Still trying to figure the grey level of an 18% grey card (was: If I shoot a grey card, should this

Discussion in 'Digital Photography' started by Alan F Cross, Feb 29, 2004.

  1. Alan F Cross

    Alan F Cross Guest

    I had several responses on this, all giving different answers!! I have
    also seen three definitions of the meaning of 18% grey:

    Definition 1: An analysis of 'average scenes' (whatever that may be)
    showed they were 18% reflective. Can't imagine there is such a thing as
    an average scene that would be in any way useful!

    Definition 2: the mid point of a 5-stop scale. I can see that 100/18 is
    around 2.5 stops. This sounds more plausible, but if you work on a
    6-stop range, the point moves to 12.5% so there's little justification
    for the figure.

    Definition 3: It's just an arbitrary figure to which most exposure
    meters are calibrated, by convention (and some do something else).

    Perhaps the truth is a combination of these. But there must be a value
    (between 0 and 255) that represents the same shade of grey as an 18%
    card. I know that there is the gamma question, but surely this is to
    essentially remove the non-linearity of the display tube, not to distort
    the grey-scale itself.

    A mid-grey that is scanned and then printed should look the same, no
    matter how screwed up it is on the display. I would have thought that
    the tube should *try* to display the same grey that is being scanned and
    being printed (within the constraints of reflective vs transmissive
    viewing).

    So, the question remains: if I create a grey of 127 or 128, *should* it
    look like an 18% grey card? If not, what level of grey should?

    The root of my question is the following problem:
    When I send mono work out for printing, I attach a grey scale of equal
    steps (0, 16, 32, 48,.....240, 255). It is easy to recognise 0 and 255
    when printed, but how do I tell them that their rendition of mid-grey is
    too light or too dark?

    I would need a full wedge to prove linearity across the range, and to
    ensure that there is no black or white clipping. But I really want a
    separate grey patch, labelled "this should look like and 18% grey card
    when printed". Perhaps this is 127/128, or perhaps it's something else
    (and that is the question!) The only reason to choose 18% grey is that
    they would certainly have a reference card available to compare.

    I'd appreciate any further comments on this perplexing (but essentially
    simple) issue.

    TIA
    --
    Alan F Cross
    Alan F Cross, Feb 29, 2004
    #1
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  2. Alan F Cross

    Robertwgross Guest

    Re: Still trying to figure the grey level of an 18% grey card (was: If I shoot a grey card, should this end up a

    Alan, shoot a Kodak 18% gray card and be done with it.

    ---Bob Gross---
    Robertwgross, Feb 29, 2004
    #2
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  3. Alan F Cross

    Don Coon Guest

    "Alan F Cross" <> wrote in message
    news:...
    > I had several responses on this, all giving different answers!! I have
    > also seen three definitions of the meaning of 18% grey:
    >
    > Definition 1: An analysis of 'average scenes' (whatever that may be)
    > showed they were 18% reflective. Can't imagine there is such a thing as
    > an average scene that would be in any way useful!
    >
    > Definition 2: the mid point of a 5-stop scale. I can see that 100/18 is
    > around 2.5 stops. This sounds more plausible, but if you work on a
    > 6-stop range, the point moves to 12.5% so there's little justification
    > for the figure.
    >
    > Definition 3: It's just an arbitrary figure to which most exposure
    > meters are calibrated, by convention (and some do something else).
    >
    > Perhaps the truth is a combination of these. But there must be a value
    > (between 0 and 255) that represents the same shade of grey as an 18%
    > card. I know that there is the gamma question, but surely this is to
    > essentially remove the non-linearity of the display tube, not to distort
    > the grey-scale itself.
    >
    > A mid-grey that is scanned and then printed should look the same, no
    > matter how screwed up it is on the display. I would have thought that
    > the tube should *try* to display the same grey that is being scanned and
    > being printed (within the constraints of reflective vs transmissive
    > viewing).
    >
    > So, the question remains: if I create a grey of 127 or 128, *should* it
    > look like an 18% grey card? If not, what level of grey should?
    >
    > The root of my question is the following problem:
    > When I send mono work out for printing, I attach a grey scale of equal
    > steps (0, 16, 32, 48,.....240, 255). It is easy to recognise 0 and 255
    > when printed, but how do I tell them that their rendition of mid-grey is
    > too light or too dark?
    >
    > I would need a full wedge to prove linearity across the range, and to
    > ensure that there is no black or white clipping. But I really want a
    > separate grey patch, labelled "this should look like and 18% grey card
    > when printed". Perhaps this is 127/128, or perhaps it's something else
    > (and that is the question!) The only reason to choose 18% grey is that
    > they would certainly have a reference card available to compare.
    >
    > I'd appreciate any further comments on this perplexing (but essentially
    > simple) issue.


