contrast in p&s digital cameras vs film

On Oct 14, 9:05 am, "Roger N. Clark (change username to rnclark)"
<usern....TakeThisOut@qwest.net> wrote:
> H.S. wrote:
> > Hello,
>
> > I was wondering if anybody can comment on the quality of contrast in the
> > pictures taken with a point and shoot digital camera compared to the one
> > obtained on 35mm film.
>
> > I have seen pictures from Canon A520 and a few older models. I can
> > usually pick them out from the ones scanned from negatives quite easily.
> > The ones taken with digital cameras usually appear to have less contrast
> > and less amount of colors (less saturated colors?).
>
> > Anybody know of any recent digital cameras in which the colors are
> > better and we can have more contrast? I know this may appear to be a bit
> > vague, but related comments are welcome.
>
> The main reason is that film has a toe in its characteristic
> curve and digital cameras are linear.

Is that so? My reading of the Gurney-Mott business (a couple of years
ago and very superficial) led me to conclude that the formation of the
latent image on film is also a linear process (as long as you're not
in the region of low or high intensity reciprocity failure). The
characteristic curve comes when you develop it. So I don't see how
this is any different from digital capture, where the detection is
linear and you then apply a curve. I'm not an expert and just scanned
the paper quickly, so may have completely misunderstood it.

I'd say the difference the OP see is because of the processing, which
I think deserves a lot more attention than people seem to think. I
know this is also what you say below, but I think saying that one is
linear and the other isn't is not accurate (as it refers to different
stages of capture/development in each case). But maybe I am wrong.


> They are also linear
> at the low end after the "gamma" tone curve is applied.
> Learn to use curves to add an s-curve response to give a
> film-like response. You can boost contrast in camera, but
> post processing gives more control over shadow and highlight detail.
>
 >> Stay informed about: contrast in p&s digital cameras vs film 

On Oct 14, 6:23 pm, "Roger N. Clark (change username to rnclark)"
<usern....TakeThisOut@qwest.net> wrote:
> acl wrote:
> > On Oct 14, 9:05 am, "Roger N. Clark (change username to rnclark)"
> > <usern....TakeThisOut@qwest.net> wrote:
> >> H.S. wrote:
> >>> Hello,
> >>> I was wondering if anybody can comment on the quality of contrast in the
> >>> pictures taken with a point and shoot digital camera compared to the one
> >>> obtained on 35mm film.
> >>> I have seen pictures from Canon A520 and a few older models. I can
> >>> usually pick them out from the ones scanned from negatives quite easily.
> >>> The ones taken with digital cameras usually appear to have less contrast
> >>> and less amount of colors (less saturated colors?).
> >>> Anybody know of any recent digital cameras in which the colors are
> >>> better and we can have more contrast? I know this may appear to be a bit
> >>> vague, but related comments are welcome.
> >> The main reason is that film has a toe in its characteristic
> >> curve and digital cameras are linear.
>
> > Is that so? My reading of the Gurney-Mott business (a couple of years
> > ago and very superficial) led me to conclude that the formation of the
> > latent image on film is also a linear process (as long as you're not
> > in the region of low or high intensity reciprocity failure). The
> > characteristic curve comes when you develop it. So I don't see how
> > this is any different from digital capture, where the detection is
> > linear and you then apply a curve. I'm not an expert and just scanned
> > the paper quickly, so may have completely misunderstood it.
>
> > I'd say the difference the OP see is because of the processing, which
> > I think deserves a lot more attention than people seem to think. I
> > know this is also what you say below, but I think saying that one is
> > linear and the other isn't is not accurate (as it refers to different
> > stages of capture/development in each case). But maybe I am wrong.
>
> Film has a portion of the characteristic curve that
> is linear on a log-log plot. The slope varies with
> developing and type of film. Slope can be close to 1 in
> some film+developer combinations. But that does not change the
> fact that film has a toe.

