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Choosing a bits/channel mode

To get good-quality output, you need to capture or input a wide range of tonal values. One of the greatest challenges to a photographer 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 can capture. Most advanced amateur and professional digital SLR cameras capture from 12 to 16 bits of accurate data per channel, and the resulting photos contain an abundance of 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 the better digital cameras, scans from a high-resolution device will contain an abundance of pixels in all the tonal ranges.

In Photoshop, you have a choice of three bit depths, available on the Image > Mode submenu: 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 factor in 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. A–B The Levels and Curves commands, 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 has 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 files in CMYK or RGB mode.
  • 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.
  • 16-bit images can be successfully edited and adjusted in Photoshop, with just 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. Filters on the other submenus aren’t available, and you can’t use the Art History Brush tool.
  • When you print your file, you need to convert your 16-bit images to 8-bit (Image > Mode > 8 Bits/Channel).

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

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