    Have you tried scanning a grey card?
    Don Coon, Feb 29, 2004
    #3
  4. Alan F Cross

    Tony Spadaro Guest

    A grey card comes out at about RG&B 160 on a reasonably calibrated
    monitor.

    --
    http://www.chapelhillnoir.com
    home of The Camera-ist's Manifesto
    The Improved Links Pages are at
    http://www.chapelhillnoir.com/links/mlinks00.html
    A sample chapter from my novel "Haight-Ashbury" is at
    http://www.chapelhillnoir.com/writ/hait/hatitl.html
    "Alan F Cross" <> wrote in message
    news:...
    > I had several responses on this, all giving different answers!! I have
    > also seen three definitions of the meaning of 18% grey:
    >
    > Definition 1: An analysis of 'average scenes' (whatever that may be)
    > showed they were 18% reflective. Can't imagine there is such a thing as
    > an average scene that would be in any way useful!
    >
    > Definition 2: the mid point of a 5-stop scale. I can see that 100/18 is
    > around 2.5 stops. This sounds more plausible, but if you work on a
    > 6-stop range, the point moves to 12.5% so there's little justification
    > for the figure.
    >
    > Definition 3: It's just an arbitrary figure to which most exposure
    > meters are calibrated, by convention (and some do something else).
    >
    > Perhaps the truth is a combination of these. But there must be a value
    > (between 0 and 255) that represents the same shade of grey as an 18%
    > card. I know that there is the gamma question, but surely this is to
    > essentially remove the non-linearity of the display tube, not to distort
    > the grey-scale itself.
    >
    > A mid-grey that is scanned and then printed should look the same, no
    > matter how screwed up it is on the display. I would have thought that
    > the tube should *try* to display the same grey that is being scanned and
    > being printed (within the constraints of reflective vs transmissive
    > viewing).
    >
    > So, the question remains: if I create a grey of 127 or 128, *should* it
    > look like an 18% grey card? If not, what level of grey should?
    >
    > The root of my question is the following problem:
    > When I send mono work out for printing, I attach a grey scale of equal
    > steps (0, 16, 32, 48,.....240, 255). It is easy to recognise 0 and 255
    > when printed, but how do I tell them that their rendition of mid-grey is
    > too light or too dark?
    >
    > I would need a full wedge to prove linearity across the range, and to
    > ensure that there is no black or white clipping. But I really want a
    > separate grey patch, labelled "this should look like and 18% grey card
    > when printed". Perhaps this is 127/128, or perhaps it's something else
    > (and that is the question!) The only reason to choose 18% grey is that
    > they would certainly have a reference card available to compare.
    >
    > I'd appreciate any further comments on this perplexing (but essentially
    > simple) issue.
    >
    > TIA
    > --
    > Alan F Cross
    Tony Spadaro, Feb 29, 2004
    #4
  5. Alan F Cross

    mark_digital Guest

    "Alan F Cross" <> wrote in message
    news:...
    > So, the question remains: if I create a grey of 127 or 128, *should* it
    > look like an 18% grey card? If not, what level of grey should?


    A few years ago there was a discussion in this group along the same line you
    seem to be asking. I'm sure it made a few go out and buy a gray card and
    understand a bit better about nuetral gray and it's visual perception under
    varying light sources and intensities.
    If you printer and paper were capable of producing a sample that could
    reflect 18% gray then your problem would be solved.
    mark_digital, Feb 29, 2004
    #5
  6. Alan F Cross

    Guest

    In message <>,
    Alan F Cross <> wrote:

    >Perhaps the truth is a combination of these. But there must be a value
    >(between 0 and 255) that represents the same shade of grey as an 18%
    >card.


    That would be (0.18^(1/2.2))*255 = ~117. Most cameras and RAW
    converters target ~127, though.
    --

    <>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
    John P Sheehy <>
    ><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
    , Feb 29, 2004
    #6
  7. Alan F Cross

    Guest

    In message <>,
    Alan F Cross <> wrote:

    >So, the question remains: if I create a grey of 127 or 128, *should* it
    >look like an 18% grey card? If not, what level of grey should?


