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Author Topic: 12bit vs 14bit, once more  (Read 4614 times)
Panopeeper
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« on: March 02, 2009, 10:38:14 AM »
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I posted following on DPReview, and the majority of the respondends posted, that they don't see any difference between the 12 and 14 bit versions, and this is somewhat disturbing. The difference is small, but on my monitor it is unambiguous; it is like the difference between sharpening with slightly different parameters. If people don't see that difference, then they don't need a good camera and good lenses, do they?

Anyway, I present my finding here too, and let's see what you see.

I selected some old shots with my 40D and tried if they exhibit some advantage of the 14bit depth. I have spent considerable time on this issue, when I got the 40D, trying to prove the usefulness of the 14bit depth, but without success. My aim was to show, that posterization can arize if very fine transitions are represented with only 12 bits. No success. Though there *are* such cases, they occur by chance; at least I failed.

Now I took a different approach: perhaps the greater bit depth offers some advantage in complex, fine details, in contrast to quasy-uniform patches.

Well, nothing world-shattering, but I can say with certainty, that the difference to the advantage of 14bits is there, perceivable, though I can demonstrate it only after much pushing strongly underexposed areas. I know I am not the first having done this, but I documented it in details.

The 14bit images are not only showing more details, but they are sharper (sharpening, noise reduction are turned off, except for the minimum scene sharpening); though I guess this is the same, i.e. more details along edges conveys sharpness.

Here are two high quality JPEGs with crops of the 12bit and 14bit versions side by side:
No, they are not here; they are at the end. I don't know how to insert the attachments in between the text.

The differences can be seen much better in overlayed format; here are some TIFFs with crops from the same interesting scenery, shot at different ISOs; they are only a few hundred KB small:

http://www.panopeeper.com/Download/12vs14b...759_ISO0200.tif
http://www.panopeeper.com/Download/12vs14b...762_ISO0200.tif
http://www.panopeeper.com/Download/12vs14b...763_ISO0400.tif
http://www.panopeeper.com/Download/12vs14b...776_ISO0800.tif

Then two large twolayer TIFFs:

http://www.panopeeper.com/Download/12vs14b...777_ISO1600.tif
http://www.panopeeper.com/Download/12vs14b...829_ISO1600.tif
 
For those, who want to make their own raw conversion, I uploaded the two pairs of raw files in DNG format (I made the modification of the raw data in DNG). Processed in ACR, all adjustments are identical, except for the exposure for equalizing the brightness, as ACR did not do that on its own. Btw, the adjustment parameters are in the files, i.e. if someone loads them in ACR, one gets the same result that I got.

Please, only those should download the raw files, who really want to work with them, for my server gives me much space but not much bandwidth, and if the limit gets exceeded, then my site gets blocked for that day.

So, the DNG files (two shots, both in 12bit and 14bit format):

http://www.panopeeper.com/Download/40D0177...O1600_12bit.dng
http://www.panopeeper.com/Download/40D0177...O1600_14bit.dng

http://www.panopeeper.com/Download/40D0182...O1600_12bit.dng
http://www.panopeeper.com/Download/40D0182...O1600_14bit.dng

So, let's start searching for the easter eggs.
« Last Edit: March 02, 2009, 10:39:54 AM by Panopeeper » Logged

Gabor
fike
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« Reply #1 on: March 02, 2009, 11:55:32 AM »
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On a crummy, uncalibrated,business-monitor, the difference is noticeable at the pixel level.  I have been wondering the same thing you have on this topic.  I was wondering if you could really get any usable increase in dynamic range by making multiple exposure versions from one 14-bit raw image and then merging them to HDR.  My preliminary experiments show that the improvement is pretty minor, though maybe noticeable.  


Should we change your name to Pixel-Peeper?
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Fike, Trailpixie, or Marc Shaffer
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TrailPixie.net

I carry an M43 ILC, a couple of good lenses, and a tripod.
Panopeeper
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« Reply #2 on: March 02, 2009, 12:10:44 PM »
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Quote from: fike
Should we change your name to Pixel-Peeper?
I am a pixel peeper. The unit of digital photography is pixel, not 8x12, though paper dynosaurs have a hard time to learn this.
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Gabor
Tim Lookingbill
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« Reply #3 on: March 03, 2009, 12:07:55 AM »
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I understood the advantage of higher bit level was to reduce the appearance of posterization when editing only. If you apply a before and after tone correction curve of some sort on the samples provided I think it would be more clear as to the advantage of having a higher bit level file. Remember the preview is always in 8bit when viewing unedited images regardless of their underlying bit level of data recorded.

Now I may be misunderstanding just where the higher bit level is measured from since I've never been sure about this from all that I've read on the subject. Bit level is a data oriented concept since the preview is in 8 bit. So I have to ask is the bit level measured before or after demosaicing takes place? And at which point does the raw file once it's opened and viewed in a raw converter become 16bit or does it become 16 bit after the file is saved to tiff? IOW what underlying bit level are we at when we just edit according to an 8 bit preview in a raw converter?
« Last Edit: March 03, 2009, 12:10:59 AM by tlooknbill » Logged
Panopeeper
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« Reply #4 on: March 03, 2009, 01:01:29 AM »
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That's a lot of questions, Tim.

1. Bit depth in the raw data

Normally (i.e. if not lossily encoded) the raw data is linear, meaning that an spot with twice the illumination of another spot is represented with twice as high pixel values an the others. The bit depth limits the number of tone levels the camera can record; however, the actual number of levels is sometimes much less than the bit depth would allow (sometimes it is a fraction of the possible levels).

