Method for producing an electronic image from a photographic element

A photographic element, is disclosed which includes a support and at least three silver halide emulsion layers, that records exposure information. The exposure information is recorded in three image-recording units and wherein the spectral sensitivities of said image-recording units are chosen such that the average color error, .DELTA.E*.sub.ab, is less than or equal to 3.1. .DELTA.E*.sub.ab is computed for a specified set of test colors of known spectral reflectance, and the light source is specified as D.sub.65. .DELTA.E*.sub.ab is the average CIE 1976 (L*a*b*) .DELTA.E*.sub.ab between the CIE 1976 (L*a*b*)-space coordinates of said test colors and the CIE 1976 (L*a*b*)-space coordinates corresponding to transformed exposure signals. The transformed exposure signals are formed by applying an exposure-space matrix to the exposure signals derived from the photographic element to transform the derived exposure signals to exposure signals corresponding to the color-matching functions of the CCIR Recommendation 709 primary set. The exposure-space matrix is derived so as to minimize ##EQU1## and noise-gain factor, .PSI., defined as the sum of the square roots of the sum of the squares of each row of the elements in the exposure space matrix is less than or equal to 6.5.

CROSS-REFERENCE TO RELATED APPLICATION 
Reference is made to commonly-assigned U.S. patent application Ser. No. 
08/469,062 filed Jun. 6, 1995 entitled "Photographic Elements Which 
Achieve Colorimetrically Accurate Recording" by Giorgianni et al, the 
disclosure of which is incorporated herein. 
FIELD OF THE INVENTION 
The present invention relates to a method of producing an electronic image 
using photographic elements whose spectral sensitivities are chosen to 
achieve specific color reproduction and noise performance. 
BACKGROUND OF THE INVENTION 
In classical black-and-white photography a photographic element containing 
a silver halide emulsion layer coated on a transparent film support is 
imagewise exposed to light. This produces a latent image within the 
emulsion layer. The film is then photographically processed to transform 
the latent image into a silver image that is a negative image of the 
subject photographed. Photographic processing involves developing 
(reducing silver halide grains containing latent image sites to silver), 
stopping development, and fixing (dissolving undeveloped silver halide 
grains). The resulting processed photographic element, commonly referred 
to as a negative, is placed between a uniform exposure light source and a 
second photographic element, commonly referred to as a photographic paper, 
containing a silver halide emulsion layer coated on a white paper support. 
Exposure of the emulsion layer of the photographic paper through the 
negative produces a latent image in the photographic paper that is a 
positive image of the subject originally photographed. Photographic 
processing of the photographic paper produces a positive silver image. The 
image bearing photographic paper is commonly referred to as a print. 
In a well known, but much less common, variant of classical black-and-white 
photography a direct positive emulsion can be employed, so named because 
the first image produced on processing is a positive silver image, 
obviating any necessity of printing to obtain a viewable positive image. 
Another well known variation, commonly referred to as instant photography, 
involves imagewise transfer of silver ion to a physical development site 
in a receiver to produce a viewable transferred silver image. 
In classical color photography the photographic element contains three 
superimposed silver halide emulsion layer units, one for forming a latent 
image corresponding to blue light (i.e., blue) exposure, one for forming a 
latent image corresponding to green exposure and one for forming a latent 
image corresponding to red exposure. During photographic processing, 
developing agent oxidized upon reduction of latent image containing grains 
reacts to produce a dye image with developed silver being an unused 
product of the oxidation-reduction development reaction. Silver is removed 
by bleaching and fixingduring photographic processing. The image dyes are 
complementary subtractive primaries--that is, yellow, magenta and cyan dye 
images are formed in the blue, green and red image recording units, 
respectively. This produces negative dye images (i.e., blue, green and red 
subject features appear yellow, magenta and cyan, respectively). Exposure 
of color paper through the color negative followed by photographic 
processing produces a positive color print. Again, bleaching and fixing 
remove developed silver and residual silver halide that would otherwise 
adversely affect the color print. 
In one common variation of classical color photography reversal processing 
is undertaken to produce a positive dye image in the color photographic 
element, commonly referred to as a slide, the image typically being viewed 
by projection. In another common variation, referred to as color image 
transfer or instant photography, image dyes are transferred to a receiver 
for viewing. 
