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

"Zebedee" wrote in message
...
I spent ages working out all the details. I came to the conclusion that if
you measured the area of a perfect print from a 35mm negative or 35mm
slide
in inches and then divided the dimensions by 150 you'd be able to work out
the vertical/horizontal pixels of the image. Then simply multiply the two
together to get megapixels. That's the theory anyway.

In practice, how big is the biggest print you normally make? If your
normal
biggest print is 10x8 then 3 megapixels is all you ever need (two at a
pinch).

But the biggest limitation is your printer. How many of us can afford an
A3
or greater printer or even the ink to make A3 prints?

How many A4 prints can you hang on your wall?

I decided to settle on 3 megapixels. It's adequate for my needs and as
with
slides, I ensure my photos are perfect before I squeeze the button. I
claim
3 megapixels is the perfect equivalent of 35mm for most purposes. 6mp just
eats up storage space for no visible advantage.

--
Yours

Zebedee

(Claiming asylum in an attempt
to escape paying his debts to
Dougal and Florence)



You may claim it, but that don't make it so. There is a decided difference
between files from my Canon D30 (3mp) and my wife's 10D (6mp) cameras. 3mp
is most definitely not the equivalent of film for anyone who is enlarging
beyond 4x6.
I have a Canon 9000 printer that prints photo quality A3+ prints, we both
regularly print to that size and A4, we have about 20 16x20 inch frames
hanging on the wall in our stairwell, alone, as we speak. I have a show
coming up in which more than half the images need to be printed A3+. Your
theory won't work for me, and I'll bet that in a short time, you'll realize
that you are dissatisfied with the images you are getting utilizing that
theory, too.

--
Skip Middleton
http://www.shadowcatcherimagery.com

"Zebedee" wrote in message
...
I spent ages working out all the details. I came to the conclusion that if
you measured the area of a perfect print from a 35mm negative or 35mm
slide
in inches and then divided the dimensions by 150 you'd be able to work out
the vertical/horizontal pixels of the image. Then simply multiply the two
together to get megapixels. That's the theory anyway.

In practice, how big is the biggest print you normally make? If your
normal
biggest print is 10x8 then 3 megapixels is all you ever need (two at a
pinch).

But the biggest limitation is your printer. How many of us can afford an
A3
or greater printer or even the ink to make A3 prints?

How many A4 prints can you hang on your wall?

I decided to settle on 3 megapixels. It's adequate for my needs and as
with
slides, I ensure my photos are perfect before I squeeze the button. I
claim
3 megapixels is the perfect equivalent of 35mm for most purposes. 6mp just
eats up storage space for no visible advantage.

--
Yours

Zebedee

(Claiming asylum in an attempt
to escape paying his debts to
Dougal and Florence)



You may claim it, but that don't make it so. There is a decided difference
between files from my Canon D30 (3mp) and my wife's 10D (6mp) cameras. 3mp
is most definitely not the equivalent of film for anyone who is enlarging
beyond 4x6.
I have a Canon 9000 printer that prints photo quality A3+ prints, we both
regularly print to that size and A4, we have about 20 16x20 inch frames
hanging on the wall in our stairwell, alone, as we speak. I have a show
coming up in which more than half the images need to be printed A3+. Your
theory won't work for me, and I'll bet that in a short time, you'll realize
that you are dissatisfied with the images you are getting utilizing that
theory, too.

--
Skip Middleton
http://www.shadowcatcherimagery.com

"Zebedee" wrote in message
...
..

Just why would anybody print at more than 150dpi when that's the maximum
the
eye can see?

--
Yours

Zebedee

(Claiming asylum in an attempt
to escape paying his debts to
Dougal and Florence)



For one thing, 300dpi makes for smoother transitions.

--
Skip Middleton
http://www.shadowcatcherimagery.com

"Zebedee" wrote in message
...
..

Just why would anybody print at more than 150dpi when that's the maximum
the
eye can see?

--
Yours

Zebedee

(Claiming asylum in an attempt
to escape paying his debts to
Dougal and Florence)



For one thing, 300dpi makes for smoother transitions.

--
Skip Middleton
http://www.shadowcatcherimagery.com

"Zebedee" writes:

"Chris Loffredo" wrote in message
...
Zebedee wrote:
I have 50x60 (cm) B&W photo paper which I use for the right pictures.
I doubt 3 (or 6) megapixels will do the job...

