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Wednesday, May 30, 2007

The Bit-Depth Decision

8-bit versus 16-bit workflow is among the least understood aspects of photography for most professionals. This primer will get you up to speed quickly.

Editing the file in an 8-bit wide-gamut space increases the likelihood of banding. If you instead work with a high-bit file, you have more data between the original bits, so as you edit the file, the total data loss isn't as great. Bottom line: if you're working with a color space as large or larger than Adobe RGB (1998), seriously consider working in high bit. The same pundits who suggest we don't need to work in high bit often tell us that we don't need to work with a color space larger than sRGB, despite the fact that our capture devices and most of our output devices exceed this color gamut.

Again, do you want to capture and reproduce all the colors at your disposal or do you feel comfortable throwing away data? It's your data, so it's your call, but I don't see the logic of painting yourself in a corner with your data. Being informed about the issues surrounding a high-bit workflow makes it easier to make these kinds of decisions, just like evaluating how best to handle that 500-widget photo shoot or whether or not to shoot RAW or JPEG for any particular assignment.

Bit-Depth And File Formats

Speaking of JPEG, be aware that this file format doesn't support high-bit data, only 8-bit. So if you're concerned about getting high-bit data out of your D-SLR, you have to shoot RAW. Many users recognize that Photoshop can convert an 8-bit file to 16-bit and wonder if that provides any advantages. Unfortunately, no.

If you started with a high-bit file and converted to 8-bit, the additional data is thrown away; you can't get it back. The reason Photoshop allows such conversions are situations where you might build a composite and paste an 8-bit image into a 16-bit image. This can't be accomplished unless all the documents have the same bit-depth (and for that matter, the same color space). So while you can convert from a lower bit-depth to a higher bit-depth, unless you're doing this kind of composite work, there's no real benefit in doing so. Much like starting with a high-resolution file, if you interpolate it down and then interpolate it up to the original size, you don't have the same original data.

Go With What Will Work For You

Ultimately, how you wish to process your data from capture to output is up to you. While there are those who say they've never seen any advantage to working in high bit, the math is undeniable. Altering pixel values results in data loss, but there's no way to predict if and when that may manifest degradation upon output. A high-bit workflow ensures this is unlikely to ever happen today or in the future. Note that for some users, even a 16-bit workflow doesn't provide enough bits. And note that in Photoshop CS2, you have the option to work with 32-bit documents. For most readers, this isn't a necessary option and is really for those working in HDR (High Dynamic Range) capture, a new and emerging technology. The point is that when this kind of capture is available in more digital cameras, be prepared to work with ultra-high-bit data documents.



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