Ad
Ad
Ad
Pages: [1] 2 3 »   Bottom of Page
Print
Author Topic: The useful bit depth  (Read 23722 times)
Panopeeper
Sr. Member
****
Offline Offline

Posts: 1805


« on: November 29, 2007, 08:01:49 PM »
ReplyReply

There is a new topc on the Digital Cameras, Backs and Shooting Techniques forum about 16-bit DSLRs. Someone stated, that even MF cameras don't utilize the 16 bit range.


Has someone conducted a thorough test to determine, if the full bit depth of the camera is in fact useful?

Alternatively, does anyone have images with very high dynamic range and the full usage of the bit depth, suitable for a pixel peeping analysis?

Such a demo image should contain very fine, well defined structure in the bright as well as dark areas and exposed to the right ( and then +4EV :-). I found silk flowers particularly suitable for such analysis.
« Last Edit: November 29, 2007, 08:02:05 PM by Panopeeper » Logged

Gabor
amsp
Sr. Member
****
Offline Offline

Posts: 778


« Reply #1 on: November 29, 2007, 08:31:07 PM »
ReplyReply

Here's a crazy idea, let's go out and do some actual photography instead
« Last Edit: November 29, 2007, 08:32:06 PM by amsp » Logged
bjanes
Sr. Member
****
Offline Offline

Posts: 2714



« Reply #2 on: November 29, 2007, 08:49:51 PM »
ReplyReply

Quote
There is a new topc on the Digital Cameras, Backs and Shooting Techniques forum about 16-bit DSLRs. Someone stated, that even MF cameras don't utilize the 16 bit range.
Has someone conducted a thorough test to determine, if the full bit depth of the camera is in fact useful?

Alternatively, does anyone have images with very high dynamic range and the full usage of the bit depth, suitable for a pixel peeping analysis?

Such a demo image should contain very fine, well defined structure in the bright as well as dark areas and exposed to the right ( and then +4EV :-). I found silk flowers particularly suitable for such analysis.
[{POST_SNAPBACK}][/a]

Lacking test data, why not just look at the published specs from Kodak and Dalsa, who make the chips used in these backs. They claim 70-72 db or 12 f/stops. The Nikon D3 can do around 11.6 stops in tests by [a href=\"http://forums.dpreview.com/forums/read.asp?forum=1021&message=25627719]EJ Martin[/url].

He quite properly notes, "Beware that other criterion for evaluating dynamic range are used by some. For instance, dpreview and imaging-resource photograph step charts and analyze the result after running the image through raw conversion. While perhaps more applicable to the end user's aims, this approach convolves the properties of the camera with those of the raw conversion software, and so you have to ask how much of the result is attributable to the camera and how much to the raw conversion software being used. To my mind, direct measurement of the raw data without raw conversion (which is what I did) gives an unambiguous measure of the camera's capabilities."
« Last Edit: November 29, 2007, 08:50:45 PM by bjanes » Logged
Panopeeper
Sr. Member
****
Offline Offline

Posts: 1805


« Reply #3 on: November 29, 2007, 09:08:11 PM »
ReplyReply

Quote
They claim 70-72 db or 12 f/stops

This says nothing about the actually used bit depth. If we apply the "1% law", then 12 stops could utilize even 17 bits (ignoring the question,how one would use the result).
Logged

Gabor
bjanes
Sr. Member
****
Offline Offline

Posts: 2714



« Reply #4 on: November 29, 2007, 10:31:45 PM »
ReplyReply

Quote
This says nothing about the actually used bit depth. If we apply the "1% law", then 12 stops could utilize even 17 bits (ignoring the question,how one would use the result).
[{POST_SNAPBACK}][/a]

To encode a DR of 12 stops with integer gamma 1 encoding only takes 12 bits. That would leave only 1 level in the darkest f/stop. You could use a 17 bit ADC, and then 12th f/stop would contain 32 levels, well short of your goal. However, the dynamic range is determined by the noise floor in most situations, rather then by running out of levels. As you state, the result might not be usable because of noise.

With linear encoding, you can not get a 1% error across the entire range, since the relative error is not constant, but increases at the lower end of the scale. For a constant 1% error, you would need to use log encoding. See this [a href=\"http://www.anyhere.com/gward/hdrenc/hdr_encodings.html]post[/url].

