Resolution and print size

Discussion in 'Digital Photography' started by Marc Wossner, Jan 23, 2007.

  1. Marc Wossner

    Marc Wossner Guest

    Hi ng,

    I´ve a problem understanding digital camera resolution and max print
    sizes for files derived by those cameras. I take the Canon EOS-D60 as
    an example. The D60 has a pixel size of 7.4 microns, so there are 136
    pixels/mm. However, that doesn't mean that the camera will actually
    resolve 136 lines per mm. The real useful resolution will be 70-80% of
    that, something like 105 lines per mm. Also, this is lines, while film
    and lens resolution is always given in line pairs, and it takes two
    lines to make a line pair. So the D-60 will actually resolve about 53
    line pairs/mm at best. - I know that it makes no sense to compare
    resolution in lines/mm as the sensor and 35 mm film are different in
    size. Lines/picture height are better. For the D60 this means that
    it´s measured resolution limit of 1600 lines/picture height is
    equivalent to a 35 mm camera resolution of 1600 / 2 / 24 = 33 line
    pairs per mm. - Anyway, if I take those 53 lp/mm into the formula to
    calculate system resolution like 1/T = 1/l + 1/f = 1/400+1/53 =
    1/0,0214 = 46,8 lp/mm and divide this value by the resolution limit of
    the eye for 10 inches (6,88 lp/mm), I reach a max magnification of
    x6,8. - I know that this formula gives only a rough approximation. -
    The sensor is 22.7 x 15.1 mm, so max print size should be 6 inches
    wide. Now I found a value based on experience that says that D60 images
    printed at 200 dpi (that´s a full 10x15 inch print) look very good and
    sharp. That´s consistent with other statements I found for other
    cameras that all give values for max print size that are higher than
    can be expected from theoretical resolution alone. It´s quite clear to
    me that our perception of sharpness is based on more than resolution
    alone, that grain/noise plays an important role as well and that a
    camera like the D60 produces images that are virtually noise free. But
    as resolution still matters can someone explain to me how those figures
    correlate or where I made a mistake in calculating them?

    Marc Wossner
    Marc Wossner, Jan 23, 2007
    #1
    1. Advertising

  2. Marc Wossner

    SimonLW Guest

    "Marc Wossner" <> wrote in message
    news:...
    Hi ng,

    I´ve a problem understanding digital camera resolution and max print
    sizes for files derived by those cameras. I take the Canon EOS-D60 as
    an example. The D60 has a pixel size of 7.4 microns, so there are 136
    pixels/mm. However, that doesn't mean that the camera will actually
    resolve 136 lines per mm. The real useful resolution will be 70-80% of
    that, something like 105 lines per mm. Also, this is lines, while film
    and lens resolution is always given in line pairs, and it takes two
    lines to make a line pair. So the D-60 will actually resolve about 53
    line pairs/mm at best. - I know that it makes no sense to compare
    resolution in lines/mm as the sensor and 35 mm film are different in
    size. Lines/picture height are better. For the D60 this means that
    it´s measured resolution limit of 1600 lines/picture height is
    equivalent to a 35 mm camera resolution of 1600 / 2 / 24 = 33 line
    pairs per mm. - Anyway, if I take those 53 lp/mm into the formula to
    calculate system resolution like 1/T = 1/l + 1/f = 1/400+1/53 =
    1/0,0214 = 46,8 lp/mm and divide this value by the resolution limit of
    the eye for 10 inches (6,88 lp/mm), I reach a max magnification of
    x6,8. - I know that this formula gives only a rough approximation. -
    The sensor is 22.7 x 15.1 mm, so max print size should be 6 inches
    wide. Now I found a value based on experience that says that D60 images
    printed at 200 dpi (that´s a full 10x15 inch print) look very good and
    sharp. That´s consistent with other statements I found for other
    cameras that all give values for max print size that are higher than
    can be expected from theoretical resolution alone. It´s quite clear to
    me that our perception of sharpness is based on more than resolution
    alone, that grain/noise plays an important role as well and that a
    camera like the D60 produces images that are virtually noise free. But
    as resolution still matters can someone explain to me how those figures
    correlate or where I made a mistake in calculating them?

