16-Bits/Channel vs. 8-Bits/Channel_

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A debate is raging on the benefits of using 16-Bits/Channel files, also known as high-bit, as opposed to the more traditional 8-Bits/Channel files. Basically, and speaking in nutshells, a 16-BPC image can contain 65,536 levels, whereas an 8-BPC image can contain only 256 levels. (In fact, Photoshop shows only 32,768 levels for images in 16-BPC, which is closer to 15-BPC; it also sees any file above 8-BPC as 16-BPC.) Therefore, it seems natural to assume that because 16-BPC images contain more bits, they must contain more information and be superior in every way to images in 8-BPC mode.

Based on the "more bits = more information" theory, the advocates of 16-BPC maintain that you can achieve superior results if you work in high-bit mode. However, the advocates of a 8-BPC workflow maintain that although for a very limited number of images that may be true, for the majority of the images the extra overheads in file size, RAM, larger and faster scratch disks, slower workflow, and so forth do not justify the end results, which are very hard to discern when images are output to print.

Both camps agree that there is more flexibility during image editing in 16-BPC because of fewer quantization errors and, therefore, less banding and overall image degradation, though some of this banding may not actually translate to print. Quantization errors are attributed to the rounding off of numbers when fractions are recalculated to the nearest binary number; only binary numbers, not fractions, can represent digital values. But to benefit from editing in 16-BPC, you must start with a file in 16-BPC mode.

You may have noticed that Photoshop gives you the option of changing from 8-BPC mode to 16-BPC mode. If you fall for this option, don't be fooled into thinking you will somehow increase the detail. Changing modes upward can be likened to changing a file in a small color space to a larger color space, or a family of four moving from a small apartment to a large mansion. Though they may find that they have more space to move around, they ostensibly remain the same width and height and have maintained the same number of members. In other words, you will have more space between the colors but not necessarily more colors (more space between the family members but no additional offspring). If anything, you will increase the chance of degradation by having to make larger adjustment moves and introducing quantization errors.

There is a middle way being adapted by digital photographers who work in Raw mode:

1. Process the raw file in Camera Raw and then open it in Photoshop in 16-BPC mode.

2. Do any major tonal and color corrections.

3. Save the file as a master file.

4. Duplicate the document.

5. Convert it down to 8-BPC.

6. Do any major edits that require hefty resources, such as multiple adjustment layers, duplicate blending layers, layer styles, multiple type layers, and so on.

7. Optimize the 8-BPC version for output.

NOTE Printers, overall, can handle only 8-BPC files. If you send a 16-BPC file to a printer, it will be converted on the fly to 8-BPC before output.

While this debate is raging, you may wish to do your own tests, which are easy to perform:

1. Duplicate a 16-BPC file.

2. Convert the copy to 8-BPC (Image^ Mode ^ 8-Bits/Channel).

3. Perform the same edits on the original and the copy (use adjustment layers and drag them into the other file).

4. Send the files to your desktop printer, or convert the 16-BPC to 8-BPC and then send both to a four-color offset printer and a photographic printer for good measure, such as a Fuji Frontier or a LightJet.

If you find no discernible difference between the prints, or the difference is insignificant, you will be in the best position to decide whether to work in 16-BPC or only in 8-BPC mode from the get-go and enjoy cruising through your workload.

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