    I would think that the answer depends on the paper used. Paper is in
    its own little world of low contrast, and blacks that are grey in the
    real world. I don't think prints even attempt to center around a grey
    card.
    --

    <>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
    John P Sheehy <>
    ><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
    , Feb 29, 2004
    #7
  8. Alan F Cross

    Guest

    In message <PAd0c.38058$%>,
    "Tony Spadaro" <> wrote:

    > A grey card comes out at about RG&B 160 on a reasonably calibrated
    >monitor.


    Huh? Monitors don't have RGB values. They are passive analog devices,
    displaying voltages created by the gfx chips. An average exposure will
    be about 127 with most cameras and RAW converters. I've seen 117 as
    well (which is what 18% grey should be) in one context, (but I don't
    remember where).
    --

    <>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
    John P Sheehy <>
    ><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
    , Feb 29, 2004
    #8
  9. Alan F Cross

    Tony Spadaro Guest

    Quite wrong. If you would take the time to compare a grey card to the greys
    available in Photoshop you will find - that if your monitor is fairly well
    calibrated you will get about 160. Don't talk theory when it takes vary
    little work to see that your are flat out wrong. If you don't have a grey
    card - buy one.

    --
    http://www.chapelhillnoir.com
    home of The Camera-ist's Manifesto
    The Improved Links Pages are at
    http://www.chapelhillnoir.com/links/mlinks00.html
    A sample chapter from my novel "Haight-Ashbury" is at
    http://www.chapelhillnoir.com/writ/hait/hatitl.html
    <> wrote in message
    news:...
    > In message <PAd0c.38058$%>,
    > "Tony Spadaro" <> wrote:
    >
    > > A grey card comes out at about RG&B 160 on a reasonably calibrated
    > >monitor.

    >
    > Huh? Monitors don't have RGB values. They are passive analog devices,
    > displaying voltages created by the gfx chips. An average exposure will
    > be about 127 with most cameras and RAW converters. I've seen 117 as
    > well (which is what 18% grey should be) in one context, (but I don't
    > remember where).
    > --
    >
    > <>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
    > John P Sheehy <>
    > ><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
    Tony Spadaro, Feb 29, 2004
    #9
  10. Alan F Cross

    Guest

    In message <kog0c.55216$>,
    "Tony Spadaro" <> wrote:

    >Quite wrong. If you would take the time to compare a grey card to the greys
    >available in Photoshop you will find - that if your monitor is fairly well
    >calibrated you will get about 160. Don't talk theory when it takes vary
    >little work to see that your are flat out wrong. If you don't have a grey
    >card - buy one.


    You're not making one bit of sense. Inability to communicate and
    inability to detect failed communication and initiate a retry is an
    epidemic disease, and you are infected.

    Where is this "160" figure coming from?

    A grey card's level in a room depends totally on ambient lighting.
    --

    <>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
    John P Sheehy <>
    ><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
    , Feb 29, 2004
    #10
  11. Alan F Cross

    Alan F Cross Guest

    In message <PAd0c.38058$%>, Tony
    Spadaro <> writes
    >A grey card comes out at about RG&B 160 on a reasonably calibrated
    >monitor.


    It shouldn't have anything to do with the monitor!
    --
    Alan F Cross
    Alan F Cross, Feb 29, 2004
    #11
  12. Alan F Cross

    Alan F Cross Guest

    In message <>,
    writes
    >In message <>,
    >Alan F Cross <> wrote:
    >
    >>So, the question remains: if I create a grey of 127 or 128, *should* it
    >>look like an 18% grey card? If not, what level of grey should?

    >
    >I would think that the answer depends on the paper used. Paper is in
    >its own little world of low contrast, and blacks that are grey in the
    >real world. I don't think prints even attempt to center around a grey
    >card.


    What has it got to do with the paper used? Any media variations should
    be taken care of in the printer profiling and the driver. You shouldn't
    be adjusting your image to each media used, you should be adjusting the
    printer transfer characteristic.
    --
    Alan F Cross
    Alan F Cross, Feb 29, 2004
    #12
  13. wrote in news::

    > A grey card's level in a room depends totally on ambient lighting.
    >


    Completely correct.

    You cannot map a grey card to any level in your digital picture
    or on your monitor. A grey card simply reflects 18% of the light.
    A monitor does not reflect light - it emits light.