50cm = 19.7 inches
60cm = 23.6 inches

19.7 x 150 = 2955 pixels
23.6 x 150 = 3540 pixels

2955 x 3540 = 10.4607 megapixels

It could be a little stretch for a 6mp camera or you could even use the
Kodak 14mp SLR

Having said that, it's a really unusual size and more suited to medium
format than for 35mm.

I have, over the years, been more unhappy than not in printing 35mm up
to a size slightly smaller than that -- 16x20.

I have a 16x24 print (slightly smaller than the example under
discussion) from a 6mp shot from my Fuji S2 that looks better than the
16x20 prints I've had made from film. But I haven't worked very hard
on making first-rate 16x20 prints from 35mm; I gave up fairly early.
Which also means I haven't tried it with modern films. Still, the
16x24 inkjet print looks *great*.
--
David Dyer-Bennet, , http://www.dd-b.net/dd-b/
RKBA: http://noguns-nomoney.com/ http://www.dd-b.net/carry/
Pics: http://dd-b.lighthunters.net/ http://www.dd-b.net/dd-b/SnapshotAlbum/
Dragaera/Steven Brust: http://dragaera.info/

"Zebedee" writes:

"Chris Loffredo" wrote in message
...
Zebedee wrote:
I have 50x60 (cm) B&W photo paper which I use for the right pictures.
I doubt 3 (or 6) megapixels will do the job...

50cm = 19.7 inches
60cm = 23.6 inches

19.7 x 150 = 2955 pixels
23.6 x 150 = 3540 pixels

2955 x 3540 = 10.4607 megapixels

It could be a little stretch for a 6mp camera or you could even use the
Kodak 14mp SLR

Having said that, it's a really unusual size and more suited to medium
format than for 35mm.

I have, over the years, been more unhappy than not in printing 35mm up
to a size slightly smaller than that -- 16x20.

I have a 16x24 print (slightly smaller than the example under
discussion) from a 6mp shot from my Fuji S2 that looks better than the
16x20 prints I've had made from film. But I haven't worked very hard
on making first-rate 16x20 prints from 35mm; I gave up fairly early.
Which also means I haven't tried it with modern films. Still, the
16x24 inkjet print looks *great*.
--
David Dyer-Bennet, , http://www.dd-b.net/dd-b/
RKBA: http://noguns-nomoney.com/ http://www.dd-b.net/carry/
Pics: http://dd-b.lighthunters.net/ http://www.dd-b.net/dd-b/SnapshotAlbum/
Dragaera/Steven Brust: http://dragaera.info/

nitzsche wrote:
OK, I'll take a shot at it...

It used to be "Film is cheap,' now it's "Cameras are cheap."

1. What is the resolution of a 35mm film anyway?
- For practical purposes, it's infinite.

2. What about the print? 300dpi
- Unless you're printing posters, it's not relevant.
But I want to *know* exactly how large prints you can make at "standard"
resolution with the different formats.


3. exactly does e.g. 6 megapixels mean
- 6.3 megapixels is 6,291,456 sensors.
So, it's *really* equivalent to about 2M of true RGB data???

4. Can the inaccuracy associated with the above mentioned
interpolation be measured
- Film will almost always be better, but it's what the outside eyes see
that matters.

5. geometric distortions, noise, flat field bias etc.
- That's a lens issues, not sensor/film issues
There are lens issues, but those are not the ones I'm talking about.
CCDs at least do have the problem that the light sensitivity of each
pixel or sensor is not quite the same. And there may be varying offsets,
too, i.e. each pixel doesn't quite have the same opinion on what "black"
is. Also, the individual sensors aren't necessarily evenly distributed
or positioned exactly right. Then there is the "smear" between adjacent
pixels, which is one of the arguments against CCD and for CMOS, I think.


6. And the chromic aberration effects?
- As far as I know, all digicams are prone to purple fringing, which is
something you don't see on any cheap slr.

My two cents worth.

nitzsche wrote:
OK, I'll take a shot at it...

It used to be "Film is cheap,' now it's "Cameras are cheap."

1. What is the resolution of a 35mm film anyway?
- For practical purposes, it's infinite.

2. What about the print? 300dpi
- Unless you're printing posters, it's not relevant.
But I want to *know* exactly how large prints you can make at "standard"
resolution with the different formats.


3. exactly does e.g. 6 megapixels mean
- 6.3 megapixels is 6,291,456 sensors.
So, it's *really* equivalent to about 2M of true RGB data???