    Marc Wossner

    Just take the # of pixels on the long side of the image, and divide by 300
    dpi for high quality prints, 250dpi for good quality or 200dpi for fair
    quality, ect. to get the recommended max print size. Very basic and it has
    always worked for me.

    When you start splitting hairs with numbers, you have to consider lens
    sharpness and contrast, actual resolution of the printer, illumination
    levels of print to be viewed and so on.
    -S
    SimonLW, Jan 23, 2007
    #2
    1. Advertising

  3. >pairs per mm. - Anyway, if I take those 53 lp/mm into the formula to
    >calculate system resolution like 1/T = 1/l + 1/f = 1/400+1/53 =
    >1/0,0214 = 46,8 lp/mm and divide this value by the resolution limit of
    >the eye for 10 inches (6,88 lp/mm), I reach a max magnification of
    >x6,8. - I know that this formula gives only a rough approximation. -
    >The sensor is 22.7 x 15.1 mm, so max print size should be 6 inches
    >wide. Now I found a value based on experience that says that D60 images
    >printed at 200 dpi (that´s a full 10x15 inch print) look very good and
    >sharp.


    I think a better way of looking at your numbers is this:

    Up to 6" wide (or so), you get (almost) no increase in quality from
    more pixels, because the increase in resolution is beyond the
    resolving power of the human eye.

    However, equipment is not perfect, and if any stage of your workflow
    introduces fuzziness (which it surely does), you'll find the 6" figure
    growing. Suppose, for example (and this is probably true), that you
    use a printer that only prints at 200dpi. Then up to 10x15 or so you
    get (almost) no increase in quality from more pixels.

    It is also true, as you note, that we perceive sharpness based not
    only on resolution. This is why sharpening a low resolution image can
    make it look sharp, even at the expense of detail. Similarly, I have
    seen 3'x4' images printed on canvas from very low resolution images,
    and they look great. I suspect this has something to do with the
    coarse texture of the canvas, but I don't know for sure.

    -Joel

    ----------------------------------------------------------------------------
    Free Tanach and Mishna printouts in Hebrew: http://liturgy.lashon.net/
    ----------------------------------------------------------------------------
    Dr. Joel M. Hoffman, Jan 23, 2007
    #3
  4. ? "Marc Wossner" <> ?????? ??? ??????
    news:...
    Hi ng,

    I´ve a problem understanding digital camera resolution and max print
    sizes for files derived by those cameras. I take the Canon EOS-D60 as
    an example. The D60 has a pixel size of 7.4 microns, so there are 136
    pixels/mm. However, that doesn't mean that the camera will actually
    resolve 136 lines per mm. The real useful resolution will be 70-80% of
    that, something like 105 lines per mm. Also, this is lines, while film
    and lens resolution is always given in line pairs, and it takes two
    lines to make a line pair. So the D-60 will actually resolve about 53
    line pairs/mm at best. - I know that it makes no sense to compare
    resolution in lines/mm as the sensor and 35 mm film are different in
    size. Lines/picture height are better. For the D60 this means that
    it´s measured resolution limit of 1600 lines/picture height is
    equivalent to a 35 mm camera resolution of 1600 / 2 / 24 = 33 line
    pairs per mm. - Anyway, if I take those 53 lp/mm into the formula to
    calculate system resolution like 1/T = 1/l + 1/f = 1/400+1/53 =
    1/0,0214 = 46,8 lp/mm and divide this value by the resolution limit of
    the eye for 10 inches (6,88 lp/mm), I reach a max magnification of
    x6,8. - I know that this formula gives only a rough approximation. -
    The sensor is 22.7 x 15.1 mm, so max print size should be 6 inches
    wide. Now I found a value based on experience that says that D60 images
    printed at 200 dpi (that´s a full 10x15 inch print) look very good and
    sharp. That´s consistent with other statements I found for other
    cameras that all give values for max print size that are higher than
    can be expected from theoretical resolution alone. It´s quite clear to
    me that our perception of sharpness is based on more than resolution
    alone, that grain/noise plays an important role as well and that a
    camera like the D60 produces images that are virtually noise free. But
    as resolution still matters can someone explain to me how those figures
    correlate or where I made a mistake in calculating them?

