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Converting 8 bit images to 16 bit - any benefits?

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Old 07-24-2011, 06:02 PM
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Converting 8 bit images to 16 bit - any benefits?

In another thread I posted the following about my current belief and understanding relating to converting 8 bit files to 16 bit i.e. I doubted that any real benefits would be had and further that there may be potential to make matters worse by taking this course. Quote:
When I started using Photoshop I used to convert 8 bits to 16 bits in the belief that I would be gaining something. My revised view is that it may be possible but there are risks associated that need to be understood - I have seen/introduced posterisation into my own images which could be attributable to editing original 8 bit as 16 bit.

So now this is my current thinking. Of course I accept my thinking may be out of date, plain wrong or just a load of c**p and would welcome different views


If an image is available as anything over 8 bit then I will edit in 16 bit. This includes scanning and acquiring from DSLR. In my case I thought my DSLR was 12 bit but it is actually 12 bit compressed which I believe equates to a real bit depth of only 9.5 bits!

There is a problem when converting 8 to 16 bit which may not be seen or we are even aware of. The original 8 bit image has 256 levels when converted to 16 bit it will have 32769 (think PS is actually 15 bit hence losing 32000+ levels). This must mean that there are huge gaps in the histogram. AFAIK PS histogram of a 16 bit image has been converted to an 8 bit view therefore the gaps are probably not apparent. Depending on editing steps taken it is conceivable that the gaps will increase even more due to spreading the 8 bit level information over the new 16 bit levels?


There was some civil and polite discussion with differing views put forward; however this discussion caused a drift off topic and therefore I am starting this thread in the hope of gaining a better understanding.
Due to my comment about having experienced posterisation in the past it was requested that I post an example or two for opinion. I know that this is going to sound like a ‘cop out’ but I just cannot find the examples – I am still looking and will post if and when I find them.
As it is somewhat embarrassing to make this kind of statement and not able to show some evidence I decided that I would select an image and have a play to see if I could repeat issues I experienced by mildly abusing the image file. While I was not able to get any posterisation (probably poor choice of image due to a bland sky!) my results showed no appreciable differences between the 8 bit edit and the 16 bit edit. I do accept that the results of just one test and the conditions I chose to apply prove nothing and there are probably better ways to test and make informed conclusions. But for what it is worth this is what I did and my results.
  • Original image taken with 3Mp Fuji camera - I know, bland and uninteresting but it was the best I could find in the time frame
  • Duplicated the image and converted one to 16 bit
  • Applied the following to both 8 and 16 bit images
  • Applied levels layer and reduced Output to 100 and 155
  • New levels layer and adjusted shadows and highlights to just touch each end of histogram
  • Curves layer and applied an S curve
I scrutinised both images at 100% trying to find any differences - I was not expecting to see improvement over the original (cannot make a silk purse out of a sows ear!) of course but simply what differences. In particular I was looking for losses in the 8 bit that would no show up so much in 16 bit. I found nothing.

Then converted the 16 bit back to 8 bit and looked again - found no difference! The histograms in the second image tell the story. Left hand image 8 bit original histogram after the levels and curves adjustment. Right hand image 16 bit. Original histogram to the left. Right hand histogram after converting the image back to 8 bit.

I was a little surprised that I could not pick up anything between the 8 or 16 bit versions particularly as the 8 bit histogram looks so poor.

So as I have not had an epiphany with this short test I am left thinking either my test was woefully inadequate, my logic totally flawed, wrong type of image to highlight differences any combination of these.

Just so all is clear I am merely trying to establish what benefits if any from converting an 8 bit image to 16 bit for editing. This does not relate to the debates about 16 bit editing as 8 bit - in that case I am all for keeping in 16 bit for as long as possible and just cannot subscibe to the view that it is a waste of time

Anyone?

As I finish this I am just about to embark on the adventure of changing ISP's (tomorrow) - think I would rather visit the dentist. Hope I am not let down like my last change - 1 month without service!!!
Anyway I'll be back
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Old 07-24-2011, 08:02 PM
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Re: Converting 8 bit images to 16 bit - any benefi

Converting the original data from 8-bit to 16-bit provides nothing useful for that original data. But of course, if you paste higher bit data into that newly converted data, or build gradients, edit that data severely etc, then yes, it can be somewhat useful. The original data is suck in its state. You didn’t improve it by converting it to high bit.

The bottom line is, if you start with high bit data, keep it that way.
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Old 07-24-2011, 09:54 PM
freezehead freezehead is offline
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Re: Converting 8 bit images to 16 bit - any benefi

Yeah, I think there's no differences when you convert 8 to 16 bit 'cause what it does is just "interpolate" more values between 2 consecutive value of 256 values that 8 bit created
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Old 07-24-2011, 11:47 PM
ftp-Jeff ftp-Jeff is offline
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Re: Converting 8 bit images to 16 bit - any benefi

No, it will do nothing to help you... Depending on the job, but I mostly process out of Capture 6 into 16 bit..... Do the whole retouch until client is happy. When it is time to supply Certified proof, I then convert to 8 bit....
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Old 07-25-2011, 12:05 AM
kav kav is offline
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Re: Converting 8 bit images to 16 bit - any benefi

Quote:
Originally Posted by andrewrodney View Post
Converting the original data from 8-bit to 16-bit provides nothing useful for that original data. But of course, if you paste higher bit data into that newly converted data, or build gradients, edit that data severely etc, then yes, it can be somewhat useful. The original data is suck in its state. You didn’t improve it by converting it to high bit.

