CH633139A5 - APPARATUS HAVING A COLOR MONITOR FOR ANALYZING AND SEPARATING COLORS OF AN ORIGINAL DOCUMENT IN ORDER TO VIEW COLOR CORRECTIONS. - Google Patents

Description

The present invention relates to an apparatus having a color monitor for analyzing and separating the colors of an original document for viewing color corrections on the monitor for printing the original document.

In the graphic arts, when you have to reproduce color documents, such as photographs, you start by making a color selection using a device called a “scanner”.

The present invention relates to an apparatus for determining the color separation conditions as defined in claim 1 wherein the original document is first analyzed to provide electrical signals representing the components of the image, then these image signals are corrected to obtain the desired print quality. These signals are processed to produce an image on a color monitor that closely resembles that which will be printed, and during this process the corrected image signals are further corrected. The apparatus of the invention thus makes it possible to immediately view the conditions for separation of the colors and the effect of the corrections.

To reproduce by print an original color document, such as a photograph, one generally proceeds in three phases. The first phase is the selection of colors using a “scanner” which provides black and white films for each of the primary colors. The second phase is the plate printing or preparation of the printing plates for each primary color. The third phase is the printing proper using the plates mounted on the printing press, generally in four colors.

This technique does not make it possible to obtain control images before the final printing, which makes it very difficult to apply corrections to the intermediate phases.

For example, if the hue of my color is not correct in the original, each color must be corrected during the intermediate phases (essentially during selection), but it is very difficult to judge whether the corrections will have the desired effect.

To solve this problem, devices have recently been proposed capable of providing a synthetic image on a television screen so that the operator can immediately know the effect of his corrections.

Hazeltine Research Inc. has released a color selection control device that is described in the U.S. patent. No. 3 131252. The Applicant itself has developed an original device which is described in the US patent. No. 3,972,066. Finally, the published German patent application No. 2,607,623 in the name of Rudolf Hell GmbH concerns an assembly comprising a color selection apparatus and a device capable of producing a synthetic control image.

A major difficulty in all of these methods is obtaining a television image that closely resembles the image that will be printed. Furthermore, the practical use of these devices requires the introduction of various parameters which must be as simple as possible.

The Hazeltine device was put on the market, but has had only very limited success because the color resemblance is not good.

With regard to the HeE GmbH device which has also been marketed, the color similarity is not satisfactory and the adjustments are somewhat delicate. On the other hand, the Applicant's device has been fairly favorably received because its color simulation process gives relatively satisfactory results.

The main object of the present invention therefore is an apparatus facilitating the selection of colors for printing a color document. More specifically, this device makes it possible to visualize color corrections by means of a relatively similar image which is produced on a color monitor. In addition, operating the device is simple, efficient and reliable.

The apparatus of the invention comprises the elements mentioned in claim 1.

The accompanying drawings show by way of nonlimiting example an embodiment of the subject of the invention.

Figure i is an overall block diagram of the apparatus of the invention also showing the control panel.

Figure 2 is a block diagram of the filtering system.

Figure 3 is a plan view of a three-color circular filter.

Figure 4 is a waveform obtained with the filter system of Figure 2.

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FIG. 5 is an electrical diagram of the adjustment circuits. The original color document is placed in a set of black and white levels of the color signals. analyzer 100 which provides three representative synchronous signals

Figure 6 is an electrical diagram of the clipping circuits. color components Y, M and C. The document is placed

FIG. 7 is a block diagram of the correction circuits on an analysis table 101 which includes a color light source. 5 stable 104, a diffusing plate and a transparent plate

FIGS. 8 to 11 illustrate the operation and the structure 102 on which the original document 103 is placed, which may be of the masking circuit; more specifically, Figure 8 shows a positive or negative film. A television camera 110 is a target with colored bars, FIGS. 9 and 10 are diagonal mounted above the analysis table perpendicular to the grams of waveforms of image signals and FIG. 11 document 103.