I realise that. What I am trying to say is this: When one says that
digital capture is linear, one is referring to the raw data. The
equivalent object in film capture isn't a developed slide or negative,
but the latent image (before development). And, as far as I remember,
the effect there is also linearly related to the light
intensity*exposure time; it is after development that you get a
nonlinear response, just like after raw conversion you get a nonlinear
response (if you've applied a curve).

I say that because I keep seeing statement like "digital is linear and
film isn't" as explanations of all sorts of things, and this puzzles
me because in one case we are discussing fully developed negatives/
slides while in the other completely undeveloped data.

But, as I said, maybe I am wrong and the latent response isn't linear.

> This is illustrated in Figure 8b at:http://www.clarkvision.com/imagedetail/dynamicrange2
>
> On a print, some point on the toe is set to black, and that
> is the main effect giving nice blacks. Try it in a photo
> editor on a digital camera image: use the curves tool,
> and somewhere near the low end, pull the curve down.
> Contrast goes up (also try boosting the highs).
> This is the same effect as printing and exposing the print
> to give nice black somewhere above zero response.
> You can do this with levels tool too, but the transition
> is not smooth; I prefer curves.
>
> Roger
>
>
>
> >> They are also linear
> >> at the low end after the "gamma" tone curve is applied.
> >> Learn to use curves to add an s-curve response to give a
> >> film-like response. You can boost contrast in camera, but
> >> post processing gives more control over shadow and highlight detail.
 >> Stay informed about: contrast in p&s digital cameras vs film 

On Oct 14, 7:00 pm, "Roger N. Clark (change username to rnclark)"
<usern....RemoveThis@qwest.net> wrote:
> acl wrote:
> > I realise that. What I am trying to say is this: When one says that
> > digital capture is linear, one is referring to the raw data. The
> > equivalent object in film capture isn't a developed slide or negative,
> > but the latent image (before development). And, as far as I remember,
> > the effect there is also linearly related to the light
> > intensity*exposure time; it is after development that you get a
> > nonlinear response, just like after raw conversion you get a nonlinear
> > response (if you've applied a curve).
>
> > I say that because I keep seeing statement like "digital is linear and
> > film isn't" as explanations of all sorts of things, and this puzzles
> > me because in one case we are discussing fully developed negatives/
> > slides while in the other completely undeveloped data.
>
> > But, as I said, maybe I am wrong and the latent response isn't linear.
>
> Film is linear at the low end plus an offset (fog + transmission
> of the emulsion), but at the high end, it is logarithmic because
> once a grain has been excited by a photon, another photon
> hitting the same grain won't add anything to the latent image.
> This is what gives print film such high-end response without
> saturating.

Yes, that's the explanation for why highlights are so much easier on
film!

> (It typically takes a couple of photons to excite
> a grain, but once done, the grain is no longer sensitive to
> light; photons must hit other grains to contribute to the image.)

Yes but until this (=you start getting many photons/grain during your
exposure) occurs, the response is linear. No?

>
> The standard curve applied in digital cameras is still linear
> at the low end. See Figure 8a in the web page I gave.
> So the shadows in a digital camera image shows linear
> response when raw linear conversion, jpeg (without excessive
> contrast added), or raw conversion with a standard curve applied.
> That is different than shadows in film (print or slide) which
> has the toe.

Well as I tried to say twice, that, ie
> So the shadows in a digital camera image shows linear
> response when raw linear conversion, jpeg (without excessive
> contrast added), or raw conversion with a standard curve applied.
has nothing to do with the fact that sensors respond linearly to
light, but is a result of the curve applied. No? Which is why I say
that how you convert is important.
 >> Stay informed about: contrast in p&s digital cameras vs film 

