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Author Topic: 8 or 16 bit  (Read 8727 times)
DeeJay
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« on: January 05, 2011, 08:01:02 PM »
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Hi there,

I've always converted RAWs to TIFs in 16 bit, Even though the files are only 8 bit to begin with. I was told that this is the best thing to do for retouching. Can anyone please confirm this?

Thanks,

DJ
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Peter_DL
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« Reply #1 on: January 05, 2011, 08:20:04 PM »
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I've always converted RAWs to TIFs in 16 bit, Even though the files are only 8 bit to begin with. I was told that this is the best thing to do for retouching. Can anyone please confirm this?

You have 8 bit RAWs ?

Peter

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D_Clear
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« Reply #2 on: January 05, 2011, 10:02:37 PM »
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Hi Deejay,

RAW files are typically 12, 14, or more bits. If yours are 8 bits you may want to review your workflow something is amiss.

At the risk of inciting the small but vocal 'eloquent-yet-misinformed' group in this forum, the short answer is yes, generally speaking it is better to begin retouching/finishing with the maximum information in the file, which would be the 16 bit option in PS.

In crude terms, the path from capture to print, etc., is a reductive one from the standpoint of image data, it makes sense to discard information only by choice, or when necessary. Given this, starting with the most information possible for any given file is a good strategy.

Though the higher bit rate is often considered to be unseen due to some monitor, or printer, or visual judgment limitations, one of the practical reasons why we work with files in this fashion is because it will handle more manipulation in PS without suffering deterioration as can be seen at lower bit rates.

In my work we see this all the time when we shoot D3X and Phase P65+ side by side on assignments, the D3X as great as it is, will start to show 'cracks' while the Phase will not.

Hope this helps you

DC
www.dermotcleary.com
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DC
DeeJay
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« Reply #3 on: January 06, 2011, 12:24:23 PM »
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Thanks, yes that was the reason I had believed also.

And sorry, correct, they are 12 bit files. I was confusing myself with the choice between 8 bit and 16 bit conversions.

Thanks,
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Peter_DL
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« Reply #4 on: January 07, 2011, 07:07:40 AM »
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... correct, they are 12 bit files. I was confusing myself with the choice between 8 bit and 16 bit conversions.

Yes, Raw files are typically 'high' bit (> 8 ),
and subsequent 'heavy lifting' in the Raw converter is supposed to be high bit as well,
independent whether 8 or 16 bit are selected for output (of course we can't know for every software around).

Then it all depends on the purpose:
rendering from ProPhoto RGB to print is certainly better done at 16 bit,
whereas 8 bit may be enough for some retouching on sRGB files for a slide show or a Frontier print.

Peter

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Guillermo Luijk
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« Reply #5 on: January 07, 2011, 03:05:01 PM »
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Just some comments:

  • Not all RAW files are >=12 bits. Compact cameras usually have 10-bit RAW files (enough for them since noise dithers risk of any posterization). The Leica M8 has 8-bit non-linearly encoded RAW files (again enough for them).
  • PS is NOT a 16-bit editing tool, it's 15-bit. As soon as we open a 16-bit file in Photoshop half the levels are lost by rounding to 15 bit (32768 possible values). This is still a robust bitdepth for edition.
  • Even if a source image is 8-bit (e.g. a JPEG file), it's recommended to switch to 16-bit at the very beginning if heavy processing is to be applied to it, specially when converting to wide gamut profiles (e.g. Prophoto RGB).

Regards
« Last Edit: January 07, 2011, 03:45:21 PM by Guillermo Luijk » Logged

sniper
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« Reply #6 on: January 08, 2011, 05:10:56 AM »
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Just some comments:

  • Not all RAW files are >=12 bits. Compact cameras usually have 10-bit RAW files (enough for them since noise dithers risk of any posterization). The Leica M8 has 8-bit non-linearly encoded RAW files (again enough for them).
  • PS is NOT a 16-bit editing tool, it's 15-bit. As soon as we open a 16-bit file in Photoshop half the levels are lost by rounding to 15 bit (32768 possible values). This is still a robust bitdepth for edition.
  • Even if a source image is 8-bit (e.g. a JPEG file), it's recommended to switch to 16-bit at the very beginning if heavy processing is to be applied to it, specially when converting to wide gamut profiles (e.g. Prophoto RGB).