    Hi,
    I printed a full-size A4 (larger than 8X10")with a cheapo Kodak CX 7300 and
    a Canon Pixma IP 4300 and looks perfect, much better than any B&W prints I
    did in my film era, save colour.(With some german glossy paper, 25 euros for
    50 A4 sheets, compu color by Felix Schoeler).Surely you have a better camera
    than mine?
    Hope this helps,


    --
    Tzortzakakis Dimitrios
    major in electrical engineering
    mechanized infantry reservist
    dimtzort AT otenet DOT gr
    Tzortzakakis Dimitrios, Jan 23, 2007
    #4
  5. > I´ve a problem understanding digital camera resolution and max
    > print sizes for files derived by those cameras.


    I have historically used the 300 dpi guide, but find that with
    digital cameras, I can get pretty good results with a minimum of
    about 240 dpi - 250 dpi of resolveable detail, perhaps because
    with digital there is no grain or other such distorting factors
    to deal with.

    This depends on a number of factors, such as the quality of the
    camera / ccd / lens, the ISO level of the shot, lighting levels
    and type of object being shot.

    For outdoor nature shots, I can get away with as low as 200 dpi
    and still be somewhat satisfied, but for shots of people,
    anything below the 240-250 dpi range and I can start to notice
    things.

    A good 5mp camera like the Oly C5050 can give you great looking,
    300+ dpi prints in 4x6 and 5x7 and still accommodate some
    cropping. But for 8x10's, I think 5mp can be stretching it for
    non-nature type shots, like portraits, etc.

    That's just my personal feeling though. I'm not trying to
    indicate that it's right for everybody - it is just what I have
    found to be my preferences over the years.
    Paul D. Sullivan, Jan 23, 2007
    #5
  6. Marc Wossner

    Marc Wossner Guest

    As you all state the common dpi values is the traditional resolution
    measure of line pairs per mm or lines per picture with or picture
    height not relevant when calculating the resolution of a digital
    imaging system? - I still use silver film and try to figure out the
    theoretical foundations before I switch to digital.

    Marc Wossner
    Marc Wossner, Jan 25, 2007
    #6
  7. Marc Wossner wrote:

    > As you all state the common dpi values is the traditional resolution
    > measure of line pairs per mm or lines per picture with or picture
    > height not relevant when calculating the resolution of a digital
    > imaging system? - I still use silver film and try to figure out the
    > theoretical foundations before I switch to digital.


    An interesting aside, Marc - my video projector has a basic 1440 x 1080
    pixels resolution, but it displays video at fantastic resolution at a 10
    foot wide screen size. To my eye, I can't imagine having any more detail
    in some of the images I'm seeing on a good broadcast. My thought is that
    all that matters is how big the resultant image is in your eye. If I sat
    5 feet away from my screen, it wouldn't fare as well. So I sit about 20
    feet back, and it is impressive and amazing.

    I have also seen very large paper prints from various digital (and film)
    cameras at exhibitions and shows. I guess the proof is in the pudding,
    so try various outrageous sizes and see at what point it breaks down.
    Probably doable anywhere above 100 DPI.

    Gary Eickmeier
    Gary Eickmeier, Jan 25, 2007
    #7
  8. "Marc Wossner" <> wrote:
    >
    > As you all state the common dpi values is the traditional resolution
    > measure of line pairs per mm or lines per picture with or picture
    > height not relevant when calculating the resolution of a digital
    > imaging system? - I still use silver film and try to figure out the
    > theoretical foundations before I switch to digital.


    Forget the theory: look at the images.

    This guy complains about moiré and fine text in street signs getting messed
    up, but it sure looks to me that the 5D and 645 (actually, 6x6 cropped to
    slightly smaller than 645) are pretty much equivalent for prints 17x26" and
    smaller.

    http://www.shortwork.net/equip/review-1Ds-SQ-scantech/

    David J. Littleboy
    Tokyo, Japan
    David J. Littleboy, Jan 25, 2007
    #8
  9. Marc Wossner

    Marc Wossner Guest

    > On 25 Jan., 15:29, "David J. Littleboy" <> wrote:
    > > "Marc Wossner" <> wrote:

    >
    > > As you all state the common dpi values is the traditional resolution
    > > measure of line pairs per mm or lines per picture with or picture
    > > height not relevant when calculating the resolution of a digital
    > > imaging system? - I still use silver film and try to figure out the
    > > theoretical foundations before I switch to digital.


    > Forget the theory: look at the images.


