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Author Topic: Leica M Monochrom review  (Read 18850 times)
BartvanderWolf
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« Reply #60 on: May 12, 2012, 12:40:39 PM »
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To me the 80% of Nyquist would mean that 80% of the linear resolution of the sensor is the true resolution. This means that in terms of megapixels 80%*80%=64% of the sensors megapixels correspond to the true resolution of the sensor.

Hi Hans,

Unfortunately a simple and objective testshot of a testchart will demonstrate that it's not the 'true' resolution, but something subjective and that makes it a hard to use metric for comparisons (a bit like the Foveon X3 claim, not based on reality).

Cheers,
Bart
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Hans Kruse
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« Reply #61 on: May 12, 2012, 01:34:08 PM »
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So what is the true resolution of a Bayer filter camera compared to a non Bayer filter camera? Wink
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BartvanderWolf
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« Reply #62 on: May 12, 2012, 02:03:09 PM »
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So what is the true resolution of a Bayer filter camera compared to a non Bayer filter camera? Wink

For luminance, Bayer CFA or not, close to (90-99% of) the Nyquist frequency (which is determined by the sensel pitch), and for chrominance it's the same or down to almost half (depending on the actual colors and their luminance contribution). The exact limiting resolution also depends on the subject contrast.

If you want the actual number, that varies and depends on how a particular lens and sensor (with or without OLPF, and/or microlenses) interact. The resulting system MTF curve will reveal that, and can be derived from a suitable test target (such as the one I proposed here, but there are also others). The test with the D800 versus the D800E confimed that, as did other tests (first lens tested there resolved 95.8% of Nyquist, on a Bayer CFA filtered sensor) here on LuLa with that test target. The Raw converter one uses also makes some difference.

In general, the non-Bayer CFA camera could have a benefit of a few percent, only a few (given how much a CFA filtered camera can resolve).

Cheers,
Bart
« Last Edit: May 12, 2012, 04:22:14 PM by BartvanderWolf » Logged
BJL
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« Reply #63 on: May 12, 2012, 02:04:27 PM »
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So what is the true resolution of a Bayer filter camera compared to a non Bayer filter camera? Wink
Taking numbers from posts in this forum, the answer is that the use of a Bayer CFA reduces resolution to between 70% and 96.5% of what you would get without, depending on how you define and measure "resolution". (Unless you are a hard-core Foveonist using red-blue resolution test patterns, in which case the one true answer is 50%).

With the various ways that resolution can be quantified, (such as 50% MTF or the visible limit of seeing any contrast on the image of a high contrast test pattern, which is more like 5% MTF), saying anything more precise will draw criticism from one side of the other.

Given the imprecision, and the utter unimportance to artistic photography  of being more precise, I will go with 4/5ths of the linear resolution, 2/3rds of the effective pixel count. I like these small, simple fractions because they avoid the false veneer of precision given by percentages and numbers cited to three decimal places.

In fact, photography has a wonderful and familiar unit for measuring fractional changes in aperture size, sensitivity and such: the "stop", for a linear factor of 1.4 and area or time factor of two. So I declare that use of a CFA costs about 1/2 stop of resolution.

P. S. Bart is, I believe, using the "barely visible on a test pattern" criterion, which gives the upper end of my numerical range, minimizing the resolution loss cause by the CFA.
« Last Edit: May 12, 2012, 02:07:12 PM by BJL » Logged
dreed
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« Reply #64 on: May 12, 2012, 02:04:34 PM »
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So what is the true resolution of a Bayer filter camera compared to a non Bayer filter camera? Wink

I think what people are trying to say is that...

For bayer, "effective MP" = 2/3(bayerMP)
For B&W, "effecitve MP" = "MP"

And the other way is if...
if a camera has x MP in a bayer array and another camera has x MP in a B&W sensor, then the B&W sensor is equivalent to 3/2(x) in a bayer matrix.