    /Roland
    Roland Karlsson, Feb 29, 2004
    #13
  14. Alan F Cross

    Guest

    In message <Xns949E960127CB3klotjohan@130.133.1.4>,
    Roland Karlsson <> wrote:

    > wrote in news::
    >
    >> A grey card's level in a room depends totally on ambient lighting.
    >>

    >
    >Completely correct.
    >
    >You cannot map a grey card to any level in your digital picture
    >or on your monitor. A grey card simply reflects 18% of the light.
    >A monitor does not reflect light - it emits light.


    So what the hell was he talking about? I can see why people killfile
    him; he writes, but doesn't read.
    --

    <>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
    John P Sheehy <>
    ><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
    , Feb 29, 2004
    #14
  15. Alan F Cross

    Guest

    In message <>,
    Tony Gartshore <> wrote:

    >Funny isn't it, I don't even have Photoshop and yet I knew exactly what
    >you meant as soon as I read it..


    People who don't really read and just look for keywords to agree with or
    pounce on generally get that communicative feeling, even if
    communication isn't happening.

    Anyway, any solid-shaded grey object comes out at 127 in photoshop with
    most cameras and software, not 160.

    >I was always taught that if I didn't have a grey card available then to
    >take an exposure reading off the back of my hand. The reflectance value
    >of caucasian skin being approx 18%. May not be 100% accurate, but a
    >good, err, 'rule of thumb'.


    Maybe a sicilian or a black Irish (my paternal grandmother was one of
    these, and my sister has a dark complexion), or someone with a South of
    France tan, but most caucasians are about a stop more reflective than
    18% grey.
    --

    <>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
    John P Sheehy <>
    ><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
    , Feb 29, 2004
    #15
  16. Alan F Cross

    Guest

    In message <>,
    Alan F Cross <> wrote:

    >In message <>,
    >writes
    >>In message <>,
    >>Alan F Cross <> wrote:
    >>
    >>>So, the question remains: if I create a grey of 127 or 128, *should* it
    >>>look like an 18% grey card? If not, what level of grey should?

    >>
    >>I would think that the answer depends on the paper used. Paper is in
    >>its own little world of low contrast, and blacks that are grey in the
    >>real world. I don't think prints even attempt to center around a grey
    >>card.

    >
    >What has it got to do with the paper used? Any media variations should
    >be taken care of in the printer profiling and the driver. You shouldn't
    >be adjusting your image to each media used, you should be adjusting the
    >printer transfer characteristic.


    Doifferent paper and ink combinations have different dynamic ranges,
    regardless of what the software tries to do.
    --

    <>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
    John P Sheehy <>
    ><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
    , Feb 29, 2004
    #16
  17. Alan F Cross

    Don Stauffer Guest

    Re: Still trying to figure the grey level of an 18% grey card (was: If Ishoot a grey card, should this end up as 127 grey?)

    An 18% grey card has a reflectivity of 18%.

    Now, how it is used in exposure determination is something else. This
    is to a large degree up to judgement and desire of photographer when you
    use manual metering. All of your 'definitions' could apply.

    Alan F Cross wrote:
    >
    > I had several responses on this, all giving different answers!! I have
    > also seen three definitions of the meaning of 18% grey:
    >
    > Definition 1: An analysis of 'average scenes' (whatever that may be)
    > showed they were 18% reflective. Can't imagine there is such a thing as
    > an average scene that would be in any way useful!
    >
    > Definition 2: the mid point of a 5-stop scale. I can see that 100/18 is
    > around 2.5 stops. This sounds more plausible, but if you work on a
    > 6-stop range, the point moves to 12.5% so there's little justification
    > for the figure.
    >
    > Definition 3: It's just an arbitrary figure to which most exposure
    > meters are calibrated, by convention (and some do something else).
    >
    > Perhaps the truth is a combination of these. But there must be a value
    > (between 0 and 255) that represents the same shade of grey as an 18%
    > card. I know that there is the gamma question, but surely this is to
    > essentially remove the non-linearity of the display tube, not to distort
    > the grey-scale itself.
    >
    > A mid-grey that is scanned and then printed should look the same, no
    > matter how screwed up it is on the display. I would have thought that
    > the tube should *try* to display the same grey that is being scanned and
    > being printed (within the constraints of reflective vs transmissive
    > viewing).
    >
    > So, the question remains: if I create a grey of 127 or 128, *should* it
    > look like an 18% grey card? If not, what level of grey should?
    >
    > The root of my question is the following problem:
    > When I send mono work out for printing, I attach a grey scale of equal
    > steps (0, 16, 32, 48,.....240, 255). It is easy to recognise 0 and 255
    > when printed, but how do I tell them that their rendition of mid-grey is
    > too light or too dark?
    >
    > I would need a full wedge to prove linearity across the range, and to
    > ensure that there is no black or white clipping. But I really want a
    > separate grey patch, labelled "this should look like and 18% grey card
    > when printed". Perhaps this is 127/128, or perhaps it's something else
    > (and that is the question!) The only reason to choose 18% grey is that
    > they would certainly have a reference card available to compare.
    >
    > I'd appreciate any further comments on this perplexing (but essentially
    > simple) issue.
    >
    > TIA
    > --
    > Alan F Cross


