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Author Topic: Canon 40D Dynamic Range test: 9 f-stops  (Read 37601 times)
Guillermo Luijk
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« Reply #40 on: February 19, 2008, 05:34:59 PM »
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Guillermo,

an off-topic but important subject.

I guess you borrowed the Sony A700 from someone to make the DR test, right? That camera had firmware version 2 that time. I found a horrendeous issue with that (in that shot): at ISO 200 (and where else? I have only that image) it operates only with 3000 levels in 12bit mode. With firmware v3 it goes up to 3500 (still a crap).
[a href=\"index.php?act=findpost&pid=176011\"][{POST_SNAPBACK}][/a]

I remember that we were discussing about the A700 RAW file having levels beyond 4095, but the histogram was plenty of holes. David Coffin told me such high end point in the histogram was due to 8-bit RAW decompression. They can go beyond 4095, but they will never produce more than 4095 different non-null values:

"Hi Guillermo, Now I see what's happening. It's in the sony_arw2_load_raw()function. The Sony DSLR-A700 supports two formats: packed with 12 bits per pixel, and compressed with 8 bits per pixel (a fixedcompression ratio achieved by sacrificing quality as needed). Decompressing the 8-bit data yields values from 0 to 8191. To maintain compatibility with the 12-bit packed mode, I doubled the latter. This allows the user to specify the same darkness and saturation values for both data formats." David Coffin explained."

My Canon 350D also reaches just 3000 levels in a deeply populated RAW histogram
« Last Edit: February 19, 2008, 05:35:09 PM by GLuijk » Logged

Panopeeper
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« Reply #41 on: February 19, 2008, 06:27:35 PM »
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Guillermo,

the above has nothing to do with what I referred to. In the meantime I found more shots from the firmware v1 and v2. Images with *all* ISOs have only 3000 levels, except 3200 and above, which have even less.

Then version 3 came, and Sony did not say a word, but things have changed; now there are 3500 levels. Still not stellar, but much better.

Tell the owner of the camera you used for the comparison that new firmware should be loaded. 3000 levels in a modern DSLR is a shame.
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Gabor
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« Reply #42 on: February 19, 2008, 06:32:50 PM »
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Btw, the 350D creates about 3850 levels. How did you arrive at 3000 levels?
« Last Edit: February 19, 2008, 06:33:34 PM by Panopeeper » Logged

Gabor
John Sheehy
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« Reply #43 on: February 19, 2008, 06:35:46 PM »
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Tell the owner of the camera you used for the comparison that new firmware should be loaded. 3000 levels in a modern DSLR is a shame.
[a href=\"index.php?act=findpost&pid=176062\"][{POST_SNAPBACK}][/a]

3000 unique levels is sufficient with the read noise levels at base ISO.  Most 12-bit Canon DSLRs have barely more than 3000 in most (useful) ISOs.

In this particular case, of course, the issue may not be a scaling problem but a clipping problem, in which case the 3500 levels should be recommended.
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Panopeeper
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« Reply #44 on: February 19, 2008, 07:44:40 PM »
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3000 unique levels is sufficient with the read noise levels at base ISO
No, it is not enough. This is bound to posterisation.

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Most 12-bit Canon DSLRs have barely more than 3000 in most (useful) ISOs

Maybe most of your Canon DSLRs. One of mines has 3970 levels, the other has over 15000. The very worse I know of is the 30D with only 3300 levels. The next one is the 5D with 3570; a far cry from 3000.
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Gabor
Guillermo Luijk
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« Reply #45 on: February 19, 2008, 08:06:02 PM »
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Btw, the 350D creates about 3850 levels. How did you arrive at 3000 levels?
My fault, the image under test was not fully exposed. I have taken a fully exposed ISO100 image (deep shadows to 3-channel blown highlights histogram), and got:

Filled levels:
  R: 3844 (5,9% of available in 16 bits)
  G: 3845 (5,9% of available in 16 bits)
  B: 3845 (5,9% of available in 16 bits)

Dynamic range:
  R: 3844, range [252..4095]

Don't pay attention to the RGB distinctions since my histogram program does not recognize yet the Bayer distribution, but the figures (~3850) match yours.

 that's disappointing. Does it have a higher black level or simply doesn't reach 4095?
« Last Edit: February 19, 2008, 08:19:47 PM by GLuijk » Logged

John Sheehy
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« Reply #46 on: February 19, 2008, 10:19:52 PM »
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Are you telling me the 5D has less levels than the 350D?   that's disappointing. Does it have a higher black level or simply doesn't reach 4095?
[a href=\"index.php?act=findpost&pid=176086\"][{POST_SNAPBACK}][/a]

Levels shmevels.  The levels are wrong, anyway, because of noise.