Regards

I am led to believe this only puts a 16 bit "wrapper" on the 8 bit jpeg and doesn't actually make it a real 16 bit?

Wayne
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Schewe
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« Reply #7 on: January 08, 2011, 11:32:33 AM »
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  • PS is NOT a 16-bit editing tool, it's 15-bit. As soon as we open a 16-bit file in Photoshop half the levels are lost by rounding to 15 bit (32768 possible values). This is still a robust bitdepth for edition.

Actually, PS is 15 bit plus 1 level...the range of values is 0-32768 for a total of 32769 levels...the reason being (as stated by some PS engineers) is it's helpful to have an exact middle value for processing algorithms...
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BartvanderWolf
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« Reply #8 on: January 08, 2011, 11:42:30 AM »
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Actually, PS is 15 bit plus 1 level...the range of values is 0-32768 for a total of 32769 levels...the reason being (as stated by some PS engineers) is it's helpful to have an exact middle value for processing algorithms...

There are probably other reasons as well (because 2^16-1=65535 would have the same benefit), e.g. accomodating for some overflow without loss of precision during calculations.

Cheers,
Bart
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ejmartin
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« Reply #9 on: January 08, 2011, 11:54:26 AM »
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Working with difference images would be a real pain if you didn't allow negative values.
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emil
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« Reply #10 on: January 08, 2011, 03:24:45 PM »
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I am led to believe this only puts a 16 bit "wrapper" on the 8 bit jpeg and doesn't actually make it a real 16 bit?
The point of switching to 16 bit is not making it real 16 bits, but making it more robust against strong pp.

Download this 8-bit TIFF file: 8bitposterization.tif, with 2 curves applied to a smooth gradient. If done in 16-bit mode the image remains unaltered, but if we stay in 8-bit mode a clear posterization will appear because of the 8-bit rounding caused by the first curve:


Switching to more than the original 8 bits will not improve the effective bitdepth of any resulting image, but will prevent posterization as in the extreme example above.

Regards
« Last Edit: January 08, 2011, 03:28:42 PM by Guillermo Luijk » Logged

Peter_DL
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« Reply #11 on: January 09, 2011, 09:40:48 AM »
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Great demonstration !
The curve settings are quite strong, however, it illustrates the point very well.

Thanks Guillermo.

Peter

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geodome99
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« Reply #12 on: January 15, 2011, 01:26:28 AM »
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This is one of the most widely discussed topics at seminars and industry conferences.

I had recently read a very informative article by Dan Margulis, who by the way is one of the industry's leading pioneers and was among the first individuals inducted into the Photoshop Hall of Fame.

The article was first published in September 1997 in Computer Artist Magazine and appeared in Professional Photoshop Fourth Edition in 2002 as well as the Makeready Archive, Column 25.  The article is entitled 'Resolving the Resolution Issue'.  I suggest that everyone read it.

Quoting a small portion of the article:

'As for the gradient, just because an orange
tastes good doesn’t mean that a keyboard
does. A gradient is original, first-generation
art, from which any variation is an error.
A digital photograph is anything but; it’s
already been mangled by whatever device
captured the data, not to mention whatever
screwup the user has added.'

Hope this helps clarify things a bit.
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digitaldog
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« Reply #13 on: January 16, 2011, 12:21:21 PM »
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This is one of the most widely discussed topics at seminars and industry conferences.

I had recently read a very informative article by Dan Margulis, who by the way is one of the industry's leading pioneers and was among the first individuals inducted into the Photoshop Hall of Fame.

The article was first published in September 1997 in Computer Artist Magazine and appeared in Professional Photoshop Fourth Edition in 2002 as well as the Makeready Archive, Column 25.  The article is entitled 'Resolving the Resolution Issue'.  I suggest that everyone read it.

