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Author Topic: 8 or 16 bit  (Read 10048 times)

Schewe

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Re: 8 or 16 bit
« Reply #20 on: January 16, 2011, 03:40:59 PM »

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.

See, that's the problem with the way Dan set up the argument that 16 bit doesn't offer any benefit over 8 bit.

His "rules" were, well, tuned to make 8 bit processing just about the same as 16 bit. You couldn't add a gradient based adjustment because the gradation was synthetic. You couldn't use a super-wide color space because, well, Dan doesn't believe ProPhoto RGB is a color space a professional should use. BTW, he also has stated that he doesn't think Camera Raw is a professional tool because a lack of a pure luminance based curve, so he suggests professionals process images at flat defaults and do all your tone and color correction in Photoshop (where he makes his living).

It's pretty easy to prove that using ProPhoto RGB in 8 bits/channel is suboptimal. Adobe RGB and sRGB are less bad when you start with a decent 8 bit image but you can break an image and introduce banding in both color spaces in 8 bit. You can also set up a scanner (Dan doesn't do a lot of digital capture–he's not a photographer you know). If you do base tone and color corrections in a scanner and then do light edits in sRGB or Adobe RGB on the 8 bit/channel scans, you'll prolly be ok...

Course, my preference is to use ProPhoto RGB, in 16 bit/channel, do most of my optimizing in Camera Raw (or Lightroom) and work in Photoshop in ProPhoto RGB and maintain the full 16 bit for the final images. I also print out of Photoshop using 16 bit output to my Epson printers on Mac so I never need to drop to 8 bit unless I'm preparing images for the web. I don't have banding or posterization issues in my images...YMMV.
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digitaldog

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Re: 8 or 16 bit
« Reply #21 on: January 16, 2011, 03:51:45 PM »

See, that's the problem with the way Dan set up the argument that 16 bit doesn't offer any benefit over 8 bit.

Bruce summed it up perfectly:
Quote
If one takes this technique to its logical conclusion, Dan's 16-bit challenge would become "When considering all images showing no 16-bit advantage, 16-bit images show no advantage."
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Andrew Rodney
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alain

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Re: 8 or 16 bit
« Reply #22 on: January 16, 2011, 03:52:00 PM »

This is one of the most widely discussed topics at seminars and industry conferences.
...

Probably after lots off beer.

The cost of 16-bit is so low it's a non issue. It would be foolish not to use.


I do remember 9-pin dot-matrix printers and yes it was readable,  quality wise I do prefer 600ppi laser printers.
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geodome99

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Re: 8 or 16 bit
« Reply #23 on: January 16, 2011, 03:53:26 PM »

Hi Andrew

Thanks for the link.  I will most definitely have a look.

I'm not really a Dan M advocate, or anybody else's for that matter.  I am just trying to find out the differences between the 2 ideals.

Cheers

G
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Alan Klein

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Re: 8 or 16 bit
« Reply #24 on: January 17, 2011, 12:46:19 AM »

Slightly off-topic, but is there any advantage to scanning film with a flat bed scanner using 16 bit rather than 8 bit?  Or is the scan process inaccurate enough so 8 will do?  (All the scans I did to date are 8 bit but you guys are getting me thinking I should change to 16 bit in the future.).  What will happen to my file size?  (at 8 bit, 2400 resolution,  120 film scans around 100meg.)
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digitaldog

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Re: 8 or 16 bit
« Reply #25 on: January 17, 2011, 12:57:43 PM »

Slightly off-topic, but is there any advantage to scanning film with a flat bed scanner using 16 bit rather than 8 bit?  Or is the scan process inaccurate enough so 8 will do?  (All the scans I did to date are 8 bit but you guys are getting me thinking I should change to 16 bit in the future.).  What will happen to my file size?  (at 8 bit, 2400 resolution,  120 film scans around 100meg.)

IF you were to do NO additional work on the image, if you got the scanner to scan in all corrections (which we assume is happening high bit) AND converting to the output space, there would be no advantages. But that’s a very, very unlikely scenario. Its probably the case you’ll do corrections and convert the data to multiple differing output color spaces. So you’d want to scan and save out high bit.
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Andrew Rodney
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Alan Klein

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Re: 8 or 16 bit
« Reply #26 on: January 17, 2011, 01:01:16 PM »

Would the 16 bit double or quadruble the file size?
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digitaldog

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Re: 8 or 16 bit
« Reply #27 on: January 17, 2011, 01:09:17 PM »

Would the 16 bit double or quadruble the file size?

