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A camera’s ability to reproduce accurate colors is a major factor in how good your photos turn out. Photos with dull colors can be boring, photos with oversaturated colors can look unnatural, and photos with inaccurate colors can look ugly. All cameras handle color differently, which is why we test color accuracy. We test this by photographing an industry standard GretagMacbeth ColorChecker test chart and comparing the known colors of the chart with the colors the camera reproduces. The ColorChecker consists of 24 tiles of commonly photographed colors from around the color spectrum. The image below shows the results for the Pentax M40. The outside squares show the colors the M40 reproduces, the inside squares show the ideal colors of the test chart corrected for luminance, and the inner rectangles show the ideal colors of the chart under a perfectly even exposure.
As you can see, not all of the inner squares match up perfectly with the outer squares. Note how different the blues and yellows are. The camera appears to significantly undersaturate yellows, and shift blues toward purple. This makes some blues skies look purple. The graph below confirms this in a more quantitative way. The colors of the test chart are shown on the color spectrum as squares, while the colors the camera reproduces are shown as circles. Then lines connecting the circles and squares show the extent of the color error.
The graph shows that yellows and blues are quite inaccurate. This affects many photos you will take, whether they include blue skies, yellow flowers, or light skin tones. In addition to these inaccuracies, the camera tends to undersaturate, meaning a lot of your colors will look dull, and you may have to take the time to boost them on your computer. Overall, the M40’s color accuracy is considerably below average.
*We test resolution by photographing an industry standard resolution test chart under bright, even light. We vary focal length and exposure settings to find the settings that produce the sharpest images. Imatest, our powerful third-party image analysis software, evaluates resolution in terms of line widths per picture height (lw/ph). This corresponds to the number of equally-spaced alternating black and white lines that can fit across the image frame of the camera before becoming blurred.
The 8-megapixel Pentax M40 produces the sharpest images at ISO 50, f/5.9, and a focal length of 19mm. The camera resolves 1488 lw/ph horizontally with 1.4 percent oversharpening, and 1575 lw/ph vertically with 3.3 percent oversharpening. These results put the M40 below average for 2007 point-and-shoots, though it is good to see the camera doesn’t oversharpen too much. However, the corners of the image are quite blurry and unfocused, there is some color moiré in the stripes, and there is obvious barrel distortion. These issues will show up in your photographs and won’t look nice.
Noise – Manual ISO*(6.47)
*If you have ever owned a digital camera you have probably noticed ugly graininess in photos taken in low light. This graininess is known as "noise," and is similar to the static on your TV or the background hiss from your stereo system. But unlike film grain, digital image noise almost always looks ugly. Noise appears in many varieties, from monochromatic sandy grains to colored splotches. The amount of noise in an image is intrinsically greater at high ISO sensitivities.
We test noise levels by photographing a test chart under bright, even studio light at all ISO sensitivities. The Pentax M40 has disappointingly high noise at ISO 50 and 100, but from ISO 200 to 800 noise levels stay decently low. At ISO 1600 and 3200, however, there is so much noise your images will be barely useable. The M40 doesn’t appear to apply much noise reduction, which allows more detail to show through even if noise levels are high. Despite high noise levels at ISO 1600 and 3200, the M40 scores better than average for a 2007 point-and-shoot.
Noise – Auto ISO*(1.06)
*We also set cameras to Auto ISO to test noise levels. This test is performed under the same bright studio lights as our other tests. The Pentax M40 chooses a very odd ISO 640 under the Auto setting, which yields high noise, but not notably high for such a high ISO sensitivity. This suggests that the EXIF data may be inaccurate in Auto mode. Still, the camera has significantly more noise than we would like to see in such bright shooting conditions.
A camera cannot reproduce accurate colors without good white balance. A camera must be able to adjust to different lighting conditions in order to accurately reproduce colors. Without proper white balance, images can take on odd color casts, often yellow or blue. We test white balance by photographing the ColorChecker test chart under four types of light: flash, fluorescent, outdoor shade, and tungsten. We test the Auto white balance setting as well as the appropriate white balance presets found in the White Balance menu.
*We could not test the white balance accuracy using flash because the lack of a focus assist light prevents the camera from focusing in the dark. White balance accuracy under fluorescent light is good, though it fares poorly under outdoor shade and tungsten light. Images taken outdoors have a blue color cast, and in tungsten light they take on a strong yellow cast.
The white balance presets are more accurate than the auto setting. Outdoor shade and tungsten light are significantly more accurate, though still not great. Accuracy under fluorescent light is fairly accurate, though not quite as accurate as the Auto setting. Using manual white balance will always be the best way to white balance the M40.
Still Life Sequences
Click to view the high-resolution images.
|Still Life Scene|
|ISO 50||*ISO 50*|
|*ISO 100*||ISO 100|
|ISO 200||ISO 200|
|*ISO 400*||*ISO 400*|
|*ISO 800*||*ISO 800*|
|*ISO 1600*||*ISO 1600*|
|*ISO 3200*||*ISO 3200*|
*Low Light – 30 lux
*We also test video quality in low light at 30 lux. The Pentax M40 has decent color accuracy in low light, and quite low noise. The problem, however, is that it has trouble focusing in low light. Regardless of how much noise there is, you want videos to be in focus.
*We record footage of the resolution test chart to determine the sharpness of video clips. Video is shot in Standard Definition, 640 x 480, so video resolution will always be much less than still photo resolution. In Movie mode, the M40 records 255 lw/ph horizontally with 14.6 percent undersharpening, and 350 lw/ph vertically with 13 percent undersharpening. This undersharpening actually helps the video detail by not introducing image artifacts when it is compressed. There are very few signs of moiré or jagged lines.
To evaluate the motion capture of digital camera video, we shoot moving cars and pedestrians on the street. The M40’s video is significantly overexposed in bright sunlight, and the highlights smear the frame. The exposure also changes drastically, creating a flashing effect, and the motion stutters. The good news is the camera effectively captures detail, and doesn’t show significant image artifacting. Overall, like most digital cameras’ Movie modes, the M40’s video quality leaves a lot to be desired.
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