How many pixels in an 8x10 neg?

Discussion in 'Large Format' started by bill_youmans, Oct 3, 2000.

  1. A coffee break discussion prompted the following question:

    <p>

    How many pixels would a file contain if an 8x10 digital back were available (color or B/W)?

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    Seems there was a National Public Radio story that a consumer camera available in 2001 will have a 10 megapixel chip as standard equipment, rendering images equal to any film-based effort. I was arguing that in a 1/15th of a second, an 8x10 piece of film can collect huge amounts of "pixel" information, probably dwarfing 10 megapixels. Anybody know?

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    Thanks in advance - Bill
     
  2. Well, here's my rough answer: in round figure an 8x10 negative is
    about 200x250 mm. If we say that a good B&W film is capable of
    resolving well over 100lpm (again, just round figures), then you need
    at least 200 pixels per mm. LF lenses won't match that resolution, but
    you'll still need it to replicate the tonal gradation.

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    That gives 200x200x250x200 = 2 billion pixels. That is 200 times the
    size of that 10Mpixel chip, and that is almost certainly an
    underestimate!

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    Not only that, but I think I'm right in saying that each pixel uses
    several bytes for 24-bit colour rendition, and it's clear that for an
    uncompressed image you will need several GigaBytes of storage. I hate
    to think what the power supply would be like.

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    So, if my arithmetic is right, and you're planning that week-long
    photographic trip into the backwoods with current digital technology,
    you'd better hire half a dozen pack mules and a portable generator!

    <p>

    Huw Evans.
     
  3. "rendering images equal to any film-based effort. "<p> Yeah, but I'm
    sure they weren't considering LF...as most people don't.
     
  4. Huw,

    <p>

    You're right about color rendition - that requires a minimum of 3
    pixels (R, G, B). 24 bit color likely requires more, but this is
    beyond my specific knowledge.

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    I think I also recall that a 35mm negative contains roughly 25-30
    megapixels of data, but don't quote me on that. If right, though,
    digital is still a long ways away from a mano a mano quality
    comparison with film at any format. I wonder when the dramatic
    improvements we have seen in digital will run out of gas in the face
    of practical limitations on miniturization, and whether this will be
    before or after digital exceeds chemistry in data storage capacity.
    It's easy to say now that digital will ultimately win out, but I
    question whether it's really that simple (see the human brain).

    <p>

    Wow, I fell into an unanticipated philosophical twist. ;-)
     
  5. we can also look at this from the other end. it requires about
    300dpi to achieve truly visually-satisfying reproduction (print)
    quality (for example, the reproductions in a high-quality fine art
    book). 300 x 10" = 3000 pixels across, 300 x 8" = 2400 pixels high -
    that translates to 7.2 million pixels. at 24-bit resolution, that is
    about 173MB file size. at 600dpi (to allow for 16x20 enlargements
    for exhibition purposes), you would be looking at file sizes of about
    690MB. this level of image quality is within the capability of
    existing technology (well, i admit you need a lot of RAM), and i
    would guess variations of it will be common in the near future. on
    the downside, if kodak wont even make a b/w film in 4x5 readyload
    anymore because the market is too small, who in the world do you
    think will manufacture an 8x10 digital back? (i wonder how long it
    will be before the LOC accepts any form of digital imaging - digital
    files, digital prints, and/or digitally printed "negatives" or some
    other form of hard-copy "original", as part of its archival
    collections...)
     
  6. I have done some experiments digitising film to see what you can get
    out of it and does appear that the limiting factor is lens technology.

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    You can see the grain in Provia F at about 6000 dpi but above 3-4000
    dpi the lenses I have used have not provided any more information.

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    At 3000 dpi this produces a 720 MegaPixel image (2 GBytes (24 bit)).

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    If you are interested the results of scans at 1600, 3000, 6000 and
    12,000 dpi they are at:-
    http://193.113.131.213/pg/dpi/?lf2

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    Viewing the images requires your browser to run a Java applet. I will
    have a none java system by the end of the month.

