Field of the Invention
[0001] The present invention is relates to a silver halide light-sensitive photographic
material and, especially, to a silver halide light-sensitive photographic material
which comprises silver halide emulsion containing silver halide grains of which storage
stability is improved by incorporating therein a specific novel compound.
Background of the Invention
[0002] Recently, the improvement in the preservation stability of the silver halide light-sensitive
photographic materials has been a strong demand as well as the demand for high sensitivity
and low fog.
[0003] In the image-forming technology using silver halide light-sensitive photographic
materials, it is well known that two steps are necessary to form an image. That is;
(a) a step of imagewise exposing a silver halide light-sensitive photographic material
to light to form a latent image; and (b) a step of developing thus imagewise exposed
photographic material to convert the formed latent image into a silver image or a
dye image.
[0004] Concerning these processes, for instance, there is a detailed description in "The
Theory of the Photographic Process", by James.
[0005] The formation of latent image is a microscopic change of state in silver halide crystal
by exposure and the latent image itself is essentially unstable.
[0006] Therefore, the latent image is liable to be decayed or intensified with the lapse
of time between exposure and development.
[0007] The decay of latent image is called, in the field of photographic industry, "latent-image
fading" and the latter is called "latent image progression".
[0008] Generally, the behavior of the latent image depends strongly upon the storage condition
of the exposed light-sensitive material and, for example, the latent-image fading
or the latent image intensification is remarkable in the preservation under high temperature.
On the other hand, the latent-image fading hardly be caused when the light-sensitive
material is stored under low temperature.
[0009] One method to solve this problem is to carry out development process immediately
after imagewise exposure. Another method is simply to store the exposed photographic
material under cool condition.
[0010] These are the simplest methods from chemical point of view, but they are not necessarily
welcomed to the customer.
[0011] In fact, for example, it is often the case that the imagewise exposed photographic
material is left as it is for a period of several months without undergoing development.
[0012] In the case of multi-layered color photographic materials, the latent image fading
or the latent image intensification causes imbalanced photographic behavior between
layers, which results in imbalanced color balance and deteriorates color reproduction.
[0013] In order to prevent the latent image intensification, various attempts have been
made. For example, there have been proposed a method of using a hardener which is
capable of releasing an acid to lower pH of the emulsion layer, disclosed in Japanese
Patent Publication No. 51-9 109(1976); a method of adding a rhodium compound and an
iridium compound at the time of preparing of emulsion, which is disclosed in Japanese
Patent 0.P.).Publication No. 48-6875(1973); a method of adding a heterocyclic mercapto
compound to a silver halide emulsion prepared by using a rhodium compound, which is
disclosed in Japanese Patent Publication No.57-23250(1982); a method of adding a hydroxy-aza-indorizine
compound and a nitrogen-containing heterocyclic compound having a mercapto group to
a silver halide emulsion containing a rhodium compound disclosed in Japanese Patent
O.P.I. Publication No. 53-127714(1988).
[0014] However, these conventional methods were not necessarily satisfactory in view of
its specific manner of preparation or insufficient effects, etc.
Summary of the Invention
[0015] The object of the present invention is, therefore, to provide a silver halide light-sensitive
photographic material comprising a silver halide emulsion of which preservation stability
and, especially, anti-latent- image fading property is improved.
[0016] The object of the present invention was found to be achieved by a silver halide light-sensitive
photographic material which comprises a compound represented by the following formula
[I].