For example, an error of 1 pixel value would have minimal significance in the highlights where the average pixel value might be 250 and the relative error 0.4%. In the shadows at a pixel value of 10, it would be 10%.
« Last Edit: November 29, 2007, 10:51:32 PM by bjanes » Logged
Panopeeper
Sr. Member
****
Offline Offline

Posts: 1805


« Reply #5 on: November 29, 2007, 11:28:44 PM »
ReplyReply

Quote
With linear encoding, you can not get a 1% error across the entire range

With the "1% law" I was referring to the claim regarding the minimum difference between lightnesses in order to be perceivable.
Logged

Gabor
jimgolden
Sr. Member
****
Offline Offline

Posts: 405


WWW
« Reply #6 on: November 29, 2007, 11:47:01 PM »
ReplyReply

Quote
Here's a crazy idea, let's go out and do some actual photography instead
[a href=\"index.php?act=findpost&pid=157141\"][{POST_SNAPBACK}][/a]


HEAVENS NO!!!!
Logged
rainer_v
Sr. Member
****
Offline Offline

Posts: 1120


WWW
« Reply #7 on: November 30, 2007, 12:59:46 AM »
ReplyReply

phase-leaf-hasselblad-sinar have 16bit and use 14bit. two bits are "unused".
Logged

rainer viertlböck
architecture photographer
munich / germany

www.tangential.de
TechTalk
Sr. Member
****
Offline Offline

Posts: 295


« Reply #8 on: November 30, 2007, 02:52:15 AM »
ReplyReply

Here's another wild idea. How about people that are interested in dynamic range and bit-depth go out and pick up a book to learn something about the subject before discussing it on a message board. Once they discover that analog dynamic range and digital bit-depth are two completely separate things (one being a measurement of data and the other a resolution scale applied to collected data) they will understand why you want 16-bits of resolution in a 12-stop dynamic range image.

Simply put–you get more tonal levels in each f-stop of image data. This becomes increasingly important as you move down the brightness scale and the number of levels become increasingly smaller in the shadow areas. The "unused" bits of data are the ones that you don't want to use because they have the fewest number of levels and is where banding occurs.
Logged
amsp
Sr. Member
****
Offline Offline

Posts: 778


« Reply #9 on: November 30, 2007, 04:35:36 AM »
ReplyReply

Quote
HEAVENS NO!!!!
[a href=\"index.php?act=findpost&pid=157168\"][{POST_SNAPBACK}][/a]

 
Logged
jpop
Newbie
*
Offline Offline

Posts: 20


« Reply #10 on: November 30, 2007, 05:47:14 AM »
ReplyReply

Quote
Simply put–you get more tonal levels in each f-stop of image data. This becomes increasingly important as you move down the brightness scale and the number of levels become increasingly smaller in the shadow areas. The "unused" bits of data are the ones that you don't want to use because they have the fewest number of levels and is where banding occurs.
[a href=\"index.php?act=findpost&pid=157191\"][{POST_SNAPBACK}][/a]

Perhaps even a little simpler is that Dynamic Range is how big your Pizza is and Bit Depth is simply how many slices you cut it into.  Cutting a 6" pizza in half and again cutting the half in half and so on continually leaves a smaller and smaller slice.  A larger pizza (Dynamic Range) will leave you with larger slices through the same process and something that might fill your belly up.
Logged

John Popp
Dodd Camera
Professional Division
John Sheehy
Sr. Member
****
Offline Offline

Posts: 838


« Reply #11 on: November 30, 2007, 07:58:13 AM »
ReplyReply

Quote
Here's another wild idea. How about people that are interested in dynamic range and bit-depth go out and pick up a book to learn something about the subject before discussing it on a message board. Once they discover that analog dynamic range and digital bit-depth are two completely separate things (one being a measurement of data and the other a resolution scale applied to collected data) they will understand why you want 16-bits of resolution in a 12-stop dynamic range image.

Simply put–you get more tonal levels in each f-stop of image data. This becomes increasingly important as you move down the brightness scale and the number of levels become increasingly smaller in the shadow areas. The "unused" bits of data are the ones that you don't want to use because they have the fewest number of levels and is where banding occurs.
[a href=\"index.php?act=findpost&pid=157191\"][{POST_SNAPBACK}][/a]

There is no countour banding occuring in any digital camera's RAW data, if it is at least 12 bits.  There is far too much noise for bit depth to be a significant limitation.  All countour banding or posterization you see comes from conversion routines and limitations of the display.

There really is no real world place for your theory to apply, except in computer-generated graphics.
Logged
John Sheehy
Sr. Member
****
Offline Offline

Posts: 838


« Reply #12 on: November 30, 2007, 08:01:58 AM »
ReplyReply

Quote
Perhaps even a little simpler is that Dynamic Range is how big your Pizza is and Bit Depth is simply how many slices you cut it into.  Cutting a 6" pizza in half and again cutting the half in half and so on continually leaves a smaller and smaller slice.  A larger pizza (Dynamic Range) will leave you with larger slices through the same process and something that might fill your belly up.
[a href=\"index.php?act=findpost&pid=157219\"][{POST_SNAPBACK}][/a]

You have succeeded in making me hungry.