4. Can the inaccuracy associated with the above mentioned
interpolation be measured
- Film will almost always be better, but it's what the outside eyes see
that matters.

5. geometric distortions, noise, flat field bias etc.
- That's a lens issues, not sensor/film issues
There are lens issues, but those are not the ones I'm talking about.
CCDs at least do have the problem that the light sensitivity of each
pixel or sensor is not quite the same. And there may be varying offsets,
too, i.e. each pixel doesn't quite have the same opinion on what "black"
is. Also, the individual sensors aren't necessarily evenly distributed
or positioned exactly right. Then there is the "smear" between adjacent
pixels, which is one of the arguments against CCD and for CMOS, I think.


6. And the chromic aberration effects?
- As far as I know, all digicams are prone to purple fringing, which is
something you don't see on any cheap slr.

My two cents worth.

Stephen H. Westin wrote:
Toralf writes:
[ snip ]



Be that as it may, some of the questions I'd like to have answered are
these:

1. What is the resolution of a 35mm film anyway?


It's hard to say, as the resolution limit is different from that of a
digital sensor. Rather than a hard limit, you get less information and
more blur and noise as you increase resolution in scanning a piece of
film.


I think I read
somewhere that a colour negative is at least 3000dpi. Is that
correct?


It's in the ballpark. [ ... ]
OK. Thanks


How about black&white?


Well, the data sheet on Kodak Technical Pan, which is an extreme upper
bound, has MTF at 50% at 180 c/mm or so. That's for ISO 25, developed
in Technidol. That's Kodak Tech Pub P-255, available at
http://www.kodak.com/global/en/professional/support/techPubs/p255/p255.jhtml?id=0.1.18.14.21.22.16&lc=en.
For Plus-X, at ISO 125, Tech Pub F-4018 (at
http://www.kodak.com/global/en/professional/support/techPubs/f4018/f4018.jhtml?id=0.1.18.14.21.20.16&lc=en)
rates it at 50 lp/mm at 1.6:1 contrast, 125 at 1000:1 (which you
aren't likely to reach it practice).

So I think we can say that scanning film at more than, say, 360
samples/mm (about 9,000 samples/inch) is pretty much useless. In most
circumstances, 100 samples/mm or 2,540 /inch is plenty. So we're in
the region of 9MP for a normal 24x36mm 35mm film frame.
I that would be 9MP without any sort of interpolation, though. But then,
like I said, you get the error introduced by the scanner instead...



(Yeah I know, a film doesn't have
pixels in exactly the same sense as a digital image, but it *is*
made up of discrete elements after all.)


But they aren't spaced on a regular grid, so things look a lot different.
Exactly. It would still be fun to know exactly how many "points" there
are, though.


2. What about the print? 300dpi?


Well, there are lots of variables involved there. One of the little
secrets that the "film-only" zealots don't seem to mention is that to
view the film, it must either be scanned, projected, or printed. I
have heard the claim that scanning digitally loses quality, but so do
the other two processes. How good are the optics in your enlarger or
slide projector? How perfectly is either one focused? I really don't
know what sort of degredation is involved, but it seems that it might
be on the same order as through the camera optics, or worse. And lens
MTF's usually aren't quoted beyond 40 cycles/mm! Check the Zeiss or
Canon Web sites if you don't believe me.
I believe you. I just wish that someone would show me the numbers and/or
do the maths so I could really compare the different "errors".

Of course, film has the advantage that most errors perhaps are
introduced later in the chain that the actual image capture. In other
words, if you get lousy results because of a bad scan or projection, you
still have the film to go back to.


3. I know that the most common sensors are made up of individual
elements for the red, 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 former. Except for the Foveon sensor in the Sigma SD9/SD10, which
has about 3.5 million sites, each of which detects all three channels.
Yeah, I know. I think the Foveon technology is really interesting, but
I'm not too convinced about the current implementation or, *cough*, the
camera producer that uses it.


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
[ ... ]

Not really. The reality is that sensing all channels at each location
is a Good Thing, other factors being equal, but the color filter array
isn't as bad as you might think. First of all, the three color
channels aren't completely uncorrelated, so the information from a red
sensel can be used to help estimate the red and green values at that
point.
Fair enough. I still think they're stretching the reality a bit, though,
when they're talking about e.g. 6M pixels when all they have is 6M
*sensors*.