is a block diagram of the masking circuit. 10 In camera 110, a three-color filter (red, blue and

Figure 12 is a block diagram of the circuits which 111) is mounted between the analyzer tube and the focal lens to introduce a gray scale on the monitor screen. variable 112. Filter 111 is a disk divided into three sectors

To print a color document, equal, a 111R red, a 111G green and a 111B blue in full color. Rota-such as a photograph, it is first necessary to select the filter 111 around its axis is controlled in synchro-

color components using a device called "scanning with the analysis of each color in the document." So,

ner ”which produces four films corresponding to the main colors during the selection of yellow, it is the blue area 111B which is mayors yellow, magenta and cyan, plus black. In what follows, these in front of the analyzer tube. Likewise, during the selection of the colors will be designated by their English abbreviations, magenta and cyan, those are respectively the optional green ranges Y, M, C and Bl. The printing plates are 111G and red 111R which are opposite of the analyzer tube.

then prepared from these four films and mounted on 20 image signals resulting from the analysis of document 103

the four-color printing machine. are transferred to a memory 140 via a If the color or gradation of the original is not satisfied; control circuit 120 of the camera and a health adjustment circuit, color corrections or dimming are effected at black and white level 130. The circuit 120 controls the different

killed in order to obtain good quality printed images. 110 camera functions including conversion

These color or gradation corrections are normally positive / negative, focus, magnification, etc. The circuit carried out at the color selection stage, although it is level 130, makes it possible to adjust the reference signals.

it is possible to carry out certain touch-ups limited to the 0% and 100% rence stage supplied by the camera to their exact levels, preparation of the plates, for example by "point bite". using buttons 904 and 905 on the control panel 900.

The color corrections are however delicate because it is The level adjustment circuit makes it possible in particular to compensate

hard to imagine the effect they will have on reproduction 30 Ser variations in the intensity of the light source, the

final. The operator only has filters selection films, etc. The memory 140 records successively which carry four black and white silver images including the signals of the selection components Y, M and C. For this,

optical densities correspond to the components Y, M, C and one can use a disk or integrated circuit memory.

B1. During the analysis operation, the recording of each

To solve this problem, various color systems have been proposed, Y, M and C is controlled by a teme button capable of producing a synthetic control image. push button 908 which also drives an electric motor weak- Whatever the process used, the major difficulty is getting it to turn the filter 111. The levels of a synthetic image faithfully resembling the image output signals from memory 140 are individually adjustable

which will be printed. More specifically, the control image is also for the three components by a circuit 150 which is formed on a three-color cathode ray tube by the addition of three 40 controlled by buttons 906 and 907. The primary color adjustment circuits which are red ( R), blue (B) and black and white level green 130 and 150 allow to adjust in a

(G), while the printed image is synthesized to a certain extent the levels of the output signals relative to

tractive primary colors Y, M, C and Bl. The colors those of the reference signals.

Since the primary and the synthesis methods are completely different, the outputs of the adjustment circuit 150 are applied to an annuity, it is not surprising that we obtain different results from the 45 white level adjustment circuit which is controlled. by rent. In addition, if two color electrical signals have gain potentiometers 909 and 910.

values of 10% and 15% representing the densities of the components. In summary, the system described so far uses a single corresponding color casants, their additive synthesis in mèra and three filters to provide color signals Y, M and the tube. cathodic gives respective densities of 10% and C which are successively memorized. It is obvious that one 15%. However, in the case of the printed image, the colors 50 could also use a camera with three analyzer tubes provided are superimposed and the subtractive synthesis gives densities of fixed filters to directly produce three signals of neck-weaker than 10% and 15%. them, which would eliminate the need for memorization. The sys-

In summary, the process of reproducing the images as the invention is however preferable because it eliminates the colors are fundamentally different and there have not been possible variations due to the dispersion of the characteristics of the ble tubes so far from obtain acceptable similarity on a monitor55 analyzers, which facilitates the correction process. In addition, the control. making and maintaining the camera is much simpler

