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Author Topic: Is This The End Game?  (Read 13187 times)
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« Reply #100 on: July 18, 2005, 06:15:16 PM »
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"but the information captured is without any possible doubt 3 times less."

Bernard,

This is absolutely not the case. A Bayer matrix reduces resolution by a maximum of 30%. This is basic digital imaging 101. Please do some reading before making catagorical statements which are seen to be untrue by anyone that has a bit of exposure to the available literature.

Michael
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lepingzha
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« Reply #101 on: July 18, 2005, 10:58:41 PM »
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Just for completeness, here is the link to the "add noise to
make D2x image more film like" post in DPreview forums:

http://forums.dpreview.com/forums....3552930

I only mentioned that to my eyes the added noise made
the image look more natural.  This has nothing to do
with the general quality of DPreview forum discussions,
to anyone with a sound sense of logic.  At least nothing
was labeled "bull" in the DPreview forum...

Don't take me wrong that I shoot both film and digital
and I have been speaking with my experiences with
Lightjet/Chromira printing which is already more
tolerate to digital artifacts than inkjet.  Raw conversion
algorithm and post processing are crutial to the image's
feel, both on screen and on prints, which makes the D2x
images much more film like than those from 1DsII.
My master images has from dozens to near hundred of
local contrast enhansing masked layers which applies
to both film and digital images, from the process I learn
the limitations of the both technology.

Clark stated clearly that there are huge resolution gap
between B&W, color negative, and pro slide films, and I
agree both the D2x and 1DsII are beyond the 645 print
film level.  However for Velvia it is very different.  What
made me speak was nothing but Michael's stretch that
the P45 will beat scanned 8x10 in all cases.  Again this
is a discussion group of landscape photography, and
over 90% of the film based landscape photographer
shoot chromes not negatives.

Look again at Michael's 1Ds vs. Pentax 67 comparison:

http://www.luminous-landscape.com/reviews/shootout.shtml

He first said the digital crop appears to have lower
resolution because it is enlarged too much to match the
scanned film crop.  Two paragraph later he concluded
that the 1Ds has a better resolution than the scanned
chrome.  Maybe this is just the logic and science of the
new age?

Drum scans emphersize film grains.  Try the Imacon
FlexTight 949 where they made improvement over
848/646 to make the grains much less visible while
retain the image details.  Their FlexTouch software
dust and scratch removal feature is better than
digital ICE and does not slow the scans down, based
on my experience too, so my scanned skys are almost
as clean as those from digital.

I am a medical imaging expert working in a major R&D
lab.  What I learned is that any sharp cut of the long
response curve tail, be it the spatial frequency expressed
in MTF, or a natural sound's extended harmonic structure,
creates unnatural artifacts.  Lens and film both have long
MTF tails, and the 10um grain size is the statistical mean
not the size smallest contributing elements.  As I mentioned
it is exactly why after 20 years audio engineers are learning
the 40-80KHz components are so crutial to the base tone
definition and impact making wavefront building so that their
inclusion in SACD or DVD-A are essential -- our ear can not
hear the pure harmonics but our skin will certainly feel the
sharper rising edge of the air pressure change.  The abrupt
cut of the MTF in digital capture at the Nequist frequency
(as well as the total artifacts beyond that) has a similar
effect to the normal CD's abrupt cut of the audio frequency
at 20kHz, which contributes to their harsh sounding well
known to many (not the MP3 generation).

The 30% resolution lost from Bayer interpolation is statistical,
and as with any statistics there are exceptions.  For an example
of interpolation failure checkout Clark's color pattern capture
comparisons:

http://www.clarkvision.com/imagedetail/fil...xl.digital.html

Bye everyone.

Best regards,
Leping Zha, Ph.D.
www.lepingzha.com
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BernardLanguillier
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« Reply #102 on: July 19, 2005, 11:11:45 PM »
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Jonathan,

Thanks for these examples.

I was already aware that there are ways to improve the appearance of images taken with a Bayer sensor. I am saying appearance, since each of the transformation you apply does of course reduce the actual informational content of the image. Fortunately, this loss is more than compensated by the morphing into a more eye pleasing look.

Your previous point was about the poor informational content of the Foveon generated data. That's the part I am most interested in to be honnest with you.

Cheers,
Bernard
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« Reply #103 on: July 21, 2005, 12:54:12 AM »
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This is pixel peeping to the Nth degree. That's fine with me. Just bear in mind that the final results on the print will probably ignore most of the subtleties discussed, and if they don't, our eyes will.
Ray,

I think that we all agree with you. The engineer in me in speaking in this thread, the photographer is sleeping somewhere...

As I said, I am in no way an expert in image processing or binary logic. I have only been trying to confront my common sense and understanding of basic physical mechanisms with the knowledge of those in the know.