    Not so easy if something keeps nagging your mind. But I agree with you:
    Image quality of the 5D is absolutely stunning.

    >
    > This guy complains about moiré and fine text in street signs getting messed
    > up, but it sure looks to me that the 5D and 645 (actually, 6x6 cropped to
    > slightly smaller than 645) are pretty much equivalent for prints 17x26" and
    > smaller. http://www.shortwork.net/equip/review-1Ds-SQ-scantech/


    So there´s the question again: How can you print that large from the
    resolution the 5D gives?
    When you calculate 4368 pixels * 0,7 = 3057,6 lines / 2 = 1529 line
    pairs / 35,8 mm you reach 42,7 lp/mm.
    I don´t know the true resolution of the lens, but as it´s a prime
    lens let´s assume 100 lp/mm.
    Taking it into account like this 1/T = 1/43 + 1/100 makes it a system
    resolution of 30 lp/mm worst case.
    The images presented are printed at 17x26" so that´s a magnification
    of x18.
    Divide the 30 lp/mm by the 2 lp/mm that are necessary for that diagonal
    you get a max magnification of x15.
    But the guy shows clippings that appear sharp from 10" and for that
    distance you need 6,88 lp/mm to have a sharp impression.
    Note that those figures are all based on "normal" 20/20 vision or max
    resolvable detail of 1 minute of an arc (see Norman Koren´s site for
    the calculation: http://www.normankoren.com/Tutorials/MTF.html).
    As I know that you are quite knowledgeable from various other threads
    David, can you explain me how this is possible, or better, where my
    possible misconception is?

    Marc
    Marc Wossner, Jan 25, 2007
    #9
  10. I hate math... lol...

    > So there´s the question again: How can you print that large
    > from the resolution the 5D gives?
    > When you calculate 4368 pixels * 0,7 = 3057,6 lines / 2 = 1529
    > line pairs / 35,8 mm you reach 42,7 lp/mm.
    > I don´t know the true resolution of the lens, but as it´s a
    > prime
    > lens let´s assume 100 lp/mm.
    > Taking it into account like this 1/T = 1/43 + 1/100 makes it a
    > system resolution of 30 lp/mm worst case.
    > The images presented are printed at 17x26" so that´s a
    > magnification of x18.
    > Divide the 30 lp/mm by the 2 lp/mm that are necessary for that
    > diagonal you get a max magnification of x15.
    > But the guy shows clippings that appear sharp from 10" and for
    > that distance you need 6,88 lp/mm to have a sharp impression.
    > Note that those figures are all based on "normal" 20/20 vision
    > or max resolvable detail of 1 minute of an arc (see Norman
    > Koren´s site for the calculation:
    > http://www.normankoren.com/Tutorials/MTF.html).
    > As I know that you are quite knowledgeable from various other
    > threads David, can you explain me how this is possible, or
    > better, where my possible misconception is?
    >
    > Marc
    Paul D. Sullivan, Jan 25, 2007
    #10
  11. "Marc Wossner" <> wrote:
    > On 25 Jan., 15:29, "David J. Littleboy" <> wrote:
    > > "Marc Wossner" <> wrote:

    >
    > This guy complains about moiré and fine text in street signs getting
    > messed
    > up, but it sure looks to me that the 5D and 645 (actually, 6x6 cropped to
    > slightly smaller than 645) are pretty much equivalent for prints 17x26"
    > and
    > smaller. http://www.shortwork.net/equip/review-1Ds-SQ-scantech/


    So there´s the question again: How can you print that large from the
    resolution the 5D gives?
    <<<<<<<<<<<<<

    Well, don't ask me; I think printing 645 larger than 13x19 is nuts. But 35mm
    folks make 16x20s all the time. (I saw an exhibit of 20x30s at the Nikon
    gallery here that was incredibly soft mush; they looked bad from across the
    room.)

    Seriously, though, if you have a decent image, the larger you print it, the
    better it looks. Even if the result is mush. So no one has ever been unhappy
    with a large print they've made from their own images.

