Digital quality (vs 35mm): Any real answers?

David Dyer-Bennet wrote:

Gordon Moat writes:

[an *extremely* detailed and clear discussion of many of the issues in
the topi in the subject line]

First, *very* nice explanation! It obviously involved quite a bit of
work.

Second, I think one very important point often missed in this
discussion is that digital and film images enlarge entirely
*differently*.

Even a first-rate slow film image acquires grain (clumps) as it's
enlarged enough. A digital image *doesn't*. It gradually gets
softer, but there is no underlying grain structure to appear (the
underlying pixel structure doesn't appear because the decent
interpolation algorithms prevent it).

True to a point. In an article in LFI 06/2003 (Leica Fotographie International),
Erwin Puts test the new Fuji Astia 100F and Kodak E100G. One of his remarks is
quite interesting. He states that he could not ". . . detect any grain at an
enlargement of factor 40 with both films." He also wrote, "One starts to see
individual grain clouds only at a magnification factor of 100". His comments of
the magnification factors were for using a microscope. To be fair, I have been
critical of comments from Erwin Puts in the past, and I have e-mailed him on a few
occasions. To his credit, he is good at answering e-mails, and explaining his
methods and calculations. If you are a little more curious, I suggest getting a
copy of the article, or sending him an e-mail.

Consider that few of us make prints beyond 10x magnification, especially from 35
mm. I have quite a few Chromira and LightJet prints that are 10" by 15" and show
absolutely no grain at all. To go much larger might mean inkjet prints, since it
is getting tougher to find places that still do large chemical prints. I should
also point out that getting good quality large chemical prints is not easy, and
there are many quality issues.

The few really large prints that have been done from my images were posters. Those
were commercially printed, and also showed no grain structure. They were all done
from scanned film, since that is the way I do my work. This is an example of
printing methods, and post processing, affecting the output.

To qualify all this, it is tough to get really large prints from film at high
quality. It is easier to get large inkjet prints. It is easier for someone without
lots of skill to get acceptable and pleasing prints on a desktop inkjet from
direct digital, than it is from any other method.

Direct digital may not have grain problems, though it can often have aliasing
errors that show up in very large prints, or have some colour fringing issues.
Again, there are ways in post processing to avoid those problems, similar to the
ways that film scans can also be altered in editing software. On the basis of
editing in software, there is no difference between direct digital and scanned
film, since both are just manipulating digital image files.



An experienced film photographer looking for flaws in a big print from
digital may be looking for the wrong thing; one of the things I look
for is how the grain is doing, and in a print from a digital original,
I'm not going to find any.

As a professional, I have to look at colour first, before any other aspects of an
image. This is where direct digital has fallen short, though it is close in many
situations. Where colour is important in work, is when there is architecture,
automotive, product, fashion, or food imagery, as the main subject matter. It is
also tough to get good scans from film, though it helps when editing to have the
transparency in view on a light table. It also helps sometimes to send dupes of
the transparencies to the printer, so they can better match colours. All these are
issues that few enthusiasts ever encounter.



This difference in how they enlarge probably accounts for part of the
wide range of discussion about what "equivalent" resolutions are.
Some people mind grain more than others, some people's eyes are
probably more attuned to noticing some kinds of softness or missing
details than others, so they'll have different tolerances for various
size prints from film and digital originals.

I only judge grain in the final print, and not on a monitor. I have seen images on
a monitor that looked horrible, and then printed smooth. I also have some 24" by
36" prints done from Kodak TriX. Everyone knows TriX is grainy in comparison to
many other films. These large prints were done as part of a series by a master
printer, and even with all the care and knowledge, only two out of four prints
were acceptable to me. Everyone who has seen those prints really likes them. The
size also means that people rarely ever walk up to them really close, though if
they did, they would see grain. I think grain can be a creative choice as well,
and some images convey a certain mood or feeling when they are photographed on
grainy films.

Ciao!

Gordon Moat
A G Studio
http://www.allgstudio.com Updated!

David Dyer-Bennet wrote:

Gordon Moat writes:

[an *extremely* detailed and clear discussion of many of the issues in
the topi in the subject line]

First, *very* nice explanation! It obviously involved quite a bit of
work.

