Method of and apparatus for masking a master for reproduction

A negative to be printed is masked. The mask, or an image of the mask in the plane of the negative, or both the mask and the image, have a low resolution of 0.1 to 2 line pairs per millimeter.

CROSS-REFERENCE TO RELATED APPLICATION 
This application contains subject matter similar to that disclosed in the 
commonly-owned patent application Ser. No. 07/832,839 of Knut Oberhardt 
et. al. filed Jan. 18, 1992 for "Photographic Copier With Masking Device 
and Coping Method", now U.S. Pat. No. 5,155,524. 
BACKGROUND OF THE INVENTION 
The invention relates generally to the reproduction of a master. 
More particularly, the invention relates to a method of and an apparatus 
for masking a master, especially a photographic master, preparatory to 
reproduction. 
When photographs have large brightness variations in individual regions, 
the bright zones are frequently overexposed and the dark zones frequently 
underexposed in copies of the photographs. Consequently, details and fine 
structures are very poorly, or not at all, reproduced on the copies. 
The German Offenlegungsschrift 31 41 263 describes a method of copying 
color diapositives on reversal paper using masks for contrast reduction. 
The diapositive is placed in direct contact with phototropic glass and 
ultraviolet light or the like is then passed through the diapositive into 
the glass. A black-and-white mask representing a negative of the 
diapositive is thus produced in the phototropic glass. The composite of 
mask and diapositive is thereupon illuminated in the opposite direction 
while remaining in the same position. The diapositive is thereby 
reproduced on the reversal paper with low contrast. 
Due to the direct contact between the masking glass and the diapositive, a 
relatively sharp mask is produced in this method and is sharply imaged on 
the reversal paper. To obtain copies of high quality, it is necessary for 
the mask and the diapositive to be practically one hundred percent in 
register during exposure. However, this is precluded because the 
materials, namely, the film material and the glass, are different. During 
the very intensive exposure, the materials are heated relatively strongly 
and expand to different degrees. The copies obtained are then of lower 
quality and the dark/bright gradations of the mask which do not precisely 
register with the dark/bright gradations of the diapositive are clearly 
visible. 
If, as described in the Offenlegungsschrift, the method is employed in a 
large laboratory with automatic copiers, additional difficulties arise 
because of rapid, jerking movements to which the composite of masking 
glass and diapositive is subjected between the individual stations. 
Shifting can again occur and even more strongly influence the quality of 
the copies. 
SUMMARY OF THE INVENTION 
It is an object of the invention to provide a reproduction method for 
masters which enables copies of better quality to be obtained. 
Another object of the invention is to provide a masking method which can 
cause small relative displacements, or differential expansion, of master 
and mask to have little, if any, effect on copy quality. 
A further object of the invention is to provide a reproduction apparatus 
for masters which can yield copies of better quality. Is 
An additional object of the invention is to provide an apparatus having a 
masking arrangement which can cause small relative displacements, or 
differential expansion, of master and mask to have little or no effect on 
copy quality. 
The preceding objects, as well as others which will become apparent as the 
description proceeds, are achieved by the invention. 
One aspect of the invention resides in a method of reproducing a master, 
particularly a photographic master. The method comprises the steps of 
masking the master, and copying the masked master on photosensitive 
material. The masking step includes generating a mask, preferably a 
black-and-white mask, which represents a negative of the master. At least 
one of the masking and copying steps is performed in such a manner that 
the mask, or a reproduction of the mask in the plane of or on the master, 
or both the mask and the reproduction, have low resolution. 
In one embodiment of the method, the mask has low resolution and the 
copying step comprises sharply focusing the mask on the photosensitive 
material. The resolution of the mask may be 0.1 to 2 line pairs per 
millimeter and can advantageously be 0.7 line pair per millimeter. 
