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Choosing a bits per channel mode

To get good-quality output from any device, you must capture or input a wide range of tonal values. One of the challenges in photography is capturing detail in the shadow areas of a scene. The wider the dynamic color range of the camera, the more subtleties of color and tone it is capable of capturing. Most advanced amateur and professional digital SLR cameras capture from 12 to 16 bits of accurate data per channel, and the resulting photos contain abundant pixels in all levels of the tonal spectrum.

Consumer-level scanners capture 10 bits of accurate data per channel, whereas high-end professional scanners can capture up to 16 bits of accurate data per channel. Like photos from the better digital cameras, scans from a high-resolution device contain an abundance of pixels in all the tonal ranges.

Three bit depths are available on the Image > Mode submenu in Photoshop: 8, 16, and 32 Bits/Channel mode. At the present time, 16 Bits/Channel mode offers the most advantages. 32 Bits/Channel mode may be the mode of choice for high-end photographic work in the future, but at the moment Photoshop doesn’t support it sufficiently to make it a practical choice.

Another requirement for getting good-quality output is the ability to preserve the full tonal range of your images as you edit them in Photoshop. Because they contain more pixels, 16-bit images are better able to withstand the wear and tear of editing and resampling. Levels and Curves adjustments, for example, remove pixel data and alter the distribution of pixels across the tonal spectrum. After editing, the reduction in image quality will be visible on high-end print output of an 8-bit image, but not of a 16-bit image, because the latter contains more pixels in all parts of the tonal spectrum.

To summarize, the following are some basic facts about 16-bit files that you should know:

  • Photoshop can open 16-bit CMYK and RGB files.
  • 16-bit files can be saved in the following widely used formats: Photoshop (.psd), Large Document (.psb), PDF (.pdf), PNG (.png), TIFF (.tif), and JPEG2000 (.jpf).
  • 16-bit images can be successfully edited and adjusted in Photoshop, with merely a few restrictions. Most of the filters on the Blur, Noise, Render, Sharpen, and Other submenus on the Filter menu are available, as is the Distort > Lens Correction filter, whereas filters on the other submenus are not.
  • When you print your file, you will need to convert your 16-bit images to 8-bit (Image > Mode > 8 Bits/ Channel).

If system or storage limitations prevent you from working in 16 Bits/Channel mode, consider taking this two-stage approach: Perform your initial tonal corrections (such as Levels and Curves adjustments) on the original 16 Bits/Channel version, then convert it to 8 Bits/Channel for further editing.

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