2. Bit depth in the preview and in JPEG

The preview embedded in the raw file is, like the "normal" JPEG created by the camera, 8 bit per channel, i.e. 24 bit per pixel, because the pixels have three components at this stage. However, the data in the JPEG is not linear; it is adjusted to the human eye's perceptivity: we can perceive tiny differences in the dark tones, but only much larger differences in the bright region. This transformation or mapping depends on the color space, but is is (mostly) a power function, like y=x^(1/2.2) in Adobe 1998 RGB.

For example if the linear data contains 4096 levels, then the first 20 levels will be projected on 14 levels (with sRGB):

0000-0019: 000, 001, 002, 002, 003, 004, 005, 006, 006, 007, 008, 009, 009, 010, 011, 012, 012, 013, 014, 014

about 20 levels are projected to a single level in the middle of the range:

2000-2019: 186, 186, 186, 186, 186, 186, 186, 186, 186, 186, 186, 186, 186, 186, 186, 186, 186, 186, 186, 187

and the last 36 levels all will become 255.

This is often called "gamma encoding" (and some innumerates are calling the linear data "linear gamma encoded").

3. The raw conversion is between these two formats. If you are creating 16bit TIFF from the raw file, then that is usually "gamma encoded", though some converters do support linear output. The 16bit data allows higher precision resulting from interpolation/averaging. It is useful for editing and conversions, as many operations involve interpolations: resizing, curves, levels, color space conversion, free transform, sharpening, etc. I guess the majority of operations includes interpolations. Note, that at this stage we are talking about three times the bit depth per pixel.

This is a highly disputed subject, just like the merit of 14bit depth in raw vs. 12bit. I convert my raw images almost always in ProPhoto RGB, 16bit, and keep them in that form (with a few layers they can become quite large; my panos need usually many hundred megabytes in compressed form). When I create a presentation version (web or printing), then I crop, resize, sharpen, flatten, add signature, convert in sRGB, and at the very end convert it in 8bit form, for JPEG or TIFF (the latter for prints).
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Gabor
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« Reply #5 on: March 03, 2009, 09:19:41 PM »
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What you are doing is invalid.

The 40D RAW files are natively 14 bit.
It cannot shoot in 12 bit RAW mode.
You are compressing or truncating the 14 bit RAW's to create 12 bit DNG's

Only the camera DSP can optimumly scale the sensor data to the RAW color space.
You have distorted the  space and the data with your compression.
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Panopeeper
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« Reply #6 on: March 03, 2009, 10:18:20 PM »
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Quote from: mhecker*
What you are doing is invalid.
...
Only the camera DSP can optimumly scale the sensor data to the RAW color space.
You have distorted the  space and the data with your compression.
I wonder how you know

a. what the camera needs to do,

b. what I can do.
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Gabor
Tim Lookingbill
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« Reply #7 on: March 04, 2009, 12:20:58 AM »
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Panopeeper,

I already pretty much understand what you wrote in responding to my last post. Sorry for the loaded questions. I guess I didn't make myself more clear since you didn't cover what I was getting at.

So to put it simply:

Can the difference between 12 bit and 14 bit captures be seen when editing a raw file in any raw converter of choice?
« Last Edit: March 04, 2009, 12:22:04 AM by tlooknbill » Logged
Panopeeper
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« Reply #8 on: March 04, 2009, 10:24:39 AM »
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Quote from: tlooknbill
Can the difference between 12 bit and 14 bit captures be seen when editing a raw file in any raw converter of choice?
Only in *extreme* circumstances. My own demonstration above is not valid; as it turned out, the difference is due to an ACR "issue" in conjunction with increasing the intensity by 5 EV.
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Gabor
douglasf13
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« Reply #9 on: March 06, 2009, 05:31:13 PM »
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Quote from: Panopeeper
I am a pixel peeper. The unit of digital photography is pixel, not 8x12, though paper dynosaurs have a hard time to learn this.

  It seems like you wouldn't use ACR if pixel-peeping is your thing, but thanks for the work.
« Last Edit: March 06, 2009, 05:32:54 PM by douglasf13 » Logged
JamesA
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« Reply #10 on: March 07, 2009, 01:06:26 PM »
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When my high end 19" CRT died, I was sad.  When I got an LCD, I was sadder still.  Where DID the tonal and colour gamuts go that I had been used to?
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Panopeeper
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« Reply #11 on: March 07, 2009, 01:20:02 PM »
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Quote from: douglasf13
It seems like you wouldn't use ACR if pixel-peeping is your thing
Pixel peeping is not "my thing", but I am not afraid of it, for I do understand it. I don't see why this would preclude using of ACR. However, real pixel peeping starts *before* ACR, in the unadultered raw image; at that stage much of the truth is visible.
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Gabor
douglasf13
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« Reply #12 on: March 07, 2009, 02:01:09 PM »
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Quote from: Panopeeper
Pixel peeping is not "my thing", but I am not afraid of it, for I do understand it. I don't see why this would preclude using of ACR. However, real pixel peeping starts *before* ACR, in the unadultered raw image; at that stage much of the truth is visible.

  Gotcha on the pixel peeping before conversion.  Makes sense.  As far as LR/ACR, from the way it implements WB (and how the level of noise depends on WB setting,) to built in NR even when set to 0, Adobe is not the way to go for pixel peeping.
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