Pentax K20D Image Quality

Saturation & Hue Accuracy
Bright, intense colors with moderate oversaturation of strong blues, reds, and greens.

Saturation. The Pentax K20D's default settings push most colors by quite a bit, especially blues, greens, and reds. Overall, images were very bright and punchy, with color that was a little over the top for a prosumer SLR. You can, however, always 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 K20D lean toward the warm side, but many consumers prefer the "healthier" appearance of warmer skin tones. 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 K20D showed a few color shifts relative to the correct mathematical translation of colors in its subjects, but had pretty good accuracy overall. Most noticeable was a shift in orange toward yellow, with some shifts in cyans and blues as well. Hue is "what color" the color is.

Saturation Adjustment
The Pentax K20D has a total of nine saturation settings available, four above and four below the default saturation. The adjustment is quite effective, and the fine steps between settings mean you can program the camera to just the level of saturation you prefer.

The table above shows results with the default as well as the two extreme saturation settings, for both our previous and new outdoor portrait scenes. Click on any thumbnail above, then click again to see the full-sized image. You can see more in the "Outdoor" Portrait Saturation series here.

Exposure and White Balance

Indoors, incandescent lighting
Warm results with Auto and 2,900 Kelvin, slightly cool with Incandescent, though good color with Manual white balance setting. Average exposure compensation required.

Indoors, under normal incandescent lighting, color balance was very warm with the Auto white balance setting, with a strong orange cast. Results with the Incandescent setting were a bit on the cool side, with a slightly bluish cast. The 2,900 Kelvin setting, which should match our lights, resulted in a warm cast as well. The Manual setting was the most neutral and accurate. The Pentax K20D required an average amount of positive exposure compensation for our new indoor scene, at +0.3 EV. Overall color with the Manual white balance setting looks quite good, though the blue flowers appear slightly purple. (Many digital cameras reproduce these flowers with a dark, purplish tint, so the Pentax K20D actually performs a little better than average here.) 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
Bright colors overall, though a tendency toward a warm cast and slightly high contrast under harsh lighting. Slightly better than average exposure accuracy.

Outdoors, the Pentax K20D tended toward a warmer color balance, though overall color was pretty good. The K20D performed slightly better than average in terms of exposure, requiring about +0.7 EV exposure compensation for the "Sunlit" portrait above. (We're accustomed to needing +1.0 EV for this shot.) The Pentax K20D's default contrast is a little high, producing a few washed-out highlights and dark shadows under the deliberately harsh lighting, but the K20D did better than average here as well. The far-field shot of the house came out just slightly overexposed at the K20D's default exposure setting, which is also better than average.

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

Resolution
Very high resolution, 1,800 ~1,900 lines of strong detail from in-camera JPEG, about the same from processed RAW file.

Our laboratory resolution chart revealed distinct line patterns down to about 1,900 lines per picture height horizontally, and about 1,800 lines in the vertical direction. Extinction of the pattern occurred at around 2,500 lines in both directions. When processing the K20D's DNG files using Adobe Camera Raw, we got similar resolution results. 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
Sharp images overall, though slightly high default sharpening and contrast leads to visible edge-enhancement artifacts on high-contrast subjects. Some minor noise suppression visible in the shadows.

Sharpness. The Pentax K20D's default sharpening and contrast is a little on the high side, leading to some visible edge enhancement artifacts ("halos") around high contrast areas such as branches against the blue sky, such as shown in the crop above left. 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 some minor noise suppression in the darkest areas of the model's hair, where a few individual strands are blurred together in the darker areas. The camera's overall response here is better than average, especially considering the 14.5-megapixel resolution. 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
As noted above, the Pentax K20D is a little heavy-handed when applying sharpening at its default settings, leading to visible sharpening artifacts in camera JPEGs. A little more detail without as many artifacts can be obtained from carefully processing RAW files though. Take a look below, to see what we mean:

In the table above, mousing over a link at the bottom will load the corresponding crop in the area above, while clicking on the link will load the full-res image. Examples consist of in-camera Super Fine ("Premium" setting) JPEG and RAW file processed through Adobe Camera Raw version 4.4.1, then sharpened in Photoshop. (For the Pentax K20D's images, I found best results with fairly strong but tight 400% unsharp masking with an 0.3 pixel radius.)

Note: ACR renders colors somewhat differently than either the K20D or the Pentax software, so the greens in the trees are rather different. Still, there's no mistaking the increase in fine detail and reduction in artifacts though, regardless of changes in color or tone.

ISO & Noise Performance
Low noise at the normal sensitivity settings, with very good results to ISO 800. However, big jumps in noise at the highest settings, but with better than average detail retention.

The Pentax K20D produced low noise at its lower sensitivity settings, remaining quite clean through ISO 400. ISO 200 is very similar to 100, and ISO 400 only shows minor detail loss compared to ISO 200. Noise is still well controlled at ISO 800, with a very fine "grain" pattern and good detail retention -- a pleasant surprise for a 14.5-megapixel APS-C size sensor. At ISO 1,600, we start to see some loss of detail as well as noise reduction artifacts. Chroma noise starts to become more readily apparent in darker tones and shadows, however detail is still fairly strong as the noise "grain" pattern remains fairly tight. ISO 3,200 and 6,400 are of course worse, with increased blurring and more obvious purple and green chroma noise blotches, as the K20D's noise reduction attempts to hide the increase in noise. Still, a very good performance overall considering the resolution of the K20D's sensor, and the fact that the K20D's default contrast and sharpening are a little on the high side (which tends to exaggerate noise). Note that these shots were taken with firmware v1.00 and the 2-second self-timer, so the hot pixels seen are expected. We've confirmed v1.01 does fix the problem in our Still Life and Multi target series. See the Print Quality section below, to find out what the recommended maximum size print is at each ISO setting.

