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Claims  |
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We claim:
1. The method for the partial electronic retouching of colors in color
images, in which color signals obtained by point-by-point and trichromatic
scanning of color originals are digitized and the digital color values of
the individual color components are stored in a storage medium, and in
which the stored color values are corrected by color correction values, so
as to obtain retouched colors comprising the steps of:
(a) defining color increments values (.DELTA.Y, .DELTA.M, .DELTA.C,
.DELTA.K) for said individual color components, said color increment
values respectively representing the smallest amount of correction for
said color values (Y, M, C, K) per retouching step;
(b) selecting a positive or negative direction of retouching;
(c) identifying the pairs of locus-coordinates of the image points to be
retouched in the color image by marking the locationally allocated points
in a coordinate identification device (digitizer) with a marking means of
said device, such as a coordinate pen cursor;
(d) during coordinate identification simultaneously determining the desired
retouch strength for each image point to be retouched by generating a
retouch factor (r) for each identified pair of locus-coordinates with said
marking means, guiding said marking means similar to a retouch brush over
that area of the coordinate identification device which corresponds to the
area of the color image to be retouched, said retouch factor (r)
representing a plurality of color increment values which are to be summed
or to be subtracted at each image point which is to be retouched;
(e) generating correction values (Y.sub.R, M.sub.R, G.sub.R, K.sub.R) for
each image point which is to be retouched by multiplying the retouch
factor (r) with the individual color increment values;
and
(f) correcting said color values (Y, M, C, K) of the image points which are
to be retouched by adding for positive retouching and subtracting for
negative retouching said corresponding correction values (Y.sub.R,
M.sub.R, C.sub.R, K.sub.R) of said image points in order to obtain
corrected color values (Y', M', C', K') representing the retouched colors
in said color image.
2. The method according to claim 1 wherein the retouch factor (r) of an
image point is generated by the number of contacts of said marking means
with said corresponding point in said coordinate identification device,
whereby the retouch factor (r) increases (intensification for positive
retouching) or decreases intensification for negative retouching) by an
incremental amount on each contact.
3. The method according to claim 1, wherein the retouch factor (r) of an
image point is generated by the pressure of the marking means on the
corresponding point in said coordinate identification device, whereby the
retouch factor (r) increases (intensification for positive retouching) or
decreases (intensification for negative retouching) by an amount
proportional to the pressure.
4. The method according to claim 1, wherein the retouch factor (r) of an
image point is generated from the dwell time of said marking means on the
corresponding point in said coordinate identification device, whereby the
retouch factor (r) increases (intensification for positive retouching) or
decreases (intensification for negative retouching) by an amount
proportional to the dwell time.
5. The method according to claim 1, further comprising the steps of:
(a) displaying said color original or said retouched color image on a color
monitor for visual control;
(b) generating a moveable light mark on the screen of said color monitor;
and
(c) synchronizing the motion of said light mark with the motion of the
marking means of said coordinate identification device, said light mark
visibly indicating in said color original or said retouched color image
the image points marked by said marking means.
6. The method according to claim 1 or 5, further comprising the steps of:
(a) transferring the color values (Y, M, C, K) of the color image from said
storage medium into an image refresh memory;
(b) writing the generated retouch factors (r) of the image points to be
retouched into a retouch memory;
(c) reading out synchronously the retouch factors (r) from said retouch
memory and the color values (Y, M, C, K) from said image refresh memory;
(d) generating said correction values (Y.sub.R, M.sub.R, C.sub.R, K.sub.R);
(e) correcting said read out color values (Y, M, C, K) by said generated
correction values (Y.sub.R, M.sub.R, C.sub.R, K.sub.R) to obtain said
retouched color values (Y', M', C', K'); and
(f) converting said color values (Y, M, C, K) of said color original or
said retouched color values (Y', M', C', K') of said retouched color image
into control signals for said color monitor.
7. The method according to claim 6, wherein the generated retouch factors
(r) are respectively written into the retouch memory during the blanking
interval of said color monitor.
