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04-06-2008, 06:39 PM   #1
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Camera Raw and bit depth question

So, I've begun using Adobe Camera Raw (in CS2) for my RAW processing and I have a question for those familiar with it. There's an area of the ACR window in the lower left pertaining to workflow. One of the items has me a bit (pun intended) stumped. Bit depth lists 2 options: 8-bit and 16-bit.

My question is, given that RAW images come out of my K10D with a bit depth of 12-bit, what should I be using? If I select 8-bit, will I be losing information in the image? I would tend toward choosing 16-bit, as it's higher than the bit depth of my image, but would that mean there's some extrapolation done to the image?

Or am I not understanding something about the bit depth of a RAW image and how it fits in the workflow? Any feedback from you kind folks would be greatly appreciated.

04-06-2008, 06:46 PM   #2
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Basically, Photoshop does not have a 12 bit option, so they are asking if you want to open the file in 16 bit or 8 bit. Obviously 8 bit drops the color down a little. 16 bit does nothing to the amount of color in the resulting file, you just have a little head room for editing purposes. Which one to use depends on what you intend to do with the image once it's in Photoshop.
04-06-2008, 06:53 PM   #3
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QuoteOriginally posted by molarade Quote
So, I've begun using Adobe Camera Raw (in CS2) for my RAW processing and I have a question for those familiar with it. There's an area of the ACR window in the lower left pertaining to workflow. One of the items has me a bit (pun intended) stumped. Bit depth lists 2 options: 8-bit and 16-bit.

My question is, given that RAW images come out of my K10D with a bit depth of 12-bit, what should I be using? If I select 8-bit, will I be losing information in the image? I would tend toward choosing 16-bit, as it's higher than the bit depth of my image, but would that mean there's some extrapolation done to the image?

Or am I not understanding something about the bit depth of a RAW image and how it fits in the workflow? Any feedback from you kind folks would be greatly appreciated.
A few things. Adobe really only works in 15bit in 16 bit mode. That sounds weird but that's what I've been told.
In case your wondering Abobe is not my editor, preferring to use Corel Photopaint.
One of the reasons:
Adobe Math
Hope I didn't mis-understand my source...
another fun reference:
Clarkvision: Raw Converter Shadow Detail
Photoshop does 15-bit processing and I believe that is causing some issues with the "16-bit" processed data. I've been experimenting doing more and more processing in ImagesPlus as it does scientifically correct math (64-bit processing, but I don't believe that 64 or even 32 bits are really warranted-it's more the math).
I think this experiment shows that the main reason people have been having trouble with Margulis' challenge is not that 16-bits is not better, but the unusual way photoshop processes data.

funny thing about Mr. Clark is he basically states 8 bit is fine, but later states he does all his editing in 16bit. Go figure...
However, few of my images require high precision over a large dynamic range. So the vast majority only need 8-bit processing, or photoshop 15-bit processing, or even 8-bit jpegs. For example, the Kissing Herons image, above, produces a similarly great print when processed as an 8-bit tif with all processing in Photoshop (from raw conversion to final output).
Clarkvision: Digital Workflow
In the photo editor

* 1) I only do 16-bit editing. If the starting file is 8-bit (e.g. jpeg), the first step is to convert to 16-bits/channel.

With that statement I see no reason to shoot jpg only to expand compressed and truncated data ...

Next your RAW files are 12 bit. As you work on them the math will expand them to 15bit.
So your files aren't extrapolated at all but will be expanded when editing.
8 bit will lose information but w/ little photoshopping not real crucial BUT it is like the raw vs jpg arguement. My humble opinion is always work in the highest bit depth till finished.
If you save as jpg it will be truncated to 8 bit and compressed.

Last edited by jeffkrol; 04-06-2008 at 07:21 PM.
04-06-2008, 06:53 PM   #4
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QuoteOriginally posted by davemdsn Quote
Basically, Photoshop does not have a 12 bit option, so they are asking if you want to open the file in 16 bit or 8 bit. Obviously 8 bit drops the color down a little. 16 bit does nothing to the amount of color in the resulting file, you just have a little head room for editing purposes. Which one to use depends on what you intend to do with the image once it's in Photoshop.
This is absolutely correct. When I do anything in Photoshop I always have used 16 bit It gives you lea way to process. 8 bit leaves no room at all. I would much rather have the head room for processing.

04-06-2008, 07:28 PM   #5
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Basically 8-bit can give you only 256 different possible colors for each pixel. That is plenty for viewing a picture, but use 16-bit if you intend to do any heavier processing, curves, colors, recovering shadows or highlights.

8-bit is only enough for light processing, sharpening, or other adjustments that don't mess much with the color/lightness dynamics, if you try to do a major curves adjustment on this mode you'll get posterization.

extreme example:

(stolen from here)
04-06-2008, 08:08 PM   #6
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I think, although I could be wrong, that you need to step down to 8 bit if you want to save the image in ".jpg" format - ".jpg" is not even available as a drop down choice when you do "save as..." if you're editing in 16-bit mode. ".jpf" is, which is something called "jpeg 2000" - apparently JPEG for the modern 16-bit world.

Problem is, if you save in 16 bit ".jpf", some other editors like Picasa don't recognize it.


.
04-07-2008, 05:06 AM   #7
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Thanks to everyone for their input. Looks like I'll stick with 16-bit throughout and go down to 8-bit when saving for the web.
04-07-2008, 06:15 PM   #8
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QuoteOriginally posted by jsherman999 Quote
I think, although I could be wrong, that you need to step down to 8 bit if you want to save the image in ".jpg" format - ".jpg" is not even available as a drop down choice when you do "save as..." if you're editing in 16-bit mode. ".jpf" is, which is something called "jpeg 2000" - apparently JPEG for the modern 16-bit world.

Problem is, if you save in 16 bit ".jpf", some other editors like Picasa don't recognize it.

.
You can use .TIFF for 16-bit or 24-bit images, it's an universally accepted format, and Picasa will open it. JPEG is only inteded for viewing, never archival, it's a lossy format.

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