Second, I think one very important point often missed in this
discussion is that digital and film images enlarge entirely
*differently*.

Even a first-rate slow film image acquires grain (clumps) as it's
enlarged enough. A digital image *doesn't*. It gradually gets
softer, but there is no underlying grain structure to appear (the
underlying pixel structure doesn't appear because the decent
interpolation algorithms prevent it).

True to a point. In an article in LFI 06/2003 (Leica Fotographie International),
Erwin Puts test the new Fuji Astia 100F and Kodak E100G. One of his remarks is
quite interesting. He states that he could not ". . . detect any grain at an
enlargement of factor 40 with both films." He also wrote, "One starts to see
individual grain clouds only at a magnification factor of 100". His comments of
the magnification factors were for using a microscope. To be fair, I have been
critical of comments from Erwin Puts in the past, and I have e-mailed him on a few
occasions. To his credit, he is good at answering e-mails, and explaining his
methods and calculations. If you are a little more curious, I suggest getting a
copy of the article, or sending him an e-mail.

Consider that few of us make prints beyond 10x magnification, especially from 35
mm. I have quite a few Chromira and LightJet prints that are 10" by 15" and show
absolutely no grain at all. To go much larger might mean inkjet prints, since it
is getting tougher to find places that still do large chemical prints. I should
also point out that getting good quality large chemical prints is not easy, and
there are many quality issues.

The few really large prints that have been done from my images were posters. Those
were commercially printed, and also showed no grain structure. They were all done
from scanned film, since that is the way I do my work. This is an example of
printing methods, and post processing, affecting the output.

To qualify all this, it is tough to get really large prints from film at high
quality. It is easier to get large inkjet prints. It is easier for someone without
lots of skill to get acceptable and pleasing prints on a desktop inkjet from
direct digital, than it is from any other method.

Direct digital may not have grain problems, though it can often have aliasing
errors that show up in very large prints, or have some colour fringing issues.
Again, there are ways in post processing to avoid those problems, similar to the
ways that film scans can also be altered in editing software. On the basis of
editing in software, there is no difference between direct digital and scanned
film, since both are just manipulating digital image files.



An experienced film photographer looking for flaws in a big print from
digital may be looking for the wrong thing; one of the things I look
for is how the grain is doing, and in a print from a digital original,
I'm not going to find any.

As a professional, I have to look at colour first, before any other aspects of an
image. This is where direct digital has fallen short, though it is close in many
situations. Where colour is important in work, is when there is architecture,
automotive, product, fashion, or food imagery, as the main subject matter. It is
also tough to get good scans from film, though it helps when editing to have the
transparency in view on a light table. It also helps sometimes to send dupes of
the transparencies to the printer, so they can better match colours. All these are
issues that few enthusiasts ever encounter.



This difference in how they enlarge probably accounts for part of the
wide range of discussion about what "equivalent" resolutions are.
Some people mind grain more than others, some people's eyes are
probably more attuned to noticing some kinds of softness or missing
details than others, so they'll have different tolerances for various
size prints from film and digital originals.

I only judge grain in the final print, and not on a monitor. I have seen images on
a monitor that looked horrible, and then printed smooth. I also have some 24" by
36" prints done from Kodak TriX. Everyone knows TriX is grainy in comparison to
many other films. These large prints were done as part of a series by a master
printer, and even with all the care and knowledge, only two out of four prints
were acceptable to me. Everyone who has seen those prints really likes them. The
size also means that people rarely ever walk up to them really close, though if
they did, they would see grain. I think grain can be a creative choice as well,
and some images convey a certain mood or feeling when they are photographed on
grainy films.

Ciao!

Gordon Moat
A G Studio
http://www.allgstudio.com Updated!

"William Graham" writes:

snip

That means a 24 x 36 mm sensing plane would need about 12 megapixels to have
the same resolution as film. Digital cameras are not too far from that
now....Perhaps in another couple of years..........

Huh? The Kodak almost-14MP DCS Pro 14n shipped over a year ago. And
the DCS Pro SLR/n has replaced it, using an improved sensor. It uses
Nikon-mount lenses, and there is a Canon-mount sibling, the
SLR/c. Several people are using these in lieu of medium-format film
equipment, as they feel the image quality is better.

