contrast in p&s digital cameras vs film

Discussion in 'Digital Photography' started by H.S., Oct 14, 2007.

  1. H.S.

    H.S. Guest

    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.

    thanks,
    ->HS
    H.S., Oct 14, 2007
    #1
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  2. 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. 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.

    Roger
    Roger N. Clark (change username to rnclark), Oct 14, 2007
    #2
    1. Advertising

  3. H.S.

    acl Guest

    On Oct 14, 9:05 am, "Roger N. Clark (change username to rnclark)"
    <> 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.
    >
    acl, Oct 14, 2007
    #3
  4. acl wrote:
    > On Oct 14, 9:05 am, "Roger N. Clark (change username to rnclark)"
    > <> 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.
    >>

    >
    >
    >
    Roger N. Clark (change username to rnclark), Oct 14, 2007
    #4
  5. H.S.

    acl Guest

    On Oct 14, 6:23 pm, "Roger N. Clark (change username to rnclark)"
    <> wrote:
    > acl wrote:
    > > On Oct 14, 9:05 am, "Roger N. Clark (change username to rnclark)"
    > > <> 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.
    acl, Oct 14, 2007
    #5
  6. 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
    Roger N. Clark (change username to rnclark), Oct 14, 2007
    #6
  7. H.S.

    acl Guest

    On Oct 14, 7:00 pm, "Roger N. Clark (change username to rnclark)"
    <> 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.
    acl, Oct 14, 2007
    #7
  8. acl wrote:
    > On Oct 14, 7:00 pm, "Roger N. Clark (change username to rnclark)"
    > <> 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
    Roger N. Clark (change username to rnclark), Oct 14, 2007
    #8
  9. H.S.

    acl Guest

    On Oct 14, 9:55 pm, "Roger N. Clark (change username to rnclark)"
    <> wrote:
    > acl wrote:
    > > On Oct 14, 7:00 pm, "Roger N. Clark (change username to rnclark)"
    > > <> 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.
    acl, Oct 14, 2007
    #9
  10. 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
    Doug McDonald, Oct 14, 2007
    #10
  11. H.S.

    H.S. Guest

    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
    H.S., Oct 14, 2007
    #11
  12. H.S.

    acl Guest

    On Oct 14, 10:37 pm, Doug McDonald <mcdonald@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
    acl, Oct 14, 2007
    #12
  13. H.S.

    acl Guest

    On Oct 14, 10:53 pm, "H.S." <> 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.
    acl, Oct 14, 2007
    #13
  14. H.S.

    acl Guest

    On Oct 14, 9:55 pm, "Roger N. Clark (change username to rnclark)"
    <> wrote:
    > acl wrote:
    > > On Oct 14, 7:00 pm, "Roger N. Clark (change username to rnclark)"
    > > <> 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=Afficher&cote=030206&nbre=17
    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)?
    acl, Oct 15, 2007
    #14
  15. acl wrote:
    > On Oct 14, 9:55 pm, "Roger N. Clark (change username to rnclark)"
    > <> wrote:
    >> acl wrote:
    >>> On Oct 14, 7:00 pm, "Roger N. Clark (change username to rnclark)"
    >>> <> 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=Afficher&cote=030206&nbre=17
    > 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
    Roger N. Clark (change username to rnclark), Oct 15, 2007
    #15
  16. Doug McDonald wrote:

    > 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


    Doug,
    I know of only one person who stacked scanned film astrophotos.
    Did a great job, by the way, and the response need not
    be linear for it to work, especially the same subject exposed
    the same amount of time. People do that now with jpegs.
    But scanned film brought out more faint detail than one could
    print anyway, so it was/is a win/win situation.

    Roger
    Roger N. Clark (change username to rnclark), Oct 15, 2007
    #16
  17. On Oct 14, 9:07 am, acl <> wrote:
    > On Oct 14, 9:05 am, "Roger N. Clark (change username to rnclark)"
    >
    >
    >
    > <> 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.


    Depends on the film. Some are quite linear, others are quite S-
    curved. Look at the characteristic curves of various films.
    Don Stauffer in Minnesota, Oct 15, 2007
    #17
  18. H.S.

    acl Guest

    On Oct 15, 3:33 pm, Don Stauffer in Minnesota <>
    wrote:
    > On Oct 14, 9:07 am, acl <> wrote:
    >
    >
    >
    > > On Oct 14, 9:05 am, "Roger N. Clark (change username to rnclark)"

    >
    > > <> 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.

    >
    > Depends on the film. Some are quite linear, others are quite S-
    > curved. Look at the characteristic curves of various films.



    I was talking about the latent image. See here:
    > > ... led me to conclude that the formation of the
    > > latent image on film is also a linear process...
    acl, Oct 15, 2007
    #18
  19. "Roger N. Clark (change username to rnclark)" <> wrote:
    >
    > The main reason is that film has a toe in its characteristic
    > curve and digital cameras are linear. 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.
    >


    I think that *most* P&S users do NOT post process their images and often go
    directly from SD card to upload to the processor. Those that do post
    processing are probably mostly limitted to red-eye removal or cropping. I
    think a relatively few P&S users do true post processing as you describe.

    --
    Thomas T. Veldhouse

    Ninety percent of the politicians give the other ten percent a bad reputation.
    -- Henry Kissinger
    Thomas T. Veldhouse, Oct 15, 2007
    #19
  20. H.S.

    H.S. Guest

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

    > film-like response. You can boost contrast in camera, but


    er ... how can one do that?
    H.S., Oct 15, 2007
    #20
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