The table above shows the effect of different noise reduction settings. As you can see, higher levels of NR no only result in slightly cleaner looking images, but also less detail. It's a trade-off, and it's nice that Pentax has provided multiple levels of noise reduction for the K20D, allowing the user to decide how much noise versus detail loss is acceptable.

Extremes: Sunlit and low light tests
High resolution with strong overall detail, but slightly high contrast with strong highlights. Fairly good low-light performance, capable of capturing bright images under average city street lighting, and much darker conditions with manual intervention.

Sunlight. The Pentax K20D produced slightly high contrast with some washed-out highlights and deep shadows under the harsh lighting of the test above, but performed better than most in this regard. Shadow detail is pretty good, despite some minor image noise. Our previous outdoor portrait with Marti looked best at +0.7 EV. Some areas look a little hot, but Marti's face was a bit too dim at +0.3 EV, and a bit too bright at +1.0 EV. Our new outdoor target required +1.0 EV exposure compensation for a reasonably bright face, though +0.7 EV wasn't bad either. Be sure to use fill flash in situations like the one shown above; it's better to shoot in the shade when possible.

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.)

Contrast Adjustment. We really like it when a camera gives us the ability to adjust contrast and saturation to our liking. It's even better when those adjustments cover a useful range, in steps small enough to allow for precise tweaks. Just as with its saturation adjustment, the Pentax K20D's contrast setting meets both challenges, though it could have used slightly more range on the minus side.

At its lowest contrast setting, the K20D did a pretty good job of preserving highlight detail, with much fewer blown highlights, while maintaining fairly natural-looking (if a bit pink) skin tones, and holding nice detail in the shadows. The K20D captures good color outdoors, though again, just slightly on the warm side. Overall, very good results here, though colors are a little flat (see below).

The series of shots above shows results with the minium, normal and maximum contrast adjustment settings. While you can see the extremes, it's hard to really evaluate contrast on small thumbnails like these, click on any thumbnail to go to the full-size image. The Pentax K20D's contrast adjustment worked well, however it had quite an effect on color saturation. Contrast and saturation are actually fairly closely coupled, so this is unfortunately not unusual.

Pentax's Expanded Dynamic Range. It seems like every SLR manufacturer is offering an "expanded" dynamic range mode these days, and Pentax has joined the club with the K20D (and K200D). As always, it should be noted that these dynamic range optimization modes do nothing to increase the fundamental dynamic range of the camera: That's purely a factor of the sensor and associated electronics. What it does is attempt to optimize use of the available dynamic range, pulling some of the extreme tonal values into the visible range.

The two shots above show the results with Pentax's D-Range Off and On, both with +1.0EV compensation. As you can see from the crops, turning it on does retain highlights much better. Unlike most other systems that also lighten up darker areas, there's very little effect in the shadows (other than to make what appear like hot pixels more visible). Still, this is much better performance than the K200D, where we saw little difference in highlight retention.

Low light. The Pentax K20D performed well on the low-light test, capturing usable images at the lowest light level with the lowest sensitivity setting (ISO 100). The image there is a little dim, as the longest shutter speed is 30 seconds, though bulb mode could be used to get around that. As expected, noise increases as ISO goes up and light levels go down, but remains fairly low below ISO 3,200, and the K20D offers multiple high-ISO NR level settings to let you decide how much detail to trade away (see the last three table columns). There are some signs of horizontal banding at higher ISOs, as well as just a few hot pixels evident at lower light levels. (Note though that the 2-second self-timer was used for these shots, and firmware v1.01 that addresses the hot pixel issue under these conditions was not installed for this series.) Color balance looked very good with the Auto white balance setting at lower ISOs, but images had a purple cast at higher ISOs.

The K20D's autofocus system struggled a bit in low-light, as it was only able to focus down to just past the 1/4 foot-candle light level unassisted. (The K20D does have an autofocus-assist light, but it uses the camera's flash tube as the illuminator, and so requires the flash system to be engaged for it to work.) 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 K20D do much better than point & shoots, but you still shouldn't expect a quick autofocus lock with moving subjects.

Print Quality
Great print quality, good color, sharp 16 x 24-inch prints.

The Pentax K20D's printed output is really impressive, able to output usable 16 x 24-inch prints from both ISO 100 and 200 shots. They're slightly soft, but really quite good. ISO 200 shots print the same as 100, producing a good 16x20 or great 13x19. ISO 400 images do just fine at 13x19, both sharp and crisp at this very large size. ISO 800 shots are still quite good at 13x19, though some chroma noise begins to creep into the shadows and other dark areas. At 11x14, they're still there, but less noticeable, and detail is good. ISO 1,600 shots start to lose contrast from the greater noise overall, but still print quite well at 8x10 inches. ISO 3,200 shots are also decent at 8x10, though with more noticeable grain and continued fading in darker areas thanks to noise. Even ISO 6,400 shots are usable at 5x7, which is pretty good for such a high-resolution sensor. It's an excellent performance from the Pentax K20D.

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 studio printer, and on the Canon iP5200 here in the office. (See the Canon PIXMA Pro9000 review for details on that model.)