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"This extra image information might be overkill if it weren’t for the advanced CMOS image sensors found on both the EOS 50D and EOS 5D Mark II. The pixels on both of these sensors have improved fill factors and lower read noise than those in previous Canon sensors in their class, with the larger-sized pixels on the EOS 5D Mark II providing low-noise performance that’s a notch better than the EOS 50D at every comparable ISO setting. In combination with the camera’s lower levels of background noise and amplifier noise, the EOS 5D Mark II’s 14-bit A/D converter helps to provide smoother tonal gradations, along with the potential to increase detail in bright highlights with the Highlight Tone Priority option. The EOS 5D Mark II also maintains a slightly higher dynamic range at high ISOs than the EOS 50D and the older EOS 5D it replaces.
The expanded dynamic range provides increased detail in deep shadow areas and a superior ability to open up shadows in post processing without banding and excessive noise. Detail is also improved in highlight regions, but the difference is less noticeable as a result of inherently lower noise levels in bright tones and highlight areas. However, having extra bit depth and detail in highlight areas allows a photographer to adjust exposure and contrast in post processing to reduce blown out areas without blocking up shadow areas."
"The potential for smoother tonal transitions, was just mentioned above. Any time you have a scene with a single “color” that moves from light to dark or vice versa, this is a benefit — whether it’s a wide-angle shot of a clear blue sky or a shot of a car with shiny highlights blending into darker tones along its painted body. Skin tones in portraits, especially with “hard” light sources like direct sun or on-camera flash, are another area where 14-bit conversion can mean smoother changes from specular highlights to diffused highlight skin tones.
The increased information in each file also allows cameras like the EOS 5D Mark II and EOS 50D to incorporate Canon’s Highlight Tone Priority option. With much more tonal data, Highlight Tone Priority leverages this information and preserves anywhere from 1/3 to a full stop of additional detail in bright highlights. It can make the difference between washed-out highlights vs. controlled highlights with visible texture and detail. And unlike simply changing exposure to darken an image, Highlight Tone Priority does not change the brightness level of mid-tones or shadows. There’s a chance of a small increase in digital noise in darker areas, but even at high ISOs, it’s a minor difference, and a small price to pay for the potential of added detail in bright highlight areas.
With the expanded tonal information provided by the 14-bit per channel conversion, it’s possible for the camera to make tone curve adjustments on a case-by-case basis. In addition to toning down highlight areas, underexposed areas can be lightened. This is the function of the Auto Lighting Optimizer, a new feature found on the EOS 5D Mark II, EOS 50D, and also on the EOS Rebel XSi and EOS 40D cameras. JPEG images can be fine-tuned as they’re processed and recorded; RAW images from these cameras can have tonal adjustments applied when they’re processed in Canon’s Digital Photo Professional software. Users are free to disable this feature, or set Low, Standard, or Strong levels in the EOS 50D and 5D Mark II.
Another technology that these new cameras utilize is built-in correction for lens vignetting, called Peripheral Illumination Correction. Since tones in sky or other light-colored outer areas of images have a lot more tonal information and much finer steps between them, the camera can automatically apply correction to lighten these areas without risking tonal “skipping”, banding, or noticeable increases in digital noise. Both Highlight Tone Priority and Peripheral Illumination Correction can be applied to JPEG as well as to RAW images."
"It’s a fact that different color dye or light combinations can produce similar visual sensations, which is why we are able to produce accurate colors in print, even though printing inks differ in their density and color, and printing methods range from silver halide to CMYK printing presses. The same holds true for different display technologies, paints, and clothing dyes. Metameric color pairs are those that appear exactly the same under one light source but different under another, proving that the color sensation we see is being formed by color components with different spectral properties.
A 14-bit A/D converter has the ability to map the 10-12 million true colors captured by the camera into trillions of color data combinations. This may provide a benefit down the road in a color-managed system when converting a RAW file or 16-bit TIFF file for viewing on wide variety of color displays or printing on wide gamut color printers. While a 14-bit A/D converter might not be able to produce any more “visual” colors from RAW data than a 8 or 12-bit A/D converter, its increased precision allows for higher color accuracy and smoother gradations between colors, plus additional details in dark, saturated colors that can be attributed to the increased dynamic range.
The increased precision of the 14-bit A/D converter in combination with the computational speed and power of the DIGIC processor also helps images stored in the finest quality JPEG format within the camera, although those improvements are more subtle. When using the RAW+JPEG option, photographers have the best of both worlds. JPEGs can be viewed and e-mailed quickly, while top selections stored in RAW will benefit from the advanced RAW conversion algorithms found Canon’s Digital Photo Professional software.
This is where access to the additional gradations and dynamic range gives serious photographers the ability to adjust shadow and highlight details that would have otherwise been tossed away, or create smooth gradations that might have posterized during the in-camera conversion to an 8-bit JPEG. When satisfied, the higher bit-depth image can either be stored in a non-destructive file format such as a 16-bit TIFF, or output directly to Canon imagePROGRAF ink jet printers using Canon’s advanced 16-bit export modules for Photoshop and Digital Photo Professional software.
As technology progresses, more and more display devices and printers will be compatible with the higher bit-depth image data captured by the EOS 50D, and EOS 5D Mark II, and similar cameras, and use it to automatically fine tune image quality while taking advantage of expanded dynamic range these cameras offer."
I see the difference between an 8-bit, 12-bit and 14-bit file, but perhaps it's because I'm looking for it. It's not a huge, but I believe Canon when they say having the extra data can be beneficial.