wherein R1 and R2 independently represent a hydrogen atom, an alkyl group, an alkenyl
group, an alkynyl group, an aryl group or a heterocyclic group; Z1 represents an oxygen
atom, a selenium atom, a sulfur atom, a telurium atom, an organic group represented
by -N(R7)- or -C(R8) (R9)-, provided that R1 and R2 may be bonded to each other to
form a ring; R7, R8, and R9 independently represent a hydrogen atom, an alkyl group,
an alkenyl group, an alkynyl group, an aryl group, and a heterocyclic group; R3, R4,
R5, and R6 independently represent a hydrogen atom or a substituent; Z2 represents
a group of non-metal atoms necessary to form a 5- membered or 6- membered heterocyclic
ring; and each of L1 and L2 represents a methine group.
[0017] The alkyl group represented by R1 and R2 is, for example, methyl group, ethyl group,
propyl group, iso-propyl group, n-butyl group, tert.-butyl group, n-pentyl group,
a cyclopentyl group, n-hexyl group, a cyclohexyl group, n-octyl group, or n-dodecyl
group. These alkyl groups may further be substituted by, for example, a halogen atom
such as chlorine atom, bromine atom, fluorine atom, etc.; an alkoxy group, such as
methoxy group, ethoxy group, 1,1-dimethylethoxy group, n-hexyloxy group, n-dodecyloxy
group, etc.; an aryloxy group such as phenoxy group, naphthoxy group; an aryl group
such as phenyl group, naphthyl group; an alkoxycarbonyl group such as methoxycarbonyl
group, ethoxycarbonyl group, n-butoxycarbonyl group, 2-ethylhexyloxy- carbonyl group,
etc.; an aryloxy carbonyl group such as phenoxycarbonyl group, naphthoxycarbonyl group,
etc.; an alkenyl group such as vinyl group, allyl group, etc.; a heterocyclic group
such as 2-pyridyl group, 3-pyridyl group, 4-pyridyl group, morphoryl group, pyperizyl
group, pyperazyl group, furyl group; an alkynyl group such as propynyl group; an amino
group such as amino group, N,N-di-methyl amino group, anilino group; hydroxy group,
cyano group, sulfo group, carboxyl group, and a sulfonamide group such as methylsulfonylamino
group, ethylsulfonylamino group, n-butylsulfonylamino group, n-octylsulfonylamino
group, phenylsulfonylamino group, etc.
[0018] The alkenyl group represented by R1 and R2 is, for example, a vinyl group or an allyl
group. These groups can further be substituted by the alkyl group represented by R1
and R2, and the groups as mentioned as the substituent for the alkyl group.
[0019] The alkynyl group is, for example, propagyl group. The alkynyl group may be substituted
by the alkyl group represented by R1 and R2, and the groups as mentioned as the substituent
for the alkyl group.
[0020] The aryl group represented by R1 and R2 is, for example, a phenyl group, or a naphthyl
group and these groups may also be substituted by the alkyl group represented by R1
and R2, and the groups mentioned as the substituent for the alkyl group.
[0021] The heterocyclic group represented by R1 and R2 is, for example, a pyridyl group
such as 2-pyridyl group, 3-pyridyl group, 4-pyridyl group, etc., a thiazolyl group,
an oxazolyl group, an imidazolyl group, a furyl group, a pyrollyl group, a pyrradinyl
group, a pyrimidinyl group, a pyridazinyl group, a selenazolyl group, a sulforanyl,
a pyperizinyl group, a pyrazolyl group, or a tetrazolyl group and these groups may
be substituted by the alkyl group represented by R1 and R2 and the groups mentioned
as the substituent for the alkyl group.
[0022] The substituent represented by R3, R4, R5 and R6 is, for example, an alkyl group
such as methyl group, ethyl group, n-propyl 1 group, iso-propyl group, tert.-butyl
group, n-pentyl group, cyclopentyl group, n-hexyl group, cyclohexyl group, n-octyl
group, or n-dodecyl group; an alkenyl group such as vinyl group, or allyl group; an
alkynyl group such as propargyl group; an aryl group such as a phenyl group, naphthyl
group, etc.; a heterocyclic group such as a pyridyl group, a thiazolyl group, an oxazolyl
group, an imidazolyl group, a furyl group, a pyrrolyl group, a pyrradinyl group, a
pyrimidinyl group, a pyridazinyl group, a selenazolyl group, a sulforanyl group, a
pyperidinyl group, a pyrazolyl group, tetrazolyl group, etc.; a halogen atom such
as chlorine atom, bromine atom, fluorine atom, etc.; an alkoxy group such as methoxy
group, ethoxy group, propyloxy group, n-pentyloxy group, cyclopentyloxy group, n-hexyloxy
group, cyclohexyloxy group, n-octyloxy group, n-dodecyloxy group, etc.; an alkoxycarbonyl
group such as methoxycarbonyl group, ethylethoxycabonyl group, n-butyloxycarbonyl
group, n-octyloxycarbonyl group, n-dodecyloxycabonyl group, etc.; an aryloxycarbonyl
group such as phenyloxycarbonyl group, naphthoxycarbonyl group, etc.; a sulfonamide
group such as methylsulfonylamino group, ethylsulfonylamino group, n-butylsulfonylamino
group, n-hexylsulfonylamino group, cyclohex- ylsulfonylamino group, n-octylsulfonylamino
group, n-dodecylsulfonylamino group, phenylsulfonylamino group, etc.; a sulfamoyl
group such as aminosulfonyl group, methylaminosulfonyl group, dimethylaminosulfonyl
group, n-butylaminosulfony group, n-hexylaminosulfonyl group, cyclohexylaminosulfonyl
group, n-octylamino- sulfonyl group, n-dodecylaminosulfonyl group, phenylaminosulfonyl