However, your analogy doesn't work.  DR has nothing to do with absolute size, or breakdown.  It's about the ratio of maximum recordable signal, to the lowest usable signal.  The lowest usable *could*, theoretically, be limited by the number of levels, but in reality, it is mainly determined by analog noise.
Logged
bjanes
Sr. Member
****
Offline Offline

Posts: 2714



« Reply #13 on: November 30, 2007, 08:54:58 AM »
ReplyReply

Quote
Here's another wild idea. How about people that are interested in dynamic range and bit-depth go out and pick up a book to learn something about the subject before discussing it on a message board. Once they discover that analog dynamic range and digital bit-depth are two completely separate things (one being a measurement of data and the other a resolution scale applied to collected data) they will understand why you want 16-bits of resolution in a 12-stop dynamic range image.

Simply put–you get more tonal levels in each f-stop of image data. This becomes increasingly important as you move down the brightness scale and the number of levels become increasingly smaller in the shadow areas. The "unused" bits of data are the ones that you don't want to use because they have the fewest number of levels and is where banding occurs.
[{POST_SNAPBACK}][/a]

An excellent post. Analog DR and bit depth are two separate things, but they are related in that to record a given DR, a minimum bit depth is needed. The number of levels required in the darkest f/stop of a given DR is also determined by bit depth. [a href=\"http://www.normankoren.com/digital_tonality.html]Norman Koren[/url] discusses these concepts on his web site. Since the eye is less sensitive to levels in the darkest f/stop, he suggests that 8 levels are need there to prevent banding.

This chart illustrates these concepts for 12, 14, and 16 bit images with a linear tone curve. For a 12 bit image the maximum DR is 12 stops, but there is only one level in the darkest f/stop and the data here would not be usable. If 8 levels are required in the darkest f/stop for a usable image, then the DR is 9 stops max. The f/stops where there are insufficient levels are shown in red in my chart. Usable DR is related to bit depth, but the bit depth will be of no avail if noise obscured any visible detail in the shadows.



However, the engineering definition of DR is full well capacity/read noise, usually expressed in electrons, but since sensors are linear, one could also use ADU (analog to digital units, i.e. raw data numbers).

An example may help to clarify things. I will use the Nikon D200 for which I have data, but the same considerations would apply to medium format digital cameras for which the chip manufacturers supply data.

The full well capacity and read noise for the D200 are supplied by Roger Clark and are shown in the table below. By this definition, the D200 has 11.7 stops of DR.



However, this DR is overoptimistic for photographic purposes. First of all, the DR of the image convolves the DR of the camera and that of the raw converter, and some DR is lost during the conversion. Secondly, the photographic DR is determined by how much noise you can tolerate in the shadows. One can photograph a Stouffer step wedge and determine DR with Imatest Stepchart. The results are shown below.



The camera can detect 11.6 stops of DR, which is consistent with the engineering definition. However, for a high quality photographic image the effective DR is only 6.51 stops.

Data for the KAF 39000 chip used in some high end medium format backs are published by Kodak.

Full well is 60K electrons and read noise is 16 electrons, giving a DR of 71.4 db or 11.9 f/stops, not that much different from the D200. The DR for excellent quality photographic images would be less. I have not seen actual test results, but from a consideration of theory, I think the DR advantages of medium format may be overblown. This does not take the noise spectrum into account. With a 39K pixel image, the noise will be at a higher frequency and less objectionable to the eye than with a 10K pixel image, where the noise pattern will be coarser. In the end, one must confirm the image quality with actual photographic tests.

Bill
« Last Edit: November 30, 2007, 09:15:25 AM by bjanes » Logged
EricWHiss
Sr. Member
****
Offline Offline

Posts: 2305



WWW
« Reply #14 on: November 30, 2007, 11:21:58 AM »
ReplyReply

Quote
... By this definition, the D200 has 11.7 stops of DR.


However, this DR is overoptimistic for photographic purposes.

Full well is 60K electrons and read noise is 16 electrons, giving a DR of 71.4 db or 11.9 f/stops, not that much different from the D200.

Bill
[a href=\"index.php?act=findpost&pid=157253\"][{POST_SNAPBACK}][/a]

Hi Bill,
Definitely lot's of information, but the point to drive home is the 'useful' DR is rarely the max theoretical amount and often more like half that amount. This is where MFDB excels over DSLR since more of the max DR is usable. Perhaps up to 3-4 stops more in fact.