acl wrote:
> On Oct 14, 9:05 am, "Roger N. Clark (change username to rnclark)"
> <usern....TakeThisOut@qwest.net> wrote:
>> H.S. wrote:
>>> Hello,
>>> I was wondering if anybody can comment on the quality of contrast in the
>>> pictures taken with a point and shoot digital camera compared to the one
>>> obtained on 35mm film.
>>> I have seen pictures from Canon A520 and a few older models. I can
>>> usually pick them out from the ones scanned from negatives quite easily.
>>> The ones taken with digital cameras usually appear to have less contrast
>>> and less amount of colors (less saturated colors?).
>>> Anybody know of any recent digital cameras in which the colors are
>>> better and we can have more contrast? I know this may appear to be a bit
>>> vague, but related comments are welcome.
>> The main reason is that film has a toe in its characteristic
>> curve and digital cameras are linear.
>
> Is that so? My reading of the Gurney-Mott business (a couple of years
> ago and very superficial) led me to conclude that the formation of the
> latent image on film is also a linear process (as long as you're not
> in the region of low or high intensity reciprocity failure). The
> characteristic curve comes when you develop it. So I don't see how
> this is any different from digital capture, where the detection is
> linear and you then apply a curve. I'm not an expert and just scanned
> the paper quickly, so may have completely misunderstood it.
>
> I'd say the difference the OP see is because of the processing, which
> I think deserves a lot more attention than people seem to think. I
> know this is also what you say below, but I think saying that one is
> linear and the other isn't is not accurate (as it refers to different
> stages of capture/development in each case). But maybe I am wrong.

Film has a portion of the characteristic curve that
is linear on a log-log plot. The slope varies with
developing and type of film. Slope can be close to 1 in
some film+developer combinations. But that does not change the
fact that film has a toe. This is illustrated in Figure 8b at:
http://www.clarkvision.com/imagedetail/dynamicrange2

On a print, some point on the toe is set to black, and that
is the main effect giving nice blacks. Try it in a photo
editor on a digital camera image: use the curves tool,
and somewhere near the low end, pull the curve down.
Contrast goes up (also try boosting the highs).
This is the same effect as printing and exposing the print
to give nice black somewhere above zero response.
You can do this with levels tool too, but the transition
is not smooth; I prefer curves.

Roger

>
>
>> They are also linear
>> at the low end after the "gamma" tone curve is applied.
>> Learn to use curves to add an s-curve response to give a
>> film-like response. You can boost contrast in camera, but
>> post processing gives more control over shadow and highlight detail.
>>
>
>
>
 >> Stay informed about: contrast in p&s digital cameras vs film 

acl wrote:

> I realise that. What I am trying to say is this: When one says that
> digital capture is linear, one is referring to the raw data. The
> equivalent object in film capture isn't a developed slide or negative,
> but the latent image (before development). And, as far as I remember,
> the effect there is also linearly related to the light
> intensity*exposure time; it is after development that you get a
> nonlinear response, just like after raw conversion you get a nonlinear
> response (if you've applied a curve).
>
> I say that because I keep seeing statement like "digital is linear and
> film isn't" as explanations of all sorts of things, and this puzzles
> me because in one case we are discussing fully developed negatives/
> slides while in the other completely undeveloped data.
>
> But, as I said, maybe I am wrong and the latent response isn't linear.

Film is linear at the low end plus an offset (fog + transmission
of the emulsion), but at the high end, it is logarithmic because
once a grain has been excited by a photon, another photon
hitting the same grain won't add anything to the latent image.
This is what gives print film such high-end response without
saturating. (It typically takes a couple of photons to excite
a grain, but once done, the grain is no longer sensitive to
light; photons must hit other grains to contribute to the image.)

The standard curve applied in digital cameras is still linear
at the low end. See Figure 8a in the web page I gave.
So the shadows in a digital camera image shows linear
response when raw linear conversion, jpeg (without excessive
contrast added), or raw conversion with a standard curve applied.
That is different than shadows in film (print or slide) which
has the toe.