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    Regards
     
  7. Juggling numbers doesn't actually tell us very much about image quality.
    If you consider the fact that every grain in a film can only be 'on' or 'off', i.e. developed on not, then film itself is very much a digital medium.
    Now consider the nature of a pixel: Sure, it covers a much larger area than a film grain, but it's also capable of showing a whole gamut of brightness levels, from absolute black to pure white. Which is really closer to showing a truly analogue tone scale; film grain, or pixels?
    The way that the human eye sees things must also be taken into consideration. The eye accepts regular patterns of dots as a continuous tone, much more readily than it accepts the random scattering you get with film grain. A coarse grained photographic print has many more grains per inch than a good 133 to 200 screen magazine or book illustration, but the book illustration appears to be smoother in tone than the print. The regular matrix of pixels gives a better impression of truly continuous tone than film grain.
    IMHO comparing film directly with a digital image, on a purely numerical basis, is like comparing apples with bananas, but if you want some numbers, I think we ought to start with the human eye.
    The eye can resolve at best about 8 lppm at normal reading distance. Even if you increase this to 10 lppm or 20 pixels/mm, this only works out to 82 megapixels to cover a 20" x 16" print. The final viewing size is much more important than the negative or film size.
    Or, if you want the hypothetical equivalent of film: We'd need at least 255 film grains to show the same tonal range as a single pixel, and this involves a film area equivalent to at least a 16 micron square pixel. (The pixels in consumer digicams are about 5 microns square BTW). This is about 2.5 megapixels/square inch; you work out the numbers, they're far lower than the gigapixels that have been bandied about previously.
    Anyway, wait until we've seen the results from the new full 35mm frame-sized CCD camera announced at Photokina. (At last the digital design boys have realised that size does matter.) It's only 6 megapixels, but this is well in excess of the 2.5 mp/sq. inch that I mentioned earlier.
    I think quite a few eyebrows are going to be raised by it.
    Leaf, LightPhase, and the rest should start worrying about their future.
     
  8. Hmmmm....I've often estimated this myself, and usually come up with
    about the same number - 4000 dpi. The Kodak DCS-660, with 3Mx2M
    array, would need to have twice the linear resolution to confidently
    capture the detail in a 35mm negative (were the array 36mm x 24mm,
    which it is not).

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    The 100 l/mm number would require 200 pixels/mm minimum. (In signal
    processing, we call this 2x point the Nyquist sampling rate.) This
    already gives over 5000 dpi. In practical signal processing, we'd
    oversample somewhat. I could even argue that 4 pixels/line pair were
    required. (For those who can visualize it, imagine sampling a square
    wave right at the transitions - you'd get no variation.)

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    I usually start this mental exercise with about 50 l/mm to compare
    with 35mm film, so my "required" resolution is less than what I just
    showed.

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    Any way you slice it, you find that the VERY EXPENSIVE,
    top-of-the-line sensors today aren't close to capturing the
    information that film can.

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    You can follow the "300 dpi for print" rules and come up with smaller
    numbers. Of course, when you choose a resolution, you have to know
    how big your biggest enlargment or cropping will ever be. I'm a
    proponent of capturing all you can when you take the picture. It's
    kind of like cropping. If you take too much image (too much
    information) when you take the picture, you can crop. Likewise, if
    you take too many pixels, you can always downsample.

    <p>

    OK. I want to blather on more, but I'll stop now.
     
  9. Check this site
    for a comparison
    of various
    digital cameras
    to each other,
    and to 35mm Kodak
    E100 slide film.
    It seems that the
    6MP imager used
    in the Kodak 660
    and the Phase One
    med. format back
    (also using the
    6MP imager)
    captures more
    detail than 35mm
    film. Very
    interesting! http://www.imagingspectrum.com/portraitcomparison.htm
     
  10. Don't really think you can come to that conclusion from
    these "tests." The type of digitizing for the film, compression for
    display etc. don't give a true method of comparing detail. Plus the
    digital pictures were "sharpened" with software giving a bias towards
    appearing to have more detail.

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    The only way you could really make a comparison is to use a lens
    resolution chart, enlarge the film onto paper to show the area with
    the most discernable line pairs per millimeter, and then perform the
    same test for the digital camera with output to a Lightjet or like
    printer with no software manipulations to the digital file. This
    isn't a real test as there were no controls applied to the process.
    It's only a sloppy presentation of some comparisons masquerading as
    information.
     
  11. Sharpening wont create detail that isnt in the file. I didnt say
    sharper (but they are), but do indeed contain more detail. Like it or
    not, digital is coming of age. Digital solutions for LF are taking
    over studio work by the droves. Pros who make thier living with the
    images they create are finding that digital is making that easier. See
    how you feel about digital imaging in another 5 years.
     