Quoting a small portion of the article:

'As for the gradient, just because an orange
tastes good doesn’t mean that a keyboard
does. A gradient is original, first-generation
art, from which any variation is an error.
A digital photograph is anything but; it’s
already been mangled by whatever device
captured the data, not to mention whatever
screwup the user has added.'

Hope this helps clarify things a bit.

Dan’s wrong! And as another Hall of Fame member (along with Jeff Schewe who will agree with me), you can dismiss this idea of Dan’s as discussed so well here regarding his high bit challenge:
http://www.brucelindbloom.com/index.html?DanMargulis.html

So all the camera manufacturers, the scanner manufacturer’s, those that support high bit editing (Photoshop to Lightroom to Capture 1 to Bibble etc), those that provide 16-bit output to the print Path (Canon, Epson) are wrong? This is a long standing Dan belief system that only Dan and those who read and accept what he says without looking farther believe, a belief system more about getting attention than about proper digital imaging concepts.
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Andrew Rodney
Author “Color Management for Photographers”
http://digitaldog.net/
Eric Myrvaagnes
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« Reply #14 on: January 16, 2011, 01:39:52 PM »
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Oh, goody! It's been a while since Dan M has been mentioned here. He's always good for a little entertainment.

Eric
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-Eric Myrvaagnes

http://myrvaagnes.com  Visit my website. New images each season.
digitaldog
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« Reply #15 on: January 16, 2011, 02:00:31 PM »
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Oh, goody! It's been a while since Dan M has been mentioned here. He's always good for a little entertainment.

Yup, some urban legends refuse to die <g>
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Andrew Rodney
Author “Color Management for Photographers”
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geodome99
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« Reply #16 on: January 16, 2011, 02:04:37 PM »
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Pissing matches are unprofessional.

I still don't see any proof that 16 bit is that much better.
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digitaldog
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« Reply #17 on: January 16, 2011, 02:14:58 PM »
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I still don't see any proof that 16 bit is that much better.

Much better or any better?

The problem with simplistic statements about this is:
1. We have no idea where the data will be output. Dan shows an “example” in his halftone printed book that proposes to prove there is no difference to the data loss converting to and from Lab 22 times (as if the number of times one converts is key here, its not, the data loss occurs the first time in greatest number). What what about output to a fine art ink jet? An Ink jet or other output device with 2009, 2011 or 2015 technology?
2. What if the image is edited any number of times after? Do we know how well 24 bits holds up on one or 100 differing edits?
3. What about subsequent color space conversions (we have to do this at least once to print the damn thing).
4. What about the simple math that provides more bits than we can use when we do all of the above in high bit but not in 24 bit?
5. The fact that most every modern capture device provides more than 24 bit color anyway? So we should not use that data provided? Why are these devices high bit?

FWIW, years ago I did post a real image to his list that illustrated visible data loss with a simple edit, but because it was in ProPhoto RGB, the rules of the challenge changed once again and was dismissed. The Lindbloom piece illustrates that kind of tactic.
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Andrew Rodney
Author “Color Management for Photographers”
http://digitaldog.net/
geodome99
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« Reply #18 on: January 16, 2011, 02:26:19 PM »
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I'm from Missouri.

Show me.
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digitaldog
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« Reply #19 on: January 16, 2011, 02:34:52 PM »
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I'm from Missouri.

Show me.

View the example images I provided to Dan’s list years ago. They are on my idisk. 16bit challenge folder. You can even load the DNG and run the tests yourself. Render 8-bit and 16-bit, run the action to sharpen the image.

My public iDisk:

thedigitaldog

Name (lower case) public
Password (lower case) public

Public folder Password is “public” (note the first letter is NOT capitalized).

To go there via a web browser, use this URL:

http://idisk.mac.com/thedigitaldog-Public
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Andrew Rodney
Author “Color Management for Photographers”
http://digitaldog.net/
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