So a 36MP bayer is more realisticly a 24MP sensor, or at least produces the same amount of detail as would a 24MP B&W sensor.

I think I got that right :*)
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lenelg
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« Reply #65 on: May 12, 2012, 02:19:57 PM »
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And back in the 70´s, my extreme audiophile friend would plug his new amplifier into an oscilloscope instead of a loudspeaker, and fall into rapture watching the beautiful waveform, not bothering to listen to the music..
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prairiewing
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« Reply #66 on: May 12, 2012, 03:54:42 PM »
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Mr. Reichmann has the eloquence to communicate technical details in an intuitive manner, and especially this makes these articles stand out. This is what good teaching is about. Absolute details are not neccessary in this context: informative, insightful articles about photography.

As a photographer I completely agree and thank you for stating it so well.
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Pat Gerlach
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« Reply #67 on: May 13, 2012, 01:31:58 AM »
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There seems to be a lot of confusion in this thread about what's true or not, and what's exaggerated or not, and who's an expert or not.

Let's get down to basic principles. A red pixel in the Bayer type system has to block both green and blue light. The green pixel has to block both blue and red light, and so on.

If there were no overlap between the 3 primary colors, as much as 2/3rds of the light impinging upon the sensor would be blocked. However, there is an overlap, so the net effect of removing the color filter array is probably about one stop more light reaching the sensor with any given exposure.

If one were to remove the CFA from any Bayer type sensor, I therefore presume the manufacturer could raise base ISO by one full stop, yet still retain the same SNR and DR.

If the D800 were not only offered with an option of no AA filter, but also the option of no CFA filter, then the CFA-less version (D800BW) would have 14 stops of DR at ISO 200, instead of ISO 100, and would have greater resolution by a degree which exceeds the difference between the D800 and D800E.

Anyone care to dispute that?  Grin
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sandymc
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« Reply #68 on: May 13, 2012, 04:58:50 AM »
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There seems to be a lot of confusion in this thread about what's true or not, and what's exaggerated or not, and who's an expert or not.

Let's get down to basic principles. A red pixel in the Bayer type system has to block both green and blue light. The green pixel has to block both blue and red light, and so on.

If there were no overlap between the 3 primary colors, as much as 2/3rds of the light impinging upon the sensor would be blocked. However, there is an overlap, so the net effect of removing the color filter array is probably about one stop more light reaching the sensor with any given exposure.

If one were to remove the CFA from any Bayer type sensor, I therefore presume the manufacturer could raise base ISO by one full stop, yet still retain the same SNR and DR.

If the D800 were not only offered with an option of no AA filter, but also the option of no CFA filter, then the CFA-less version (D800BW) would have 14 stops of DR at ISO 200, instead of ISO 100, and would have greater resolution by a degree which exceeds the difference between the D800 and D800E.

Anyone care to dispute that?  Grin

For a practical sensor, no, that's probably not right. It assumes that a monochrome sensor would not have a filter, which is probably wrong. You could have a "naked" sensor, but there are at least two reasons why there probably would be a filter: (a) varying sensitivity to wavelength of the sensor itself (usually corrected for by the matrix in raw processing of a CFA sensor, but there's no matrix here). Also (b) human's perception of luminance differs by color. If you don't filter to get the sensor output to conform to what us humans perceive as luminance, the images will appear "muddy" or "wrong".

So you would probably need a single color filter (versus a 4 color bayer filter) on a mono sensor. It should certainly pass more light in total than a bayer array, but not 100%. This would be a design trade-off for the manufacturer - more sensitivity versus a more natural color response. You would also hopefully have a IR filter, else you'd end up with out-of-focus IR contamination blurring your otherwise beautiful high-res image.

In fact, somewhat ironically, the most important characteristic of a monochrome sensor is probably its color response. So, I certainly hope that the M Monochrom has a filter of some sort. Hopefully Leica have tuned the M Monochrom to be similar to some of the classic B&W films. Sad that this aspect was entirely missed in the review.