According to another embodiment of the method, the mask has high 
resolution, i.e., is sharp, and the copying step comprises forming a low 
resolution reproduction of the mask on the master. This reproduction of 
the mask may again have a resolution of 0.1 to 2 line pairs per millimeter 
and preferably has a resolution of 0.7 line pair per millimeter. 
In accordance with a further embodiment of the method, both the mask and 
the reproduction thereof on the master have low resolution. The mask and 
its reproduction may here each have a resolution of 0.1 to 2, and 
advantageously 0.7, line pairs per millimeter. 
The method may further comprise the step of scanning the master to generate 
density values. At least one of the masking and copying steps is then 
performed using such density values. 
The result obtained in each of the three embodiments outlined above is an 
unsharp or diffuse intensity distribution on the photosensitive material 
or paper. The unsharpness is such that the sharp image of a line of the 
master always lies within the range of the unsharp image of the 
corresponding line of the mask. The unsharpness or diffuseness of the 
intensity distribution on the photosensitive paper depends upon the 
particular magnification. For example, with a conventional small format 
film and an experimentally tested mask resolution of 0.7 line pair per 
millimeter, the resolution of an image of the mask in the plane of the 
master should lie approximately at the upper boundary of the given range 
for a master having a size of 0.8.times.1.1 centimeters and approximately 
at the lower boundary of the given range for a master having a size of 
20.times.25 centimeters. 
The mask may be generated in a variety of ways. For instance, the mask may 
be produced immaterially and stored in an electronic memory in the form of 
pixels, i.e., the operation of generating the mask may be performed 
electronically in a memory. Exposure of the photosensitive paper may then 
be carried out pointwise using a cathode ray tube or a laser. It is 
possible here to enter data on the master in a memory and to account for 
such data in the data for the mask. In this case, exposure of the 
photosensitive paper takes place directly without the master. When the 
master is transparent, it is further possible to expose via the master and 
to additionally employ data on the mask in calculating the exposure data. 
The copying step then comprises transmitting copy light to the 
photosensitive paper through the master. In each of these two procedures, 
a reduction in contrast as well as an increase in contrast may be 
achieved. 
An immaterially generated mask which exists solely as a set of data has the 
added advantage that the data set can be processed as desired, and the 
method may further comprise the step of processing the mask so that a 
region of the mask having a predetermined intensity is imaged on the 
photosensitive paper on a reduced scale. For instance, dark regions of the 
mask may be reduced somewhat so that the corresponding bright/dark 
transitions always lie within the dark zones of the copy and are 
accordingly less noticeable. This allows the quality of the copy to be 
further increased. 
The mask may also be generated materially using a phototropic masking 
element which may comprise phototropic glass, a phototropic foil or glass 
having a phototropic coating. When the master is transparent and the 
operation of generating the mask is performed using a phototropic masking 
element, the copying step may comprise transmitting copy light to the 
photosensitive paper through the master and the masking element, i.e., 
exposure of the photosensitive paper may take place via the master and the 
mask. 
An intermediate stage between a purely immaterial mask and a purely 
material mask can be achieved with an electronically adjustable masking 
element or matrix. Since the mask fundamentally exists as a data set, 
there is the advantage that the mask can be changed. On the other hand, 
exposure can be carried out in the conventional manner employed for 
material masks. Thus, when the master is transparent and the operation of 
generating the mask is performed using an electronically adjustable 
masking element or matrix, the copying step can comprise transmitting copy 
light to the photosensitive paper through the master. Pointwise exposure 
is not necessary. By way of example, a liquid crystal display or 
electronically adjustable light valve arrangement can be used as a 
transparent masking matrix. The masking element or matrix can likewise 
include a plasma display. Furthermore, reflective, electrooptical 
components whose reflectivity can be changed region-by-region are on the 
market and can be used to generate the mask. 