Have I not clearly demonstrated that unless the number of levels drops so low that the read noise goes well below 1.4 of those levels, that the number of levels are irrelevant?

The 5D does not have state-of-the-art read noise levels at low ISOs.  Not for Canon, anyway.  The lowest read noise on the 5D is about 2.0 ADU; higher than the 40D (translated to 12 bits) and the 400D.
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John Sheehy
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« Reply #47 on: February 19, 2008, 10:34:43 PM »
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No, it is not enough. This is bound to posterisation.

That's only true if a RAW converter shortchanges low-level RAWs in precision.  It is not the fault of the RAW data.

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Maybe most of your Canon DSLRs. One of mines has 3970 levels, the other has over 15000. The very worse I know of is the 30D with only 3300 levels. The next one is the 5D with 3570; a far cry from 3000.
[a href=\"index.php?act=findpost&pid=176084\"][{POST_SNAPBACK}][/a]

A far cry?  Log(3570/3000)/log(2) = 0.25 stops maximum, potential, of any difference (posterization difference in the deep shadows in the total absence of read noise).  There is too much read noise in any Canon, even at base ISO, for this potential to be realized.

I have *NEVER* seen posterized RAW conversions, given enough calculation precision, from any camera, except slightly in the Pentax K10D in deep shadows at ISO 100.

You should really spend 10% of the time that you do grumbling about levels, looking at the destruction noise does to potential posterization.  These are not 1982 raytraces we're looking at; we're looking at real captures dithered by noise.  We need less noise; not more levels to more accurately record noise.
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Panopeeper
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« Reply #48 on: February 19, 2008, 10:44:26 PM »
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Are you telling me the 5D has less levels than the 350D?   that's disappointing. Does it have a higher black level or simply doesn't reach 4095?

BL average 128, saturation: 3690

This low number of levels created the too good reputation of the 5D as a "low noise" camera. That's rubbish. The low noise is due to the lack of levels; there are only 12 levels for everything past the 8th EV, and this everything includes the useless noise as well.

DPR's DR analysis is based on the smoothness. I bet, with Jonathan's method, i.e. based on the analysis of retained details, the 5D would not look so good. The two methods should be used together.
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Gabor
Ray
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« Reply #49 on: February 20, 2008, 02:03:14 AM »
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BL average 128, saturation: 3690

This low number of levels created the too good reputation of the 5D as a "low noise" camera. That's rubbish. The low noise is due to the lack of levels; there are only 12 levels for everything past the 8th EV, and this everything includes the useless noise as well.

DPR's DR analysis is based on the smoothness. I bet, with Jonathan's method, i.e. based on the analysis of retained details, the 5D would not look so good. The two methods should be used together.
[a href=\"index.php?act=findpost&pid=176112\"][{POST_SNAPBACK}][/a]

I'm sure I mentioned this before, somewhere. Surely it's not just the number of levels in each pixel that counts, but the total number of pixels as well. The 5D has  50% more pixels than the 350D.
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Guillermo Luijk
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« Reply #50 on: February 20, 2008, 06:06:57 AM »
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BL average 128, saturation: 3690

This low number of levels created the too good reputation of the 5D as a "low noise" camera. That's rubbish. The low noise is due to the lack of levels; there are only 12 levels for everything past the 8th EV, and this everything includes the useless noise as well.
OK I can see that in last DCRAW version, Dave prints now the black and also saturation points he uses to scale (5D RAW):

Scaling with darkness 128, saturation 3692, and multipliers 2.015625 1.000000 1.468750 1.000000


But I have to agree with John that in terms of EV dynamic range, the difference is not so notorious and we should look at other parameters such as noise.
After all, having HALF the levels just means losing the last f-stop of the DR.
You mean the low noise of the 5D is thanks to level aggregation?
« Last Edit: February 20, 2008, 06:08:25 AM by GLuijk » Logged

John Sheehy
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« Reply #51 on: February 20, 2008, 07:58:40 AM »
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After all, having HALF the levels just means losing the last f-stop of the DR.
[a href=\"index.php?act=findpost&pid=176155\"][{POST_SNAPBACK}][/a]

And that's only if there were no noise.  Even in the absence of read noise, the DR can be limited by the maximum number of photons.
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Panopeeper
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« Reply #52 on: February 20, 2008, 11:10:11 AM »
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After all, having HALF the levels just means losing the last f-stop of the DR

What is "just" on this? Have not you noticed yet, that the advance in DR is in tenths of a stop?

Furthermore, the shadow range is not "grown up" yet. We need much more levels (but clean levels) to create better images. As of now, if you want to enhance for example the 9th stop, you have to work with 3-5 different levels; that's a joke.

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You mean the low noise of the 5D is thanks to level aggregation?

I mean I wonder how the 5D's DR would look with Jonathans method.
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Gabor
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