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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-7 produces an almost identical color response to its predecessor, the K20D, which will be good to know for potential upgraders. 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-7 Compare to:  
      
      
      
      
BrightNaturalPortraitLandscape
VibrantMutedBWAdobe RGB

Artificial light White Balance

Under artificial light the automatic white balance setting does an average job and can't be trusted if white balance is crucial. However, switching to the corresponding presets gets you near perfect results. Under tungsten light you now get the option between 'subtle' or 'strong' correction. 'Subtle' will preserve some of the warm lighting's atmosphere while 'strong' will correct the color cast almost completely. The preset for fluorescent light works perfectly as well. For perfectionists there is also a fine-tunable custom white balance option.

Incandescent - Auto WB
Red: 3.2%, Blue: -8.5%, Average
Incandescent - Incan. subtle preset WB
Red: 10.4%, Blue: -16.0%, Poor
 
Incandescent - Incan. strong preset WB
Red: 0.8%, Blue: -1.0%, Excellent
 

Fluorescent - Auto WB
Red: 6.6%, Blue: -13.10%, Average
Fluorescent - Daylight white preset WB
Red: -0.10%, Blue: 1.5%, Excellent

Flash

The K-7's flash performance is very similar to the K20D and indeed most current digital SLRs. The metered exposure is very good in the portrait shot while the sample shot of the color chart, due to the predominantly white background, is slightly underexposed. 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. The K-7 allows both techniques, offering separate the 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 more information in the brightest part of the picture, the windows on the office building.

Shadow correction doesn't alter the underlying exposure and instead uses a tone curve correction to pull out additional shadow detail. Both techniques create a little more noise in the shadow regions, but the results aren't objectionable at ISO 200.

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

High Dynamic Range (HDR)

In addition to the highlight- and shadow correction options the K-7 also features a High Dynamic Range (HDR) option - it's the first DSLR camera to feature in-camera HDR processing (though Sony now has a two shot system in the Alpha 550). HDR images attempt to capture the dynamic range of a scene by combining multiple exposures into one.

For its HDR implementation the K-7 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 two settings for HDR - Standard and Strong (and, of course, off). We have tested the K-7's HDR function on the same high contrast scene as above.

High Dynamic Range Off 100% Shadow Crop 100% Highlight Crop
High Dynamic Range Standard 100% Shadow Crop 100% Highlight Crop
High Dynamic Range Strong 100% Shadow Crop 100% Highlight 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. The K-7 does not seem to be compensating for camera shake or subject movement during the HDR processing step. This can result in ghosting and/or blurred images even in good light.

Examples of blurring due to camera shake (left) and subject movement (right).

Distortion/CA correction

The K-7 has options to correct for geometric distortion an lateral chromatic aberation in DA and DFA lenses. The choice to correct the image is recorded in the RAW file so will be applied if you use the supplied software - it isn't recognised by Adobe Camera Raw, however, so your images will only be corrected if using JPEGs or the provided software.

Using distortion correction rather reduces the usefulness of a 100% viewfinder, since you can't predict how much of the edge of the image will be removed when the distortion is being removed. The K-7's live view doesn't show a corrected image either, so you'll have to compose by dead reckoning if you're using a lens with significant distortion (The kit lens at wide-angle, in this instance).

JPEG with distortion and CA corrected 100% crop
RAW converted with Adobe Camera Raw 100% crop

As you can see, the distortion correction option does a good job - corners are soft but that's just as true of the uncorrected image. CA correction doesn't work as well, however, still showing some signs of fringing towards the corner of the image.

Overall Image Quality / Specifics

At base ISO the K-7's JPEG shows good detail and natural colors. At default settings it uses less in-camera sharpening than the K20D and is therefore a little softer without being too soft. The images respond well to a mild unsharp-mask and for those who want maximum detail it's worth shooting in RAW and applying some careful sharpening during the conversion process. Using decent lenses to satisfy the Pentax sensor's hunger for resolution won't do any harm either.

Dynamic range, especially in the highlights, measures slightly lower on the K-7 than on its direct competitors which can occasionally lead to clipped highlights. Slightly underexposing in RAW, then pulling the brightness up in processing can help avoid this, of course. Having said that the Pentax offers a fairly efficient highlight correction feature that essentially does this automatically. It can be combined with the shadow correction feature for those dreaded high contrast scenes and if there aren't any moving subjects in the frame the HDR mode is another good option squeezing a bit of extra dynamic range out of the K-7.

While overall at base ISO the K-7 is doing a very decent job at higher sensitivities the pictures does change a little. JPEG noise is visibly and measurably higher than on other cameras in this class. The Pentax retains relatively good detail up to the highest ISO settings but also shows a large amount of both luminance and chroma noise. Increasing the in-camera reduction does not really solve the issue as it results in pretty heavy blurring of detail. Surprisingly the K-7's RAW noise is actually on a similar level as the competition (but measurably higher than the K20D!) which leads to the conclusion that the Pentax JPEG engine and especially the noise reduction component aren't working as well as some of its rivals which deliver a more balanced mix between noise reduction and detail retention. For maximum image quality in low light situations your best bet is shooting RAW and applying your own noise reduction cocktail in post processing.

We found the metering generally to be reliable with the occasional slight over-exposure in bright conditions. All in all the K-7 delivers good image quality in good light but its JPEG output struggles slightly against the competition in low light scenarios. Apart from a slightly different tone curve, weaker default sharpening and slightly higher (!) RAW noise the K-7 output is very similar to the K20D. Therefore, purely from an image quality point of view, there is no pressing need for K20D users to upgrade.

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