    >>>>>>>>>>>>>>>

    When you calculate 4368 pixels * 0,7 = 3057,6 lines / 2 = 1529 line
    pairs / 35,8 mm you reach 42,7 lp/mm.
    I don´t know the true resolution of the lens, but as it´s a prime
    lens let´s assume 100 lp/mm.
    Taking it into account like this 1/T = 1/43 + 1/100 makes it a system
    resolution of 30 lp/mm worst case.
    <<<<<<<<<<<<<<<<

    Let's see. The 5D produces 2912 x 4374 pixels (plus or minus a few depending
    on the RAW converter), and digital images tend to have a practical
    resolution of about one line pair per 3 pixels. So that's 970 lp/in or 38
    lp/mm. OK. Our numbers agree<g>.

    In real life, the 5D produces about 240 ppi at 12x18 (1/2" borders on 13x19
    paper). The prints look gorgeous. That's a 12x enlargement with 3 lp/mm
    resolution. That's pretty cool, because film look really really bad at a 12x
    enlargement. Either grainy or mushy or both.

    >>>>>>>>>>>>>>>>

    The images presented are printed at 17x26" so that´s a magnification
    of x18.
    Divide the 30 lp/mm by the 2 lp/mm that are necessary for that diagonal
    you get a max magnification of x15.
    But the guy shows clippings that appear sharp from 10" and for that
    distance you need 6,88 lp/mm to have a sharp impression.
    <<<<<<<<<<<<<<<<<

    My theory on what's going on here is that your "you need 6,88 lp/mm to have
    a sharp impression" is due to misinformation from the dizzy Leica folks.

    What they do is shoot high contrast (1:1000) test charts and assume that
    their real life images achieve similar levels of detail capture; they think
    that tests with strobe illuminated charts with the camera bolted to granite
    test bench somehow relates to handheld street shooting. My experience
    shooting film (and the data sheets from the mfrs) is that you see nothing of
    the sort in real life images _other than street signs_. Film types (and
    I've made this mistake myself) will look at a street sign image and think
    how cool it is that their camera resolves it, while failing to notice that
    the textures at that enlargement not only aren't captured, but are
    completely swamped by the grain noise.

    >>>>>>>>>>>>>>>>

    Note that those figures are all based on "normal" 20/20 vision or max
    resolvable detail of 1 minute of an arc (see Norman Koren´s site for
    the calculation: http://www.normankoren.com/Tutorials/MTF.html).
    As I know that you are quite knowledgeable from various other threads
    David, can you explain me how this is possible, or better, where my
    possible misconception is?
    <<<<<<<<<<<<<<<<

    He's looking at film images that are grossly soft as well. I've printed a
    lot of test images at that magnification from film, and they're mush.

    David J. Littleboy
    Tokyo, Japan
    David J. Littleboy, Jan 26, 2007
    #11
  12. > In real life, the 5D produces about 240 ppi at 12x18 (1/2"
    > borders on 13x19 paper). The prints look gorgeous. That's a
    > 12x enlargement with 3 lp/mm resolution. That's pretty cool,
    > because film look really really bad at a 12x enlargement.
    > Either grainy or mushy or both.


    That is one of the great things about digital - no grain.

    My 5mp Oly C5050 does 8x10 at 240 ppi and it looks at least as
    good as 8x10's that I have taken and had printed with my 35mm
    film camera. Sometimes it is obviously clearer even if the level
    of detail is not as great overall.
    Paul D. Sullivan, Jan 26, 2007
    #12
  13. Marc Wossner

    Marc Wossner Guest

    On 26 Jan., 01:42, "David J. Littleboy" <> wrote:
    > "Marc Wossner" <> wrote:
    > > On 25 Jan., 15:29, "David J. Littleboy" <> wrote:
    > > > "Marc Wossner" <> wrote:

    >
    > > This guy complains about moiré and fine text in street signs getting
    > > messed
    > > up, but it sure looks to me that the 5D and 645 (actually, 6x6 cropped to
    > > slightly smaller than 645) are pretty much equivalent for prints 17x26"
    > > and
    > > smaller. http://www.shortwork.net/equip/review-1Ds-SQ-scantech/So there´s the question again: How can you print that large from the