Second, images have some sort of spatial structure, and modern
demosaicing algorithms try to detect that to deduce missing
values.
Yes. I assume those algorithms do quite a good job, too. The mere
existance of any sort of "post processing" still makes me sceptical,
though; I think it can never beat getting all components directly from
the sensor like you usually do with a scanner.

Finally, the sampling rate is higher for the green channel, to
which the human visual system is most sensitive, both in luminance and
resolution.


5. And how about those other parameters I mentioned briefly above -
like different kinds of geometric distortions, noise, flat field
bias etc.? Can those be compared with the ones of plain old film?


Yup. Lots of them are only being noticed now with digital sensors
behind the same lenses that people have used for years with film.
I suspect that it's a matter of display more than anything else;
the magnification on screen at a 1:1 pixel magnification is huge
for most cameras, and people can use the little eyedropper to see
just how much the illumination falls off in the corner of the frame.
Possibly.

Maybe digital photos are actually a good way to test the quality of lenses?


6. And the chromic aberration effects? How serious are they these
days? And are the full-frame sensors that are actually found in
some high-end cameras now, in any way comparable to film in that
respect?


Chromatic aberration is basically in the lens. Doesn't matter
what sensor is behind it.
Well, maybe "chromatic aberration" wasn't the right expression to use.
(Right, I really ought to know more about this, as we see the same
things on our scanners...) The point was, I know that CCDs are quite
sensitive to various errors or inaccuracies introduced at the edges of
the lens, or just to the angle at which the beam hits it. The question
was really how important those effects are.



Well, maybe some people will say I have a somewhat critical or
conservative attitude towards digital cameras, but I actually think
you ought to be a bit sceptical when something "new and wonderful"
comes a long; new technology is too often introduced for technology's
own sake, IMO.


Oh, sure. But there are a number of photographers who are putting away
their 4.5x6 film cameras because they see better quality out of the
Kodak DCS 14 MP cameras. In a functional way, the best digitals are
pretty good, though their limitations are different from those of film
cameras.
Probably. I guess what's put me off so far is really the higher price
(I don't think that can be justified if they are "just as good as" or "a
little better than" film) combined with the shorter life-span and/or
limitations introduced by the fact that the "film" is glued to the the
camera body. As I've mentioned briefly earlier, I'm really dreaming
about consumer-level digital cameras with a more modular construction.
Imagine having the sensor in a socket with a standardised bus interface
- like the CPU, memory or card bus a computer - so you could replace it
when something better came along, or keep different sensors with
different caracteristics. Wouldn't that be nice?

Anyhow, some where good answers, there. Thanks.

- Toralf

Stephen H. Westin wrote:
Toralf writes:
[ snip ]



Be that as it may, some of the questions I'd like to have answered are
these:

1. What is the resolution of a 35mm film anyway?


It's hard to say, as the resolution limit is different from that of a
digital sensor. Rather than a hard limit, you get less information and
more blur and noise as you increase resolution in scanning a piece of
film.


I think I read
somewhere that a colour negative is at least 3000dpi. Is that
correct?


It's in the ballpark. [ ... ]
OK. Thanks


How about black&white?


Well, the data sheet on Kodak Technical Pan, which is an extreme upper
bound, has MTF at 50% at 180 c/mm or so. That's for ISO 25, developed
in Technidol. That's Kodak Tech Pub P-255, available at
http://www.kodak.com/global/en/professional/support/techPubs/p255/p255.jhtml?id=0.1.18.14.21.22.16&lc=en.
For Plus-X, at ISO 125, Tech Pub F-4018 (at
http://www.kodak.com/global/en/professional/support/techPubs/f4018/f4018.jhtml?id=0.1.18.14.21.20.16&lc=en)
rates it at 50 lp/mm at 1.6:1 contrast, 125 at 1000:1 (which you
aren't likely to reach it practice).

So I think we can say that scanning film at more than, say, 360
samples/mm (about 9,000 samples/inch) is pretty much useless. In most
circumstances, 100 samples/mm or 2,540 /inch is plenty. So we're in
the region of 9MP for a normal 24x36mm 35mm film frame.
I that would be 9MP without any sort of interpolation, though. But then,
like I said, you get the error introduced by the scanner instead...



(Yeah I know, a film doesn't have
pixels in exactly the same sense as a digital image, but it *is*
made up of discrete elements after all.)