In order to avoid substantially greater illumination intensities and longer 
exposure times upon masking, it is of advantage to design the mask so that 
its brightest location produces virtually no darkening effect. A 
transilluminated mask should have its maximum transparency at this 
location. The operation of generating the mask is performed in such a 
manner that the mask has a region of maximum brightness corresponding to a 
predetermined zone of the photosensitive paper, and the copying step 
includes limiting darkening of the predetermined zone to that resulting 
from the characteristics of the paper, i.e., limiting darkening to the 
unavoidable dimming effect caused by the paper. 
The method of the invention can be applied with advantage in large 
laboratories having printers or copiers which include automatic exposure 
control units and serve to make paper prints of negative or positive 
films. The density values of the masked master (harmonized densities) must 
here be used for exposure control, and the method further comprises the 
steps of determining the density values for the masked master and 
calculating an amount of copy light for the copying step using such 
density values. The copying step comprises automatically controlling 
exposure of the photosensitive paper. 
In a preferred embodiment of the method, the amount of copy light is 
obtained purely mathematically. The step of determining the density values 
for the masked master here comprises scanning the master, or measuring the 
master by means of a scanner, to obtain first density values, and deriving 
second density values for the mask from the first density values. The 
calculating step is thereupon performed using the first and second density 
values. The first density values for the master may be stored, and the 
second density values for the mask may be obtained from the first density 
values by means of special algorithms. The amount of copy light is now 
calculated from the two sets of density values, namely, the first density 
values for the master and the second density values for the mask. 
The amount of copy light may be calculated in other than a purely 
mathematical manner. To this end, the method again comprises the steps of 
scanning the master to obtain first density values, and deriving second 
density values for the mask from the first density values. However, in 
this case, the mask is generated using the second density values, and the 
density values for the masked master are determined by once more scanning 
the master after the latter has been masked with the thus-generated mask. 
The density values obtained by measurement of the masked master provide 
the basis for calculation of the amount of copy light. 
The two procedures outlined above for calculating the amount of copy light 
allow the copying operation to be fully automated. With the aid of a 
decision logic circuit, a determination can be made, e.g., based on the 
range of contrast, as to whether a mask should be generated and, if so, 
how the mask should be designed. The method here further comprises the 
steps of scanning the master to obtain density values, and automatically 
determining the degree of masking using the density values. By means of 
such a procedure, copies or prints of high quality can be produced fully 
automatically. 
In order to make the method of the invention suitable for the very exacting 
field of professional photography, it is necessary to make provision for 
manual intervention by an operator. This can be achieved in an 
advantageous manner by displaying a first image of the master while 
unmasked, and displaying a second image of the master while masked. An 
operator then has the opportunity to evaluate the images and adjust the 
same if required. The images can be displayed in color or in 
black-and-white. A single color or black-and-white monitor can be used to 
display the images or, alternatively, two separate color monitors or two 
separate black-and-white monitors can be employed. The images can be 
produced on the basis of density values obtained by scanning the master. 
The operator can adjust the degree of masking and this will change the 
image in which the master is masked. The effect of an adjustment in the 
degree of masking can be immediately evaluated by the operator on the 
monitor exhibiting the image of the masked master. 
The operator can further adjust the density and color of each image by 
modifying the image signals, i.e., the density values for the three 
primary colors red, green and blue, generated during scanning of the 
master. Modification of the density values and colors is visible in each 
of the images. 
Another aspect of the invention resides in an apparatus for reproducing a 
master, particularly a photographic master. The apparatus comprises means 
for measuring the density of the master, means for masking the master, and 
means for positioning the master at a predetermined location. The masking 
means includes an electrically adjustable masking element such as, for 
instance, a masking matrix. The apparatus further comprises means for 
copying the masked master when the master is at the predetermined 
location, and the processing means includes means for calculating mask 
density and controlling the masking element. The processing means has 
input means for the receipt of density signals from the measuring means 
and output means including at least one output for the transmission of 
control signals to the masking element. 
The apparatus of the invention is particularly well-suited for carrying out 
the method according to the invention. 
The copying means may include a shutter while the processing means may 
include means for determining and controlling exposure time. The output 
means of the processing means then includes at least one additional output 
for the transmission of control signals to the shutter. 