Cheers,
Bernard
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« Reply #104 on: July 21, 2005, 05:54:42 PM »
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If you read up on information theory, you'll discover that not only is this indeed the case, but it is provable to the point of being axiomatic. Whether it is the result of a degree of uniformity or redundancy in the image data (which is always the case in real-world images) or some other factor is irrelevant. The legitimate presence of patterns or uniform areas in an image still reduces the amount of information required to describe the subject with whatever level of accuracy you choose to specify.
Jonathan,

You are of course correct, but my point about the lossless compressibility of an image was that it doesn't proof anything in terms of the gap between information and data RESULTING from the demoisaicing alone, which was our initial topic.

I do also agree with you that no information will be created in the process of demoisaicing and gamma application from 12 to 16 bits, but my only point was that it is impossible to measure this by checking lossless compressibility rate because of the other reasons why the initial 12 bits image itself can be compressed.

I am well aware that legitimate areas of uniformity contain less information than the un-compressed data size would suggest, and this is the very reason that I was evokating.

Regards,
Bernard
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lepingzha
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« Reply #105 on: July 17, 2005, 12:19:37 AM »
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For those deeply in the topic I recommend the scientific study
over Bayer array based digital capture vs. film, on both
resolution and dynamic range, at ClarkVision.  You can start
from the equivalent digital resolution chart at:

http://clarkvision.com/imagedetail/film.vs.digital.1.html

which states Michael's projection that the P45 would provide
scanned 8x10 film quality highly improbable.

Leping Zha
Landscape Photogrpher and Ph.D. in Physics
www.lepingzha.com
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« Reply #106 on: July 18, 2005, 08:45:01 AM »
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“the dithering introduced by film's grain structure significantly reduces the effective usable lp/mm for any subject matter that is not high-contrast black & white, typically by a factor of 3 to 5. In contrast,..”

I think this explains what I was so curious about, which is why is a print of a 1Ds2 resolution chart so much superior to the print from the higher resolving film? Of course this really makes me wonder what I will see from the significantly higher MP sensors like the forthcoming Phase One 39MP back.

Can anyone explain the correlation between MP and resolution? Apparently pixel size plays a part too? As well as filters, software, etc.? Does it follow (or not) that a 16 MP camera (given the same quality optics) will resolve more than a 10MP camera? I remember being amazed at the quality I was seeing when I bought a 1Ds a few years ago. Michael’s announcement about the appearance of a 31 and 39 MP back surprised me too. It will very interesting to see where all this goes over the next few years.
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« Reply #107 on: July 18, 2005, 06:24:20 PM »
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Undersharpened if anything at all. I compiled a photoshop action that sharpenes the non edge area as well so that there is pore definition on the face while sharpening the edges more vigirously for a more film like 'look'. I can't say that I'm a huge fan of the unresolved plastic look given to skin by these sharpening programs, seems a shame to waste all that resolution and is hardly necessary for a little kids face. That pic would look soft in print, certainly not oversharp as I doubt it has had print sharpening applied yet.
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Ray
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« Reply #108 on: July 18, 2005, 10:45:57 PM »
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The lack of detail in some white checks would, to me, indicate a bit of overexposure.  
Jonathan! Overexposing an image! Do you realize what you are saying? Is this even conceivable  Cheesy .
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« Reply #109 on: July 20, 2005, 12:25:41 AM »
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That's fairly easy. There's only marginally more visually useful image information in a Foveon image (exactly how much more is debatable, but it's safe to say that it's somewhere between 120% and 200% of what's contained in a Bayer file) but it's buried in 300% of the data of an equivalent Bayer RAW file.

A minor quibble: Saying that "each of the transformation you apply does of course reduce the actual informational content of the image" is not correct when working in 16-bit mode. When you open a 12-bit Bayer RAW file and expand it to 16 bits per channel (actually 15 data bits and a sign bit) RGB mode, you are expanding the data, but not the amount of real information. You've expanded approximately 8 bits of real image information per pixel (remember that Bayer RAWs can be losslessly compressed to about 2/3 of their original size) into 45 bits per pixel (15 bits x 3 channels) of RGB data. So unless you're doing enough editing to accumulate 7 bits worth of rounding errors per color channel (which would only ever happen if you're adding fairly healthy doses of film grain or other noise to the image) the only thing actually "lost" during editing is the non-informational data that was created when initially converting the RAW data to RGB format.