    > resolution the 5D gives?
    > <<<<<<<<<<<<<
    >
    > Well, don't ask me; I think printing 645 larger than 13x19 is nuts. But 35mm
    > folks make 16x20s all the time. (I saw an exhibit of 20x30s at the Nikon
    > gallery here that was incredibly soft mush; they looked bad from across the
    > room.)
    >
    > Seriously, though, if you have a decent image, the larger you print it, the
    > better it looks. Even if the result is mush. So no one has ever been unhappy
    > with a large print they've made from their own images.
    >
    > When you calculate 4368 pixels * 0,7 = 3057,6 lines / 2 = 1529 line
    > pairs / 35,8 mm you reach 42,7 lp/mm.
    > I don´t know the true resolution of the lens, but as it´s a prime
    > lens let´s assume 100 lp/mm.
    > Taking it into account like this 1/T = 1/43 + 1/100 makes it a system
    > resolution of 30 lp/mm worst case.
    > <<<<<<<<<<<<<<<<
    >
    > Let's see. The 5D produces 2912 x 4374 pixels (plus or minus a few depending
    > on the RAW converter), and digital images tend to have a practical
    > resolution of about one line pair per 3 pixels. So that's 970 lp/in or 38
    > lp/mm. OK. Our numbers agree<g>.
    >
    > In real life, the 5D produces about 240 ppi at 12x18 (1/2" borders on 13x19
    > paper). The prints look gorgeous. That's a 12x enlargement with 3 lp/mm
    > resolution. That's pretty cool, because film look really really bad at a 12x
    > enlargement. Either grainy or mushy or both.
    >
    > The images presented are printed at 17x26" so that´s a magnification
    > of x18.
    > Divide the 30 lp/mm by the 2 lp/mm that are necessary for that diagonal
    > you get a max magnification of x15.
    > But the guy shows clippings that appear sharp from 10" and for that
    > distance you need 6,88 lp/mm to have a sharp impression.
    > <<<<<<<<<<<<<<<<<
    >
    > My theory on what's going on here is that your "you need 6,88 lp/mm to have
    > a sharp impression" is due to misinformation from the dizzy Leica folks.


    > What they do is shoot high contrast (1:1000) test charts and assume that
    > their real life images achieve similar levels of detail capture; they think
    > that tests with strobe illuminated charts with the camera bolted to granite
    > test bench somehow relates to handheld street shooting. My experience
    > shooting film (and the data sheets from the mfrs) is that you see nothing of
    > the sort in real life images _other than street signs_. Film types (and
    > I've made this mistake myself) will look at a street sign image and think
    > how cool it is that their camera resolves it, while failing to notice that
    > the textures at that enlargement not only aren't captured, but are
    > completely swamped by the grain noise.
    >
    > Note that those figures are all based on "normal" 20/20 vision or max
    > resolvable detail of 1 minute of an arc (see Norman Koren´s site for
    > the calculation:http://www.normankoren.com/Tutorials/MTF.html).
    > As I know that you are quite knowledgeable from various other threads
    > David, can you explain me how this is possible, or better, where my
    > possible misconception is?
    > <<<<<<<<<<<<<<<<
    >
    > He's looking at film images that are grossly soft as well. I've printed a
    > lot of test images at that magnification from film, and they're mush.


    No. I do analog photography for a long time and started studying the
    perception side to make better use of the medium. That´s where all I
    know is derived from. The 6,88 lp/mm are calculated using only figures
    of our visual system. Koren´s site explains this and all the
    informations are backed up by a lot of scientifc research. 1 minute of
    an arc *is* the resolution limit of the *average* human and the 6,88 is
    based on that. But you can also reach it from another side:

    cycles/degree = 600/Snellen denominator = 600/20 = 30 cycles/degree
    cycles/degree * (180/pi) * (1/distance in mm) = 30 * (180/pi) * (1/250
    mm) = 6,87 lp/mm

    As stated this is an average value and a lot of people can see much
    better, in the range of 60 cycles/degree.
    That´s what I know and where it comes from. It holds true in analog
    photography and that´s why I don´t understand what´s going on in the
    digital case.

    Marc
    Marc Wossner, Jan 26, 2007
    #13
  14. Marc Wossner

    Guest

    Forgive my selective editing, David, but in these three bits, I think
    you summed it up well.

    On Jan 26, 10:42 am, "David J. Littleboy" <> wrote:
    > Seriously, though, if you have a decent image, the larger you print it, the
    > better it looks. Even if the result is mush...


    > My theory on what's going on here is that your "you need 6,88 lp/mm to have
    > a sharp impression" is due to misinformation...