In each of the classical forms of photography noted above the final image 
is intended to be viewed by the human eye. Thus, the conformation of the 
viewed image to the subject image, absent intended aesthetic departures, 
is the criterion of photographic success. 
It is well known to those skilled in the art that the colors reproduced on, 
or produced from, a photographic color-imaging element generally are not 
colorimetric matches of the colors originally photographed by the element. 
Colorimetric errors can be caused by the color recording and color 
reproduction properties of the photographic element and system. The 
distinction between the color recording and color reproduction properties 
of a photographic element is fundamental. Color recording by a 
photographic element is determined by its spectral sensitivity. The 
spectral sensitivity of a photographic element is a measure of the amount 
of exposure of a given wavelength required to achieve a specific 
photographic response. Color reproduction by a photographic imaging system 
depends not only on the color recording properties of the capturing 
element as described above, but also on all subsequent steps in the image 
forming process. The color reproduction properties of the imaging element 
or system can vary the gamma, color saturation, hue, etc. but cannot fully 
compensate for problems caused by spectral sensitivities which are not 
correlates of the human visual system. Metamers are an example of such a 
problem. Metamerism occurs when two stimuli with different spectral 
reflectance appear identical to the eye under a specific illuminant. A 
photographic element whose spectral sensitivities differ from that of the 
human visual system record the stimuli differently. Once recorded as 
disparate, a photographic element's color reproduction will only amplify 
or minimize that difference. 
In certain applications, it is desirable to form image representations that 
correspond more closely to the colorimetric values of the colors of the 
original scene recorded on the photographic color-imaging element rather 
than form image representations which correspond to the reproductions of 
those colors by the element itself. Examples of such applications include, 
but are not limited to, the production of medical and other technical 
images, product catalogues, magazine advertisements, artwork 
reproductions, and other applications where it is desirable to obtain 
color information which is a colorimetrically accurate record of the 
colors of the original scene. In these applications, the alterations in 
the color reproduction of the original scene colors by the color recording 
and color reproduction properties of the imaging element are undesirable. 
To achieve absolute colorimetric accuracy during recording, the 
photographic element's spectral sensitivity must be color-matching 
functions. Color-matching functions are defined as the amounts of three 
linearly independent color stimuli (primaries) required to match a series 
of monochromatic stimuli of equal radiant power at each wavelength of the 
spectrum. A set of three color stimuli is linearly independent when none 
of the stimuli can be matched by a mixture of the other two. Negative 
amounts of a color stimulus are routine in color-matching functions and 
are interpreted as the amount of that color stimulus which would be added 
to the color being matched and not to the mixture itself. Color-matching 
functions for any real set of primaries must have negative portions. It is 
possible to functionally transform from one set of color-matching 
functions to any other set of color-matching functions using a simple 
linear transformation. By using the color-matching functions which 
correspond to the primaries of the intended output device or medium as the 
photographic element's spectral sensitivities, no additional color signal 
processing is necessary. 
The selection of spectral sensitivities for colorimetric recording is based 
on the primaries of the imaging system in question. The primaries in a 
photographic system are defined by the imaging dyes of the element used to 
form the final reproduction of the recorded image, the spectral 
composition of which is all positive. Color-matching functions for a set 
of all-positive primaries contain negative responses. Within the realm of 
known photographic mechanisms, it is not possible to produce a 
photographic element having spectral sensitivities whose response is 
negative. 
To date, no available photographic system has been developed which has 
spectral sensitivities which approximate a set of color-matching functions 
or a linearly combination thereof. Numerous ranges of spectral 
sensitization have been claimed for specific color reproduction advantage, 
but none approximate color-matching functions as spectral sensitivities 
and therefore do not have colorimetrically accurate color recording or 
reproduction. 
A photographic element could be built using all-positive color-matching 
functions as spectral sensitivities, but these color-matching functions 
would not correspond to the primaries of the photographic system. Those 
skilled in the art will recognize that linear exposure-space signal 
processing (matrixing) would be required to transform the linear exposures 
recorded by all-positive color-matching-function spectral sensitivities to 
the linear exposures corresponding to the display primaries of the system. 