Roger
 >> Stay informed about: contrast in p&s digital cameras vs film 

On Oct 14, 9:55 pm, "Roger N. Clark (change username to rnclark)"
<usern....TakeThisOut@qwest.net> wrote:
> acl wrote:
> > On Oct 14, 7:00 pm, "Roger N. Clark (change username to rnclark)"
> > <usern....TakeThisOut@qwest.net> wrote:
> >> (It typically takes a couple of photons to excite
> >> a grain, but once done, the grain is no longer sensitive to
> >> light; photons must hit other grains to contribute to the image.)
>
> > Yes but until this (=you start getting many photons/grain during your
> > exposure) occurs, the response is linear. No?
>
> It seems like it might be, but I'm not sure. See below.

In fact this thread got me interested again in this, but I could not
find anything very recent in a cursory search (there are review
articles from the 40s and so on, and a book that is also ancient). But
the Gurney-Mott paper seems to be the answer. I'll try to unearth it
again and read it.

>
>
>
>
>
> >> The standard curve applied in digital cameras is still linear
> >> at the low end. See Figure 8a in the web page I gave.
> >> So the shadows in a digital camera image shows linear
> >> response when raw linear conversion, jpeg (without excessive
> >> contrast added), or raw conversion with a standard curve applied.
> >> That is different than shadows in film (print or slide) which
> >> has the toe.
>
> > Well as I tried to say twice, that, ie
> >> So the shadows in a digital camera image shows linear
> >> response when raw linear conversion, jpeg (without excessive
> >> contrast added), or raw conversion with a standard curve applied.
> > has nothing to do with the fact that sensors respond linearly to
> > light, but is a result of the curve applied. No? Which is why I say
> > that how you convert is important.
>
> I would say conversion is a post processing step so anything
> can apply. One need not actually convert the raw data,
> simply split the data out and get 3 images, one in red,
> a second in green, and a third in blue, with no modification
> or manipulation of the data.
>
> It seems like film low level response might be linear,
> but I can't see why chemically regarding the characteristic curve
> it would change to a curve in the toe. So I don't know
> what film does at the latent image stage. But does that
> matter, as the latent image can not be viewed and must be
> chemically processed to see, unlike digital camera raw data.
> I don't think you can develop film, say Fuji Sensia,
> or Tri-X and not get a curving toe.
>

Well I wasn't trying to make a philosophical point; I was trying to
say that the fact that the response at some point in the capture
process is linear doesn't directly result in "flat" or whatever
output. And I drew an analogy to illustrate what I mean, namely, that
film also seems to react linearly before development, so any
difference in the results can't be due to that (we ignore the
difference in high intensities).

Anyway, my response to the OP would be that canon compact cameras seem
to do better than others (that I tried, ie minolta and fuji) in terms
of colour. Or he can get a photoshop plug in or a program to take an
image and simulate some type of film (most are very bad though). Or
process it himself in photoshop, gimp, paintshop etc (I think
paintshop has automatic tools for this too). In short, play with the
various tools and techniques until it finally works like he wants.
 >> Stay informed about: contrast in p&s digital cameras vs film 

acl wrote:
> On Oct 14, 7:00 pm, "Roger N. Clark (change username to rnclark)"
> <usern....DeleteThis@qwest.net> wrote:

>> (It typically takes a couple of photons to excite
>> a grain, but once done, the grain is no longer sensitive to
>> light; photons must hit other grains to contribute to the image.)
>
> Yes but until this (=you start getting many photons/grain during your
> exposure) occurs, the response is linear. No?

It seems like it might be, but I'm not sure. See below.
>
>> The standard curve applied in digital cameras is still linear
>> at the low end. See Figure 8a in the web page I gave.
>> So the shadows in a digital camera image shows linear
>> response when raw linear conversion, jpeg (without excessive
>> contrast added), or raw conversion with a standard curve applied.
>> That is different than shadows in film (print or slide) which
>> has the toe.
>
> Well as I tried to say twice, that, ie
>> So the shadows in a digital camera image shows linear
>> response when raw linear conversion, jpeg (without excessive
>> contrast added), or raw conversion with a standard curve applied.
> has nothing to do with the fact that sensors respond linearly to
> light, but is a result of the curve applied. No? Which is why I say
> that how you convert is important.

