High-Resolution Digicams; Do Major Megapixel Counts Aid Or Hinder Image Quality? Page 2

Pixel Size: D-SLRs Vs. Digicams
The image quality concerns refer primarily to ultrahigh-resolution digicams and not to D-SLRs. The latter employ comparatively oversized sensors with larger--and hence, more light sensitive--pixels. Such cameras should generate much cleaner data, producing less of a challenge for their processing engines at any ISO level. (Editor's Note: This is also the argument used by so-called "medium format" digital camera makers as to the superiority of their larger sensors vs. APS-C size sensors found in D-SLRs. Obviously that's a story for another day.)

Compare the size of a "large" 8.8x6.6mm sensor from a digicam to a typical 23.6x15.8mm D-SLR sensor and it's easy to imagine the relative size of the photosites (pixels) as well. Much smaller photosites can lead to some image-quality issues with ultrahigh-resolution compact cameras, although more sophisticated processors may produce a significant improvement. Photo Courtesy of Sony.

But just how small or large are the sensors employed by the latest cameras? That data is available in the specifications for some cameras, but requires a web search for certain other models. Our comparison chart lists the dimensions for the sensors most commonly used in high-resolution digicams and D-SLRs. Information on actual pixel size is rarely published. After extensive searching, I was able to find some data about pixel size in 8MP digicams, but not about the 12MP cameras.

Even so, the following information provides a practical glimpse at how a sensor's dimensions affect pixel size. My research revealed that the pixel size on an 8MP digicam's 1/1.7" type sensor is approximately 2.7x2.7 microns. (A micron is one thousandth of a millimeter.) That's miniscule when compared to the 6.4x6.4 micron size in an 8MP D-SLR with a 22.2x14.8mm sensor, for example. Obviously, we have even greater pixel size discrepancies when comparing a 12MP digicam (with the 1/1.7" sensor) to a D-SLR camera.

The chart below lists common sensors from small to large. All of the 12MP digicams that had been announced at the time of this writing employed the 7.6x5.7mm CCD but it's possible that some subsequent models may use other sensor sizes.

Comparison Chart
Sensor Type
Actual Dimensions
Comments
1/2.5" 5.76x4.29mm A very small sensor rarely used in digicams with 6MP or higher resolution.
1/1.8" 7.18x5.32mm This sensor is used in some 8MP and 10MP although other models employ the 1/1.7" sensor.
1/1.7" 7.6x5.7mm A slightly larger sensor that may become common in many (but perhaps not all) 12MP digicams.
2/3" 8.8x6.6mm The largest sensor readily available for digicams but not in use at the time of this writing.
4/3" CCD or new NMOS 18x13.5mm The sensor used in Olympus, Panasonic Lumix, and Leica D-SLRs.
Unique Foveon X3 sensor 20.7x13.8mm Available only in Sigma SD-series D-SLRs and in the new Sigma (14MP) DP1 digicam.
Canon APS-C format CMOS Approximately 22.2x14.8mm Canon's proprietary sensor used in most consumer-grade EOS cameras (except the EOS 5D).
APS-C format CCDs Approximately 23.6x15.8mm Various sensors of similar sizes, used in Fuji, Nikon, Pentax, and Sony D-SLRs.
Canon full-frame 35.8x23.9mm The 35mm film size sensor used in the EOS 5D and some pro EOS cameras.

Resolution And Sharpening
Theoretically, 12 million vs. 10 million pixels should produce greater resolution. That may be true but it's not apparent in ISO 100 images viewed at high magnification on a monitor or in oversized prints. (Comparing a 12MP digicam to a 6MP D-SLR might be more revealing in this respect.) At a glance, fine detail seems to be sharper in the images made by one of the two digicams, but only because of a much stronger level of in camera sharpening at default. Setting the other cameras to a higher sharpening level negates that difference.

Any full-featured digicam or D-SLR can be set to a high level of sharpening for a crisper look, but that does not increase the resolution of fine detail. As seen in these examples the 10MP D-SLR (Photo A) is more capable of superior definition of fine detail than the 12MP digicam (Photo B). (Both images made with multi-segment metering, Auto WB and ISO 100 in Cannes, France.)

I took these photos as a quick, informal test to compare D-SLR image quality at ISO 400 (Photos A) with digicam image quality at ISO 100 (Photos B). At high magnification--or when viewing the small portion of each picture in an 8x10" print--it's apparent that the D-SLR image is slightly cleaner and exhibits slightly better resolution, in spite of the higher ISO level. (Images were made with large/fine JPEG capture in Taormina, Sicily.)
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