Think of a 15-inch cylinder with 8 inches of oil in it. That's the honest-to-goodness genuine image information. Now add 7 inches of water so that the cylinder is full to the brim. That's equivalent to converting the RAW file to RGB. Now drain off 3-4 inches of water from the bottom of the cylinder. You've just done enough editing to create enough of a "toothcomb" effect in the histogram that only every 8th or 16th level is populated. (That's pretty tough to do in a normal image editing workflow; even working in 100% 8-bit mode, you rarely get gaps more than 4-8 levels wide unless you're doing really extreme level or curve adjustments.) You still have 7 inches of oil, it's just sitting on less water (non-informational data) than it was before. Does that make sense? Or have I bored everyone to sleep already?
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« Reply #110 on: July 21, 2005, 04:47:47 PM »
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That's why I did the file size comparison before doing the sharpening. I agree that the Bayer image probably has some demosaicing artifacts and other things that are difficult or impossible for the compression algorithm to distinguish from real image information. (I'd even go so far as to say that the inability to distinguish such artifacts from true image information is probably an attribute of a well-written RAW converter.) The reason the sharpened files are larger is certainly because the sharpening process "created" bits that while not real image information, cannot be distinguished from real image information by the compression algorithm, and therefore increase file size. I don't know that thaere is any way to measure the amount of "true" information in an image file, it would certainly require a much better definition of "image quality" than currently available, so that differences between my test crops could be meaningfully quantified beyong general observations regarding appearance and JPEG2000 file size. I'm guessing that there is an information theory doctoral thesis on the subject begging to be written, but I don't have the advanced math background and other skills necessary to devise such a thing.
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« Reply #111 on: July 21, 2005, 12:38:20 AM »
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This is pixel peeping to the Nth degree. That's fine with me. Just bear in mind that the final results on the print will probably ignore most of the subtleties discussed, and if they don't, our eyes will.
Actually, all this theory has a practical application; try the 8-bit/16-bit JPEG level tweaking exercise I outlined previously as a demonstration. This is the theory underlying the practical reasons for editing as much as possible in 16-bit mode instead of 8-bit mode; an (admittedly long-winded) explanation why 16-bit editing is better than 8-bit editing.
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« Reply #112 on: July 17, 2005, 04:31:11 PM »
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Forget anything else, why doesn't someone come through with a decent solution to expanded DR in the highlights? As MR has pointed out, it's not necessarily about the pixel count any more, even at the high end.
Fuji has. see the S 3Pro.
It is not a "big chip", but definetly designed to adress the "highlights issue" I suspect that the Idea will not go un noticed.
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Ray
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« Reply #113 on: July 18, 2005, 11:31:12 AM »
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So a 100% MTF target will be recorded bettter by film (because the edges are either black or white) but with anything photographed in the real world digital's advantage in this respect immediately becomes clear.
I understand your point, Michael, and I certainly have no strong desire to go back to film. Haven't shot any film in years. But high contrast targets do exist in the real world; car number plates, menus on restaurant windows, strands of whispy grass glinting in the sunlight, all manner of documents that don't easily fit onto a flatbed scanner etc.

I merely make the point that if you wanted to demonstrate the superior resolving power of 35mm film compared with the 1Ds, you could probably do so by choosing your film and subject matter carefully. As always, it's the best tool for the job that's important and there's no doubt that a 1Ds is a better tool for most photographic jobs than any type of 35mm film.

It's a pity that Kodak have discontinued Technical Pan. I wouldn't be surprised if this film could compare quite favourably with the 1Ds with low contrast subject matter.
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« Reply #114 on: July 18, 2005, 07:50:37 PM »
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This is a myth perpetrated by the Foveon crowd. A Bayer array does NOT lower resolution a factor 3x, EXCEPT if you are imaging in primary blue or primary red.

~SNIP~

I have found that typically, in white light, the combination of Bayer array and anti-aliaising filter in a Canon DSLR lowers resolution to roughly 85% that the pixel pitch should be capable of. I have obtained that %age from my own chart testing and it seems to agree with DPReview measurements.
Amen -- and a brilliant marketing campaign by Foeveon to be sure. However isn't it interesting that their real-world results have yet to match the hype?  Wink

FTR, my own experiences echo the 85%, but only with the best raw converters.
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« Reply #115 on: July 18, 2005, 10:23:33 PM »
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So one would need to apply a bit of blurring to the image and decrease the contrast to make it more film like?
I don't think one would need to apply blurring. Jonathan has already stated that he applied mid-tone sharpening. Maybe less mid-tone sharpening would help. As regards contrast, I see an unnatural lack of detail in some of the highlights of the white grid pattern on the girl's dress. It's like a dress that has its own illumination. But as I said, I accept the fact that Jonathan has just exaggerated an effect to make a point.
The lack of detail in some white checks would, to me, indicate a bit of overexposure.  The detail is held in the red/white checks.

I'm still looking for an explanation of "FULL of interpolation artifacts and gross oversharpening".  Seems like someone with a Ph.D. in physics could describe what they see in fairly precise terms.