I would say conversion is a post processing step so anything
can apply. One need not actually convert the raw data,
simply split the data out and get 3 images, one in red,
a second in green, and a third in blue, with no modification
or manipulation of the data.

It seems like film low level response might be linear,
but I can't see why chemically regarding the characteristic curve
it would change to a curve in the toe. So I don't know
what film does at the latent image stage. But does that
matter, as the latent image can not be viewed and must be
chemically processed to see, unlike digital camera raw data.
I don't think you can develop film, say Fuji Sensia,
or Tri-X and not get a curving toe.

Roger
 >> Stay informed about: contrast in p&s digital cameras vs film 

On Oct 14, 10:37 pm, Doug McDonald <mcdonald.TakeThisOut@SnPoAM_scs.uiuc.edu>
wrote:
> Roger N. Clark (change username to rnclark) wrote:
>
>
>
> > It seems like film low level response might be linear,
> > but I can't see why chemically regarding the characteristic curve
> > it would change to a curve in the toe. So I don't know
> > what film does at the latent image stage. But does that
> > matter, as the latent image can not be viewed and must be
> > chemically processed to see, unlike digital camera raw data.
> > I don't think you can develop film, say Fuji Sensia,
> > or Tri-X and not get a curving toe.
>
> Most B&W negative film is quite linear in the toe, and only
> in the toe.

But you are talking about developed film, yes?

> Remember that it has fog. To see the linearity you
> have to measure the transmission in the toe region, correct for
> the possibility of overlapping grains if the transmission drops much below
> 85% (after compensation for surface reflection) and then
> subtract off the background. Just before CCDs obsoleted film,
> astrophotographers took multiple short exposures where the
> transmission of the negative in regions of maximum broad field
> density (i.e. excluding stars) was about 20 to 50%, scanned
> them and added them together. This produced lower limiting
> broad field density than using one long exposure, simply
> because one no longer lost information to overlapping grains.
> But it was very very ticklish business.
>
> Doug McDonald
 >> Stay informed about: contrast in p&s digital cameras vs film 

Roger N. Clark (change username to rnclark) wrote:

>
> It seems like film low level response might be linear,
> but I can't see why chemically regarding the characteristic curve
> it would change to a curve in the toe. So I don't know
> what film does at the latent image stage. But does that
> matter, as the latent image can not be viewed and must be
> chemically processed to see, unlike digital camera raw data.
> I don't think you can develop film, say Fuji Sensia,
> or Tri-X and not get a curving toe.
>


Most B&W negative film is quite linear in the toe, and only
in the toe. Remember that it has fog. To see the linearity you
have to measure the transmission in the toe region, correct for
the possibility of overlapping grains if the transmission drops much below
85% (after compensation for surface reflection) and then
subtract off the background. Just before CCDs obsoleted film,
astrophotographers took multiple short exposures where the
transmission of the negative in regions of maximum broad field
density (i.e. excluding stars) was about 20 to 50%, scanned
them and added them together. This produced lower limiting
broad field density than using one long exposure, simply
because one no longer lost information to overlapping grains.
But it was very very ticklish business.

Doug McDonald
 >> Stay informed about: contrast in p&s digital cameras vs film 

On Oct 14, 10:53 pm, "H.S." <hs.saDELETEME....TakeThisOut@gmail.com> wrote:
> acl wrote:
>
> > Well I wasn't trying to make a philosophical point; I was trying to
> > say that the fact that the response at some point in the capture
> > process is linear doesn't directly result in "flat" or whatever
> > output. And I drew an analogy to illustrate what I mean, namely, that
> > film also seems to react linearly before development, so any
> > difference in the results can't be due to that (we ignore the
> > difference in high intensities).
>
> > Anyway, my response to the OP would be that canon compact cameras seem
> > to do better than others (that I tried, ie minolta and fuji) in terms
> > of colour. Or he can get a photoshop plug in or a program to take an
> > image and simulate some type of film (most are very bad though). Or
> > process it himself in photoshop, gimp, paintshop etc (I think
> > paintshop has automatic tools for this too). In short, play with the
> > various tools and techniques until it finally works like he wants.
>
> It's been very interesting reading all the posts in this thread. Gives
> me some information that I wasn't very clear about (had only heard it
> mention here and there) and it has prompted me to know about it and
> experiment with the digital pics. I use gimp, and tried a few curve
> setting last night and liked the improvements.
>