  12. Everyone seems to like to say 600 dpi is the starting point.
    But realistically 600 dpi will not give you a "photo quality image"
    when printed. It takes at least 1200 dpi to print an acceptable
    "print". So you can double all the numbers you favor.
    But it doesn't matter to me in the least if digital is comparable to,
    or exceeds the "clarity" of film.
    Photography is a craft unto itself. I view it much the same as any
    other - the results are more often treasured for their artistic value
    and the appreciation of the artisanship that went into the final
    product.
    I think of the comparison as being similar to mass production. Why
    would anyone want hand-built, solid oak furniture made by a talented
    craftsman when they can buy a mass-produced, particle board/veneered
    piece at half the price? Which is most appreciated, and which will be
    treasured for decades or longer?
    Digital is to film what video tape is to film. Imagine video tape on a
    70 foot theater screen.
     
  13. No need to imagine videotape on a 70 foot screen, you can go and see it, practically anywhere, because movie theatres are rapidly moving towards all digital distribution.
    The use of crude black and white bar test patterns tells us absolutely nothing about the percieved quality of an imaging system except its ability to pass crude resolution tests.
    Waving figures of 300, 600, and 1200dpi about is meaningless, unless you tell us the context. Is that on film, in a scanner, in a final print, or what? Is that a dye-sub or light-jet print, or a crappy fixed-dot-size ink-jet?
     
  14. "Sharpening wont create detail that isnt in the file. I didnt say
    sharper (but they are), but do indeed contain more detail."

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    While that is true, the sharpened image will have the visual
    appearance of being sharper which gives the illusion of more detail.

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    The problem with the comparisons is that the test methodology used is
    flawed.

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    1. We do not know the amount of magnification of the images.

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    2. The film was digitized. This alone negates the entire comparison
    process. We do not know if number of pixels it was digitized at was
    appropriate for the amount of magnification. Further, we do not know
    if the film scan captured the maximum resolution of the film! Hence
    the need to use a fixed, know target such as a lens resolution chart
    instead of an aribitrary comparison of a portrait.

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    For example, while I might get away with 3000 ppi scan for an 8x10
    from 35mm, if I want to go to a 48 inch wide print, I will have to
    have the film digitized at about 11,000 ppi. The same holds true for
    examining small areas of film to look for details after it has been
    digitized as this is, in effect, an enlargement,

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    3. The only way to compare the true resolution capabilities is
    through controlled tests of the entire imaging "system," and not
    through poorly thought out comparisons.

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    As to your comment, "See how you feel about digital imaging in
    another 5 years."

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    I feel fine about digital imaging. I use it daily. I've had papers
    published by the Society of Photo-optical Instrumentation Engineers
    on image processing of digitized infrared video. I also use digital
    imaging in my personal photographic work. I just don't to buy into a
    presentation that is really pseudo-photoscience.

    <p>

    I test video equipment for resolution, imaging, dynamic range etc.
    with image quality evaluated before and after digitizing. From my
    perspective, the tests were not setup and carried out correctly as
    the total imaging systems (digital and photographic) were not
    compared equally because of the test methodology used.
     
  15. Steve, you apparently did not check out the url. They give all
    details of the images, and the scanning resolution (5700 DPI) on an
    Imacon Precision II Film Scanner. You can see the grain (or dye
    clouds) in the scanned film image. Some of the skin texture is
    obscured by the grain in the scanned film image, not in the Phase One
    image. This is also an old CCD (at least 5 years old). They also give
    the magnification (in equivalent print sizes, both 11x16 size, and
    16x24 size).
     
  16. I've checked out their website, and I stand by my statement that
    their methodology is flawed.
     
  17. These images were not printed. These are the image files, so printing
    has nothing to do with it. As far as scanning the film, if enough
    resolution was used to reveal the dye clouds, I dont see what a
    further increase in scanning resolution has to do with it, as the
    resolution used shows the limits of the film. Regardless
    of your opinion of the methology, I find the results interresting, and
    speaks a lot for the state of digital imaging, especially considering
    it is still in its infancy. Check out the images on the Hasselblad web
    site from thier new digital camera (at only 4MP, the images are
    superb). It will be interresting to see the images from Kodaks new
    16MP imager due out early next year.
     
  18. Check out the website of Foveon, Inc. of Santa Clara, CA. It shows an
    8 foot (96 inch) tall photograph captured with a 35 mm version of the
    16 megapixel sensor chip. It will blow your mind. Hassleblad will be
    making MF camera with an enlarged version of this ch
     
  19. The web page is
    http://aolsearch.aol.com/dirsearch.adp?knf=1&query=large%20formAT%20HO
    ME%20PAGE%20
     
  20. David:

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    That URL didn't work for me. This one did: www.foveon.net
     

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