(I am willing to guess that at this level of enlargement one is beginning to see a bit of moire/pixelization - I'm still trying to sort that out - along the edges.  Just as when one enlarges film too much and starts to see grain patterns.)
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« Reply #116 on: July 19, 2005, 10:11:24 AM »
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OK Bernard, points taken - but don't they have a Geisha District in Nagoya?   (or is Luminous Landscape more correct fun?)
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BernardLanguillier
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« Reply #117 on: July 20, 2005, 02:14:14 AM »
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Hi Jonathan,

Regarding Foveon, where did you get these 120 to 200% values from if I may ask? Aren't those figures experimental data that were impacted by the noise resulting of the Foveon implementation of the multi-layer sensor idea? I still don't see any theoretical justification for those.

Besides, interesting example, I believe that I understand your point.

On the other hand, most image manipulations affect the whole range of densities, and not just these empty bits that were added when converting the RAW file into a 16 bits space.

Your example would probably be closer to the reality if water and oil were mixed to create a suspension. Removing a fixed amount of liquid on the top would affect less oil than if no water had been added, but it will still affect some.

I agree with you that the result will most probably have zero visual impact, and that the image will in the end probably
look better as I wrote above, but basic entropic theory can be applied to image manipulation. If 2 things have become the same at a given moment in time, the information that existed in the form of their initial difference (potential energy) will never be recovered if it once lost.

Anyway, this purely theoretical discussion having no impact on actual photography, we could probably agree that our positions are close enough?

Regards,
Bernard
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« Reply #118 on: July 21, 2005, 12:21:40 AM »
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Just a confirmation. I assume that you call "real image information" the most significant 8 bits based on the assumption that both display and print are 8 bits devices?
No, I'm basing that on the fact that 12-bit RAW files can be losslessly compressed to about 66% of their original size, therefore there is only approximately 8 bits per pixel of non-redundant image information in a typical Bayer-sensor RAW file. This varies somewhat depending on subject matter and ISO, but that's a whole 'nother discussion.

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Besides, one question. When a 12 bits RAW image is converted into a 16 bits tiff, my understanding is that a mapping was performed so that the max value in 12 bits (11111111 1111) becomes the max value in 16 bits (11111111 11111111). One could think that this would leave 4 bits of un-used values throughout the range, but my understanding is that this is mostly not the case since:

- the demozaiquing is basically an averaging process whose ouput does benefit from the additional set of values existing in 16 bits compared to the 12 bits input,
- the gamma application,
- ...

-> the result of the RAW conversion is probably most of the time a fully populated 16 bits file, not just a file whose 12 bits are populated, and then zeros added.

Do you agree with this?

Yes, so far we are in agreement.

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Although I agree with you that the least significant bits will be affected first, those do contain useful image information if my understanding of the 12 -> 16 bits mapping is correct. I agree with you that the impact of these least significant bits is by definition very small, but IMHO actual image information will be lost even when working in a 16 bits mapping of an image generated by a 12 bits sensor.

That's where you're getting off track. While it is true that the demosaic/interpolation process can generate discrete values on the lowest-order bits, (the lowest 4 bits are not always 0000 or 1111 or whatever) that does not mean that any actual image information is going into those bits. What is going into those bits is guesswork from the demosaic/interpolation algorithm and not actual image data, unless you're doing something really weird like converting with the exposure set to -4 stops and the entire image is being crammed into the left side of the histogram. Because of that, the data in those bits is no more "real" than if you simply padded all the binary values with 0000 or 1111 to make the 12-bit to 16-bit transition. They're just calculated to be more visually pleasing than 0000 or 1111. As such, they are just as expendable with regard to edit-induced entropic losses as 000 or 1111 would be. The real image information is still safely tucked away in the high-order bits, but now with an additional 4 bits of mathematical guesswork and fakery to absorb the entropic destruction of typical image editing.
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« Reply #119 on: July 21, 2005, 08:32:18 PM »
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Jonathan,

Yep, I think that we nearly agree on everything.

The only part that of which I am not 100% convinced yet, but I am not saying that you are wrong, just that you didn't convince me yet () is the part where you are seemingly saying that the first 2 editions of a 16 bit RAW converted file (resulting, for the sake of discussion, in the loss of 2 bits each) will only damage artificially created data that was not present as information in the 12 bits RAW file in the first place.

I am convinced that the edition of the 16 bit file will have little practical impact on the image, but I still don't see clearly why you can claim that no actual image information is stored in those 4 bits of least importance that will be killed first.

I can take the math if needs to (or at least I could a few years back...).

Don't worry if you don't have the time for this, this really has become bit peeping now...

Cheers,
Bernard
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