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Author Topic: Converting 8 bit files to 16 bit files in Photoshop CS3  (Read 9269 times)
iCanvas
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« on: April 03, 2009, 08:19:52 AM »
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Hi all,

My files were originally processed in 8 bit files years ago.  There is an option in Photoshop CS3 for converting 8 bit files to 16 bit files, but is it worth it?  Will there be any better printed quality with possibly more detail in the shadows? I know that the files will double in size and storage is not a problem for me.  Any thoughts?

Gar
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KeithR
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« Reply #1 on: April 03, 2009, 08:40:52 AM »
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Quote from: iCanvas
Hi all,

My files were originally processed in 8 bit files years ago.  There is an option in Photoshop CS3 for converting 8 bit files to 16 bit files, but is it worth it?  Will there be any better printed quality with possibly more detail in the shadows? I know that the files will double in size and storage is not a problem for me.  Any thoughts?

Gar
In a word, no. 8 bits is 8 bits. Converting to 16 bits only spreads out the 8 bits you already have. It would just increase your file size with no benefit of a true 16 bit file.
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gss
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« Reply #2 on: April 03, 2009, 09:37:35 AM »
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Quote from: KeithR
In a word, no. 8 bits is 8 bits. Converting to 16 bits only spreads out the 8 bits you already have. It would just increase your file size with no benefit of a true 16 bit file.

This is counter-intuitive to me.  I would have thought that it would depend on whether he wished to do further processing.  Doesn't converting to 16 bits before making modifications help make things 'not worse'?

Certainly if no more post is being done, then converting wouldn't help.
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Paul Sumi
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« Reply #3 on: April 03, 2009, 12:50:46 PM »
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Quote from: iCanvas
My files were originally processed in 8 bit files years ago.

Does "processed" mean that you have access to the original sources (print, neg, slide) or RAW files?  The reason I ask is that, in the intervening years, image processing and RAW conversion tools have improved.  And your own image processing skills may have made similar advances.

If this is the case, you may want to consider re-doing some or all of your images using best practices (16 bit, pro photo color  space, etc).

I have found in my own work that I am now able to properly process some RAW files that were beyond my skill and knowledge to do so when I first made the image.

Paul

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digitaldog
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« Reply #4 on: April 03, 2009, 02:10:10 PM »
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Like converting sRGB to ProPhoto RGB, the only time this is at all useful is if you're copying and pasting differing color spaces or bit depths. That is, you've got to paste 8-bit data into a 16-bit composite (or sRGB into ProPhoto RGB). Otherwise, don't waste your time.
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Andrew Rodney
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Jack Flesher
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« Reply #5 on: April 03, 2009, 04:44:29 PM »
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I usually realize a bit of improvement in working up an 8-bit sRGB file if I first convert it to 16-bit Adobe RGB using a perceptual rendering intent (with black-point compensation). I find the resulting file can be pushed around more aggressively in post without obvious issues, most notably is elimination of banding in broad areas of even hue and tonality.  It may be a relatively small gain, but I feel it is usually worth the time taken to do it for those types of files.  Personally I shoot RAW, so it isn't a regular issue for me,  but occasionally get an 8-bit sRGB from somebody wanting a large print and use the above before starting manipulations.  

Cheers,
« Last Edit: April 03, 2009, 08:47:22 PM by Jack Flesher » Logged

digitaldog
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« Reply #6 on: April 03, 2009, 04:48:34 PM »
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Quote from: Jack Flesher
I usually realize a bit of improvement in working up an 8-bit sRGB file if I first convert it to 16-bit Adobe RGB using a perceptual rendering intent (with black-point compensation). I

Interesting considering that there's no table in either profile to produce a Perceptual rendering intent. You might want to check this: set some info sample points on the image, toggle between RelCol and Perceptual, they will be the same.
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Andrew Rodney
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« Reply #7 on: April 03, 2009, 05:33:45 PM »
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Quote from: Jack Flesher
I usually realize a bit of improvement in working up an 8-bit sRGB file if I first convert it to 16-bit Adobe RGB using a perceptual rendering intent (with black-point compensation).