8. The method according to claim 1, wherein the amounts of said individual
incremental values are defined in a manner such that the incremental
change of the retouch value obtained for one retouching step is not
discernible by the operator.
9. The method according to claim 8, wherein the amounts of said individual
incremental values are selected to be smaller than the least significant
bit (LSB) of the color values (Y, M, C, K).
10. The method according to claim 1, wherein the defining step of said
individual increment values is further defined by:
(a) selecting a desired target color which may be obtained by said
retouching process; and
(b) subdividing each color value (Y, M, C, K) of said target color into the
same plurality of individual color incremental values (.DELTA.Y, .DELTA.M,
.DELTA.C, .DELTA.K) for determination of the smallest increment of
correction per retouching step.
11. The method according to claim 1, wherein the defining step of the
individual increment values is further defined by:
(a) measuring a desired target color in said color image, which may be
obtained by said retouching process; and
(b) subdividing each color value (Y, M, C, K) of said target color into the
same plurality of individual colorincremental values (.DELTA.Y, .DELTA.M,
.DELTA.C, .DELTA.K) for determination of the smallest increment of
correction per retouching step.
12. The method according to claim 1, wherein the defining step of said
individual increment values is further defined by:
(a) determining a desired target color, which may be obtained by said
retouching process;
(b) determining an initial color, from which the retouching process may be
started;
(c) generating the difference of the color values (Y, M, C, K) of said
target color and said initial color; and
(d) subdividing each difference into the same plurality of individual color
incremental values (.DELTA.Y, .DELTA.M, .DELTA.C, .DELTA.K) for
determination of the smallest increments of correction per retouching
step.
13. The method according to claim 10 or 11, wherein the individual
increment values (.DELTA.Y, .DELTA.M, .DELTA.C, .DELTA.K) are formed as
quotients from the color values (Y, M, C, K) of the target color and the
number of correction steps desired to obtain said target color.
14. The method according to claim 12, wherein the individual increment
values (.DELTA.Y, .DELTA.M, .DELTA.C, .DELTA.K) are formed as quotients
from the differences of color values and the number of correction steps
desired to obtain said target color from said initial color.
15. The method according to claim 12 or 14, wherein the differences of the
color values of a target color and of an initial color represent the color
values of a retouch color.
16. The method according to claim 12 or 14, wherein the target color and
the initial color are separation colors.
17. The method according to claim 1, further comprising the steps of:
(a) defining a desired target color, which may be obtained by said
retouching process;
(b) defining an initial color, from which said retouching process may be
started; and
(c) subtracting color correction values (Y.sub.R, M.sub.R, C.sub.R,
K.sub.R) from the color values (Y, M, C, K) of said initial color so as to
brighten said initial color, whereby said target color is "white".
18. The method according to claim 1, further comprising the steps of:
(a) defining a desired target color, which may be obtained by said
retouching process;
(c) defining an initial color, from which said retouching process may be
started; and
(c) adding color correction values (Y.sub.R, M.sub.R, C.sub.R, K.sub.R) to
the color values (Y, M, C, K) of said initial color so as to darken said
initial color, whereby said target color is "black".
19. The method according to claim 1, further comprising the steps of:
(a) defining an initial color, from which said retouching process may be
started;
(b) adding color correction values (Y.sub.R, M.sub.R, C.sub.R, K.sub.R) to
the color values (Y, M, C, K) of said initial color so as to darken said
initial color, whereby the color values (Y, M, C, K) of the initial color
increase proportionally during the retouching process until the greatest
color value of the initial color has achieved its maximum density (black),
and then
(c) continuing the retouching process by adding selected color correction
values to said color values of said initial color, whereby the color
values (Y, M, C) of the chromatic components of said initial color retain
their values and only the color value (K) of the non-chromatic component
of said initial color increases up to the maximum density.