And medium-format backs reached 16MP some years ago; the best current
single-shot backs have 22MP.

--
-Stephen H. Westin
Any information or opinions in this message are mine: they do not
represent the position of Cornell University or any of its sponsors.

[ ... ]


3. I know that the most common sensors are made up of individual
elements for the read, green and blue channels, arranged in a special
pattern, whose data is somehow interpolated into RGB pixels. But what
exactly does e.g. 6 megapixels mean in that context? Does it mean that
the sensor has (just) 6 million elements, or that data from a higher
number (like 18 or 24 million) is combined into 6 million RGB pixels?

The same question more bluntly put: When Canon/Nikon/Pentax is talking
about 6MP, is that just a big a lie as the one about 10MP on Sigma
cameras? (I'm hoping not, as I think the Sigma/Foveon way of counting
really takes the cake.)
OK. I've been thinking a bit about the "luminance" argument that has
popped up a number of times (but not a lot, so I may have overlooked
something), and I'm not sure I'm convinced - although it depends a bit
on how you see it.

It seems to me that one of the key weaknesses of the standard "pattern"
sensor is actually that it cannot capture luminance. When you're looking
through a filter, there is simply no way you can tell white light apart
from light of the colour associated with that filter! Furthermore, the
real problem seems not to be photographing a large area in one of the
primary colours like someone suggested, but rather to capture tiny spec
of a distinct colour - especially if that colour is such that one or two
of the components are different from the surrounding data, and the
other(s) the same. For instance, imagine taking a picture of a small
read dot against a completely white background. Now, assume that the
size of that dot's projection onto the sensor matrix is one pixel, and
that it falls on a red pixel sensor. Surely, this will mean that the dot
won't show up at all on the picture - as there is no way the red sensor
can distinguish it from all the white points surrounding it, and the
adjacent green and blue sensors won't "see" it at all. If, on the other
hand, it falls on a e.g. green sensor, it should indeed show up, as that
sensor won't register any light at all, but there is no way of telling
it's exact colour - all you know is that it's not green or colour that
has a green component. (But it may be black or any shade of blue, read
or purple.)

For an exact representation of a dot do be guaranteed, the dot would
have to be of a size equivalent to at least 4 sensor elements (when the
matrix is made up of sets of one red, one blue and two green) - or more
than 3, anyway. By this argument, you could say that the real resolution
is actually the equivalent of 1/4 of the number of pixel sensors, or
1.5MP for a "6MP sensor".

However, I admit that if the projection "touches" two elements instead
of just one - and it has to be larger than one pixel to do that - the
chance of getting the value right is much greater, and if it touches at
least tree, chances are that there is at least one of each colour
channel, in which case a correct colour should be guaranteed. In other
words, it's fair to assume that a size of "two point something" pixels
is sufficient for a correct representation of our little spec.

So, I'd say that for purposes of quality comparisons, a 6MP array has
neither 6 million pixels or the very conservative 1.5, but something in
between. It's actually tempting to guess that the "effective" number of
pixels is somewhere near the 3M the foveon has if you count the way
they'll teach you at most schools except the Sigma marketing academy.
(Which would mean that the sensors are equally good, but that Sigma are
the greatest liers...)

Furthermore, the luminance phenomenon is indeed useful in one sense,
namely that it allows for a good interpolation algorithm - and it does
so *because it isn't registered*. It didn't have to be the luminance, of
course, but I think an essential requirement for reasonable
interpolation is being able to make good assumptions about some
parameter that isn't actually captured.

So, if the 6MP data is generated base on the assumption that the
luminance always makes up most of the light, and that turns out to be
true in a certain case, then maybe you can say that you *really* have
(close to) 6MP *in that particular situation.* Also, the general quality
of data produced by the camera is to a large extent determined by the
probability that the assumption will hold.

By the same token, you may make some kind of assumption about the data
from a foveon sensor or a colour scan that makes you able to interpolate
extra pixels. For instance, you can make the assumption that all pixels
have a value "right between" the adjacent pixels, and get a type of
linear interpolation algorithm. That way you can at least double the
number of pixels and get decent results in most cases, I think.