Unless you are using a V 4.0 color space profile with perceptual tables built in, you're just kidding yourself...
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digitaldog
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« Reply #8 on: April 03, 2009, 05:49:38 PM »
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Quote from: Schewe
Unless you are using a V 4.0 color space profile with perceptual tables built in, you're just kidding yourself...

Right, and I've found one V4 sRGB profile, but I've not found one for Adobe RGB (1998). There might be one floating around. Adobe certainly isn't installing them.
« Last Edit: April 03, 2009, 05:50:02 PM by digitaldog » Logged

Andrew Rodney
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« Reply #9 on: April 03, 2009, 06:58:52 PM »
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Sme issues are not as simple as some would like to see them. Following is for the non-religious (i.e. for those w/o preconcieved ideas of digital photography).

1. Of course, converting from 8bit to 16bit does not add anything to the image data except for higher storage requirement,

2. if several steps follow, which incure interpolations, the conversion may prevent certain losses. I would not venture to quantify the possible losses; I venture to say, that anyone quantifying or disquantifying the losses is an amateur not deserving an answer.

However, the possibility of cumulated loss (or gain due to the randomness) should not be ignored.

Example: I am creating a panorama. I am starting out with raw image frames. Normally, I am converting them in 16bit ProPhoto; assumed that I had not done so, the question is if it offers any advantage to do so afterwards.

So, what steps are involved in the coming process?

a. Warping the frames (called "stitching" by those, who don't understand it). Interpolation pure.

b. Blending the resulting frames. Interpolation pure.

c. Post processing the pano: selective contrast and brightness adjustments and sharpening. Sometimes trying to repare what has been blown in the previous steps. Anyway, lots of interpolation.

Now, one can say justifiedly, that thios is not the normal process for most photogs. However, other photogs are using their favourite HDR, sharpening or wharever pluf-ins. Again, lots of interpolation.

Now, substitute interpolation with loss of tonality/detail.
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Gabor
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« Reply #10 on: April 05, 2009, 08:20:10 PM »
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Short answer:

If you are not going to make any more adjustments to the file, converting to 16-bit serves no purpose.

If you are going to make more adjustments to the file, converting to 16-bit first thing after opening will allow you to apply more aggressive adjustments (curves, levels, etc.) before posterization or banding become a problem. Whether the difference is easily visible will vary considerably from image to image, but there is always some advantage to editing in 16-bit mode, even if the advantage is small.
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Guillermo Luijk
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« Reply #11 on: April 11, 2009, 10:42:06 PM »
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Quote from: digitaldog
Right, and I've found one V4 sRGB profile, but I've not found one for Adobe RGB (1998). There might be one floating around. Adobe certainly isn't installing them.
Andrew, is there some site with more info about these v4 profiles with Perceptual tables? for a proper Perceptual conversion from, let's say Adobe RGB to sRGB, would we need to have the AdobeRGB v4 profile, the sRGB v4 profile, or both?

BR
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digitaldog
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« Reply #12 on: April 12, 2009, 10:55:34 AM »
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Quote from: GLuijk
Andrew, is there some site with more info about these v4 profiles with Perceptual tables? for a proper Perceptual conversion from, let's say Adobe RGB to sRGB, would we need to have the AdobeRGB v4 profile, the sRGB v4 profile, or both?


http://www.color.org/v4spec.xalter
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Andrew Rodney
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tho_mas
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« Reply #13 on: April 12, 2009, 06:28:20 PM »
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Quote from: GLuijk
for a proper Perceptual conversion from, let's say Adobe RGB to sRGB, would we need to have the AdobeRGB v4 profile, the sRGB v4 profile, or both?
It's always the target profile that needs a table for perceptual conversion: http://www.colorwiki.com/wiki/Color_Management_Myths_21-25 (myth 21)

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tho_mas
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« Reply #14 on: April 12, 2009, 06:35:04 PM »
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Quote from: Jack Flesher
Personally I shoot RAW, so it isn't a regular issue for me,  but occasionally get an 8-bit sRGB from somebody wanting a large print and use the above before starting manipulations.
beside the question why someone should make more out of sRGB as it is... however you could try PhotogamutRGB for a perceptual conversion from sRGB into a larger print related color space ->
http://www.photogamut.org/E_idea.html
http://www.photogamut.org/E_ICC_profile.html


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