group, naphthylaminosulfonyl group, 2-pyridylaminosulfonyl group, etc.; a ureido group
such as methylureido group, ethylureido group, pentylureido group, cyclohexylureido
group, n-octylureido group, n-dodecylureido group, phenylureido group, naphthylur-
eido group, 2-pyridylaminoureido group, etc.; an acyl group such as acetyl group,
ethylcarbonyl group, propyl- carbonyl group, n-pentylcarbonyl group, cyclohexylcarbonyl
group, n-octylcarbonyl group, 2-ethylhexylcar- bonyl group, n-dodecylcarbonyl group,
phenylcarbonyl group, naphthoxycarbonyl group, pyridylcarbonyl group, etc.; a carbamoyl
group such as aminocarbonyl group, methylaminocarbonyl group, dimethylaminocarbonyl
group, propylcarbonylamino group, n-pentylcarbonylamino group, cyclohexylcarbonylamino
group, n-oc- tylcarbonylamino group, 2-ethylhexylcarbonylamino group, n-dodecylcarbonylamino
group, phenylcarbonyla- mino group, naphthylcarbonylamino group, etc.; a sulfonyl
group such as methylsulfonyl group, ethylsulfonyl group, n-butylsulfonyl group, cyclohexylsulfonyl
group, 2-ethylhexylsulfonyl group, dodecylsulfonyl group, phenylsulfonyl group, naphthylsulfonyl
group, 2-pyridylsulfonyl group, etc.; an amino group such as amino group, ethylamino
group, dimethylamino group, n-butylamino group, cyclopentylamino group, 2-ethylhexylamino
group, n-dodecylamino group, anilino group, naphthylamino group, 2-pyridylamino group,
etc.; a cyano group; a nitro group; a carboxyl group; and a hydroxyl group. These
groups may be substituted by the alkyl group represented by R1 and the groups as mentioned
for the substituent for the alkyl group.
[0023] The ring which can be formed with R1 and R2 is, for example, a benzene ring, a naphthalene
ring, a thio- phen ring, a pyridine ring, a furane ring, a pyrimidine ring, a cyclohexane
ring, a pyrane ring, a pyrrole ring, a pyradine ring, an indole ring, etc. These groups
may be substituted by the alkyl group represented by R1 and the groups as mentioned
for the substituent for the alkyl group.
[0024] The methine group represented by substituted L1 and L2 can have a substituent. The
substituent is, for example, an alkyl group such as methyl group, ethyl group, propyl
group, etc.; an aryl group such as phenyl group, etc.; an alkoxy group such as methoxy
group, ethoxy group, etc.; an aryloxy group such as phenoxy group, etc.; a halogen
atom such as chlorine atom, bromine atom, etc.
[0025] The 5-membered or 6-membered ring is, for example, a morphorine ring, a pyperidine
ring, a pyperadine ring, a pyrroridine ring, etc. and these groups may be substituted
by the alkyl group represented by R1 and R2, and the groups as mentioned for the substituent
for the alkyl group.
[0027] The examples of synthesizing the compounds of the present invention are given below.
Other compounds may also be synthesized easily in the similar manner.
Synthesis Example 1. (synthesis of Exemplified Compound 39)
[0028] 5g of 2,5-dimethyl benzoxazole, 6.5g of morphorino benzaldehyde and 1.5g of sodium
hydride (mineral oil 60%) were dissolved in 15ml of dimethyl formamide and the mixture
was stirred for one hour in the room temperature. After the reaction was completed,
the solution was added to 200ml of water and deposited solid was filtered. After drying
solid ingredient, the object product was obtained by recrystallization using ethyl
acetate. The amount obtained was 5.7g and the yield was 52%.
Synthesis Example 2. (synthesis of Eexemplified Compound 40)
[0029] 6.1g of 6-methoxy- 2-methyl benz thiazole, 6.5g of p-morphorino benzaldehyde, 1.5g
of hydrogenated sodium hydride and 20mi of dimethylformamide were mixed under stirring
for one hour at the room temperature. After the reaction was completed, the mixed
solution was added to 200ml of water and deposited solid ingredient was filtered.
After drying the solid ingredient, the objective product was obtained through recrystalliztion
from ethyl acetate. The amount obtained was 7.2g and the yield was 60%.
[0030] The silver halide used for the photographic emulsion layer of the photographic light-sensitive
material of the present invention, any one or more selected from silver bromide, silver
iodobromide, silver chloroiodobromide, silver chlorobromide, and silver chloride can
be used. A preferable silver halide is a silver iodobromide of which silver iodide
content is not more than 30 mol%, silver bromide or silver chlorobromide.
[0031] Moreover, the silver halide grain crystals contained in the photographic emulsion
may be regular shaped crystals such as cubic, octahedral or tetradecahedral shaped
crystals; one with crystal imperfections such as one having twin planes; or irregular
shaped crystals such as spherical shaped grains; and combined one thereof.
[0032] The silver halide emulsion used for the light-sensitive material of the present invention
usually is subjected to, after physical ripening and chemical ripening, spectral sensitization.
Additives which can be used in these processes are illustrated in Research Disclosures
No.17643, No.18716, and No.308119 (They are hereinafter referred to as RD 17643, RD18716,
and RD 308119, respectively.
[0033] Page and column in RD 308119, RD 17643 and RD 18716, in which references are made,
are given below:

