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Subject: Digital projection

Digital projection

From: Tim Vitale <tjvitale>
Date: Monday, October 13, 2003
Projecting Digital 'Slide' Images
October 13, 2003

This is an enhanced version of an earlier posting to the Electronic
Media Group, American Institute for Conservation of Historic and
Artistic Works EMG-membership list. Thanks to Mike Collette and
Robin Myers of BetterLight; Peter Kraus (Agfa, retired); Ron Miller
of LaserGraphics; and Dave Dicklich, President, Projector Central
for their information and assistance.

    **** Moderator's comments: an HTML version of this document is
    found in CoOL
    <URL:http://palimpsest.stanford.edu/
        byauth/vitale/digital-projection/>

    The above URL has been wrapped for email, as have all the URLs
    in this posting. There should be no newlines.

Overview

    Now that the some of the best slide projectors are being
    discontinued (Kodak Ektagraphic III), it is time to get serious
    about the viability of using video projectors for the projection
    of film-positive, single still image Artworks, i.e., digitized
    slide(s).

    While images can be readily captured at the resolution of film
    (maximum of 4000 ppi) and beyond, projecting at that resolution
    is not possible. In JAIC, Fall/Winter 2001, there is a
    discussion of this problem, see Vitale, "TechArchaeology: Works
    by James Coleman and Vito Acconci," JAIC, F/W 2001, Vol. 40, No.
    3, pp.233-258. The highest resolution projector (QXGA format)
    from the 2001 period, the LaserGraphics LG2001 projector with
    2000 lumens output, 300:1 contrast range at $13,000, is still a
    valid recommendation based on the limitations of digital
    projection. It has been recently learned that the LG2001 is now
    a custom order from LaserGraphics and may not be manufactured
    much longer at the present one-at-a-time basis.

    More recently, JVC has produced a "best in class LCD" QXGA
    (2048x1536) video projector, the JVC DLP QX1G outputs 7000
    lumens at 1000:1 contrast, for $225,000
    <http://www.projectorcentral.com/JVC-DLA-QX1G.htm>. It is
    intended for use in movie theaters. Sony makes the next closest
    resolution projector; the just announced Qualia-004, has HD
    (1920 x 1080) resolution, with undoubted high lumen output and
    possible 6000:1 contrast (if the announcement can be believed)
    at $25,000 <http://www.projectorcentral.com/Sony-Qualia-004.htm>
    and

        <URL:http://www.image-acquire.com/sony/
            sony_qualia_004/sony_qualia_004.html>.

    Projecting slides in a slide projector (the equivalent of 32-72
    MB digital information) still yields more cost-effective and
    higher quality images than today's projected digital images,
    with their 9.4 MB of information, at the highest possible, QXGA,
    projected resolution of 2048x1436 pixels.

    When digital projection in movie theaters becomes more common,
    projector resolution should increase to a scale that is "similar
    to film". However, today it is still below the resolution of
    film, by about half an order of magnitude.

Discussion:
Resolution of Slide Film

    The most direct method of determining resolution would be to
    measure individual grain in slide film. However, actual grain
    size is almost impossible to evaluate in color reversal film for
    numerous reasons such shape of dye cloud, randomness of image
    cloud distribution with an emulsion layer, thickness of a layer
    and that fact that there are three dye layers.

    Two values are routinely used to predict resolution. RMS
    Granularity shows the degree of noise (unevenness) in a
    continuous tone, it is a measure of irregularity in a virtually
    grainless substrate. Spatial resolution predicts how much detail
    can be resolved in an ideally processed film.

    The value of 80-line-pairs/mm is the commonly quoted value for
    slide film. Fuji Velvia can actually deliver 80-lp/mm at 30%
    contrast, see below, but this is the only slide film capable of
    this performance. Most slide film has an average resolution of
    50-lp/mm.

    The often quoted resolving value, 80 lp/mm, is determined using
    high-resolution densitometer at very small contrast differences
    (10%), on film that was contact printed without the use of a
    lens. A 10% contrast difference is well below what a human could
    observe even if the film was enlarged substantially making the
    line-pairs human readable. As if to confirm this, Fuji doesn't
    report MTF values below 20-25% contrast difference in its more
    recent Film Data Sheets.