20. The method according to claim 1, further comprising the steps of:
(a) defining an initial color, from which said retouching process may be
started;
(b) adding color correction values (Y.sub.R, M.sub.R, C.sub.R, K.sub.R) to
the color values (Y, M, C, K) of said initial color so as to darken said
initial color, whereby the color values (Y, M, C, K) of the initial color
increase proportionally during the retouching process until the greatest
color value of the initial color has achieved its maximum density (black),
and then
(c) continuing the retouching process by adding selected color correction
values to said color values of said initial color, whereby the color
component retains the color value achieved at the maximum density and the
color values of the other components increase until the components achieve
the maximum density.
21. The method according to claim 1, further comprising the steps of:
(a) storing the plurality of pairs of locus-coordinates in the sequence of
their identification by said marking means of said coordinate
identification devices;
(b) calling up selected locus coordinates from said plurality in reversed
sequence; and
(c) reducing the retouch factors (r) corresponding to said selected locus
coordinates, whereby the retouch strength achieved during the preceding
retouching process within an area of said color image defined by said
selected locus coordinates is reduced true to the contours of said area.
22. The method according to claim 1, wherein the overall retouch process
can be reversed by erasing said generated retouch factors (r).
23. The method according to claim 1, further comprising the steps of:
(a) identifying simultaneously a plurality of locus-coordinates-pairs of
the image points to be retouched with said marking means of said
coordinate identification device; and
(b) generating simultaneously a plurality of corresponding retouch factors
(r), whereby the area retouched by said marking means is increased and a
plurality of image points are retouched simultaneously.
24. The method according to claim 23, wherein the retouch factors (r) are
only changed when a new pair of locus-coordinates identified with said
marking means differ from a previously identified pair of
locus-coordinates by a minimum amount in the X- and Y-direction of said
coordinate identification device, and whereby said minimum amount
determines the extension of said area of retouching.
25. The method according to claim 1, further comprising the steps of:
(a) identifying simultaneously a plurality of locus-coordinate-pairs of the
image points to be retouched with said marking means of said coordinate
identification device;
(b) generating simultaneously a plurality of corresponding retouch factors
(r), whereby the area of retouch of said marking means is increased and a
plurality of image points are retouched simultaneously;
(c) displaying said color original or said retouched color image on a color
monitor for visual control;
(d) generating a moveable enlarged light mark on the screen of said color
monitor; and
(e) synchronizing the motion of said light mark with the motion of said
marking means, said light mark making visible in said color original or
retouched color image the plurality of image points within said area of
retouch of said marking means.
26. The method according to claim 1, wherein the part of the color image to
be retouched is limited by means of an electronically generated retouch
mask.
27. Apparatus for partial electronic retouching of colors in color images
in which color signals obtained by point-by-point and trichromatic
scanning of color originals are digitized and the digital color values of
the individual color components are stored in a storage medium, comprising
(a) an image refresh memory (7) for the digital color values;
(b) a color monitor for displaying said color original or said retouched
color image;
(c) a color generator (38) for the formation of color incremental values
(.DELTA.Y, .DELTA.M, .DELTA.C, .DELTA.K);
(d) a retouch generator (39) for the formation of retouch factors (r) of
the image points to be retouched in the color image;
(e) a correction value generator (40) connected to the color generator (40)
and the retouch generator (39) for formation of correction values
(Y.sub.R, M.sub.R, C.sub.R, K.sub.R) from said color incremental values
(.DELTA.Y, .DELTA.M, .DELTA.C, .DELTA.K) and said retouch factors (r); and
(f) combining stages (15, 16, 17, 18) arranged in the color channels and
connected to said image refresh memory (7), to said color monitor (2) and
to said correction value generator (40) for the correction of the color
values (Y, M, C, K) stored in said refresh memory (7) by means of said
correction color values (Y.sub.R, M.sub.R, C.sub.R, K.sub.R) so as to
obtain retouched color values (Y', M', C', K').
28. Apparatus according to claim 27, wherein said retouch generator (39)
consists of:
(a) a coordinate identification device (50) having marking means (51),
particularly a cursor, for identifying the pairs of locus-coordinates of
image points to be retouched;
(b) an evaluation circuit (52) connected to said coordinate identification
device (50) for generating the retouch factors (r) from said pairs of
locus-coordinates; and
(c) a retouch memory (49) connected to said evaluation circuit (52) for
storing said generated retouch factors (r).