This, BTW, was probably what Leica were alluding to when they talked about it being the M Monochrom being more than just a M9 without the bayer array.

Sandy

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Aku Ankka
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« Reply #69 on: May 13, 2012, 05:38:55 AM »
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I think what people are trying to say is that...

For bayer, "effective MP" = 2/3(bayerMP)
For B&W, "effecitve MP" = "MP"

And the other way is if...
if a camera has x MP in a bayer array and another camera has x MP in a B&W sensor, then the B&W sensor is equivalent to 3/2(x) in a bayer matrix.

So a 36MP bayer is more realisticly a 24MP sensor, or at least produces the same amount of detail as would a 24MP B&W sensor.

I think I got that right :*)

The problem here is that the 2/3 guess is significantly wrong as it should be about 80% or more.
Nitpicking? Maybe, but when dealing with numbers, having proper numbers is better than the wrong ones, especially since we humans tend to round in a way that suits us and after a few such roundings the figures are way off...

Anyhow, using megapixel equivalents is a bit weird IMHO.
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Aku Ankka
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« Reply #70 on: May 13, 2012, 05:49:09 AM »
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I do not understand why one person would choose to challenge the statements of an easily identifiable person while choosing to hide anonymously behind a fake name.  What do you have to hide?  Or, are you afraid of something?  You would gain a lot of credibility by being brave and come out of hiding.  Be brave young duck!   Cool

Sorry, I'm a coward and I do have a valid reason for hiding under an assumed name.

And I for example pointed at Barts test results which are scientific evidence.

Besides, since when the name or person of the author has been relevant to the factuality of the content? Or is is only content one doesn't like that can be dismissed unless the person reveals his real identity? I could just as well use an alias which would sound like a real persons name - you'd not be able to critizice the content because of the anonimity, but would that be more honest from me?
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lumpidu
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« Reply #71 on: May 13, 2012, 07:16:18 AM »
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Hi,

independent on the theories of some experts, I read here: German Article On Heise-Photo.de, that new base ISO of 320 of the M9M to be the real hint at how many photones the Bayer Array takes away. They stated ~50 %, as those transmission curves of the Bayer array overlap. This would explain the increae of the base ISO from ISO 160 to ISO 320 from the M9 to the M9M.
There was also a hint on the same page, that Leica uses in fact "filters", so I suppose these are U/V and/or I/R filters.

Michael: what about tests for IR/UV responsiveness of the M9M? Any hints about that from your sources ?
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Bryan Conner
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« Reply #72 on: May 13, 2012, 08:02:43 AM »
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Besides, since when the name or person of the author has been relevant to the factuality of the content? Or is is only content one doesn't like that can be dismissed unless the person reveals his real identity? I could just as well use an alias which would sound like a real persons name - you'd not be able to critizice the content because of the anonimity, but would that be more honest from me?


Yes, facts are facts.  But, when I read comments from a person who does not believe in himself enough to stand behind his own information with his own name, then why should I believe in what he says.  Credibility is questioned in the beginning...in a very big way.  I do not generally believe everything that anyone says.  I will do varying amounts of research for myself depending on the credibility of the source.  I definitely trust Michael Reichmann's information much more than I trust an anonymous source calling himself a Finnish translation of Donald Duck.  As far as the information goes, this nitpicking over numbers is not important to me.  As a matter of fact, I have already forgotten the numbers.  But, I do remember and value the basic gist of Michael's article.
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BJL
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« Reply #73 on: May 13, 2012, 08:29:26 AM »
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If one were to remove the CFA from any Bayer type sensor, I therefore presume the manufacturer could raise base ISO by one full stop, yet still retain the same SNR and DR.
Basically yes, except that it is a matter of definition not choice when it comes to doubling the ISO saturation based sensitivity (what is so often refered to as base ISO, but I prefer to use the proper wording as in the ISO's documents, like ISO12232).

