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Color reproduction

Here you can see a generated GretagMacbeth ColorChecker chart, place your mouse over any of the labels below it to see the color reproduction in that mode. Select a camera/setting combination from the 'Compared to' drop-down to comparative boxes inside each patch.

The K-x produces an almost identical color response to its bigger brother, the K-7. As we've seen in other reviews the standard hues are also very similar to most other SLRs in this class, with minor saturation and brightness differences but essentially the same color response.

Pentax K-x Compare to:  
      
      
      
      
BrightNaturalPortraitLandscape
VibrantMutedMonochromeAdobe RGB

Artificial light White Balance

The K-x's white balance performance under artificial light is a bit of a double-edged sword. The presets do a very decent job (out of the fluorescent options warm white worked best for our lighting) but Auto White Balance only produces very average results. Like on the K-7 there is now an option to choose between a 'subtle' or 'strong' correction for tungsten light when using Auto WB. In theory 'subtle' will preserve some of the warm lighting's atmosphere while 'strong' will correct the color cast almost completely. Unfortunately on the K-x this does not work too well and while the 'strong' option produces a better result than its 'subtle' counterpart it is still far from perfect.

However, all in all the K-x gives you a very good tool set to get your white balance right when it counts. You can fine tune all settings, there is a custom WB option, and if you prefer to emphasize the color of a light source rather than neutralize it, the CTE setting is what you are looking for.

Incandescent - Auto subtle correction WB
Red: 10.8%, Blue: -16.6%, Poor
Incandescent - Auto strong correction WB
Red: 6.7%, Blue: -11.6%, Average
 
Incandescent - preset WB
Red: -0.5%, Blue: 2.1%, Good
 

Fluorescent - Auto WB
Red: 3.6%, Blue: -9.0%, Average
Fluorescent - Warm white preset WB
Red: 1.8%, Blue: 1.1%, Good

Flash

The K-x's flash performance does not give you any reason to worry. The metered exposure is spot on in both the portrait shot and the sample shot of the color chart. White balance is pretty much spot on and fill-flash usually does a pretty good job as well. All in all, no reason to complain here.

Dynamic Range Setting

Most current DSLR cameras sport features that aim to increase the dynamic range of in-camera JPEG output using tone curve adjustments - either by changing the exposure to protect highlights or by simply trying to pull more detail out of the shadows. Like the K-7, the K-x allows both techniques, offering separate highlight- and shadow corrections. Both are accessed under D-Range Setting in the shooting menu.

The Highlight correction is an on/off function while Shadow correction can be applied in three levels. Because it works by using a shortened exposure, Highlight correction limits the lowest ISO to 200. This is not the case with shadow correction which will allow you to use ISO 100.

In the dynamic range section of this review we demonstrate that enabling the highlight correction function adds about a stop of dynamic range to the highlight end. In the real world example below you can see that there is only marginally more information in the brightest part of the picture, the fur of the soft toy.

Shadow correction doesn't alter the underlying exposure and instead uses a tone curve correction to pull out additional shadow detail. This method creates a little more noise in the shadow regions, but the end result is not objectionable.

All correction off 100% Highlight Crop 100% Shadow Crop
Highlight Correction on 100% Highlight Crop 100% Shadow Crop
Shadow Correction level 3 100% Highlight Crop 100% Shadow Crop
Highlight Correction on + Shadow Correction level 3 100% Highlight Crop 100% Shadow Crop

High Dynamic Range (HDR)

In addition to the highlight- and shadow correction options the K-x also features a High Dynamic Range (HDR) option. HDR images attempt to capture the dynamic range of a scene by combining multiple exposures into one.

For its HDR implementation the K-x uses three images taken at 3.0 EV apart. These are then processed and the resulting image is saved as a JPEG. Like highlight- and shadow correction HDR is limited to JPEG-only shooting. There are two settings for HDR - Standard and Strong (and, of course, off). We have tested the K-x's HDR function on the same high contrast setup as above.

High Dynamic Range Off 100% Highlight Crop 100% Shadow Crop
High Dynamic Range Standard 100% Highlight Crop 100% Shadow Crop
High Dynamic Range Strong 100% Highlight Crop 100% Shadow Crop

As you would expect the HDR functionality offers a noticeable increase in dynamic range compared to a single frame. This is especially true for the highlight end where more of the previously clipped detail is revealed than with the highlight correction function. The shadows have also noticeably been lifted. Another advantage of using HDR capture over highlight or shadow correction in this situation is that there is no increase in shadow noise.

A disadvantage of Pentax' HDR implementation is that a tripod is required to obtain a sharp result. Like the K-7, the K-x does not seem to be compensating for camera shake or subject movement between the individual shots of the HDR series. This can result in ghosting and/or blurred images even in good light.

Overall Image Quality / Specifics

In many respects we were very pleased with the quality of the K-x's image output. At base ISO JPEG images show very good detail and natural colors out of the box. With some careful sharpening you can get a small extra amount of detail when converting from a RAW file but the difference is marginal and only visible at full magnification. Unlike some other cameras we've tested in the past, in the K-x's case this is definitely a compliment for the Pentax JPEG engine rather than a criticism of its RAW output.

While detail and colors at base ISO don't leave anything to complain about, what we were really, and indeed very positively, surprised about is the K-x's performance in low light. The Pentax balances the application of noise reduction and the retention of fine detail very well up to the highest sensitivities. Its high ISO output shows slightly more luminance noise (grain) than some of its direct competitors but in turn it maintains visibly more fine detail. Crucially there is also relatively little chroma noise. The end result are images with grainy, more film-like noise characteristics, that show very good detail up to the very highest sensitivities. The K-x is a lot better at high ISOs than its bigger brother, the K-7, and is no doubt one of the currently best performing APS-C cameras in low light.

With lots of light there usually comes some shade as well and the Pentax K-x is no different. Our main criticism has to be the camera's habit to clip highlights which is exacerbated by a tendency to over expose high contrast scenes. This is the result of a fairly steep default tone curve and you can slightly mitigate the problem by activating highlight extension. The difference will be marginal though. Your best bet is to dial in some negative exposure compensation in high contrast situations to avoid blowing the highlights completely. The K-x offers very little in terms of RAW headroom and therefore shooting RAW will not solve the problem entirely. However, the ability to adjust the tone curve during file conversion is no doubt very useful. All in all this issue is certainly not a deal-breaker but you should be aware of it and always try and get your exposure right; with some manual intervention where necessary.

Apart from this there are not a lot of negatives to report on. You can't rely on Auto white balance if color fidelity under artificial light is of any importance to you but the K-x is far from being the only DSLR struggling in this area. We also had a few slightly out of focus shots when the camera had confirmed focus at the time of exposure. This was just a handful though amongst our 1000+ sample shots and is well within normal limits.

All in all the K-x is perfectly capable of producing high quality image output, especially in low light. However, keep an eye on the metered exposure, especially when capturing high contrast scenes, to avoid blown highlights.

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