dynamic Range (HDR) capture mode where the camera takes three images (underexposed, normal, and overexposed) in quick succession and combines them in-camera into one image. If performed properly, this method should result in much higher dynamic range, without the additional noise penalty that comes with boosting sensitivity or lightening shadows. (In fact, it can reduce shadow noise by combining shadows from the overexposed shot.)

There are four HDR settings available: Auto, and HDR 1/2/3 providing three blend settings, and each setting has three possible exposure ranges (±1 EV, ±2 EV and ±3 EV with ±2 EV as the default ). There's also an optional Auto Align feature for use when shooting without a tripod, which is enabled by default on the K-S2.

Mouse-over the links above to compare thumbnails, and click on them to access full-resolution versions.

The Auto settings worked reasonably well on our Far-field test shot, reducing highlights and bringing out shadow detail. HDR1 mode produced a relatively realistic image though with an obvious and flat HDR look, but HDR2 and especially HDR3 resulted in an unnatural, very HDR-ish images with strong halos. As with most HDR systems there is a slight focal-length crop with Auto Align active, and watch out for ghosting that can occur when subjects move between exposures, as can be seen around leaves in the above shots.

Unlike the Pentax K-3, the K-S2's HDR mode does not support RAW or RAW+JPEG file types. (HDR is supported when shooting the K-3 in RAW mode, however the resulting RAW file is three times as large as a standard shot. The K-3 just bundles the individual captures into one file, to be processed later by their Digital Camera Utility software which can apparently blend or extract the separate RAW files.)

Dynamic Range Analysis (RAW mode)
While we once performed our own dynamic range measurements based on in-camera JPEGs as well as converted RAW images (when the camera was supported by Adobe Camera Raw), we've switched to using DxO Labs' 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.

DxOMark has not tested the Pentax K-S2 yet, but we'll update this section once they do.

Low Light. The Pentax K-S2 performed well in terms of image quality in our low-light tests, capturing clean, well-exposed images at the lowest light level (1/16 foot-candle) with the lowest sensitivity setting (ISO 100). As you'd expect, noise is higher at ISO 3200 but it remains well-controlled and very fine-grained. Unsurprisingly, the maximum ISO of 51,200 is quite noisy with noticeably less detail, and is best avoided except for small prints and in emergencies.

Color balance with Auto white balance is pretty good across ISOs and light levels, which isn't always the case, with just a slightly cool bias.

We did not detect any significant issues with hot pixels, and pattern noise (horizontal banding or streaking) is very low and difficult to detect even in deep shadows. Some heat blooming can be seen at the highest ISO emanating from the bottom right with long exposure noise reduction disabled (rightmost column above), though that's not uncommon at very high ISOs.

The Pentax K-S2's phase-detection autofocus system was only able to focus on our test subject down to just above the 1/4 foot-candle light level using an f/2.8 lens with its AF assist light turned off. That's poor performance for a DSLR, though it was able to focus in total darkness with the focus assist lamp enabled.

(Keep in mind that the longer shutter speeds here demand the use of a tripod to prevent any blurring from camera movement. 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.)

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.) Digital SLRs like the Pentax K-S2 do much better than point & shoots, but you still shouldn't expect a quick autofocus lock with moving subjects.

Print Quality
High-quality prints up to 24 x 36 inches at ISO 100-200; Nice 13 x 19 inch prints at ISO 1600; and 4 x 6 inch prints just pass the mark at ISO 25,600.

ISO 100/200 prints looks great up to 24 x 36 inches with lots of detail and bright colors. At close inspection, you can see some pixelation along some edges, but when viewed at arm's-length and farther -- a normal viewing distance for such a large print -- the image overall looks great. We'd even go as far as calling 30 x 40 acceptable for wall display, particularly at ISO 100. ISO 200 images show very very slightly softer detail in certain areas, but overall, the print sizes at this sensitivity are the same as at base sensitivity.

ISO 400 images start to display subtle shadow noise and there's some slight softening of detail, but prints still look great up to 20 x 30 inches. Overall detail is very nice and colors are still vibrant and pleasing.

ISO 800 prints top out at 16 x 20 inches, as noise becomes a bit stronger and more visible, though mainly just in shadow areas. Fine detail in most places looks really nice, but some low contrast areas (such as our tricky red-leaf fabric in our Still Life target, for example) start to show a drop in detail.

ISO 1600 images still look quite good, with prints appearing nice up to 13 x 19 inches. As with ISO 800 prints, detail looks nice overall, but low contrast areas look a bit soft, though these characteristics are now more prominent as the sensitivity rises to ISO 1600. Visible shadow noise is also more noticeable, but colors remain vibrant.

ISO 3200 prints begin to show a more pronounced drop in detail, as noise becomes an issue, though colors are still quite nice. The noise itself, however, appears more fine-grained and not drastically detrimental to prints at sizes up to 11 x 14 inches.

ISO 6400 images begin to look quite noisy with a noticeable drop in fine detail, which prevents us from calling prints larger than 8 x 10 inches acceptable.

ISO 12,800 prints struggle with lots of noise and a lack of detail, but a 5 x 7 inch print just squeaks by as the maximum size we're comfortable with.

ISO 25,600 images, similar to the previous ISO, are quite soft and noisy, and here we feel a 4 x 6 inch print is the biggest you should go at this sensitivity.

ISO 51,200 prints are too noisy and display too little detail to provide an acceptable print.

With a 20.2-megapixel sensor, the Pentax K-S2 is the second-highest resolution APS-C DSLR in the Pentax family (under the 24.3-megapixel K-3 series), so it's no surprise the K-S2 does well in the print department. At base ISO and ISO 200, the K-S2 manages really large 24 x 36 prints, though you're pretty much right at the resolution limit of the sensor at that size. As sensitivity rises, the K-S2 does well, with a nice 13 x 19 inch print at ISO 1600. At extremely high sensitivities, the K-S2 struggles with noise and detail issues like most APS-C sensors, with print sizes topping out at 4 x 6 inches at ISO 25,600. However that's very good for an APS-C camera, matching some leading 24-megapixel models.