    If the contrast difference between line-pairs is evaluated at a
    30%contrast difference, something an average human could
    observe, the spatial resolution of slide film is about 35-60
    lp/mm, using the MTF curves in (Kodak, 1986) & (FujiFilm,
    2000-2003); excluding Velvia. Using the more realistic
    resolution of 50 lp/mm, and exposing the film through a very
    high resolution 200 lp/mm lens (most lenses actually have a
    30-50 lp/mm resolution, lowering the final system resolution
    even more) the resolution of the system will be about 40 lp/mm
    (system resolving power equation, EQ1, from FujiFilm
    Professional Data Guide, AF3-141E, 2002, p 129).

        [EQ1: 1/r=1/r (film) + 1/r (lens);
        where r=resolving power and r=resolving power on each
        component]

    Using the broadest range of 35-80 lp/mm resolutions, the MTF
    values are translated to about 1800-3000 ppi, an average of 2900
    ppi resolution, before the effect of the lens resolution is
    applied. The same MTF range, excluding Fuji Velvia, would have
    an average resolution of 47.5 lp/mm or 2400 ppi (before the
    effect of the lens resolution is applied).

Comparison to Printed Images

    In the field of the printed still image, critical observers are
    beginning to think that the resolution of color reversal (slide)
    film is equivalent to 2700 ppi, or 53 lp/mm. This is excellent
    agreement with the MTF data above. Mike Collette's clients tell
    him that his scanning backs deliver the resolution of 8 x 10
    transparencies.

    The new Canon EOS 1Ds has a 2704 x 4064 pixel, full frame CMOS
    sensor. Many photographers are saying its digital image is the
    equivalent of high-resolution slide film.

RMS Granularity of Slide Film

    Kodak slide films have a RMS Granularity of between 8-13 and
    Fuji reversal film have values between 7-10. Some negative films
    have RMS Granularity rating of 5, but the negatives will be
    printed increasing its final "system" Granularity, markedly. The
    lower the Granularity, the lower the noise and the lower the
    perceived grain.

    Granularity is a root-mean-square of "density differences," from
    the mean (average density), in a film of continuous tone (1.0
    D). It has no units, and unfortunately cannot be translated into
    grain size in any way. However, Mike Collette is experimenting
    with the value using it to predict the unevenness of 12-micron
    square pixels. A 12-micron pixel is the size in his lower
    resolution BetterLight scanning backs. Preliminary equations
    suggest that the unevenness for the smaller area is 3.5 times
    greater, than that for the 48-micron test aperture. This would
    make the effective granularity for of 12x12 micron bit of film,
    an average of 35. This is a very grainy/noisy bit of film,
    indeed. The difference between neighboring bits of 12-micron
    film squares would be 35. The best Fuji film has a value of 7,
    and the worst Kodak slide film has a value of 13, using the
    standard test aperture.

    RMS Granularity measures "perceived grain" because it measures
    the unevenness of a virtually grainless emulsion composite. The
    complexity of the silver-to-dye transition, filamentation of dye
    cloud and the multiple emulsion layers mean that only "the odd"
    single dye clouds can be observed at the edges of transitions.
    In the RMS Granularity test, the measured emulsion is composed
    of numerous (hundreds) translucent grain-clouds making up the
    3-layer-emulsion (actually 9 layers) that the standardized,
    48-micron diameter, test aperture evaluates. There is no chance
    of resolving a single grain in that structure, only at the edges
    between transitions. Note that Peter Kraus projects that the
    average dye cloud probably has a size of about 25 microns, and
    that it started from a silver grain that was about 1 micron or
    less.

    However, a type of graininess can be observed in slide film.
    That graininess is the unevenness of the complex composite
    structure, its "noise." The degree of unevenness varies based on
    chemistry, physical and manufacturer variables.