The positioning means may comprise means for conveying the master along a 
predetermined path which includes the predetermined location. In one 
embodiment of the apparatus, the measuring means is disposed at a second 
location of the path upstream of the predetermined location. 
The measuring means may include means for measuring the densities of the 
master in each of the three primary colors red, green and blue. 
The copying means may further comprise a source of illumination and the 
masking element may be disposed between this source and the predetermined 
location. The copying means may also include means for holding a length of 
photosensitive is material at another location. A second embodiment of the 
apparatus comprises a directing element between the predetermined location 
and the other location for directing radiation to the measuring means. The 
directing element may be pivotable and may comprise a beam splitter. 
The calculating means may include a logic circuit. 
One embodiment of the apparatus includes first means for displaying the 
master while unmasked and second means for displaying the master while 
masked. The first and second means may each include a color monitor. The 
measuring means may here comprise a video camera, preferably a color 
camera. 
The novel features which are considered as characteristic of the invention 
are set forth in particular in the appended claims. The improved copying 
or printing method, as well as the construction and mode of operation of 
the improved copier or printer, will, however, be best understood upon 
perusal of the following detailed description of certain specific 
embodiments when read in conjunction with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIG. 1, a length or strip of color film 1 is conveyed through 
a scanning station 2. The film 1 carries a series of masters or originals 
which are to be copied or printed in the copier or printer of FIG. 1, and 
the masters or originals are here assumed to be constituted by transparent 
negatives. The scanning station 2 has a light source 3, a lens 4 and a 
diaphragm 5 which serve to scan each negative pointwise. The light beam 
which passes through the film 1 is focused by the lens 6 and split into 
its primary color components red, green and blue by dichroitic reflectors 
or beam splitters 7. The individual colored beams then impinge upon 
respective rows of measuring cells R, G and B which are sensitized to the 
corresponding colors. The cells R, G, B function to measure the densities 
of the negatives in the three primary colors red, green and blue and 
generate image signals representing the respective density values. The 
density values are stored in a memory 8 with a resolution of about 500 to 
1000 pixels. From the memory 8, the density values for each negative are 
sent to a logic circuit 9 which calculates a suitable mask for the 
respective negative. This mask, which is black-and-white, represents a 
negative of the corresponding negative on the film 1. The mask calculated 
by the logic circuit 9 is represented by density signals generated by the 
logic circuit 9, and the density values corresponding to these density 
signals are stored in a memory 10. Resultant density values are now 
calculated from the mask density values in the memory 10 and the negative 
density values in the memory 8. The resultant density values are stored in 
a memory 11. The density of a print or copy to be made from a respective 
negative is then calculated in a logic circuit 12 using the resultant 
density values in the memory 11. In individual cases, it can be useful to 
additionally employ the negative density values in the memory 8 for this 
purpose. 
Calculation of the print density on the basis of the resultant density 
values has the advantage that the "density rejection rate" of the printer 
can be reduced as compared to printing without a mask. The logic circuit 
12 normally calculates the print density based on the large area contrast 
and, as a result, errors can easily arise for negatives with very high 
contrast. However, since the large area contrast is condensed in practice 
by using the resultant density values, the calculated print densities can 
better approximate the required copy densities. 
A computing unit 13 calculates the exposure time or shutter speed from the 
print density. The exposure time, as well as the mask density values from 
the memory 10, are then entered in a shift register 14. 
After passing through the scanning station 2, the film 1 is advanced 
through a temporary storage zone 15 to a copying or printing station 16. 
As each negative enters the printing station 16, the corresponding values, 
i.e., the corresponding exposure time and corresponding mask density 
values, are recalled from the shift register 14. 
The printing station 16 includes a source 18 of copy light which is 
disposed above a condenser unit 17 having a color filter or light mixing 
arrangement 19 whose function and control are conventional and will not be 
described here. The copy light passes through the condenser unit 17 where 
its color densities are corrected and then impinges upon an electrically 
controlled masking element in the form of an LCD matrix 20 located below 
the condenser unit 17. 