In the apparatus of the present invention, an origins document.

nal is analyzed by a selection means, generally a Color signals, Y, M and C contained in the television camera memory, and a synthetic image simulating faithful- 140 are transmitted through the adjustment circuits 150 and 160 to

ment the image which will be printed is reproduced on a monitor 60 a masking circuit 200. The role of the circuit 200 is to detect

color with the necessary color corrections, to confirm the yellow, magenta, cyan, blue, green and red components and visually confirm their accuracy. In other words, while making the necessary color corrections. This kind of manipulating the correction buttons the operator can check is commonly used in conventional "scanners". Proud their effect on the monitor image and the corrections of the number of 922 buttons allow individual correction

their thus determined are recorded for the preparation of the 65 dual color signals Y, M, C, B, G and R.

plates. The masking circuit 200 is followed by an elimination circuit.

Figure 1 is an overall block diagram of the sub-color app (UCR) 280 and a reil control circuit of the invention for color selection and corrections. elimination of the 290 sub-colors. The latter determines whether

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the elimination of sub-colors and the separation of black are sufficient. The limits of these parameters were previously set using adjustment knobs 924 (UCR cut-off points) and 925 (% UCR). More specifically, a selector 923 makes it possible to obtain at will a three-color image Y-M-C, a black image only Bl or a four-color image Y-M-C-B1 on the color monitor.

The color signals Y, M, C and B1 are then applied to a clipping circuit 300. In fact, in the masking circuit 200, the signals Y, M, C and B1 undergo complicated processing involving additions, subtractions and multiplications by correction factors, so that at the exit of the circuit their levels can be lower than 0% or higher than 100%. The role of the clipping circuit is therefore to eliminate the parts which are outside the normal range 0% -100%. For the same reasons, a second clipping circuit 301 is mounted in another stage of the system.

The clipped signals are then applied to a dimming circuit 400 which corrects the gradation of the components Y, M, C and Bl. By acting on correction buttons 926, the operator can act on the compression (COMP), on the ranges light (HIGH), shadows (SHAD), contrast (CONT) and basic levels (PED) of each color signal.

The next stage is a color correction circuit 500 which converts the Y, M, C and Bl signals from the printing system into corresponding signals corrected to take account of the characteristics of the monitor. More precisely, when the signals Y, M, C and Bl of the printing system are combined by the matrix 600 into primary signals R, B and G, the zones which correspond to the secondary, tertiary and quaternary colors become excessively dark or blackish . Secondary, tertiary and quaternary colors in the Y, M and C signals must therefore be attenuated to a certain extent to lighten the corresponding areas of the monitor so as to improve the resemblance to the printed image.

The color correction circuit 500 can be that described in the U.S. patent. n ° 3 972 066 for the correction of secondary and tertiary colors. However, the secondary, tertiary and quaternary color correction circuit of FIG. 7 which is described below gives better resemblance.

The combination matrix 600 receives the signals Y, M, C and B1 from the correction circuit 500 and converts them into signals R, G and B usable by the monitor. The matrix is of the type described in the US patent. No. 3,972,066 of the plaintiff to whom the reader may refer for a more detailed description. The output signals from the matrix 600 are applied through a gray scale mixer 700 to the color monitor 800 which uses a conventional three-color tube.

Since it is difficult to assess the densities of the colors reproduced on the monitor screen 801, a gray scale 701 is added to the same screen. By comparison with this scale, the density of the colors produced by the impression.

An 805 oscilloscope allows you to examine the waveforms of input signals, corrected curves, and density signals at different points in the system. In FIG. 1, the oscilloscope 805 is connected to the output of the second clipping circuit 301, but it can be connected to other points of the system by means of switching keys 912 to 916.

We will now describe in detail the various circuits of the system of the invention.