Based on that, the comparison between the foveon and the other sensors
really boil down to comparing the quality of the interpolation for the
6MP data with the (potential) quality of the interpolating necessary to
get the same number of pixels based on the foveon output - or if you
like, the merits of the assumptions that lie behind the different
interpolations.

Cheers,


T

Stephen H. Westin wrote:
"William Graham" writes:

snip

That means a 24 x 36 mm sensing plane would need about 12 megapixels to have
the same resolution as film. Digital cameras are not too far from that
now....Perhaps in another couple of years..........


Huh? The Kodak almost-14MP DCS Pro 14n shipped over a year ago. And
the DCS Pro SLR/n has replaced it, using an improved sensor.
I think he meant *affordable* cameras with that many pixels. I've
actually been thinking when that it's when we get there that I'll buy a
digital SLR. Also, *maybe* somewhere around that range the "megapixel"
race will slow down a bit, and perhaps then a new camera won't be
obsolete after about two months...

BTW. Do you know more about this sensor? It is full-frame, right? I'm
really interested in knowing if they have resolved the problems that
have lead to the use of smaller sensors so far.
It uses
Nikon-mount lenses, and there is a Canon-mount sibling, the
SLR/c. Several people are using these in lieu of medium-format film
equipment, as they feel the image quality is better.

And medium-format backs reached 16MP some years ago; the best current
single-shot backs have 22MP.
Oh, and I'm waiting for that that, too, on a 35mm-format camera (as I've
mentioned already),
or at least dreaming about it. A replaceable back, that is. Not
necessarily a system that
would allow you to switch between digital and film, but something that
would give you more flexibility in the sensor department somehow.

I was surprised how good prints from 35mm Gigabilfilm looked.
I made 20x30cm. No grains at all and super sharp even with a x15 magnifier
directly on
the print. I think more people should try this film.

Max

"Chris Loffredo" skrev i en meddelelse
...
David J. Littleboy wrote:


20x24 is a pitiful joke from 35mm B&W films, even Tech Pan. If one has
any
sense of quality imaging at all, 11x14 is MF (645) territory. 20x24 from
6x7
would be OK, but would look better if you used LF.


I agree that 20x24 is stretching things a bit (no pun intended) using
35mm and that MF or LF would be far preferable, but with a good negative
the results are still acceptable, especially at real viewing distances.

I much more often do 30x40 cm (12x16) with fully satisfactory results
(given of course a decent negative). In a direct comparison with a MF
shot, there is a little less tonal smoothness & 3D look, but then I
wonder how much tonal smoothness & 3D look digital would have in this
case.

Chris

I was surprised how good prints from 35mm Gigabilfilm looked.
I made 20x30cm. No grains at all and super sharp even with a x15 magnifier
directly on
the print. I think more people should try this film.

Max

"Chris Loffredo" skrev i en meddelelse
...
David J. Littleboy wrote:


20x24 is a pitiful joke from 35mm B&W films, even Tech Pan. If one has
any
sense of quality imaging at all, 11x14 is MF (645) territory. 20x24 from
6x7
would be OK, but would look better if you used LF.


I agree that 20x24 is stretching things a bit (no pun intended) using
35mm and that MF or LF would be far preferable, but with a good negative
the results are still acceptable, especially at real viewing distances.

I much more often do 30x40 cm (12x16) with fully satisfactory results
(given of course a decent negative). In a direct comparison with a MF
shot, there is a little less tonal smoothness & 3D look, but then I
wonder how much tonal smoothness & 3D look digital would have in this
case.

Chris

"Stephen H. Westin" wrote in message
...
"William Graham" writes:

snip

That means a 24 x 36 mm sensing plane would need about 12 megapixels to
have
the same resolution as film. Digital cameras are not too far from that
now....Perhaps in another couple of years..........

Huh? The Kodak almost-14MP DCS Pro 14n shipped over a year ago. And
the DCS Pro SLR/n has replaced it, using an improved sensor. It uses
Nikon-mount lenses, and there is a Canon-mount sibling, the
SLR/c. Several people are using these in lieu of medium-format film
equipment, as they feel the image quality is better.