Hi, two things:
a) Don't believe what is said in this newsgroup without confirming it
somehow (Roger and Doug in this thread are reliable sources, but many
others aren't-don't make the mistake of equating a confident attitude
with actual knowledge :] )
b) About processing in general, take a look at these
http://www.ronbigelow.com/articles/articles.htm
I haven't read most of them, but they seem quite good. He has some on
curves, too. There are also numerous internet resources on what curves
do.
 >> Stay informed about: contrast in p&s digital cameras vs film 

acl wrote:

>
> Well I wasn't trying to make a philosophical point; I was trying to
> say that the fact that the response at some point in the capture
> process is linear doesn't directly result in "flat" or whatever
> output. And I drew an analogy to illustrate what I mean, namely, that
> film also seems to react linearly before development, so any
> difference in the results can't be due to that (we ignore the
> difference in high intensities).
>
> Anyway, my response to the OP would be that canon compact cameras seem
> to do better than others (that I tried, ie minolta and fuji) in terms
> of colour. Or he can get a photoshop plug in or a program to take an
> image and simulate some type of film (most are very bad though). Or
> process it himself in photoshop, gimp, paintshop etc (I think
> paintshop has automatic tools for this too). In short, play with the
> various tools and techniques until it finally works like he wants.
>

It's been very interesting reading all the posts in this thread. Gives
me some information that I wasn't very clear about (had only heard it
mention here and there) and it has prompted me to know about it and
experiment with the digital pics. I use gimp, and tried a few curve
setting last night and liked the improvements.

Thanks,
->HS
 >> Stay informed about: contrast in p&s digital cameras vs film 

On Oct 14, 9:55 pm, "Roger N. Clark (change username to rnclark)"
<usern... DeleteThis @qwest.net> wrote:
> acl wrote:
> > On Oct 14, 7:00 pm, "Roger N. Clark (change username to rnclark)"
> > <usern... DeleteThis @qwest.net> wrote:
> >> (It typically takes a couple of photons to excite
> >> a grain, but once done, the grain is no longer sensitive to
> >> light; photons must hit other grains to contribute to the image.)
>
> > Yes but until this (=you start getting many photons/grain during your
> > exposure) occurs, the response is linear. No?
>
> It seems like it might be, but I'm not sure. See below.
>
>
>
>
>
> >> The standard curve applied in digital cameras is still linear
> >> at the low end. See Figure 8a in the web page I gave.
> >> So the shadows in a digital camera image shows linear
> >> response when raw linear conversion, jpeg (without excessive
> >> contrast added), or raw conversion with a standard curve applied.
> >> That is different than shadows in film (print or slide) which
> >> has the toe.
>
> > Well as I tried to say twice, that, ie
> >> So the shadows in a digital camera image shows linear
> >> response when raw linear conversion, jpeg (without excessive
> >> contrast added), or raw conversion with a standard curve applied.
> > has nothing to do with the fact that sensors respond linearly to
> > light, but is a result of the curve applied. No? Which is why I say
> > that how you convert is important.
>
> I would say conversion is a post processing step so anything
> can apply. One need not actually convert the raw data,
> simply split the data out and get 3 images, one in red,
> a second in green, and a third in blue, with no modification
> or manipulation of the data.
>
> It seems like film low level response might be linear,
> but I can't see why chemically regarding the characteristic curve
> it would change to a curve in the toe. So I don't know
> what film does at the latent image stage. But does that
> matter, as the latent image can not be viewed and must be
> chemically processed to see, unlike digital camera raw data.
> I don't think you can develop film, say Fuji Sensia,
> or Tri-X and not get a curving toe.
>
> Roger