29. Apparatus according to claim 27, wherein said correction value
generator (40) consists of a plurality of multiplication stages.
30. Apparatus according to claim 27, further comprising an input stage (37)
connected to the color generator (38).
31. Apparatus according to claim 27, further comprising a measuring device
(8, 21, 32, 35) connected to the color generator (38) for color
measurement in the color image displayed on said color monitor (2). |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
TECHNICAL FIELD
The present invention relates to electronic reproduction technology,
particularly to a method for partial electronic retouching in color image
reproduction in which the color signals generated by means of
image-point-wise and trichromatic master scanning are digitized and the
digital color values of the individual color components are deposited in a
storage medium and in which the stored color values are altered under
control; the present invention also relates to a circuit arrangement for
implementing the method.
UNDERLYING PRIOR ART
In electronic color reproduction, three primary color measurement signals
which represent the color components red, green and blue of the scanned
image points are gained in a color scanner by means of point-wise and
line-wise opto-electronic scanning of colored masters and by means of
spectral color splitting. A color correction computer corrects the color
measurement values according to the laws of subtractive color mixing and
generates the color separation signals which are a measure for the amounts
of printing ink required in the subsequent printing.
The color separation signals are digitized and are deposited as color data
in a storage medium in order to record the color separation, if need be,
at a later point in time or at some other location or, on the other hand,
in order to unite the color data of different individual masters according
to a lay-out plan into a data set which corresponds to an overall page.
In order to record the color separation, the color data of the individual
masters or of the overall page are read out of the storage medium, are
reconverted into analog color separation signals and are supplied to write
lamps as recording elements, the light intensities of said lamps being
modulated by the appertaining color separation signals. The write lamps
expose a recording medium in the form of films point and line wise, said
films, after being developed, representing the desired rasterred or
unrastered color separations "yellow", "magenta", "Cyan" and "black" for
the production of the printing forms.
In the reproduction process, later, partial retouching (corrections of
color and/or tint value) are frequently necessary, whether to optimize the
correction carried out in the color correction computer or to take, on the
other hand, editorial changes and client's wishes into consideration. The
retouching, for example, is a matter of incorporating highlights by means
of brightening, of working up shadow passages by means of darkening, of
improving the drawing by means of brightening and darkening or, simply, of
color changes.
Whereas the correction of a color undertaken by the color correction
computer takes effect everywhere said color occurs in the master or in the
reproduced image, such a retouching is to be limited to selectable,
topically limited image areas. Added thereto is the fact that the color
influence within the image areas should frequently also be bleeding, i.e.,
gradually increasing or decreasing, in order, for example, to achieve soft
contours or to produce half shadows.
These retouchings are executed in reproduction technology either manually
with a retouch pencil in the master itself (master retouching) or, on the
other hand, are executed in the individual color separations (separation
retouching).
Typical work in master retouching, also called color retouching, are the
re-coloring and darkening by means of partial application of glazing or
covering retouch inks with the retouch brush, whereby only the color
saturation is often to be increased without changing the tint. Likewise,
the brightening of image passages by means of bleaching the color layers
in the color material with suitable chemicals. It turns out that a
re-coloring can only be carried out in such colors as arise by means of
subtractive mixing of master colors and retouch colors. Thereby, the
selection of the retouch color presumes great experience. Re-coloring in a
complementary color is practically impossible. Bleaching can lead to
disruptive tint shifts.
New color separations of the retouched master must be produced by means of
a color scanner. Retouch colors and master colors frequently exhibit
different spectral distributions so that, despite visual color
coincidence, they are differently reproduced in the color scanner, since
the color separation properties in the color scanner do not correspond to
the physiological sensitivity of the eye.
Typical work in separation retouching in a half-tone color separation are
darkening by means of applying a ray retouch color and brightening with
chemical reducers. Retouch color or, respectively, reducers must be
applied with a very wet retouch brush, so that contours which are true to
the edge are difficult to achieve. Given a raster color separation, only a
diminution of the raster points (brightening) can be achieved in a
conventional manner without extensive copying work only by means of a
so-called point etching.