The bottom line is, if you start with high bit data, keep it that way.
In response to this I'm just wondering, how do you deal with 16 bpc mode when dealing with huge composites especially in cmyk with the use of smart objects? I know not everyone deals with this but some of us do and it can slow things significantly.
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Old 07-25-2011, 09:05 AM
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Re: Converting 8 bit images to 16 bit - any benefi

I’d do as much work as humanly possible in RGB, 16-bit, then convert to CMYK, 8-bit and move on. CMYK is an output color space for a specific print condition, so one of the very last steps would be the conversion to CMYK.
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Old 07-25-2011, 07:36 PM
RobertAsh RobertAsh is offline
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Re: Converting 8 bit images to 16 bit - any benefi

Quote:
Originally Posted by kav View Post
In response to this I'm just wondering, how do you deal with 16 bpc mode when dealing with huge composites especially in cmyk with the use of smart objects? I know not everyone deals with this but some of us do and it can slow things significantly.
I'd recommend doing some careful tests like Tony W did. If you can go through your entire workflow in 8-bit and 16-bit and see no difference in the end product to your customer then you might want to weigh whether or not for your workflow there is a practical difference.

The risk there, of course is that although you might usually be able to do the job over if you found something in rare cases, if you were in a time crunch with no time to do the job again, that would hurt. There are some workflows were 8-bit all the way through can cause banding (John Wheeler demostrated a couple of examples). So whether that applies to you workflow or not, that requires testing. I've read photographers' assessments that they don't need 16-bit. But that's their workflow, not necessarily yours.

Another alternative is to upgrade your computer - faster hard drive(s) e.g. RAID 0 or RAID 5 eSATA, more cores, faster data bus and more memory. That's what I ended up doing recently. It's definitely been worth it.

Last edited by RobertAsh; 07-26-2011 at 12:04 AM.
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Old 07-25-2011, 10:59 PM
ftp-Jeff ftp-Jeff is offline
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Re: Converting 8 bit images to 16 bit - any benefi

Definately should work in 16 bit.... Yes file sizes can be large... But the hardware out there is more than capable of handling it nowdays.
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Old 07-25-2011, 11:15 PM
kav kav is offline
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Re: Converting 8 bit images to 16 bit - any benefi

Quote:
Originally Posted by RobertAsh View Post
Another alternative is to upgrade your computer - faster hard drive(s) e.g. RAID 0 or RAID 5 eSATA, more cores, faster data base and more memory. That's what I ended up doing recently.
I wanted to some time ago. The 2009 mac pro update was absolutely dismal. They basically went from an 8 core with a ton of room for ram and cut that machine in half but adopted a new architecture. 2010 update was a spec bump + 6 core added at the top. Once again I don't like their choices for the dual socket model and the 6 core feels like it could outgrow its ram unless I used expensive 8 GB sticks. I'm waiting to see what they come out with this year. i'd like something that could hold everything in ram.

Currently a RAID system wouldn't do much for me unless I used a small internal RAID0 for scratch disk space. I plan to alleviate my scratch bottleneck (which isn't too terrible) with massive amounts of ram when I upgrade my computer. Disk speeds aren't so much the bottleneck most of the time in saving the massive files. I heard adobe made a change to make this easier but waiting for it to compress everything as it saves is the real bottleneck as it's a single threaded process.

So yeah I'm hoping for some speed increases at 16 bpc levels when I do see an upgrade. Before anyone mentions it I don't really like imacs.
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Old 07-26-2011, 12:12 AM
RobertAsh RobertAsh is offline
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Re: Converting 8 bit images to 16 bit - any benefi

Quote:
Originally Posted by kav View Post
...Currently a RAID system wouldn't do much for me unless I used a small internal RAID0 for scratch disk space. I plan to alleviate my scratch bottleneck (which isn't too terrible) with massive amounts of ram when I upgrade my computer. Disk speeds aren't so much the bottleneck most of the time in saving the massive files.
Not necessarily true. Disk speeds can be the single biggest bottlenecks when reading or saving files. Or when Photoshop uses cache on disk (which is does a lot of). For large files RAID-0 can cut in half the times you spend reading and writing files.

For me, many of my files go into 100s of MB. A few are 1 GB in size or larger. So RAID 0 helps a lot.

What you may be seeing is a Photoshop quirk in its design. I found that when I doubled my memory my files save times vastly improved. Ordinarily that shouldn't be the case, but Photoshop writes a lot to and from disk. So if you don't enough memory it will clog your system with all kinds of changed data, writing to and reading from the disk cache.

But even with that out of the way (memory, yes, was the worst bottleneck in this case) my new, shorter save and read times would double if I wasn't using RAID 0.
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