OK, the best reference I found that's easily accessible to me (ie
accessible online from where I am) is this
http://archimede.mat.ulaval.ca/rcs/cgi-rcs/recherche.cgi?soumettre=Aff...er&cote
which gives a summary of the relevant points (dead time during which
the activated site repels other electrons, giving rise to high-
intensity reciprocity failure, and decay time of the Ag atom, giving
rise to low-intensity reciprocity failure). Do you, Doug, or anybody
else, have any references where I can find out estimates of these
times, and more details (up to date, preferably)?
 >> Stay informed about: contrast in p&s digital cameras vs film 

acl wrote:
> On Oct 14, 9:55 pm, "Roger N. Clark (change username to rnclark)"
> <usern... RemoveThis @qwest.net> wrote:
>> acl wrote:
>>> On Oct 14, 7:00 pm, "Roger N. Clark (change username to rnclark)"
>>> <usern... RemoveThis @qwest.net> wrote:
>>>> (It typically takes a couple of photons to excite
>>>> a grain, but once done, the grain is no longer sensitive to
>>>> light; photons must hit other grains to contribute to the image.)
>>> Yes but until this (=you start getting many photons/grain during your
>>> exposure) occurs, the response is linear. No?
>> It seems like it might be, but I'm not sure. See below.
>>
>>
>>
>>
>>
>>>> The standard curve applied in digital cameras is still linear
>>>> at the low end. See Figure 8a in the web page I gave.
>>>> So the shadows in a digital camera image shows linear
>>>> response when raw linear conversion, jpeg (without excessive
>>>> contrast added), or raw conversion with a standard curve applied.
>>>> That is different than shadows in film (print or slide) which
>>>> has the toe.
>>> Well as I tried to say twice, that, ie
>>>> So the shadows in a digital camera image shows linear
>>>> response when raw linear conversion, jpeg (without excessive
>>>> contrast added), or raw conversion with a standard curve applied.
>>> has nothing to do with the fact that sensors respond linearly to
>>> light, but is a result of the curve applied. No? Which is why I say
>>> that how you convert is important.
>> I would say conversion is a post processing step so anything
>> can apply. One need not actually convert the raw data,
>> simply split the data out and get 3 images, one in red,
>> a second in green, and a third in blue, with no modification
>> or manipulation of the data.
>>
>> It seems like film low level response might be linear,
>> but I can't see why chemically regarding the characteristic curve
>> it would change to a curve in the toe. So I don't know
>> what film does at the latent image stage. But does that
>> matter, as the latent image can not be viewed and must be
>> chemically processed to see, unlike digital camera raw data.
>> I don't think you can develop film, say Fuji Sensia,
>> or Tri-X and not get a curving toe.
>>
>> Roger
>
> OK, the best reference I found that's easily accessible to me (ie
> accessible online from where I am) is this
> http://archimede.mat.ulaval.ca/rcs/cgi-rcs/recherche.cgi?soumettre=Aff...er&cote
> which gives a summary of the relevant points (dead time during which
> the activated site repels other electrons, giving rise to high-
> intensity reciprocity failure, and decay time of the Ag atom, giving
> rise to low-intensity reciprocity failure). Do you, Doug, or anybody
> else, have any references where I can find out estimates of these
> times, and more details (up to date, preferably)?
>
I think some of the film data sheets may indicate some of these
times. It varies from film to film. I'm mostly familiar
with the low light end (even made reciprocity curves on
some films, hypered in N2 and normal, as an undergraduate in
physics). The question might be what is the 1/e loss time?
It can vary from a few minutes on bad films to hours for
the good films (like Kodak 103aF used in astronomy).
I don't remember how the manufacturers varied this effect
(chemically in the making of the emulsion).

Roger
 >> Stay informed about: contrast in p&s digital cameras vs film