In order to evaluate the retouch work, sample prints must be produced
since, particularly given separation retouchings, the effect on the
colored final product is not directly perceptible.
It has been shown that extensive retouching is still necessary even given
an electronic reproduction process, said retouching having previously been
executed purely manually with the retouch brush, presuming great
experience, being expensive and time-consuming, and, in part, only able to
be incompletely executed.
A method is already known from the U.S. Pat. No. 4,007,362 (German OS No.
24 30 762) with which later color corrections can be executed in image
areas by means of changing the stored image information. An operator
selects the positional coordinates of the image points in the image to be
corrected by means of a coordinate identification device, whereby the
address-wise access to the stored image information is created. The
operator then inputs the desired correction amounts into a computer via
the keys of an operating unit, said computer converting the stored image
information into the altered image information by means of evaluation with
multiplicative or additive magnitudes.
Although partial color corrections can be executed with the known method by
means of inputting individual correction amounts, results such as in
conventional retouching with the retouch brush can hardly be achieved,
which is viewed as being disadvantageous. For example, it may well be
difficult with the known method to create the bleeding corrections with a
gradually increasing or decreasing influence which are frequently desired
in praxis without distruptive density skips such as, for example, a half
shadow.
Further, it is viewed as being disadvantageous that an opaque or
translucent master coinciding in format with the image to be reproduced
must be stretched on the coordinate indentification device in order to
identify the positional coordinates. Such masters often do not exist,
since the original masters seldom conicide with the final format and the
electronic enlargement to the final format is only carried out in the
color scanner. Although it is specified in the said letters patent that
the coordinate identification can ensue without an opaque or translucent
master by means of a light pen at the picture screen of the monitor, this
type of coordinate identification has the disadvantage that, due to the
lesser resolution, only a rough correction ensues. Moreover, it cannot be
derived from the letters patent as to how the correction method is to be
carried out in detail.
SUMMARY OF THE INVENTION
It is therefore the object of the present invention to specify a method and
a circuit arrangement for color image reproduction with which, in
particular, bleeding retouchings as in conventional retouching with the
retouch brush can be achieved and with which, beyond that, corrections are
made possible which cannot be executed with conventional retouching.
This object, given the present invention, is achieved in that the locus
coordinates of the image points to be changed in the color image are
identified, in that, simultaneously in the coordinate identification,
location-dependent correction values (Y.sub.R, M.sub.R, C.sub.R, K.sub.R)
for the ditital color values (Y, M, C, K) of the color components to be
changed are determined for each pair of coordinates, and in that the
digital color values (Y, M, C, K) are changed by means of the locationally
allocated correction values (Y.sub.R, M.sub.R, C.sub.R, K.sub.R) in order
to obtain the retouched color values (Y', M', C', K').
It is preferably provided that color increments (.DELTA.Y, .DELTA.M,
.DELTA.C, .DELTA.K) are fixed for the color components to be changed, said
color increments respectively representing the smallest alteration amounts
for the color values (Y, M, C, K); that the locus coordinates (x, y) of
the image points to be changed in the color image are identified and at
least one retouch factor (r) is determined for determining the retouch
strength of each pair of coordinates identified (x, y), said retouch
factor specifying the plurality of color increments to be summed up for
each image point to be retouched; that the retouch factor is multiplied
with the individual color increments in order to form location-dependent,
digital correction values (Y.sub.R, M.sub.R, C.sub.R, K.sub.R); and that
the digital color values are changed by means of the locationally
allocated correction values in order to obtain the retouched color values
(Y', M', C', K').
Preferably, the digital color values are read out of the storage medium,
are changed by the correction values, and the retouched color values are
reinscribed onto the storage medium after accomplishment of the
retouching.
In an advantageous manner, the correction values are added to (positive
retouching) or, respectively, are subtracted from (negative retouching)
the locationally allocated digital color values.