    --
    Don Stauffer in Minnesota

    webpage- http://www.usfamily.net/web/stauffer
    Don Stauffer, Feb 29, 2004
    #17
  18. Alan F Cross

    Tony Spadaro Guest

    You are a complete fool - and a stubborn, blind fool at that. Since you
    cannot learn I suggest you go live in my killfile with the rest of the
    idiots. Good bye loser.
    To others who may be curious: The "160" figure comes from comparing the
    colour of a grey card with the colours on a monitor and on prints made from
    swatches of those colours. Mr Sheehy has obviously never done a single test
    in this matter - and would rather make noise than know the truth. Ignore the
    dork.

    --
    http://www.chapelhillnoir.com
    home of The Camera-ist's Manifesto
    The Improved Links Pages are at
    http://www.chapelhillnoir.com/links/mlinks00.html
    A sample chapter from my novel "Haight-Ashbury" is at
    http://www.chapelhillnoir.com/writ/hait/hatitl.html
    <> wrote in message
    news:...
    > In message <kog0c.55216$>,
    > "Tony Spadaro" <> wrote:
    >
    > >Quite wrong. If you would take the time to compare a grey card to the

    greys
    > >available in Photoshop you will find - that if your monitor is fairly

    well
    > >calibrated you will get about 160. Don't talk theory when it takes vary
    > >little work to see that your are flat out wrong. If you don't have a grey
    > >card - buy one.

    >
    > You're not making one bit of sense. Inability to communicate and
    > inability to detect failed communication and initiate a retry is an
    > epidemic disease, and you are infected.
    >
    > Where is this "160" figure coming from?
    >
    > A grey card's level in a room depends totally on ambient lighting.
    > --
    >
    > <>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
    > John P Sheehy <>
    > ><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
    Tony Spadaro, Feb 29, 2004
    #18
  19. Alan F Cross

    Tony Spadaro Guest

    If the monitor is calibrated -- even only moderately calibrated you will get
    approximately the same grey at 160 as the grey card -- isn't that clear? Try
    it. Open photoshop, make an 8x10 file and fill it with 160 grey (160R, 160G,
    160B) then hold up your grey card -- they should be close - very close. Now
    print the file -- your printer will probably add a cast to the file but it
    will still be close.

    --
    http://www.chapelhillnoir.com
    home of The Camera-ist's Manifesto
    The Improved Links Pages are at
    http://www.chapelhillnoir.com/links/mlinks00.html
    A sample chapter from my novel "Haight-Ashbury" is at
    http://www.chapelhillnoir.com/writ/hait/hatitl.html
    "Alan F Cross" <> wrote in message
    news:...
    > In message <PAd0c.38058$%>, Tony
    > Spadaro <> writes
    > >A grey card comes out at about RG&B 160 on a reasonably calibrated
    > >monitor.

    >
    > It shouldn't have anything to do with the monitor!
    > --
    > Alan F Cross
    Tony Spadaro, Feb 29, 2004
    #19
  20. <> wrote in message
    news:...
    []
    > Anyway, any solid-shaded grey object comes out at 127 in photoshop with
    > most cameras and software, not 160.

    []

    What would be a reasonable question might be:

    - if I expose for white = 255, what grey level should an 18% grey card be?

    Of course, the answer depends on what gamma correction the camera software
    has used when making the 8-bit image from the original sensor data.....

    Cheers,
    David
    David J Taylor, Feb 29, 2004
    #20
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