The mask density values recalled from the shift register 14 enter a 
converter 21 which transforms the mask density values into control 
signals. These control signals are used to activate the matrix 20 which 
generates an appropriate mask for the respective negative in the printing 
station 16. The exposure time recalled from the shift register 14 serves 
to regulate the length of time for which a shutter 22 remains open during 
exposure. 
The mask is imaged on a dispersion plate 24 via a lens unit or objective 
23. The image of the mask and the negative in the printing station 16 are 
then copied, while in register, photosensitive paper 26 by means of a lens 
unit 25. 
In FIG. 2, elements having the same function as those in FIG. 1 are 
identified by the same reference numerals. 
Referring to FIG. 2, the film 1 is conveyed through a combined scanning and 
printing station. In this combined scanning and printing station, light 
from the light source 18 travels to the dispersion plate 24 via the 
condenser unit 17, the masking matrix 20 and the lens unit 23. When a 
negative of the film 1 arrives at the combined scanning and printing 
station, a pivotable reflector 27 is initially pivoted out of the optical 
path in a non-illustrated manner. The negative is then unsharply imaged on 
a flat, black-and-white CCD 29 of a video camera 30 via a second reflector 
28 and suitable optical means. The CCD 29 generates output signals which 
represent a mask for the negative. As before, the mask is black-and-white 
and represents a negative of the negative on the film 1. The output 
signals of the CCD 29 are converted into control signals for the LCD 
matrix 20 and are stored in a memory 31. These controls signals are then 
used to activate the matrix 20 and generate a mask for the negative in the 
combined scanning and printing station. 
Once the mask has been generated so that the negative is masked, the 
reflector 27 is pivoted back into the optical path. The reflector 27 
thereupon causes a masked image of the negative to be formed on a flat, 
color CCD 32. The CCD 32 produces output signals representing resultant 
density values, i.e., density values which take into account the densities 
of both the negative and the mask, in the three primary colors red, green 
and blue. The CCD 32 is connected to the logic circuit 12 which receives 
the output signals of the CCD 32 and calculates the print density from the 
resultant density values. These values are now used to control the color 
filter or light mixing arrangement 19. 
The reflector arrangement 27,28 can here serve as a shutter. During 
exposure, both of the reflectors 27,28 are pivoted out of the path of the 
copy light. The exposure time, that is, the time for which the shutter 
constituted by the reflectors 27,28 remains open upon exposure, is 
determined by the print density in a manner which is conventional and need 
not be detailed. When the shutter 27,28 is opened, the negative in the 
combined scanning and printing station is copied on the photosensitive 
paper 26 together with the mask via the lens arrangement 25. 
In FIG. 3, the masking matrix 20 is initially transparent when a negative 
of the film 1 enters the scanning and printing station. Light from the 
light source 18 passes through the matrix 20 and then through the negative 
before arriving at the pivotable reflector 27. The reflector 27 directs 
the light to the flat, color CCD 32 which here constitutes part of a video 
camera 33. The negative is thus imaged on the CCD 32. The CCD 32 generates 
signals representing a negative color image of the negative, that is, 
signals representing the density values of the negative in the primary 
colors red, green and blue. The color image of the negative is stored in 
the memory 34. From the memory 34, the color image is transferred to a 
converter 35 which reverses the image. The resulting positive color image 
is stored in a memory 36 and then displayed on a color monitor 37. 
The negative color image in the memory 34 is simultaneously transformed 
into a black-and-white image in a converter 38, and this black-and-white 
image is stored in a memory 39. The memory 39 is connected to the logic 
circuit 9 which calculates a negative black-and-white mask. The negative 
black-and-white mask derived in the logic circuit 9 is stored in the 
memory 10. 