                                            lp/mm
                                 RMS        MTF @
    Film                     Granularity    30% contrast    ppi
    ----                     -----------     --------       ---

    Ektachrome 5071 (dup)           9           50          2540
    Vericolor 5072 (neg-pos)        9           60          3050
    Kodak EDUPE                     8.7         60          3050
    Kodachrome 25                   9           50          2540
    Kodachrome 64                  10           50          2540
    Ektachrome 50                  13           40          2030
    Ektachrome 64                  12           40          2030
    Ektachrome 100                 11           45          2290
    Ektachrome 100GX                8           60          3050
    Ektachrome 100plus EPP         11           45          2290
    Ektachrome 160                 13           35          1780
    Fuji Velvia 50 RVP              8           80          4065
    Fuji Velvia 100 RVP100F         8           80          3300
    Fuji Provia 100F RPD            9           55          2800
    Fuji Astra 100 RAP             10           45          2290
    Fuji Astra 100F RAP100F         7           65          3300
    Fujichrome EI 100              10           45          2290
    Average (w/o Velvia)           10           47.5        2410
    Average                        10           57.5        2920

Tonal Range of Slide Film

    Ideally exposed and processed slide film has a Dmax between 3.0D
    and 3.9 D; see "Kodak Films and Papers for Professionals"
    (1986); the Kodak Professional Products web site

        <URL:http://www.kodak.com/global/en/professional/
            products/colorReversalIndex.jhtml?id=0.3.10.8&lc=en;>
    and the Fuji Professional Product web site
    <http://home.fujifilm.com/products/datasheet/>.

    The following data was calculated from Density vs Exposure
    (lux-seconds) curves (Characteristic Curve) supplied by the
    manufactures. Some will argue that humans can't see detail much
    above a density of 3.4 D in a transparency. However, I believe
    that under strong light conditions (in slide projectors) the
    highest densities are valid, but this point is under contention.

           Film               Film Dmax    Contrast
           ----               ---- ----    --------
    Ektachrome 5071 (dup)       3.0 D       1000:1
    Vericolor 5072 (neg-pos)    3.9 D       8000:1
    Kodak EDUPE                 3.2 D       1600:1
    Kodachrome 25               3.8 D       6300:1
    Kodachrome 64               3.7 D       5000:1
    Ektachrome 50               3.3 D       2000:1
    Ektachrome 64               3.7 D       5000:1
    Ektachrome 100              3.4 D       2500:1
    Ektachrome 100GX            3.8 D       6300:1
    Ektachrome 100plus EPP      3.8 D       6300:1
    Ektachrome 160              3.4 D       2500:1
    Fuji Velvia 50 RVP          3.8 D       6300:1
    Fuji Velvia 10 RVP100F      3.8 D       6300:1
    Fuji Provia 100F RPD        3.4 D       2500:1
    Fuji Astra 100 RAP          3.5 D       3200:1
    Fuji Astra 100F RAP100F     3.5 D       3200:1
    Fujichrome EI 100           3.6 D       4000:1

Video Projector Contrast

    If an artist makes slides copies of the Kodak Q60 R1 color
    target (print target), and is having problems differentiating
    last few black patches, the "system" is not delivering the full
    tonal range of the chosen film.

    Many of us have been saying for years that slide film lies about
    color. The first lie is that film increases the contrast of the
    subject by a factor of about 1.5 to 1.9, an average of 1.7. I
    calculated a 1.8 contrast enhancement for Velvia 50/100. That
    is, for an input of 0.1-2.5 density, it outputs 0.2 - 3.7
    density, almost its full tonal range. The center slope of the
    "density vs exposure" (Characteristic Curve) is 1.8, while the
    overall contrast factor is 1.34; the long shoulder and toe of
    the curve are not linear, which accounts for the disparity.

    If the 24-patch gray scale in the Kodak Q 60 R1 reflective color
    target is shot using Fuji Velvia, an ideally shot and processed
    2.4 D tonal range (2.5 Dmax) will produce a transparency with a
    3.7 Dmax, assuming a 0.5 Dmin. On the gray scale, the next to
    last patch, GS22, patch #23 would be 3.45 D; GS21 (patch #22)
    would be 3.25 D; GS20 (patch #21) would be 2.7 D; and GS19
    (patch #20) would be 2.5 D.