The signal processing available in photographic elements, however, is 
inherently non-linear in nature, i.e. it operates in what is effectively a 
log-exposure space, rather than a linear-exposure space. For example, the 
amount of chemical signal processing (hereafter referred to as interlayer 
interimage) produced by a dye-forming layer of a photographic element is 
essentially proportional to the amount of silver developed and/or the 
amount of image dye formed in that layer; and both silver development and 
dye formation are in turn essentially proportional to the logarithm of the 
exposure of that layer, rather than to the exposure. Color correction may 
also be produced by other methods. For example, colored dye-forming 
couplers can be used (in negative working and other intermediary 
photographic elements), and the hues of the image-forming dyes themselves 
can be adjusted. The color correction produced by these methods, however, 
is also logarithmic in nature and not of the linear type required in order 
to use color-matching-function spectral sensitivities. 
If a conventional photographic element were to be built with all-positive 
color-matching functions, the preferred choice of spectral sensitivities 
would be an all-positive set with minimum overlap. David L. MacAdam 
derived a set of single-peaked all-positive functions with minimum overlap 
which very closely approximate color-matching functions. By minimizing the 
overlap of the spectral sensitivities, competition for light between image 
recording units during imagewise exposure and the amount of interimage 
required is minimized. Use of the MacAdam sensitivities reduces the 
problems encountered with spectral sensitivities which are color-matching 
functions but not sufficiently to make the use of such sensitivities 
practical in a conventional photographic element. 
Further, the inter-record chemical interactions available in photographic 
chemistry are limited in their ability to address individual records. For 
example, it is difficult to affect a chemical interaction from layer A to 
layer C, if layer B is located between them, without affecting layer B. 
Inter-record chemical interactions are useful in correcting for the 
effects of unwanted absorptions of the imaging dyes and optical crosstalk, 
but the control of their magnitude and specificity is limited. 
For these reasons, conventional photographic elements require spectral 
sensitivities which differ significantly from color-matching functions. 
The spectral sensitivities used in conventional photographic systems are 
designed to minimize the need for linear-space signal processing (color 
correction) because such color correction is not available from chemical 
color-correction mechanisms. Conventional photographic elements are 
therefore not well suited for applications in which the photographic 
elements of the present invention are intended. 
References can also be found in the prior art suggesting the use of 
spectral sensitivities for various purposes which differ from conventional 
sensitivities but which do not reasonably approximate color-matching 
functions. For example, U.S. Pat. No. 3,672,898 entitled MULTICOLOR SILVER 
HALIDE PHOTOGRAPHIC MATERIAL AND PROCESSES by J. Schwan and J. Graham 
describes photographic elements incorporating red, green, and blue 
spectral sensitivities of specified peak wavelengths and specified ranges 
of spectral widths which provide good color rendition and acceptable 
neutrals under a variety of illuminants such as sunlight, tungsten or 
fluorescent. 
U.S. Pat. No. 5,180,657 entitled COLOR PHOTOGRAPHIC LIGHT-SENSITIVE 
MATERIAL OFFERING EXCELLENT HUE REPRODUCTION by F. Fukazawa et al 
describes photographic elements incorporating red, green, and blue 
spectral sensitivities with specified ranges of peak wavelengths and 
increased levels of interlayer interimage for improved color reproduction, 
particularly of colors of certain difficult-to-reproduce hues. 
In each of these and other related patents and applications, the 
photographic element spectral sensitivities, described by various ranges 
of peak locations and widths, do not reasonably approximate sets of 
color-matching functions. In order to achieve acceptable color 
reproduction, either directly or from subsequent imaging processes, the 
spectral sensitivities of the photographic elements described in these 
patents represent compromises constrained by the type and amount of color 
correction available within the conventional photographic system. These 
compromises result in a colorimetrically inaccurate recording of original 
scene colors, in the form of an exposed latent image. 
Further, much of the prior an for the spectral sensitivity ranges of 
photographic elements specifies the response of the respective image 
recording units independently and a selection of any set of three in no 
way assures that the resultant photographic element's sensitivity will 
yield colorimetrically accurate recording or be satisfactory for a given 
set of imaging chemistry. The specification of a test method for 
evaluating color recording is necessary to ensure that the set of spectral 
sensitivities chosen will deliver the required performance. 
It is well known and typical in the photographic an to judge the color 
reproduction of films and film-based systems using human judgments of a 
limited number of colors (whether in patch form or contained in an image). 
The selection of colors used, images selected for judgment, and individual 
preferences play a role in the judgment of color reproduction and 
therefore cannot lead to a definitive measure of film's or imaging 
system's colorimetric capabilities. To definitively differentiate between 
the color reproduction capabilities of various spectral sensitivities, a 
quantitative measure is required. 