FIG. 2 is a block diagram of the analysis assembly which notably includes the filter 111 and the camera 110. As described previously, the original document 103 is illuminated by transparency by a light source 104. The image formed by the lens 112 of the camera is received through the filter 111 by the monochrome tube 110. The rotation of the filter 111 is controlled by an electric motor 115 in synchronism with the document analysis sequences. The color signals provided by the analyzer tube 110 are applied to video amplifiers 116 and 117. The output of amplifier 116 is applied to a clipping circuit 118 which functions as a comparator. The clipped signals are then applied to a logic circuit 119 whose output controls the recording of the video signal from the amplifier 117 in the memory 140.

Figure 3 illustrates the details of the rotary filter 111. A hole io lila is drilled in the periphery of the disc 111 and triangular windows llld are formed radially between the colored sectors. The windows llld can be holes cut in the disc 111 or transparent areas having a certain density of gray which are not part of the monochrome filters R, G and B. With such a filter, the waveforms of the Monochrome tube 110 output signals have the appearance illustrated in the diagram of Figure 4. In this figure, the pulses Tw correspond to the windows 11 ld and their amplitude is greater than the detection levels. The clipping circuit 118 2o (clipping threshold V <xp) is capable of distinguishing the pulses Tw and provides a signal whose period corresponds to the speed of rotation of the filter 111. This signal being used for the synchronization of the recording the color signals in memory 140, it is easy to eliminate the effect of sector limits 111b and 25 of windows llld.

The lila hole of filter 111 is detected to provide a reference and reset pulse.

Since the Illa hole is not used to detect the rotation speed, its position does not need to be very precise. In addition, the windows IIId provide gray references which allow the absorption of the red, green and blue filters to be determined by a simple comparison of amplitudes.

The circuit 150 for adjusting the black and white level and the circuit 160 for adjusting the white level of the color image 35 are shown in FIG. 5. An input signal, for example Y, is applied to a circuit gain adjustment 151 which is associated with variable resistors 152,153,161 and 162. The resistance 152 is a potentiometer controlled by the button 906 (MEMORY GAIN), the resistance 153 is a potentiometer controlled by the button 907 (MEMORY PED) , resistor 161 is a potentiometer controlled by button 909 (SET GAIN) and resistor 162 is a potentiometer controlled by button 910 (SET ALL).

Furthermore, the black and white level adjustment circuit 130 45 is controlled by the buttons 904 (CAMERA GAIN) and 905 (CAMERA PED). The reference levels 0% and 100% are applied 110 and the outputs of all the stages are adjusted with respect to this range to standardize the sensitivity of the camera. In addition, the parts to be printed in white may have different densities depending on the conditions of analysis of the original 103 and the operator must determine the level of density to be printed in white (no ink deposited). This parameter is entered into the machine using the gain adjustment knobs 909 and 910 (SET GAIN).

The clipping circuits 300 and 301 will now be described. As explained above, the color signals are processed by addition, subtraction and multiplication and the results can be out of the 0% -100% range. It is known that a level higher than 100% leads to a supersaturation of the 60 luminescent particles of the cathode ray tube and that this phenomenon can cause "streaks of color" in the white areas and color inversions. These phenomena adversely affect the resemblance of the image and it is necessary to clip signals above 100%. In practice, the level 65 of clipping is fixed at 102%.

The clipping circuits 300 and 301 can occupy positions different from those of FIG. 1 and it is possible to use only one clipping circuit.

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FIG. 6 is an electrical diagram of the clipping circuit 301. The signals R, G and B are respectively applied to the input terminals 370, 371 and 372. The circuit comprises transistors 373 to 378, a variable resistor 379 and terminals of output 380, 381 and 382 respectively supplying R, GetB signals.

The clipping voltage is applied to the bases of transistors 374, 376 and 378 by variable resistor 379. The emitters and collectors of transistors 374, 376 and 378 are connected to their counterparts of transistors 373, 375 and 377. In such an arrangement, the signals of Input applied to the bases of transistors 373, 375 and 377 appear clipped at output terminals 380, 381 and 382. The other clipping circuit 300 works in exactly the same way, although it operates on four color signals.