    > What they do is shoot high contrast (1:1000) test charts and assume that
    > their real life images achieve similar levels of detail capture...


    Exactly. The 300 ppi thing (which is derived from the 6.88) is almost
    useless, imo, as a guide to enlargability, unless you are only
    enlarging resolution test charts. If the image content is any of the
    following, then you can decrease that figure, sometimes dramatically:

    - close up macros without fine detail (eg flower macros, not insects
    with lots of tiny hairs..)
    - very tightly cropped portraits (because getting too close to a face
    feels uncomfortable to the viewer)
    - soft focus portraits (obviously)

    However, if your image is:
    - a landscape (is that grass/foliage/pine needles.. or mush(â„¢David)?)
    - cityscape (is that blurry bit my house, or why can't I read that
    little sign?),
    - beachscape (is that girl way back there topless?)
    - or a large group portrait (is that Uncle Ed or Aunt Martha, 3rd row,
    10th from the end?)

    I proved this to myself long ago when I first tested out the much
    maligned Sony DSCF828 (which does produce very nice and quite sharp 8Mp
    images.) I blew a series of images up to 13" x 19" prints (ie about
    190 ppi), including portraits like this one:

    http://www.marktphoto.com/portrait/slides/happiness_is.jpg
    (sorry, slightly oversharpened - you'll have to trust me that the
    original is nailed!)

    and also landscapes and other images that invited close inspection,
    like this:

    http://www.marktphoto.com/marina_details.jpg

    The portraits looked stunning, and yet the detailed shots like the
    second example looked mediocre. You would have sworn they were taken
    on two different cameras. But on close inspection, you could see that
    the portrait was indeed exactly as sharp as the other - it was a
    combination of the way you viewed the images (the portrait 'made' you
    want to view it at about 18" at which point you could see all the
    *useful* detail, right down to the detail in the irises and
    eyelashes.., but the landscape invited much closer inspection and you
    could more easily see the very slight pixellation, even at the same
    viewing distance). There's a lot of factors in this, eg diagonal
    jaggies are much more likely to show up in boat rigging than eyes...
    and of course how well you post process, what method you interpolate
    with, etc...

    Anyway, if you add it all up, your brain will tell you how sharp the
    print is, but it is very likely lying..!

    Just use the 300/200/100 thing as a vague guide and experiment..
    , Jan 26, 2007
    #14
  15. Marc Wossner

    Marc Wossner Guest

    After digging deeper into this I found a way to explain the facts that
    contradict each other at first glance.
    The following quote from an old thread lead me the way: "It´s not the
    resolution of the image on the retina that makes the difference, it´s
    the contrast of the relatively well resolved information." What
    matters here is the subjective quality factor (sqf) and the fact that
    the better contrast that most digital cameras reproduce at the spatial
    frequencys between 5 and 10 cycles/degree, which are most important
    for perceived sharpness, allows for larger prints than the resolution
    numbers alone predict. The following three websites give further
    information:

    http://www.bobatkins.com/photography/technical/mtf/mtf4.html
    http://www.imatest.com/docs/sqf.html
    http://luminous-landscape.com/forum/lofiversion/index.php/t11480.html

    Marc
    Marc Wossner, Jan 28, 2007
    #15
    1. Advertising

Want to reply to this thread or ask your own question?

It takes just 2 minutes to sign up (and it's free!). Just click the sign up button to choose a username and then you can ask your own questions on the forum.
Similar Threads
  1. Cyrus Chvala

    Re: Photo resolution translation into size of print

    Cyrus Chvala, Jul 10, 2003, in forum: Digital Photography
    Replies:
    2
    Views:
    1,083
  2. Steven M. Scharf

    D-SLR Sensor Resolution and Sensor Size Comparison Size Matters!

    Steven M. Scharf, May 14, 2004, in forum: Digital Photography
    Replies:
    32
    Views:
    5,448
    Georgette Preddy
    May 16, 2004
  3. jersie0
    Replies:
    3
    Views:
    492
    Ron Baird
    Oct 22, 2004
  4. chumpy
    Replies:
    3
    Views:
    749
    Ron Hunter
    Nov 9, 2005
  5. ftran999
    Replies:
    8
    Views:
    537
    Don Stauffer in Minnesota
    Feb 22, 2007
Loading...

Share This Page