Quantitative measures based on correlation of spectral sensitivities to a 
set of color-matching functions have been proposed. The ability to predict 
color recording capabilities of a photographic element based on the 
correlation of its spectral sensitivities to color-matching functions is 
limited, as discussed by F. R. Clapper in The Theory of the Photographic 
Process, T. H. James, 4th Ed., Macmillan, N.Y., 1977, Chapter 19, Section 
D, pp. 566-571. Clapper points out that such a correlation is unable to 
differentiate the colorimetric accuracy of sets of spectral sensitivities 
which have equal correlation to color-matching functions but significantly 
different color recording properties. Therefore, a quantitative measure 
which will more effectively differentiate the colorimetric recording 
capabilities of various sets of spectral sensitivities in commonly 
encountered imaging situations is required. Such a quantitative measure 
requires the specification of the illumination source, test colors, and 
the metric to be calculated. The distribution of test colors are selected 
such that they are evenly distributed in color space, and have spectral 
reflectance representative of the colors typically encountered in imaging. 
The following is a color test which meets all the aforementioned criteria, 
quantifies the colorimetric accuracy of a photographic element (or 
system), differentiates between the colorimetric capabilities of various 
photographic element spectral sensitivities, and simulates typical imaging 
conditions with colors which are distributed in color space and whose 
spectral reflectance is representative of real-world surface colors. For 
the test, color accuracy is judged according to the value of 
.DELTA.E*.sub.ab. .DELTA.E*.sub.ab is the average CIE 1976 (L*a*b*) color 
difference, .DELTA.E*.sub.ab, between the CIE 1976 (L*a*b*)-space (CIELAB 
space) coordinates of the test colors and the CIE 1976 (L*a*b*)-space 
coordinates corresponding to a specific transformation of the exposure 
signals recorded by the photographic element. .DELTA.E*.sub.ab computed 
for a specified set of colors of known spectral reflectance using a 
D.sub.65 illuminant. D.sub.65 is a CIE standard illuminant which is 
specified to be representative of a daylight source with a correlated 
color temperature of 6500.degree. K. The exposure signals are calculated 
using the measured spectral sensitivity of the photographic element. The 
exposure signals are transformed using a 3.times.3 matrix, Matrix M 
(applied in (linear) exposure space). The 3.times.3 exposure matrix is 
derived to minimize 
##EQU2## 
using standard regression techniques. The test colors consist of 190 
entires of known spectral reflectance specified at 10 nm increments (see 
Appendix A). 
The foregoing discussion is mathematically described as follows: The red, 
green, and blue record relative exposures captured by the photographic 
element for the i.sup.th color (H.sub.red.sbsb.i, H.sub.grn.sbsb.i, 
H.sub.blu.sbsb.i, respectively) are calculated as: 
##EQU3## 
where red, grn, blu designate the records of the photographic element, 
S.sub..lambda. is the spectral power output of the illuminant, D.sub.65 
R.sub..lambda. is the spectral reflectance of the i.sup.th test color 
I.sub..lambda. is the measured spectral sensitivity of the photographic 
element, 
and 
##EQU4## 
where E.sub..lambda. is the narrow bandwidth exposure of peak wavelength 
.lambda., required to achieve a defined density in the photographically 
processed photographic element, and values of n.sub.red, n.sub.grn, and 
n.sub.blu are determined such that 
##EQU5## 
From the CIE 1931 system, the aim tristimulus values for the i.sup.th color 
patch, X.sub.aim.sbsb.i, Y.sub.aim.sbsb.i, and Z.sub.aim.sbsb.i, are 
computed: 
##EQU6## 
where: 
##EQU7## 
are the CIE 1931 color-matching functions. 
All mathematical integrations are performed over the range from to 730 nm 
as discussed by R. W. G. Hunt in Measuring Color, John Wiley and Sons, New 
York, Chapter 2, pg. 50. 
The aim CIELAB values (L*.sub.aim.sbsb.i, a*.sub.aim.sbsb.i, 
b*.sub.aim.sbsb.i) of the i.sup.th -color patch are computed: 
##EQU8## 
X.sub.n, Y.sub.n, Z.sub.n are the tristimulus values (95.04, 100.00, 
108.89, respectively) which describe a specified white achromatic stimulus 
(D.sub.65 illuminant). 