We will now describe the color correction circuit 500. In US Pat. No. 3,972,066, it is said that the resemblance of the image of a color monitor to the printed image can be improved by correcting secondary and tertiary colors in the conversion of color selection signals to color video signals. More precisely, the secondary and tertiary components are detected from the signals Y, M and C and they are subtracted from these signals with a certain drafting coefficient to obtain corrected signals. This method gives completely acceptable results in the system of the invention, but it is however preferable to also correct the quaternary colors to improve the fidelity of the image.

Figure 7 is a block diagram of the secondary, tertiary and quaternary color correction circuit. The input signals Y, M, C and Bl are applied to the respective inputs of four amplifiers 502,503,504 and 505 whose outputs can be aligned at a level represented by a continuous signal Pj. The signal Px corresponding to the 100% level of the signals Y, M, C and Bl, is inserted in the return periods of the spot of the color signals. In addition, the signals Y, M, C and Bl are inverted, that is to say that their level is made inversely proportional to the density.

The outputs of amplifiers 502,503 and 504 are applied to three detection circuits 506,507 and 508 for secondary color signals. These circuits are NAM operators (non additive mixing) which select the strongest of their input signals (two, three or more) to transmit it to the output. The secondary color signals - YM, - MC and

- CY at the outputs of circuits 506 to 508.

The outputs of amplifiers 502, 503 and 504 are also applied to a detection circuit 509 of the composite color signal, which also contains an NAM operator and supplies the tertiary color signal - YMC.

The circuits 510, 511 and 512 are circuits for combining the secondary and tertiary components. From signals

- YM, - MC, - CY and - YMC, these circuits provide the three signals - YM + YMC, - MC + YMC and - CY + YMC.

A combination circuit 513, such as a maximum NAM operator, receives the input signals Y, M, C and B1 and provides a quaternary color signal - YMCB1.

The pure secondary components are designated by r, g, and b, the tertiary component by bl and the quaternary component by bl '. These signals are applied to adders 514, 515 and 516 after being multiplied by correction factors a, ß, y, to and e to correct the initial color signals Y, M and C.

The adders 514, 515 and 516 thus supply corrected primary signals Y ', M' and C 'corresponding to the following equations:. .

Y '= Y + rXa + gxp + blXÔ + bl'Xe

M '= M + rXa + bXy + bl Xô + bl' X s C '= C + gXß + bXv + blXÖ + bl'Xe

In the above equations, Y, M, C are the reverse primary signals and r, g, b, bl and bl 'are secondary, tertiary and quaternary positive components. Thus, the reverse primary signals Y, M and C are corrected by a certain fraction of the secondary, tertiary and quaternary components.

The correction of the secondary, tertiary and quad-io ternary components in the circuit 500 makes it possible to obtain on the monitor 800 brighter images which more resemble the printed image.

The masking circuit 200 will now be described, although known masking circuits of the type used in "scanners" can also be used.

FIG. 8 represents a target with colored bars, the analysis of which by a video camera gives the signals Y, M and C of FIG. 9. These signals are inverted, that is to say that their amplitude is inversely proportional to the density . The circuit of the present invention will be described with reference to the correction diagram of FIG. 10. It uses a minimum NAM operator, ie a circuit which detects only the weakest of the input signals Y, M and C. The signals YM, MC and CY are thus obtained by combination of the signals Y and M, M 25 and C, C and Y. By combination of the signals Y, M, C, one obtains with another operator NAM at least the YMC signal.

It can be seen in FIG. 10 that the YMC signal contains all the colors except white and that the YM signal contains all the colors except white and cyan. The YM - YMC difference therefore provides the inverted cyan signal. Likewise, the inverted yellow and inverted magenta signals are obtained by detecting the differences between MC - YMC and CY - YMC. The cyan, yellow and magenta components can be corrected by introducing the desired multiplicative factors.