Double.
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ErikKaffehr

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Re: 8 or 16 bit
« Reply #28 on: January 22, 2011, 02:11:41 AM »

Hi,

Yes, indeed. On the other hand 16 bits means in practice TIFF and that means fat files. When I did scanning I usually kept 16 bit TIFFs until final editing was done and saved as JPEG

...
The cost of 16-bit is so low it's a non issue. It would be foolish not to use.
...

alain

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Re: 8 or 16 bit
« Reply #29 on: January 22, 2011, 06:40:46 AM »

Hi,

Yes, indeed. On the other hand 16 bits means in practice TIFF and that means fat files. When I did scanning I usually kept 16 bit TIFFs until final editing was done and saved as JPEG

Eric

I just looked and a 2TB HDD was about 80 euro, so including 3 backupdrives where talking something in the range 240-300 euro for 1800000 megabyte usefull storage  or 9000 200 Megabyte 16-bit scans that are kept.  Scanning 9000 keepers is a large job.

When shooting RAW I just convert the keepers and those nr's aren't that high.  I only use jpeg for snapshots and some registrations where I won't do any editing after the raw-conversion.
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DeeJay

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Re: 8 or 16 bit
« Reply #30 on: January 22, 2011, 08:15:41 AM »

After posting this I worked on two of the same image. One 8bit and one 16bit.

The difference is substantial and apparent. When you play with contrast/colour, crunch the curves, the 8bit files breaks up, get choppy and bands long before the 16bit.

Having experimenting with it now I'll never retouch an 8bit file again.

« Last Edit: January 22, 2011, 10:41:12 AM by DeeJay »
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DeeJay

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Re: 8 or 16 bit
« Reply #31 on: January 22, 2011, 09:27:25 AM »

Double.

It doubles the size, but am I right in saying it more than doubles save time? Something I'm convinced that I've observed.
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alain

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Re: 8 or 16 bit
« Reply #32 on: January 23, 2011, 08:52:55 AM »

It doubles the size, but am I right in saying it more than doubles save time? Something I'm convinced that I've observed.

That depends on you're hardware and image size.  Most HDD's will be configured to buffer the writes also and those buffers are something like 16,32,64 MB on modern drives.  You're computers says that it's ready before the image is really written to disk.
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Philip Weber

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Re: 8 or 16 bit
« Reply #33 on: February 14, 2011, 07:42:13 PM »

This may be a dumb question but...

I'm working with 16-bit files out of Camera Raw, in Pro photo RGB. However, some Photoshop and Third Party Plug-ins require 8-bit files to do their work.

After I'm done, should I revert it back to a 16-bit file before flattening it as a TIFF or just leave it alone as an 8-bit file?

Thanks,
Phil
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Schewe

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Re: 8 or 16 bit
« Reply #34 on: February 15, 2011, 12:13:53 AM »

After I'm done, should I revert it back to a 16-bit file before flattening it as a TIFF or just leave it alone as an 8-bit file?

There is very, very little to be gained by re-converting to 16 bit. Going 16 to 8 bit is a one way operation– pretty much like a sex change operation...once you cut it off, you can never reattach what you cut off and expect it to work correctly.
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stewarthemley

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Re: 8 or 16 bit
« Reply #35 on: February 16, 2011, 05:15:42 AM »

There is very, very little to be gained by re-converting to 16 bit. Going 16 to 8 bit is a one way operation– pretty much like a sex change operation...once you cut it off, you can never reattach what you cut off and expect it to work correctly.

Brilliant analogy. Love it.
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bjanes

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Re: 8 or 16 bit
« Reply #37 on: February 16, 2011, 10:25:20 AM »

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

Guillermo,

A very nice demonstration, but we must remember that images taken with a real camera have noise, and the dithering produced by the noise will reduce posterization. Here is your 8 bit image with 2% noise applied in Photoshop using the Gaussian noise function.

8 bits per channel is usually sufficient for rendered reflection prints with a contrast ratio of up to 288:1 (8.2 stops) as in the ICC PRM. This assumes that you got everything right with the camera exposure.  Prints will be with us for a long time, but as higher dynamic range display methods become more common, we will need more bit depth.

Greg Ward
has calculated that 8 bit sRGB has a DR of 1.6 orders of magnitude (5.31 stops), allowing for a maximum of a 5% difference at the low (shadow) end, which is quite generous, since the average person can detect even smaller changes. Of course, this discussion applies only to luminance, and when color images are involved, one needs even more bit depth as when going from sRGB to ProPhotoRGB.

From a scientific and human perceptual viewpoint, the use 16 bpc makes sense, and one might as well use a wide gamut space such as ProPhoto to make use of the colors captured by the camera.

Regards,

Bill





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