The tristimulus values (X.sub.PE.sbsb.i, Y.sub.PE.sbsb.i, Z.sub.PE.sbsb.i) 
of the i.sup.th color patch for the photographic element are calculated as 
follows: 
##EQU9## 
where: 
##EQU10## 
Matrix P is the phosphor matrix for a video monitor having primaries 
defined by CCIR Recommendation 709, Basic Parameter Values for the HDTV 
Standard for the Studio and for International Programme Exchange, 
published 24 May 1990. The chromaticity coordinates (CIE 1931) of the 
primaries are red (x=0.640, y=0.330), green (x=0.300, y=0.600), and blue 
(x=0.150, y=0.060). The assumed chromaticity for equal primary signals, 
i.e. the reference white, is (x=0.3127, y=0.3290), corresponding to 
D.sub.65. Matrix P in no way influences the magnitude of .DELTA.E*.sub.ab, 
it is included so that the magnitude of the terms in matrix M are relevant 
in the noise test described below. The signals resulting after application 
of matrix M are suitable to drive a video monitor with phosphors having 
the specified chromaticities. Matrix M is derived using standard 
regression techniques and is calculated so as to minimize the quantity, 
##EQU11## 
where .DELTA.E*.sub.ab is determined for each test color as defined below. 
The transformed exposure signals of the photographic element are used to 
calculate CIELAB coordinates as follows: 
##EQU12## 
The average CIELAB color difference, .DELTA.E*.sub.ab, is defined as: 
##EQU13## 
where 
##EQU14## 
Although the color recording and/or reproduction of an imaging system is an 
important characteristic to be considered in its design, it is not the 
only factor. Preferred embodiments of the invention have, as one of their 
features. excellent signal-to-noise properties for use in hybrid imaging 
systems. Image quality aspects of photographic elements used in hybrid 
systems must therefore be considered. R. W. G. Hunt in The Reproduction of 
Colour in Photography, Printing, and Television, 4th Ed., Fountain Press, 
England, 1987, Chapter 20, Section 20.10, pp. 414-416 points out "The 
practical choice of spectral sensitivities is usually based on a 
compromise aimed at achieving a balance between several conflicting 
requirements. Thus if the coefficients of the matrix are too high, the 
signal-to-noise may be adversely affected." The matrix coefficients to 
which Hunt refers are those used to transform from the spectral 
sensitivities of a video camera to the color-matching functions which 
correspond to the primaries of the output device or medium, which in 
Hunt's discussion are the phosphors of a video system. It is therefore 
important to also consider the signal-to-noise implications of a 
particular selection of spectral sensitivities. As in the case of 
assessing the color recording capabilities of a set of spectral 
sensitivities, it is useful to have a quantitative measure of the 
signal-to-noise implications of a particular choice of spectral 
sensitivities. 
The measure used to quantify the noise implications is ".PSI.", or 
noise-gain factor. As alluded to in Hunt's reference, the noise-gain 
factor, .PSI., is computed from the matrix used to transform the 
photographic element's exposures to a specified set of color-matching 
functions. The color-matching functions chosen for reporting the noise 
results correspond to the primaries outlined in the CCIR Recommendation 
709, Basic Parameter Values for the HDTV Standard for the Studio and for 
International Programme Exchange, published 24 May 1990. The chromaticity 
coordinates (CIE 1931) of the primaries are red (x=0.640, y=0.330), green 
(x=0.300, y=0.600), blue (x=0.150, y=0.060), and the assumed chromaticity 
for equal primary signals, i.e. the reference white, is (x=0.3127, 
y=0.3290), corresponding to D.sub.65. .PSI. is the sum of the square roots 
of the sum of the squares of the elements of each row in the matrix M 
which transforms the exposure signals. Mathematically this is expressed 
as: 
##EQU15## 
where i and j represent the row and column number, respectively. 
The tests described are useful measures to predict the capabilities of a 
photographic element and to differentiate between the capabilities of 
photographic elements. The color test is designed specifically to measure 
the colorimetric accuracy of the spectral sensitivities of the 
photographic element and does not indicate the colorimetric accuracy of 
the reproduced image; it is a measure of the colorimetric accuracy of the 
recorded image only. 
