Working with 16 bits per channel

Working with 16 bits per channel


To get good-quality output from Photoshop, a wide range of tonal values must be captured at the outset. Th e wider the dynamic range of your chosen input device, the fi ner the subtleties of color and shade it can capture. Most advanced amateur and professional digital SLR cameras capture at least 12 bits of accurate data per channel.
Like cameras, scanners range widely in quality:
Consumer-level scanners capture around 10 bits of accurate data per channel, whereas the high-end professional ones capture up to 16 bits of accurate
data per channel.
Shadow areas in particular are notoriously difficult to capture well. But if your camera can capture 12 to 16 bits per channel (or you work with high-resolution scans), you will have a head start, because your fi les will contain an abundance of pixels in all levels of the tonal spectrum. Photoshop can process fi les that are in 8, 16, or32 Bits/Channel mode. All Photoshop commands are available for 8-bit fi les. Most Photoshop commands are available for 16-bit fi les (e.g., on the
Filter menu, the Liquify and Lens Correction fi lters are available, as are some or all of the fi lters on the Blur, Noise, Render, Sharpen, Stylize, and Other submenus, whereas fi lters on the other submenusare not). Too few Photoshop commands are available for 32 Bits/Channel fi les to make such fi les a
practical choice.
Although you can lower the bit depth of your fi les via the Image > Mode submenu, it’s better to keep them in 16 Bits/Channel mode. Th e editing and resampling commands in Photoshop can degrade the image quality, but the extra pixels in 16-bit images make this less of a problem.A–B The tonal adjustment commands in particular, such as Levels and Curves, remove pixel data and alter the distribution of pixels across the tonal spectrum.
Signs of pixel loss from destructive edits will be more visible in a high-end print of an 8-bit image than in a 16-bit image. Because 16-bit images contain an ample number of pixels in all parts of the tonal spectrum at the outset, more tonal values are preserved, and the resulting output is higher quality.
To summarize, these are some basic facts about 16-bit fi les to consider:
➤ Photoshop can open 16-bit fi les in CMYK orRGB mode.
➤ 16-bit fi les can be saved in many formats, suchas Photoshop (.psd), Large Document (.psb),Photoshop PDF (.pdf), PNG (.png), TIFF (.tif),
and JPEG 2000 (.jpf).
➤ From the Mac OS, you can print 16-bit fi les,provided your printer supports 16-bit printing.
➤ For commercial print output, your output service provider may request 8-bit fi les, in which case you will need to convert them after image-editing.
Note: If system or storage limitations prevent you from working with 16-bit images, consider following this two-stage approach: Perform the initial tonal corrections (such as Levels and Curves adjustments) on the 16-bits-per-channel image, then
convert it to 8 bits per channel for further editing.