A further development of the invention consists therein that the locus
coordinates of the image points to be retouched are determined in a
coordinate identification device by means of marking the locationally
allocated points with a marking device, particularly with a coordinate
pin.
Preferably, the retouch factors of the image points of the color image to
be retouched are determined from the number of contacts of the
corresponding points with the marking device of the coordinate
identification device, whereby the marking device is guided like a retouch
brush across that area of the coordinate identification device which
corresponds to the image area of the color image to be retouched.
An advantageous variation consists therein that the retouch factors for the
image points of the color image to be retouched are determined from the
pressure of the marking device on the corresponding points of the
coordinate identification device.
Another advantageous variation consists therein that the retouch factors
for the image points of the color image to be retouched are determined
from the dwell time of the marking device on the corresponding points of
the coordinate identification device.
Preferably, the retouch factors are increased or lowered by an amount at
each contacting, whereby the appertaining correction values increase
(intensification of the retouching) or decrease (reversal of the
retouching).
It is alternately provided that the retouch factors are increased given an
increase of pressure and are lowered given a decrease of pressure, whereby
the appertaining correction values increase (intensification of the
retouching) or decrease (reversal of the retouching) or, respectively,
that the retouch factors are increased or lowered by an amount in accord
with the respective dwell time, whereby the appertaining correction values
increase (intensification of the retouching) or decrease (reversal of the
retouching).
An advantageous further development consists therein that, optionally, the
unretouched color image (original image) or the retouched color image are
displayed on a color monitor for visual control, that a displaceable light
mark is mixed in in the picture screen, and that the movement of the light
mark is synchronized with the movement of the marking device of the
coordinate identification device.
To that end, it is provided that the digital color values of the color
image are loaded from the storage medium into an image repetition memory
and that the image repetition memory is cyclically read out for the
point-wise recording of the color image on the monitor.
One embodiment of the invention provides that the identified retouch
factors of the individual image points of the color image are over-written
into a retouch memory, that the retouch memory is read out synchronously
with the image repetition memory for the locational allocation of color
values and correction values, and that the digital color values are
altered by the allocated correction values.
An advantageous improvement is that the retouch factors changed by the
retouch operation are respectively over-written into the retouch memory in
a blanking gap of the image recording.
Another advantageous improvement consists therein that the retouch effect
which is respectively achieved with a change amount lies below the visible
limit and that the significance of the digital color increments is
selected smaller than the significance of the least significant bit (LSB)
of the digital color values.
In an advantageous manner, each component of a prescribed color is
subdivided into the same plurality of corresponding color increments for
determining the smallest amounts of change.
Alternatively, it is provided that each component of a color measured in
the color image is subdivided into the same plurality of corresponding
color increments for determining the smallest amounts of change.
On the other hand, it is proposed that each component of a color difference
formed of a target color and of an initial color is subdivided into the
same plurality of corresponding color increments for determining the
smallest amounts of change.
In an advantageous manner, the color increments are formed as quotients
from the respective final correction values of the individual color
components and of the plurality of contactings with which the final
correction values are to be achieved.
Preferably, the final correction values correspond to the differential
values formed of the target color and of the initial color.
Alternatively, the final correction values correspond to the color
components of a retouch color to be applied to an initial color in order
to obtain the desired target color.
Preferably, the initial color and the target color are a separation color.
An advantageous retouching method provides that an initial color is
brightened by means of subtraction of correction values from the color
values of said initial color, whereby the target color is "white".
Another advantageous retouching method consists therein that an initial
color is darkened by means of the addition of correction values to the
color values of said initial color, whereby the target color is "black".
In a further retouching method, it is proposed that the color components of
the initial color to be darkened rise in terms of proportion due to the
retouching until the greatest color component of the initial color has
reached the maximum density, and that, given continued retouching, the
chromatic color components (Y, M, C) retain the values they achieved given
their maximum density and only the achromatic color component (K)
increases up to its maximum density (black).
An alternative retouching method provides that the color components of the
initial color to be darkened increase in proportion due to the retouching
until the greatest color component of the initial color has reached its
maximum density, and that, given continued retouching, said color
component retains the value reached given the maximum density and the
other color components increase up to their maximum density.