With the emergence of computer-controlled data processing capabilities, 
interest has developed in extracting the information contained in an 
imagewise exposed photographic element instead of proceeding directly to a 
viewable image. It is now common practice to scan both black-and-white and 
color images. The most common approach to scanning a black-and-white 
negative is to record point-by-point or line-by-line the transmission of a 
light beam, relying on developed silver to modulate the beam. In color 
photography blue, green and red scanning beams are modulated by the 
yellow, magenta and cyan image dyes. In a variant color scanning approach, 
the blue, green and red scanning beams are combined into a single white 
scanning beam modulated by the image dyes that is read through red, green 
and blue filters to create three separate records. The records produced by 
image dye modulation can then be read into any convenient memory medium 
(e.g., an optical disk). Systems in which the image passes through an 
intermediary, such as a scanner or computer, are often referred to as 
"hybrid" imaging systems. 
A hybrid imaging system must include a method for scanning or for otherwise 
measuring the individual picture elements of the photographic media, which 
serve as input to the system, to produce image-bearing signals. In 
addition, the system must provide a means for transforming the 
image-bearing signals to an image representation or encoding that is 
appropriate for the particular applications of the system. 
Hybrid imaging systems have numerous advantages because they are free of 
many of the classical constraints of photographic embodiments. For 
example, systematic manipulation (e.g., image reversal, hue and tone 
alteration, etc.) of the image information that would be cumbersome or 
impossible to accomplish in a controlled manner in a photographic element 
are readily achieved. The stored information can be retrieved from memory 
to modulate light exposures necessary to recreate the image as a 
photographic negative, slide or print at will. Alternatively, the image 
can be viewed on a video display or printed by a variety of techniques 
beyond the bounds of classical photography--e.g., xerography, ink jet 
printing, dye-diffusion printing, etc. 
For example, U.S. Pat. No. 4,500,919 entitled "COLOR REPRODUCTION SYSTEM" 
by W. F. Schreiber, discloses an image reproduction system of one type in 
which an electronic reader scans an original color image and converts it 
to electronic image-bearing signals. A computer workstation and an 
interactive operator interface, including a video monitor, permit an 
operator to edit or alter the image-bearing signals by means of displaying 
the image on the monitor. When the operator has composed a desired image 
on the monitor, the workstation causes the output device to produce an 
inked output corresponding to the displayed image. In that invention, the 
image representation or encoding is meant to represent the colorimetry of 
the image being scanned. Calibration procedures are described for 
transforming the image-bearing signals to an image representation or 
encoding so as to reproduce the colorimetry of a scanned image on the 
monitor and to subsequently reproduce the colorimetry of the monitor image 
on the inked output. 
U.S. patent application Ser. No. 059,060 entitled METHODS AND ASSOCIATED 
APATUS WHICH ACHIEVE IMAGING DEVICE/MEDIA COMPATIBILITY AND COLOR 
APPEARANCE MATCHING by E. Giorgianni and T. Madden describes an imaging 
system in which image-bearing signals are converted to a different form of 
image representation or encoding, representing the corresponding 
colorimetric values that would be required to match, in the viewing 
conditions of a uniquely defined reference viewing environment, the 
appearance of the rendered input image as that image would appear, if 
viewed in a specified input viewing environment. The described system 
allows for input from disparate types of imaging media, such as 
photographic negatives as well as transmission and reflection positives. 
The image representation or encoding of that system is meant to represent 
the color appearance of the image being scanned (or the rendered color 
appearance computed from a negative being scanned), and calibration 
procedures are described so as to reproduce that appearance on the monitor 
and on the final output device or medium. 
Each of these forms of image representation or encoding, produced by 
transformations of image-bearing-signals, is appropriate and desirable for 
applications where the intent is to represent the colors of the image 
reproduced directly on, or to be subsequently produced from, the 
color-imaging element being scanned into the system. For other 
applications, however, it would be more desirable to produce an image 
representation or encoding that is a colorimetrically accurate 
representation of original scene colors, rather than reproduced colors. 
An improved photographic element for use in applications requiring 
coIorimetrically accurate representations of captured scenes would provide 
the capability to produce image representations or encoding that 
accurately represent original scene colorimetric information. The improved 
photographic element could be used to form and store a colorimetrically 
accurate record of the original scene and/or used to produce 
colorimetrically accurate or otherwise appropriately rendered color images 
on output devices/media calibrated by techniques known to those skilled in 
the art. 