[0034] Moreover, well-known photographic additives, which can be used in the present invention,
are illustrated in above-mentioned Research Disclosure as shown below.

[0035] Various couplers can be used for the light-sensitive material of the present invention
according to the color- forming required in each of color-sensitive layers. The specific
example is illustrated in above-mentioned Research Disclosure. The related description
place is shown as below.

[0036] When various additives are used for the light-sensitive material of the present invention,
these may be added by using the dispersion method described in RD 308119 XIV.
[0037] In the present invention, the support described on page 28 of above-mentioned RD
17643, page 647-8 of RD 18716, and in XVIII of RD 308119 can be used.
[0038] Auxiliary layers such as a filter layer and a inter-layer, etc. described in the
above-mentioned RD 308119 VII-K can be provided to the light-sensitive material of
the present invention.
[0039] The light-sensitive material of the present invention can take various layer arrangements
such as a conventional layer order, reverse-layer order, and the unit constitutions
described in the above-mentioned RD 308119 VII-K.
[0040] The present invention can be applied to various color photographic materials such
as the color negative film for general use or cine-use, the color reversal film for
the slide or the televisions, the color paper, the color positive films, and the color
reversal paper.
[0041] The light-sensitive material of the present invention can be subjected to the development
processing by the usual method described at pages 28 - 29 of RD 17643, page 615 of
RD 18716, and section XIX, RD 308119.
Examples
[0042] Next, the present invention is explained more specifically with reference to examples.
However, the scope of the present invention is not limited by these.
Example 1
[0043] A method of preparing emulsion EmA-1 used in this example is shown below:
Preparation of Emulsion EmA-1:
[0044] The manner of preparing emulsion EmA-1 is described.
[0046] To the above-mentioned Solution (a-1), which was violently stirred at 60°C, 0.407
mol equivalent monodispersed silver iodobromide emulsion, of which average grain size
is 0.27 µm and the silver iodide content of which is 2 mol%, was added as seed grains
and pH and pAg of the solution was controlled by use of aqueous solutions of acetic
acid and potassium bromide.
[0047] Thereafter, while controlling pH and pAg of the emulsion as shown in Table 1, aqueous
solutions of (a-2), (a-3), and (a-4) were added at the flowing rates as shown in Table
2 and Table 3 by the simultaneous double- jet mixing method. Table 1 is a grain rowth
condition of EmA-1.

[0048] Table 2 represents addition flowing rates of aqueous solutions (a-2) and (a-3) and
Table 3 represents flowing rates of aqueous solution (a-4).