1. The CFA does indeed cause a rough halving of the amount of light reaching the photosites, the Quantum Efficiency, as can be seen for Kodak sensors similar to those used by Leica in Kodak's online spec documents. EDIT: some sensors like the KAF-8300 even come in both color and monochrome versions, so the QE specs are highly comparable.
Short form: http://www.kodak.com/ek/uploadedFiles/Content/Small_Business/Images_Sensor_Solutions/Datasheets(pdfs)/KAF-8300ProductSummary.pdf
Log form with graphs of QE vs wavelength of light for the color version:
http://www.kodak.com/ek/uploadedFiles/Content/Small_Business/Images_Sensor_Solutions/Datasheets(pdfs)/KAF-8300LongSpec.pdf


2. Thus, doing without the CFA gives saturation of wells with about half the exposure (e.g. half the shutter speed at equal aperture with the same lighting) and this by the ISO:12232 definition of saturation based sensitivity would double that so-called base ISO speed.

Indeed this is what is seen with the Leica MM: its base sensitivity is 320, compared to 160 for the M9, with exposure index on the MM being a "push", overexposing and losing one stop of highlight headroom in exchange for better shadow handling.
« Last Edit: May 13, 2012, 08:34:58 AM by BJL » Logged
Petrus
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« Reply #74 on: May 13, 2012, 09:34:26 AM »
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Indeed this is what is seen with the Leica MM: its base sensitivity is 320, compared to 160 for the M9, with exposure index on the MM being a "push", overexposing and losing one stop of highlight headroom in exchange for better shadow handling.

It seems, from looking at he published DR graphs of digital cameras (have not seen one from this B&W sensor yet), that there really is only one "real ISO speed" and high ISOs are manufactured by underexposure and sacrificing DR. Just underexpose a picture at base ISO about 4 stops and correct in LR and PS. It will turn out looking just about the same as one shot at 4 stops higher ISO. This Leica has only 10000 as the highest ISO, so does that mean that the sensor DR is quite small, as they do not dare to raise ISO higher than that? I have not seen any proper tests of resolution and DR yet.
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BJL
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« Reply #75 on: May 13, 2012, 09:51:53 AM »
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It seems, from looking at he published DR graphs of digital cameras (have not seen one from this B&W sensor yet), that there really is only one "real ISO speed" and high ISOs are manufactured by underexposure and sacrificing DR.
There is a lot of ambiguity in the phrase "ISO speed", which is why I try to refer to the multiple different measures of sensitivity and exposure index in the actual ISO standard 12232.

With film, the familiar speed measure was roughly the maximum exposure index (minimum amount of light delivered to the film) that gave adequate shadow handling (loosely: noise floor four stops below the mid-tones).

The closest counterpart to that in the ISO standard for electonic sensors is the two noise based measures of maximum usable exposure index, S40 and S10. These are, roughly, the exposure index settings at which the Signal to Noise Ratio in the midtones is 40:1 and 10:1 respectively. Looking at the DXO graphs of SNR 18%, those measures are up in the thousands for good modern sensors. [See note added below.]

However, those measures are rarely used: instead most attention goes on an almost opposite measure: the saturation based base sensitivity, which is the minimum recommended exposure index below which there is inadequate highlight headroom. With modern sensors using microlenses and color filter arrays, this is in the range about 100 to 200.

I would like to see the sensitivity of a sensor decribed in the way that the ISO standard recommends: giving a range from a minimum (highlight saturation based) to a maximum (noise based, like S40). Reducing a complex mixture of sensor characteristics and performance goals to a single sensitivity number can be misleading.