An advantageous further development consists therein that the pairs of
locus coordinates of the marked points are deposited listwise in the
sequence of their identification, and that the pairs of locus coordinates
are called in in the reversed sequence, the corresponding retouch factors
are changed in the retouch memory, and the retouch which ensued during the
preceding contactings of the points is reversed true to the contours.
In a preferred manner, the entire retouching can be reversed by cancelling
the retouch memory.
The marking device can simultaneously cover a plurality of image points
lying within a retouch surface (area of the retouch brush), whereby the
plurality of image points simultaneously retouched is increased in an
advantageous manner.
It is further provided that the retouch factor determined from a pair of
locus coordinates is only changed when a new pair of locus coordinates
identified with the marking device differs from a previously identified
pair of locus coordinates by a minimal amount in X and Y direction,
whereby the minimum amount determines the expanse of the retouch surface.
A further improvement consists therein that the simultaneously retouched
image points are displayed by means of an enlarged light mark. Another
improvement provides that the image area to be retouched be limited by
means of an electonically generated mask.
A preferred arrangement for implementing the method consists of a color
generator (38) for forming the color increments (.DELTA.Y, .DELTA.M,
.DELTA.C, .DELTA.K), of a retouch generator (39) for forming the retouch
factors (r) of the image points of the color image to be retouched, of a
correction value generator (40) connected to the color generator (38) and
to the retouch generator (39) for forming the correction values (Y.sub.R,
M.sub.R, C.sub.R, K.sub.R) from the color increments and the retouch
factors, and of a respective combinatorial stage (15, 16, 17, 18)
post-connected to the image repetition memory (7) in the color channels
for the change of the color values by the correction values.
In a preferred embodiment, it is provided that the retouch generator (39)
consists of a coordinate identification device (50, 51, 52) for
determining the locus coordinates of the image points to be retouched, of
an evaluation circuit (48) connected to the coordinate identification
device (50, 51, 52) for forming the retouch factors for each pair of
identified locus coordinates, and of a retouch memory (49) connected to
the evaluation circuit (48).
In an advantageous manner, the correction value generator (40) consists of
multiplication stages.
It is further provided that an input stage (37) is connected to the color
generator (38) for specifying color components.
Preferably, the color generator (38) is connected to a device (8, 21, 32,
35) for color measurement in the displayed color image.
BRIEF DESCRIPTION OF THE DRAWINGS
In the following, the invention is described in greater detail on the basis
of FIGS. 1 through 14. These are shown:
FIG. 1: a circuit arrangement for partial electronic retouching in color
image reproduction;
FIG. 2: a flow chart relating to the manner of functioning of the device;
FIGS. 3a, b, c: graphic illustrations for determining the retouch factors;
FIG. 4: a retouch surface identified with the coordinate pin;
FIG. 5: a flow chart relating to the identification of coordinates;
FIGS. 6a, b, c, d, e: graphic illustrations for the explanation of retouch
functions;
FIGS. 7a, b, d, e: flow charts relating to the explanation of the retouch
functions;
FIG. 8: a further development of the circuit arrangement;
FIG. 9: a sample embodiment of a memory control unit;
FIG. 10: a sample embodiment of a correction value generator;
FIG. 11: a sample embodiment of a retouch generator;
FIG. 12: a further sample embodiment of a retouch generator;
FIG. 13: a sample embodiment of the retouch generator with mask memory;
FIG. 14: a variation of the circuit arrangement.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 shows the basic format of a circuit arrangement for partial
electronic retouching (retouch station) in electronic color image
reproduction and FIG. 2 shows an appertaining flow chart.
A storage medium 1 (magnetic tape; magnetic disc) in the sample embodiment
contains the digital color values for the color separations "yellow" (Y),
"magenta" (M), "Cyan" (C) and "black" (K) of an image to be reproduced,
said color values having already been corrected in a color scanner. Let
the color values have, for example, a word length of eight bits, whereby
254 grey steps are distinguished between "black" (0) and "white" (255).