[0049] Next, by adding aqueous phenylcarbamyl gelatin solution and controlling pH of the
solution, the grain emulsion was to be flocculated to perform desalinization washing.
[0050] Thus, a monodispersed emulsion EmA-1, of which silver iodide content is 8.0-mol %
and the average grain size is 0.8 µm, was prepared.
[0051] Afteradjusting pAg of EmA-1 to 8.0 and adding 2.0×10
-6 mol/mol AgX of sodium thiosulfate to the emulsion, the emulsion was chemically ripened
for a period of 60 minutes at a temperature of 55°C and pH of 5.8. Then, by adding
a solution containing 4.4×10
-7 mol/mol AgX of chloroauric acid and ammonium thiocyanate, the emulsion was ripened
furthermore for 60 minutes.
[0052] Afterwards, compounds of the present invention and comparison compounds 1-5 as shown
in table 4 were added to this emulsion and the amount of 1/10 of all added amount
of the sensitizing dye was added individually. Sensitizing dyes SD-A, SD-B and SD-C
as shown below was made to adsorb together on the grains and the spectral sensitization
was performed. Furthermore, magenta couplers M-A, M-B, and M-C were added thereto.
[0054] Each of these samples was exposed through an optical wedge to green light and then
developed according to the following processing steps. Furtheremore, samples which
were aged for one week after exposure were similarly developed. The photographic performance
was comparatively evaluated. The results thereof are shown in Table 4. A green photosensitivity
in Table 4 was represented by relative sensitivity wherein the sensitivity of the
sample 1 (comparison) was represented as 100.

[0055] The composition of the processing solution used in the respective processing steps
are given below:

[0056] (Bleaching Solution)
[0057] Ethylenediaminetetraacetic acid iron (III)

[0058] Add water to make the total vqlume 1000 ml and adjust the
[0060] Herein, sensitivity is defined by reciprocal of the exposure at which fog density
+0.1 is given. Sensitivity of the sample is represented as relative sensitivity when
sensitivity of fresh Sample No.1 is assumed to be 100.
[0061] It is understood from Table of 4 that the sensitivity of the samples of the present
invention have achieved superior results in latent image-fading property comparing
to the comparative samples.
Example 2
[0062] The following emulsions Em-1 to Em-8 was prepared and a multi-layered light-sensitive
material 101 was made.
Em-1: A mono-dispersion type silver halide emulsion containing silver halide grains
of which average grain size is 0.8 µm and average silver iodide content is 8.0 mol%
and which contain relatively low silver iodide content in the surface portion of the
grain.
Em-2: A mono-dispersion type silver halide emulsion containing silver halide grains
of which average grain size is 0.38 µm and average silver iodide content is 8.0 mol
% and which contain relatively low silver iodide content in the surface portion.
Em-3: A mono-dispersion type silver halide emulsion containing silver halide grains
of which average grain size is 0.65 µm and average silver iodide content is 8.0 mol%
and which contain relatively low silver iodide content in the surface portion.
Em-4: A mono-dispersion type silver halide emulsion containing silver halide grains
of which average grain size is 0.85 µm and average silver iodide content is 8.0 mol%
and which contain relatively low silver iodide content in the surface portion.
Em-5: A mono-dispersion type silver halide emulsion containing silver halide grains
of which average grain size is 1.20 µm and average silver iodide content is 6.0 mol%
and which contain relatively low silver iodide content in the surface portion.
Em-6: A mono-dispersion type silver halide emulsion containing silver halide grains
of which average grain size is 0.70 µm and average silver iodide content is 8.0 mol%
and which contain relatively low silver iodide content in the surface portion.
Em-7: A mono-dispersion type silver halide emulsion containing silver halide grains
of which average grain size is 1.40 µm and average silver iodide content is 8.0 mol%
and which contain relatively low silver iodide content in the surface portion.
Em-8: A mono-dispersion type silver halide emulsion containing silver halide grains
of which average grain size is 0.08 µm and average silver iodide content is 4.0 mol%
and which contain relatively low silver iodide content in the surface portion.
(EmB-1)
[0063] The emulsion EmB-1 was prepared in the same manner as emulsion Em-2 disclosed in
Japanese Patent O.P.I. Publication No. 3-241336(1991), as follows.
Preparation of silver iodide fine grains
[0064] Into a reaction vessel, an aqueous solution containing 5% by weight of ossein gelatin
was added. While stirring the solution at 40°C, a 3.5-N aqueous silver nitrate solution
and a 3.5-N aqueous potassium iodide solution were added for 30 minutes at a fixed
rate.
[0065] PAg was kept at 13.5 during the addition by a conventional pAg-controlling method.
The formed silver iodide was a mixture of β-Agl and y-Agl grains having the average
size of 0.06 µm. This emulsion is called a silver iodide fine grain emulsion.
Preparation of silver halide seed emulsion containing spherical shaped twin crystal
grains
[0067] While stirring A3 solution, solution B3 and the solution C3 were added to solution
A3 by double jet mixing method for 30 seconds and silver halide nucleii were formed.
pBr over this period of time was 1.09 - 1.15.
[0068] 1 minute 30 seconds later, solution C3 was added taking 20 seconds and ripening was
carried out for five minutes. The concentration of potassium bromide during the ripening
was 0.071 mols/literand that of ammonia was 0.63 mols/liter.
[0069] Then PH of the emulsion was was adjusted to 6.0 and the emulsion was desalted and
washed. After observation using an electron microscope, this seed emulsion was found
to be a mono-dispersion type emulsion containing grains having average grain size
of 0.36 µm and the distribution width of 18%. This emulsion is hereinafter refferred
to a seed emulsion.
[0071] The seed emulsion of 0.407 equivalent mols is added to aqueous solution A2 as above-mentioned,
violently stirred at 60°C temperature and pH and pAg have been adjusted by using acetic
acid and potassium bromide aqueous solution.
[0072] Thereafter, while controlling pH and pAg as shown in Table 5, solutions B
2 and C
2, and solution D
2 were each added, by the triple jet method, at flowing rates as shown in Tables 6
to 8.
[0073] After addition, the mixed solution was flocculated to desalt by adding phenylcarbamyl
gelatin aqueous solution to desalt and adjusting pH of the solution. Next, pH and
pAg were each adjusted to 5.80 and 8.06 at 40°C.
[0074] Thus, there was obtained monodispersed silver bromoiodide emulsion having average
grain size of 1.25 µm, an average silver iodide content of 8.0 mol% and the grain
size distribution width of 13.2%.
[0075] This emulsion hereinafter is referred to as EmB-1.
[0076] From the emulsion formula, the grain structure of EmB-1 and the volume ratio of each
phase are shown in Table 9.
[0077] Table 5 is a grain growth condition of EmB-1.