P. S. The DXO graphs of SNR 18% in the "screen" mode (per pixel) give a rough reading of the ISO noise based upper limits on exposure index. Those graphs in fact have a red line at 20dB, which is a SNR of 10:1, considered as "barely acceptable" and in fact quite visibly noisy. The stricter SNR 40:1 standard is a common guideline for excellent noise levels, and corresponds to 26dB. Looking at some of the current state of the art sensors for noise levels, the 5D3, D800 and D4, I estimate ISO S40 maximum recommended exposure index values of
D800: 1600
5D3: 2500
D4: 3200
Of course, if one is satisfied with downsizing to DXO's "print" normalised 8MP , as is probably fine for most normal prints sizes from these low light extremes, the SNR goes up. The wonderfully simple result is that the ISO S40 limits become about 6400 for all three sensors.

This equality is, I believe, because in that comparison it is the fundamentals of photon shot noise at work. To partially confirm that, photon shot noise alone should give a 4/3" sensor an S40 speed in that 8MP normalisation that is reduced in proportion to sensor area (to get equal photon count per down-sampled pixel) so 1600: and that is exactly what I see for the two best 4/3" sensors tested at DXO so far, those of the G3 and GH2. The same argument for Canon's 1.6x smaller EF-S format suggests scaling down by (1/1.6)^2, to an ISO S40 speed of 2500 --- and again, this is what the DXO measurements show for the 7D.

« Last Edit: May 13, 2012, 10:40:01 AM by BJL » Logged
Guillermo Luijk
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« Reply #76 on: May 13, 2012, 07:30:49 PM »
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"Raw Histogram
(...)
This has not been possible till now because with the raw file from a colour capable sensor the white balance is indeterminate. Depending on how the raw file is subsequently processed one of more of the colour channels might be blown. But because the MM has no white balance a true raw histogram display is possible."

Michael, with all respect, since no colour RAW histogram has been possible till now according to the article, I must then be the first human being plotting a real colour RAW histogram (Canon 350D):

Here in linear scale (not very useful to the photographer):


And here in stops (very intuitive for a photographer):


Also a representation with some gamma curve applied over the linear data would provide useful RAW histograms.

This is perfectly possible in any colour digital camera working with RAW data, it's simply that camera makers are not interested to introduce it on their cameras.

Regards

« Last Edit: May 13, 2012, 07:44:02 PM by Guillermo Luijk » Logged

Ray
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« Reply #77 on: May 13, 2012, 09:58:26 PM »
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Michael, with all respect, since no colour RAW histogram has been possible till now according to the article, I must then be the first human being plotting a real colour RAW histogram (Canon 350D):

But you are unusual and special, Guillermo. Grin Most of us are not concerned with such finer technical points, and what may be technically possible if we take a lot of trouble, especially when such achievements have certain disadvantages, perhaps in respect of the attractiveness of the review image on the camera's LCD screen, for example.
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hjulenissen
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« Reply #78 on: May 14, 2012, 12:38:28 AM »
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Where did the straw man argument that green is only responsible for luminance come from? That's not what I wrote or have ever written. They are predominantly responsible in a Bayer array, but not totally.
I see now that you have corrected that part of the review. Excellent.

Might I humbly suggest that whenever people question the accuracy of your articles (and I do know that not everyone do so in the most polite manner), the proper reaction is to figure out what they are talking about, and why it may be wrong. Jumping to the "I know more scientists than you do" argument is only slightly more mature than the classic "my dad is bigger than yours" argument.

"..straw man argument.."
"..if I have to choose between the technical information I get from the scientists and engineers working at the top digital imaging companies in Europe, Japan, and America, or you, somehow I think you'll end up being the loser.."
"...it's going to be depressing to read some of the online forums over the next few weeks, where self-proclaimed experts..."

-h
« Last Edit: May 14, 2012, 12:45:10 AM by hjulenissen » Logged
Guillermo Luijk
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« Reply #79 on: May 14, 2012, 02:07:59 AM »
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repeated............
« Last Edit: May 14, 2012, 02:11:50 AM by Guillermo Luijk » Logged

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