One requirement for the use of photographic elements capable of 
colorimetrically accurate recording is the ability to remove color 
alterations produced by the color reproduction properties of the imaging 
element. U.S. Pat. No. 5,267,030 entitled METHODS AND ASSOCIATED APATUS 
FOR FORMING IMAGE DATA METRICS WHICH ACHIEVE MEDIA COMPATIBILITY FOR 
SUBSEQUENT IMAGING APPLICATIONS, filed in the names of E. Giorgianni and 
T. Madden, provides a method for deriving, from a scanned image, recorded 
color information which is substantially free of color alterations 
produced by the color reproduction properties of the imaging element. In 
that patent, a system is described in which the effects of media-specific 
signal processing are computationally removed, as far as possible, from 
each input element used by the system. In addition, the chromatic 
interdependencies introduced by the secondary absorptions of the 
image-forming dyes, as measured by the responsivities of the scanning 
device, are also computationally removed. Use of the methods and means of 
the invention transform the signals measured from the imaging element to 
the exposures recorded from the original scene. 
The extraction of recorded exposure information from each input element 
allows for input from disparate types of imaging media, such as 
conventional photographic negatives and transmission and reflection 
positives. For the purposes of the present invention, that same process of 
extracting recorded exposure information can be used to effectively 
eliminate any contribution to color inaccuracy caused by chemical signal 
processing and by the image-forming dyes. However, the recorded exposure 
information so extracted will, in general, still not be an accurate record 
of the colorimetric values of colors in the actual original scene that was 
recorded photographically using the element, as described previously. The 
reason for this inaccurate recording is the selection of spectral 
sensitivities in conventional photographic products. 
Values of .DELTA.E*.sub.ab and .PSI. were calculated as previously 
described for a variety of commercially available photographic elements. 
Table I contains representative photographic elements from that survey. 
Spectral sensitivity was measured for negative-working photographic 
elements by determining the exposures required to achieve a density of 0.2 
above the minimum density formed in the absence of exposure. Spectral 
sensitivity for positive-working photographic elements was measured by 
determining the exposures required to achieve a density of 1.0. Included 
for reference are the MacAdam spectral sensitivities. The entry "J. Schwan 
and J. Graham" refers to spectral sensitivities selected from the ranges 
cited in U.S. Pat. No. 3,672,898 entitled MULTICOLOR SILVER HALIDE 
PHOTOGRAPHIC MATERIAL AND PROCESSES by J. Schwan and J. Graham. The entry 
"F. Fukazawa" refers to spectral sensitivities selected from ranges cited 
in U.S. Pat. No. 5,180,657 entitled COLOR PHOTOGRAPHIC LIGHT-SENSITIVE 
MATERIAL OFFERING EXCELLENT HUE REPRODUCTION by F. Fukazawa et al. 
TABLE I 
______________________________________ 
Entry Identification .DELTA.E* ab 
.PSI. FIG. 
______________________________________ 
1 Color Reversal Film #1 
7.0 3.4 1 
2 Color Reversal Film #2 
5.4 3.6 2 
3 Color Negative Film #1 
5.0 3.7 3 
4 Color Negative Film #2 
5.6 3.5 4 
5 Color Negative Film #3 
3.9 3.8 5 
6 Color Negative Film #4 
3.4 4.0 6 
7 MacAdam 0.1 7.3 7 
8 J. Schwan/J. Graham 
3.8 4.4 8 
9 F. Fukazawa 3.9 3.8 9 
______________________________________ 
The following discussion relates to the data presented in Table I. Entries 
1-6 are representative of the normal range of colorimetric accuracy for 
photographic elements currently available based on measurements of their 
spectral sensitivities. Entry 6 marks the lower limit of .DELTA.E*.sub.ab 
of the photographic elements surveyed. Entry 7 establishes the value of 
.DELTA.E*.sub.ab for the MacAdam spectral sensitivities, the residual 
error is caused by the truncation of small negative responses present in 
the color-matching functions on which the MacAdam spectral sensitivities 
are based. The spectral sensitivities of the photographic elements listed 
in Table I are shown in FIGS. 1-9. The area under each spectral 
sensitivity response is normalized to unity for convenience. 