And medium-format backs reached 16MP some years ago; the best current
single-shot backs have 22MP.

Yes.....I should have said, "Digital cameras at a reasonable price are not
too far from that now....Perhaps in another couple of years."

"Stephen H. Westin" wrote in message
...
"William Graham" writes:

snip

That means a 24 x 36 mm sensing plane would need about 12 megapixels to
have
the same resolution as film. Digital cameras are not too far from that
now....Perhaps in another couple of years..........

Huh? The Kodak almost-14MP DCS Pro 14n shipped over a year ago. And
the DCS Pro SLR/n has replaced it, using an improved sensor. It uses
Nikon-mount lenses, and there is a Canon-mount sibling, the
SLR/c. Several people are using these in lieu of medium-format film
equipment, as they feel the image quality is better.

And medium-format backs reached 16MP some years ago; the best current
single-shot backs have 22MP.

Yes.....I should have said, "Digital cameras at a reasonable price are not
too far from that now....Perhaps in another couple of years."

Gordon Moat wrote:
Toralf wrote:


Hi.

I'm still wondering about how good the image quality of modern digital
cameras (especially SLRs) really is, in particular how it compares with
35mm film. I've seen many articles on the subject on the Net, but few of
them seem to give you a lot of tangible information (I want to see the
numbers, please), and I can't help feeling that tests they refer to are
usually done to prove a point, i.e. that digital cameras are as good as
35mm, which is not the way you do proper research.


The reality is that both film and direct digital offer some goods choice to
produce images. I see them more as complimentary devices, rather than an
either/or choice.



To say a few words about myself, I'm working for a company that makes
high-accuracy, large-format scanners, so I'm not particularly impressed
when I hear e.g 6 million pixels (you need to talk about *billions* of
pixels if I'm really going to listen), and the word "interpolation"
leaves a bad taste in my mouth. But this also means I know that high
resolution isn't everything, of course; parameters like geometric
precision or signal-to-noise ratio also count a lot.


Do you work for Creo?
No. I work for a small company that makes the "Rolls Royce of scanners",
at least according to our marketing people ;-)

If you're really interested, have a look at
http://www.procaptura.com/pages/scanners/scanners.htm

[ ... ]







If you are imaging to a desktop inkjet output, then many direct digital choices
might be an easier path. It takes a great deal of knowledge to get the best
results in printing, or at least lots of trial and error.
The option of connecting the camera directly, or alternatively insert
the picture storage media into it, offered by most (all?) recent image
printers definitely appeals to me. I somehow see the transfer of my
image to a PC as a complicating factor... (And not a very good argument
for digital cameras.)

[ ... ]



4. Can the inaccuracy associated with the above mentioned interpolation
be quantified and/or measured against e.g. the error introduced by
scanning a negative with a film-scanner? And how does it compare with
pixel interpolation in the scanning sense?


A CCD film scanner uses a trilinear array,
Yeah, that's what I thought. This is the method I'm familiar with!
Although we've also tested camera units using a different, also quite
common, approach: These had 3 plain CCD arrays without filters or
anything, and a prism used to decompose the light so that each component
would an array of its own.

BTW, I've never actually seen a film scanner. Do you happen to know of
which type (flatbed, sheetfeed etc.) they are? (Or do they use methods
completely different from the ones employed by other types of scanners?)


Film grains are under 3µ in size. Film imaging chips have an optimum response
at around 6.8µ to 8µ (microns) in size. Too small reduces sensitivity to light,
while too large introduces noise. There are drum scanners that can image at
about 3µ, though they are very new, and not very common. CCD film scanners are
capable of much less than drum scanners.
OK.

We've been using 12 and 14µ pixel-arrays (I don't remember off the top
of my head which is the one currently used and which was in an older
model) on the scanners, but I'm getting off the topic, now...




I think the technology is improving all the time. Obviously, the gear available
next year will be better than the gear there is today, and will be priced
lower. I think we will see many more full 35 mm sized imaging chips in the near
future,
Yeah, that's my theory as well - but maybe it's just wishful thinking...

Apart from that, lots of good answers, there. Thanks.

- Toralf