FIG. 11 is a block diagram of the masking circuit 200. This circuit comprises amplifiers 251, 251 ′ and 251 "whose output can be aligned, selection circuits with a maximum of 252, 252", 252 "and 253, selection circuits with minimum 254,254 ', 254 "and 255, addition circuits and 40 generation of positive and negative correction signals 256, 256', 256", 257,257 'and 257 ", a control circuit 258 and adder circuits 259,259' and 259 ".

The input terminals 250, 250 'and 250 "of the circuit of FIG. 11 respectively receive the signals Y, M and C of FIGS. 9 45 and 10. The amplifiers 251, 251' and 251" selectively align the signals Y, M and C to a certain continuous level. The outputs of amplifiers 251,251 'and 251 "are connected to the selector circuits with maximum 252,252', 252" and 253, and to the selector circuits with minimum 254,254 ', 254 "and 255. The cir-50 cooked selector with maximum detect the YM signals , MC and CY in Figure 9, as well as the YMC signal which is inverted in - YMC The minimum selector signals detect the YM, MC and ÇY signals in Figure 10, as well as the YMC signal which is inverted in - YMC. The circuits for adding and generating the negative and positive correction signals 256,256 'and 256 "receive the outputs of the maximum selector circuits 252,252' and 252" to add to them the output of the maximum selector circuit 253 so as to generate negative and positive correction signals

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{- (YM-YMC), YM-YMC},

{- MC - YMC, MC - YMC},

and {- (CY - YMC), CY - YMC}.

65 The other negative and positive addition and correction circuits 257,257 'and 257 "receive the outputs of the minimum selector circuits 254,254' and 254" to add to them the output of the other minimum selector circuit 255 so as to produce

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the negative and positive correction signals {- (YM - YMC), YM - YMC}, {- (MC - YMC), MC - YMC), and {- (CY-YMC), CY — YMC}.

The relationships between correction signals and color signals are as follows:

YM - YMC = r MC - YMC = b red color blue color green color cyan color yellow color magenta color

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CY - YMC = b

- (YM - YMC) - c

- (MC - YMC) = y - (CY- YMC) = m

The control circuits 258 determine the addition ratios of the correction signals ± r, ± b, ± g, ± c, ± yet ± m (supplied by circuits 256,256 ', 256 ", 257,257' and 257") to signals Y, M and C of FIGS. 9 and 10. The addition circuit 259 receives the output of the amplifier 251 and the correction signals r, b, g, c, y and m of the control circuit 258 to carry out a algebraic addition which gives the corrected signal Y '. Likewise, the addition circuits 259 'and 259 "apply the correction signals from their control circuits 258 to the outputs of the amplifiers 251' and 251" to supply the corrected signals M'and C '.

The operation of the circuit will be described by taking the example of the color cyan. When the cyan color bar in Figure 8 is reproduced on the monitor, the portions of the Y, M and C signals in Figure 10 that correspond to that color are transmitted to the monitor. By varying the ratios of the parts of the signals Y, M and C in FIG. 9 which correspond to the cyan color, it is possible to modify the brightness, the saturation and the hue of the cyan bar on the monitor.

In the diagram in Figure 10, - (YM - YMC) = c is the color cyan. The addition or subtraction factor of the positive or negative correction signal to the cyan color signal, supplied by circuit 257 of Figure 11, is adjusted by control circuit 258, so that the correction signal is added to the signals Y, M and C in the addition circuits 259, 259 'and 259 "to produce the signals Y', M'and C '. In addition, the signals Y', M'and C 'of figure 11 are applied to the monitor and the cyan color is adjusted by the control circuit 258, which allows the brightness, saturation and hue of the cyan color to be modified. If the correction signal + c is added to the signal C making part of the signals Y, M and C of figure 10, the cyan color of figure 8 becomes white. On the contrary, if the signal - c is added to the signals Y and M being part of the signals Y, M and C, the the cyan color in Figure 8 becomes black.