But they aren't spaced on a regular grid, so things look a lot different.
Exactly. It would still be fun to know exactly how many "points" there
are, though.


2. What about the print? 300dpi?


Well, there are lots of variables involved there. One of the little
secrets that the "film-only" zealots don't seem to mention is that to
view the film, it must either be scanned, projected, or printed. I
have heard the claim that scanning digitally loses quality, but so do
the other two processes. How good are the optics in your enlarger or
slide projector? How perfectly is either one focused? I really don't
know what sort of degredation is involved, but it seems that it might
be on the same order as through the camera optics, or worse. And lens
MTF's usually aren't quoted beyond 40 cycles/mm! Check the Zeiss or
Canon Web sites if you don't believe me.
I believe you. I just wish that someone would show me the numbers and/or
do the maths so I could really compare the different "errors".

Of course, film has the advantage that most errors perhaps are
introduced later in the chain that the actual image capture. In other
words, if you get lousy results because of a bad scan or projection, you
still have the film to go back to.


3. I know that the most common sensors are made up of individual
elements for the red, 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 former. Except for the Foveon sensor in the Sigma SD9/SD10, which
has about 3.5 million sites, each of which detects all three channels.
Yeah, I know. I think the Foveon technology is really interesting, but
I'm not too convinced about the current implementation or, *cough*, the
camera producer that uses it.


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
[ ... ]

Not really. The reality is that sensing all channels at each location
is a Good Thing, other factors being equal, but the color filter array
isn't as bad as you might think. First of all, the three color
channels aren't completely uncorrelated, so the information from a red
sensel can be used to help estimate the red and green values at that
point.
Fair enough. I still think they're stretching the reality a bit, though,
when they're talking about e.g. 6M pixels when all they have is 6M
*sensors*.

Second, images have some sort of spatial structure, and modern
demosaicing algorithms try to detect that to deduce missing
values.
Yes. I assume those algorithms do quite a good job, too. The mere
existance of any sort of "post processing" still makes me sceptical,
though; I think it can never beat getting all components directly from
the sensor like you usually do with a scanner.

Finally, the sampling rate is higher for the green channel, to
which the human visual system is most sensitive, both in luminance and
resolution.


5. And how about those other parameters I mentioned briefly above -
like different kinds of geometric distortions, noise, flat field
bias etc.? Can those be compared with the ones of plain old film?


Yup. Lots of them are only being noticed now with digital sensors
behind the same lenses that people have used for years with film.
I suspect that it's a matter of display more than anything else;
the magnification on screen at a 1:1 pixel magnification is huge
for most cameras, and people can use the little eyedropper to see
just how much the illumination falls off in the corner of the frame.
Possibly.

Maybe digital photos are actually a good way to test the quality of lenses?


6. And the chromic aberration effects? How serious are they these
days? And are the full-frame sensors that are actually found in
some high-end cameras now, in any way comparable to film in that
respect?


Chromatic aberration is basically in the lens. Doesn't matter
what sensor is behind it.
Well, maybe "chromatic aberration" wasn't the right expression to use.
(Right, I really ought to know more about this, as we see the same
things on our scanners...) The point was, I know that CCDs are quite
sensitive to various errors or inaccuracies introduced at the edges of
the lens, or just to the angle at which the beam hits it. The question
was really how important those effects are.



Well, maybe some people will say I have a somewhat critical or
conservative attitude towards digital cameras, but I actually think
you ought to be a bit sceptical when something "new and wonderful"
comes a long; new technology is too often introduced for technology's
own sake, IMO.


Oh, sure. But there are a number of photographers who are putting away
their 4.5x6 film cameras because they see better quality out of the
Kodak DCS 14 MP cameras. In a functional way, the best digitals are
pretty good, though their limitations are different from those of film
cameras.
Probably. I guess what's put me off so far is really the higher price
(I don't think that can be justified if they are "just as good as" or "a
little better than" film) combined with the shorter life-span and/or
limitations introduced by the fact that the "film" is glued to the the
camera body. As I've mentioned briefly earlier, I'm really dreaming
about consumer-level digital cameras with a more modular construction.
Imagine having the sensor in a socket with a standardised bus interface
- like the CPU, memory or card bus a computer - so you could replace it
when something better came along, or keep different sensors with
different caracteristics. Wouldn't that be nice?

Anyhow, some where good answers, there. Thanks.

- Toralf