[0079] After adjusting PAg, pH and temperature of the emulsion EmB-1 at 8.5, 5.8 and 55°C,
respectively, sensitizing dyes S-5, S-6, S-7 and S-8 were added thereto and the the
emulsion was allowed to stand for 30 minutes so that dyes were adsorbed on the silver
halide grains. Then, 1.0×x10
-6 mol/mol AgX of sodium thiosulfate was added. 10 minutes later, a solution mixture
containing 2.2×10
-7 mol/mol AgX of chloroauric acid and thiocyanic acid ammonium salt was added to the
emulsion, and it was further ripened for 60 minutes. Thereafter, inventive or comparative
compounds as shown in Table are respectively added thereto.
[0080] Basic structure of the multi-layered photographic material(Sample101) is shown below:
[0081] In the following descriptions, the amount of the compound incorporated into the sample
is given in terms of gram per m
2 unless otherwise noted. Moreover, the amount of silver halide and colloidal silverwas
expressed in terms of equivalent amount of silver and the added amount of the sensitizing
dye is given in terms of mols per mol of AgX contained in the same layer.
Sample-101
[0084] The samples were exposed to yellow light through an optical wedge, and thereafter
subjected to the following photographic processing.

[0085] Compositions of the processing solutions used in each processing steps are the same
as those used in Example 1.
[0086] Relative sensitivity of the respective samples were measured by using green light.
Resaults thereof are given in Table 9.
[0087] In the table, sensitivity is defined in the same manner as in Eexample 1 and is represented
as relative sensitivity by which sensitivity of Sample 101 is to be 100.

[0088] Herein sensitivity is defined by the reciprocal of the exposure by which the density
of fog +0.1 is given and was represented with a relative value, wherein a blue sensitivity
of each fresh sample was assumed to be 100. As for the compound of the present invention
of samples 6 - 53, it is understood that the latent-image regression after exposure
is small as compared with samples 1 - 5 in which the comparison compounds were added.