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The masking circuit described above makes it possible to detect the colors cyan, magenta and yellow separately and to modify the brightness, the saturation and the hue of each of the colors red, green, blue, cyan, magenta and yellow without changing the achromatic fractions . This masking circuit is therefore relatively effective.

The mixer circuit 700, which makes it possible to introduce the gray scale, will now be described with reference to FIG. 12. Trigger pulses corresponding to each horizontal or vertical period are supplied by a generator 703 and the circuit 700 removes a part of the image signals applied to it. The gray scale signal produced by a generator 704 replaces the deleted parts of the image signals. It is thus possible to bring up the gray scale 701 on the screen of the monitor 800.

A switch 917 on the control panel removes the gray scale when it is not in use. In addition, a 918 button allows it to be moved horizontally.

Although the density measurement device is not described within the scope of the apparatus of the present invention, it is possible to incorporate therein a gray measurement device of the type described in the US patent. Applicant's No. 4,123,171. Buttons 919 to 921 are used to move the cross bar (CROSS BAR) of the density measurement device.

Furthermore, as described in the US patent. No. 3 972 066, several correction parameters can be entered separately to take account of the printing system, in particular the printing technique, the characteristics of the inks and paper, etc.

The use of the apparatus of the invention will be briefly described. The operator begins by setting the color buttons 922 and the gradation buttons 926 to zero, then acts on buttons 904,905,906 and 907 to apply standard density signals. The correction factors specific to the printing systems used are then introduced.

After that, the operator places the original document 103 on the plate 102 of the analysis system. He then sets the gain knobs 909 and 910 to set the white level and examines the synthetic image obtained on the 800 monitor.

If this image requires additional corrections, it acts on the color adjustment buttons 922 and gradation 926. During the examination of the control image, it can use the gray scale 701 and the densitometer previously. mentionned.

The final positions of the buttons 909, 910, 922 and 926 give the corrections to be applied to the separate colors for printing.

6 sheets of drawings

Claims (6)

633,139 1. Apparatus having a color monitor for analyzing and separating the colors of an original document making it possible to view on the monitor color corrections for printing the original document, characterized in that it comprises: a) a set of analysis of the original document which provides three image signals corresponding to the primary colors yellow Y, magenta M and cyan C, b) a masking circuit which corrects the color components contained in the image signals, c) a sub-color suppression circuit which processes the image signals Y, M and C according to the black image signal B1 to eliminate the sub-colors, d) clipping circuits suppressing the parts of the image signals which exceed the 100% level, e) a circuit for correcting the gradation of the image signals, f) color correction circuits which suppress at least a certain proportion of the secondary and tertiary color components contained in the image signals Y, M and C, g) a matrix for converting the signals Y, M, C and B1 into red R, blue B and green G signals, h) the color monitor reproducing an image from the R, B and G signals. 2. Apparatus according to claim 1, characterized in that the color correction circuits suppress a certain proportion of the secondary, tertiary and quaternary color components contained in the image signals Y, M and C. 2 3. Apparatus according to claim 1 or 2, characterized in that the analysis assembly comprises a single camera which is equipped with interchangeable filters for successively supplying the image signals Y, M and C, these signals being successively recorded in a memory in which they can be read synchronously. 4. Apparatus according to claim 3, characterized in that the interchangeable filters are constituted by a disc having colored sectors and transparent windows which allow the light rays to pass with an intensity greater than the level of the analysis signals, the detection of the windows producing periodic signals representative of the rotation of the filter for synchronizing the recording of image signals. 5. Apparatus according to one of claims 1 to 3; characterized in that the analysis assembly includes a black and white level adjustment circuit which maintains a constant level of black and white in the signal processing system. 6. Apparatus according to one of claims 1 to 3, characterized in that it further comprises a mixer circuit making it possible to display a scale of predetermined densities, such as a gray scale, on the screen of the color monitor. .