From the data in Table I, it is clear that conventional photographic 
elements are not sensitized to achieve colorimetric accuracy. Subsequent 
stages in the color reproduction of these photographic elements will alter 
the colorimetric performance but can not improve the colorimetric 
accuracy. The colorimetric accuracy is fundamentally limited by the 
spectral sensitivity of the photographic element. 
The data in Table I also illustrates that the prior art as manifest in the 
patents of J. Schwan and J. Graham and F. Fukazawa is insufficient in its 
specification of spectral sensitivities to produce colorimetrically 
accurate data. Because of the inter-related nature of the choice of 
spectral sensitivities, it is not possible to select, for example, the 
green spectral sensitivity independently of the red spectral sensitivity. 
The specification of spectral sensitivity must therefore be in terms of 
the colorimetric capability of the photographic element if it is to 
achieve a specified level of colorimetric accuracy. 
SUMMARY OF THE INVENTION 
This invention has as its object to provide a method of producing an 
electronic image from a photographic element which is superior in its 
colorimetric accuracy. 
This object is achieved in a method of producing an electronic image 
comprising: 
a) providing a photographic element, comprised of a support and at least 
three silver halide emulsion layers, that records exposure information, 
wherein the exposure information is recorded in three image-recording 
units and wherein the spectral sensitivities of the image-recording units 
are chosen, such that the average color error, .sub.ab, is less than or 
equal to 3.1, wherein the .sub.ab is computed for a specified set of test 
colors of known spectral reflectance, and the light source is specified as 
D.sub.65 and wherein the .sub.ab is the average CIE 1976 (L*a*b*) 
.DELTA.*.sub.ab between the CIE 1976 (L*a*b*)-space coordinates of the 
test colors and the CIE 1976 (L*a*b*)-space coordinates corresponding to 
transformed exposure signals, wherein the transformed exposure signals are 
formed by applying an exposure-space matrix to the exposure signals 
derived from the photographic element to transform the derived exposure 
signals to exposure signals corresponding to the color-matching functions 
of the CCIR Recommendation 709 primary set, and wherein the exposure-space 
matrix is derived so as to minimize 
##EQU16## 
and noise-gain factor, .PSI., defined as the sum of the square roots of 
the sum of the squares of each row of the elements in the exposure space 
matrix is less than or equal to 6.5; 
b) exposing and photographically processing the photographic element to 
produce image-bearing density records; 
c) scanning the image-bearing density records on a pixel-wise basis with an 
opto-electronic scanner to produce image-bearing electronic signals; 
d) digitizing the image-bearing electronic signals; and 
e) manipulating the electronic image-bearing signals in a computer to 
provide the electronic image. 
Another object of this invention is to provide a method of producing an 
electronic image from a photographic element in combination with selected 
optical filters which is superior in its colorimetric accuracy. This 
object is achieved in a method of producing an electronic image 
comprising: 
a) providing a photographic element, comprised of a support and at least 
three silver halide emulsion layers, that records exposure information, 
wherein the exposure information is recorded in three image-recording 
units, used in combination with a means of optical filtration external to 
the photographic element, wherein the spectral sensitivities of the 
image-recording units and optical transmission of the optical filtration 
means are chosen such that the average color error, .sub.ab, is less than 
or equal to 3.1, wherein the .sub.ab is computed for a specified set of 
test colors of known spectral reflectance, and the light source, is 
specified as D.sub.65, and wherein the .sub.ab is the average CIE 1976 
(L*a*b*) .DELTA.*.sub.ab between the CIE 1976 (L*a*b*)-space coordinates 
of the test colors and the CIE 1976 (L*a*b*)-space coordinates 
corresponding to transformed exposure signals, wherein the transformed 
exposure signals are formed by applying an exposure-space matrix to the 
exposure signals derived from the photographic element to transform the 
derived exposure signals to exposure signals corresponding to the 
color-matching functions of the CCIR Recommendation 709 primary set, and 
wherein the exposure-space matrix is derived so as to minimize 
##EQU17## 
and noise-gain factor, .PSI., defined as the sum of the square roots of 
the sum of the squares of each row of the elements in the exposure space 
matrix is less than or equal to 6.5; 
b) photographically processing the photographic element to produce 
image-bearing density records; 
c) scanning the image-bearing density records on a pixel-wise basis with an 
opto-electronic scanner to produce image-bearing electronic signals; 
d) digitizing the image-bearing electronic signals; and 
e) manipulating the electronic image-bearing signals in a computer to 
provide the electronic image.