The image to be reproduced can be both a single image as well as an
assembled printing page. The color values of a single image were
previously gained in a color scanner by means of point and line-wise
trichromatic scanning of a master, by means of color correction, and
analog-to-digital conversion of the color separation signals. The color
values of an entire printing page arose, for example, in a device for
electronic page assemblage according to the GBLP No. 14 07 487 (German OS
No. 21 61 038) by means of combination of the corrected single image color
values according to a lay-out plan. Uncorrected color values, however, can
also be deposited in the storage medium 1.
Before the recording of the color separations on film material by means of
a color scanner (offset printing) or before the production of the printing
forms by means of a graving machine (rotogravure), the images or,
respectively, color values to be reproduced are to be subjected to a
partial electronic retouching with visual control in order to optimize the
color correction undertaken in the color scanner and/or in order to take
subsequent requests for change on the part of the client into
consideration.
A color monitor 2 is present for the visual control, and an image
consisting of 512.times.512 image points can be recorded on its picture
screen 3. The color values required for the display of the image to be
reproduced or of a corresponding trimmed image are selected or calculated
by a process control computer 4 from the overall data set of the storage
medium 1 and are transmitted from there image point by image point into an
image repetition memory 7 via the data busses 5 and 6. Accordingly, the
image repetition memory 7 exhibits a capacity of 512.times.512 memory
locations of 8 bit each for each color separation.
In order to produce a still picture on the picture screen 3 of the color
monitor 2, a memory control unit 8 cyclically callsin the X/Y addresses of
the image repetition memory 7 via an address bus 9. FIG. 9 shows a sample
embodiment of a memory control unit.
The stored, digital color values F [Y,M,C,K] are read out with a read clock
onto a line 10 line-by-line and, within each line, image point-by-image
point and are forwarded via data lines 11, 12, 13 and 14 to digital
combining stages 15, 16, 17 and 18 which are designed in the sample
embodiment as digital adder stages.
In the digital adder stages 15, 16, 17 and 18 which, for example, are
executed as two's complement adders, digital correction values F.sub.R
[Y.sub.R, M.sub.R, C.sub.R, K.sub.R ] are added to (positive retouching)
or are subtracted from (negative retouching) the read-out digital color
values F in accord with the desired retouching in order to obtain the
retouched, digital color values F'[Y', M', C', K'].
The correction values F.sub.R encumbered with an operational sign are
generated in a correction circuit 19. Alternatively, the operational signs
could be omitted and, instead, corresponding control signals which switch
the adder stages to addition or subtraction could be generated in the
correction circuit 19.
The retouched digital color values F' arrive via a data bus 20 and a light
mark generator 21 to a digital-to-analog converter 22 and are converted
there into four analog color separation signals. A post-connected printing
simulation computer 23 shapes the four color separation signals, upon
consideration of the parameters of the later multi-color printing, in such
manner into the three drive signals r, g and b for the color monitor 2
that the display on the picture screen 3 conveys the same color impression
as the multi-color printing itself. Such a printing simulation computer is
extensively described, for example, in the GBLP No. 15 40 525 (German OS
No. 26 07 623).
The recording ensues according to line-jump scanning in order to obtain a
flicker-free image. In accord with technology standard in television, a
clock generator 24 generates the horizontal and vertical deflection
signals (H; V) required for image recording on lines 25 and 26 and the
line start pulses (ZS) and the image start pulses (BS) on lines 27 and 28.
The memory control unit 8 supplies horizontal and vertical synchronizing
pulses via lines 29 and 30 to the clock generator 24, so that the image
recording is synchronized with the read operation out of the image
repetition memory 7.
For marking an image point or an image point area in the displayed color
image, a light mark 31 is mixed into the picture screen 3 and said light
mark 31 can be displaced by means of prescribing X-Y coordinates by means
of a mechanical coordinate control lever 32 via an address line 33. The
prescribed coordinates (addresses) are compared to the continuously
called-in addresses in the memory c | | |