    If the duplication process produces a Velvia slide yielding only
    21 discernible gray patches (of 24), the film could be
    delivering a tonal range of about 2.6 D, or a contrast ratio of
    400:1. The Dmax would probably be at 3.1 D with a 0.5 Dmin, a
    2.6 tonal range. If the projector's Dmin can be adjusted using
    the Brightness control, from 0.0 D to 0.5 D, the projector's
    full contrast will be usable, and could reproduce the contrast
    in the slide (at lower resolution).

    Translating density into "contrast range" will help correlate
    video projector characteristics to film equivalents. Basic
    contrast ratios are:

        1.0 d=10:1 contrast ratio
        2.0 d=100:1 contrast ratio
        3.0 d=1000:1 contrast ratio
        4.0 d=10,000:1 contrast ratio;

    where contrast=antilog of D, density. Typical projectors have
    contrast ranges of:

        100:1=2.0 D
        300:1=2.47 D
        500:1=2.7 D
        3000:1=3.48 D.

    The highest contrast I've seen advertised for a LCD-based device
    is 3000:1. The average contrast range for common video
    projectors is 300:1; the lowest commonly quoted range is 100:1.
    In reality, a projector with a contrast range of 500:1 is very
    good, and 1000:1 contrast is excellent. Some consider 1000:1
    contrast an optimistic specification for today's LCD projectors.

    In conclusion, video projectors cannot match (1) the resolution
    or (2) the tonal range, of common slide film. The resolution of
    even today's best resolving devices is only about 13-29-50% of
    the perceived resolution of slide film. Some will argue that a
    projector delivering a contrast of 500:1 is as good as can be
    expected, but it is still short of the tonal range that native
    Kodachrome 25, Ektachrome 100GX and Fuji Velvia 50/100 can
    deliver, by a factor of about 10, (an order of magnitude). If
    however, the original slides have been duplicated onto Kodak
    5071, 6121 or EDUPE slide dup film, their tonal range will have
    a maximum of about 3.0 D (1000:1) if perfectly duplicated.

    Less than ideally processed slide dups may well be within the
    contrast range of selected video projectors, but never their
    resolution. Less than ideally shot and processed Velvia or
    Ektachrome 100GX could have a tonal range that is within the
    contrast range of selected video projectors, but never their
    resolution

For the Sake of Completeness: Printing & Video-Out Issues

    Printed images are generally sent to an inkjet printer between
    150 ppi and 360 ppi resolution. It is said that children with
    perfect 20-20 vision can resolve no more than 300 ppi at normal
    viewing distance. [Most digital professionals accept the figure
    as a given, but I question the value as too low.] The 150-360
    ppi images are printed at 720, 1440 or 2880 dpi on the typical
    photographic quality inkjet printer.

    The difference between output file and printer resolution, is
    that the printer lays down inkjet dot clumps of color inks at
    1440 dpi resolution, to yield "360 ppi-pitch" pixels composed of
    about 16 dots. [For a 150 ppi-pitch image, it would print 92
    dots per pseudo pixel at 1440 dpi.] The printed "1440
    dpi-elements from 360-ppi original" don't have the possibility
    of representing 16.7M colors each; rather they have just 1-8 ink
    dots for each color/black ink. The "360 ppi-pitch" pseudo-pixels
    are made up of the printer driver's best approximation of the
    target color using its available inks, at the image resolution.

    Laser photographic printers using color photographic paper (Fuji
    Crystal Archive), such as the Durst Lambda (200-400 dpi),
    Cymbolic Sciences' LightJet (200 ppi) and ZBE Chromira
    (300dpi/425ppi), blur the laser point source with multiple color
    laser dots, of varying intensity, producing pixels with 24-bit
    color depth. This continuous tone image appears significant when
    viewed under magnification but can only be printed on
    photographic papers (with their limited surface textures).
    However, when humans view without the aid of magnification,
    inkjet printers produce equivalent or better results, at much
    lower cost and on a wider variety of papers, films, cardboard's
    and plastic sheets.

    Video projector produces pixels that have a minimum of 16.7M
    possible colors. This is quite different from an inkjet-printed
    image, but similar to your CRT monitor, laptop display or
    laser-photo printer.


                                  ***
                  Conservation DistList Instance 17:34
                Distributed: Thursday, October 16, 2003
                       Message Id: cdl-17-34-011
                                  ***
Received on Monday, 13 October, 2003

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