I have a stoufer transmission step wedge and Imatest, and have tested my canon 5D, and friends 1DIII, Leica DMR.  The leica has a 1.5 stop real useable advantage over the canon 1DIII and perhaps 2 over the 5D.  My phase p20 which I haven't tested but can see from side by side images taken in studio must have about a 1.5 stop advantage over the Leica which means perhaps 3 usable stops over the Canon 1DIII (when both cameras are set to base ISO).

Eric
Logged

Authorized Rolleiflex Dealer:
Find product information, download user manuals, or purchase online - Rolleiflex USA
rainer_v
Sr. Member
****
Offline Offline

Posts: 1120


WWW
« Reply #15 on: November 30, 2007, 11:24:27 AM »
ReplyReply

Quote
Hi Bill,
Definitely lot's of information, but the point to drive home is the 'useful' DR is rarely the max theoretical amount and often more like half that amount. This is where MFDB excels over DSLR since more of the max DR is usable. Perhaps up to 3-4 stops more in fact.

I have a stoufer transmission step wedge and Imatest, and have tested my canon 5D, and friends 1DIII, Leica DMR.  The leica has a 1.5 stop real useable advantage over the canon 1DIII and perhaps 2 over the 5D.  My phase p20 which I haven't tested but can see from side by side images taken in studio must have about a 1.5 stop advantage over the Leica which means perhaps 3 usable stops over the Canon 1DIII (when both cameras are set to base ISO).

Eric
[a href=\"index.php?act=findpost&pid=157285\"][{POST_SNAPBACK}][/a]
and what about the tests where are over 11 stops measured for the canon 1d3 + 1ds3 ?
« Last Edit: November 30, 2007, 12:33:04 PM by rainer_v » Logged

rainer viertlböck
architecture photographer
munich / germany

www.tangential.de
Panopeeper
Sr. Member
****
Offline Offline

Posts: 1805


« Reply #16 on: November 30, 2007, 11:30:20 AM »
ReplyReply

Quote
The "unused" bits of data are the ones that you don't want to use because they have the fewest number of levels and is where banding occurs

There are no "unused bits" but unused levels. For example the Phase One P45+ fills all bits if exposed properly, i.e. it creates 65535 levels.

Of course most of those levels will be mapped on the same value.

Re banding: I have yet to see a (raw) image, which shows banding due to the lack of levels.

Example: the Canon 1DMkII (12bit) often showed banding in the sky, and there were hopes that the 1DMkII with 14bit will solve this. I found, that the banding was not due to the lack of levels. The MkIII too shows banding.
Logged

Gabor
EricWHiss
Sr. Member
****
Offline Offline

Posts: 2305



WWW
« Reply #17 on: November 30, 2007, 02:41:41 PM »
ReplyReply

Quote
and what about the tests where are over 11 stops measured for the canon 1d3 + 1ds3 ?
[a href=\"index.php?act=findpost&pid=157286\"][{POST_SNAPBACK}][/a]


It's a real number but not so useful for real life photography.  It's kind of like saying that a 10 mega pix camera is equivalent to say a 10 mega pix Leica M8.    Sure the amount of pixels are the same, but that's where the comparison ends.  A whole lot of cameras and most MFDB have max DR in the 11-12 stop range - and what I am saying is those numbers are misleading.   The numbers are calculated according the technical definition of the word, which was not developed with photography in mind.

That's why Imatest reports DR in 3 different sets of numbers - the highest or max will compare to the theoretical specs but is not useful for photographers as Bill notes in his post above.  

In my own tests the 1DIII had more max DR than the Leica DMR but  fully 1.5 stops less 'usable' DR.  You actually can see this amount of difference in the images pretty easily.   I can not say anything about the 1DsIII because I haven't tested it - I am only guessing it will be similar.
« Last Edit: November 30, 2007, 02:43:15 PM by EricWHiss » Logged

Authorized Rolleiflex Dealer:
Find product information, download user manuals, or purchase online - Rolleiflex USA
Anthony R
Sr. Member
****
Offline Offline

Posts: 251


« Reply #18 on: November 30, 2007, 03:34:22 PM »
ReplyReply

I'm convinced that there are MAYBE three photographers on this entire forum, and one of them runs the board. It seems that everyone else is a gearhead techno scientist.
Logged
Panopeeper
Sr. Member
****
Offline Offline

Posts: 1805


« Reply #19 on: November 30, 2007, 04:07:05 PM »
ReplyReply

Quote
I'm convinced that there are MAYBE three photographers on this entire forum, and one of them runs the board. It seems that everyone else is a gearhead techno scientist.

Here is a surprize: this section of the forums is called Equipment & Techniques.
Logged

Gabor
Pages: [1] 2 3 »   Top of Page
Print
Jump to:  

Ad
Ad
Ad