Advantages of 16bit Color Depth

This simple test clearly shows the difference between working with 16-bit and 8-bit image data. Open a 16-bit image and apply a number of simple Curves or Levels adjustments to it. Check the resulting histogram (|ctrl|-|T~]). It will probably look something like the one in figure 4-3.

Now open the same image and convert it to 8-bit (Image r Mode r8 Bits/Channel). Apply the same corrections to the resulting image and check the histogram again. It will now look more like the one in figure 4-4. The gaps in the histogram indicate image data loss that often (but not always) manifests in the form of visible halo and posterization effects.

Such artifacts are not always visible, and you shouldn't let a gappy histogram put you off using an image if it is still visually pleasing.

Why use 8-bit mode at all if 16-bit mode is so much better? Some reasons are:

► 16-bit processing takes longer.

► 16-bit data requires more memory and disk space.

► The resulting image files are larger.

► Some Photoshop tools and filters are not available in 16-bit mode in program versions that are older than the first CS release.

Before Photoshop CS1 was released, we performed our entire workflow on an 8-bit level and produced perfectly good results in the process. 16-bit processing nevertheless produces better results if you have enough computing power.

Figure 4-3: Histogram after applying some corrections to an image with 16-bit color depth.
Figure 4-4: Histogram after applying the same operations to 8-bit image data.

> 16-bit processing only makes sense if your raw material has more than 8-bit color depth (as is the case for many RAW-capable cameras). Many high-quality scanners also produce 16-bit image data.

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