A masked, positive color image is now produced in a memory 40 from the mask 
in the memory 10 and the positive color image in the memory 36. This image 
is displayed on the color monitor 41. 
A positive black-and-white mask is generated in a converter 42 from the 
negative black-and-white mask in the memory 10. The positive 
black-and-white mask from the converter 42 is stored in a memory 43. The 
memory 43 issues signals representing density values for the positive 
black-and-white mask stored therein and such signals are transformed into 
control signals for the masking matrix 20 in the converter 21. 
An operator can directly compare the unmasked image of the negative shown 
on the monitor 37 with the mechanically masked image which is shown on the 
monitor 41. Three operating knobs 44 are provided for color corrections. A 
color correction made by way of the knobs 44 operates directly on the 
color filter or light mixing arrangement 19 and is thus immediately 
visible on the two monitors 37,41. Another operating knob 45 is provided 
for correction of the mask. Correction of the unsharp mask via the 
operating knob 45 influences the mask gradation in the logic circuit 9 and 
can accordingly be immediately seen on the monitor 41. An additional 
operating knob 46 on the monitor 41 serves to correct the density. 
Correction of the density by means of the operating knob 46 affects, via 
the non-illustrated circuit for calculation of print density, the length 
of time for which the shutter 22 remains open. 
When the operator considers the image on the monitor 41 to be optimal, the 
exposure procedure can be initiated. To this end, the masking matrix 20 is 
first activated, the reflector 27 pivoted out of the optical path and the 
shutter 22 opened. The negative in the scanning and printing station, 
together with the mask, is then printed on the photosensitive paper 26 via 
the lens arrangement 25. 
It is possible, of course, to dispense with the monitor 37 and to display 
only the masked positive image on the monitor 41. However, in order to 
optimize the operator's judgment, it has been found favorable to compare 
the masked image with the unmasked image. 
The mask formed on the matrix 20, or an image of the mask on a negative, 
i.e., in the plane of the film 1, or both the mask and such image, have 
low resolution, that is, are fuzzy or unsharp. As a result, a diffuse or 
unsharp intensity distribution is obtained on the photosensitive paper 26. 
By making the mask and/or the image of the mask in the plane of the film 1 
unsharp, bright/dark gradations on the photosensitive paper 26 caused by 
the mask in response to relative shifting or differential expansion of the 
mask and a negative are greatly reduced. Print quality is thus improved. 
A negative may, for example, have a resolution of 10 line pairs per 
millimeter. In contrast, the resolution of the mask and/or the image of 
the mask in the plane of the film 1 can be between 0.1 and 2 line pairs 
per millimeter, and is preferably 0.7 line pair per millimeter. A mask of 
low resolution may be obtained by selecting a masking matrix 20 of 
appropriate coarseness. The image of the mask in the plane of the film 1 
can be made to have low resolution by appropriate adjustment, e.g., 
defocusing, of the lens unit or objective 23. 
According to one embodiment of the invention, the mask has low resolution 
and the copying operation is performed in such a manner that a sharp image 
of the mask is formed on the photosensitive paper 26. 
In accordance with another embodiment of the invention, the mask is sharp, 
i.e., has high resolution, and the copying operation is carried out such 
that an image of the mask in the plane of the film 1 has low resolution. 
An additional embodiment of the invention resides in that the mask has low 
resolution and that the copying operation is performed in such a manner 
that the image of the mask in the plane of the film 1 likewise has low 
resolution. 
Although the invention has been described with reference to the 
reproduction of photographic negatives, it can be applied as well to the 
reproduction of photographic positives. 
Without further analysis, the foregoing will so fully reveal the gist of 
the present invention that others can, by applying current knowledge, 
readily adapt it for various applications without omitting features that, 
from the standpoint of prior art, fairly constitute essential 
characteristics of the generic and specific aspects of the instant 
contribution to the art and, therefore, such adaptations should and are 
intended to be comprehended within the meaning and range of equivalence of 
the appended claims.