Method of and apparatus for processing color image

Abstract: There is provided a color image processing apparatus in which, by making use of an image reading apparatus of a digital full-color copying apparatus, the designated color to be obtained after conversion is input and stored as component ratio of color-separated image data, and monochromatic image data proportional to the gradation levels, e.g., density, lightness, luminance and so forth are obtained from the color separated image data produced from the original image,the monochromatic image data thus obtained being converted into the color separation data corresponding to the component ratio of the designated color to be obtained after conversion, thereby making it possible to preserve the hue of the designated color and to effect color conversion to the designated color having gradation proportional to the gradation of the original image.

Description: The present invention relates to an image processing apparatus and a method of image processing. The image processing apparatus is of the type comprising input means for inputting multi-level image data; hue appointing means for appointing a hue; and processing means for processing the multi-level image data in accordance with the hue appointed by the hue appointing means. Copying machines are known in which a plurality of developing units are provided for different colours, so that a monochromatic copy image may be obtained in a selected one of the different colours provided by the units. Full colour copying machines are also known which operate with a combination of developing agents of complementary colours of yellow, magenta, cyan, and black, selectable by an operator. These known techniques only provide monochromatic colour images, derived from the colours available. Thus, these known methods can only be used effectively when a mere sorting of copy images according to colour is required. Full colour copying machines are also known in which colour images may be faithfully reproduced by combining different coloured toners onto the same image. In full colour copying machines it is possible to adjust the colour reproduction so that the colour of the copy differs in some respect from that of the original. However, the problem with known techniques used for colour conversion is that tonal information is often lost during the colour conversion process. A concern of the present invention is to provide a method of and an apparatus for processing colour images which can make uniform the hue of the copy image while preserving the gradation possessed by the object image. A further concern of the present invention is to provide a method of and an apparatus for processing colour images which allows free selection of a hue when converting a colour image into a uniform hue. According to the present invention, there is provided an image processing apparatus as set out in claim 1. The invention will now be described by way of example only, with reference to the accompanying drawings in which: Fig. 1 is an illustration of a digital color copying apparatus embodying the present invention; Fig. 2 is a block diagram of a reader control unit; Fig. 3 is an illustration of protocols of a motor driver 15 shown in Fig. 2 and a CPU 22; Fig. 4A is a timing chart showing the timing of signals exchanged between a reader unit and a printer unit; Fig. 4B is a circuit diagram illustrating a video signal delivery circuit between the reader unit and a printer unit; Fig. 4C is a timing chart showing timings of signals carried by a signal line SRCOM; Fig. 5 is a circuit diagram showing the detail of the video processing unit shown in Fig. 2; Fig. 6A is a circuit diagram of masking, inking and UCR circuits; Fig. 6B is an illustration of the relationships between selection signals C 0 , C 1 and C 2 and the color signal; Figs. 7A, 7B, 7C, 7D, 7E, 7F and 7G are illustrations of generation of region signals; Figs. 8A, 8B, 8C, 8D and 8E are illustrations of color conversion; Figs. 9A, 9B, 9C, 9D, 9E, 9F, 9F-Y, 9F-M, 9F-C and 9F-BK are illustrations of gamma correction conducted for the purpose of controlling the color balance and color density; Fig. 10 is a perspective view of a laser printer unit; Fig. 11 is an illustration of a liquid crystal standard display; Fig. 12 is an illustration of the manner in which the apparatus is operated when the same is used in zooming mode; Figs. 13A and 13B are illustrations of operation of the apparatus in shifting mode; Fig. 14 is an illustration of operation of the apparatus in area appointing mode; Fig. 15 is an illustration of operation of the apparatus in color create mode; Fig. 16 is an illustration of operation of the apparatus in enlarging continuous copying mode; Fig. 17 is an illustration of operation of the apparatus in fitting synthesizing mode; Figs. 18A, 18B, 18C, 18D and 18E are illustrations of free color mode; and Fig. 19 is a control flow chart illustrating the flow of control performed when the apparatus is set in free color mode. Fig. 20 is a top plan view of the operation unit; Fig. 21 is a top plan view of a digitizer; Fig. 1 schematically shows the construction of a digital color image processing system which incorporates an image reading apparatus of the present invention. As will be seen from this figure, the image processing system has an upper portion constituting a digital color image reading apparatus 1 (referred to as "color reader", hereinafter) and a lower portion constituting a digital color image printing apparatus 2 (referred to as "color printer" hereinafter). The color reader 1 is capable of reading color image information of an original image on the basis of different colors, by a combination of a later-mentioned color separation means and a photoelectric conversion element such as CCD. The color reader 1 then converts the color information in different colors into electrical digital image signals corresponding to the respective colors. The color printer 2 is a laser beam color printer of electrophotographic type which is capable of reproducing color images of different colors in accordance with the digital image signals and performing a plurality of transfer cycles so as to print a color image in the form of digital dot patterns on a recording paper. A description will be made first as to the color reader 1. The color reader has an original 3, a platen glass 4 for carrying an original, a halogen exposure lamp 10 by which the original is scanned, a rod array lens 5 which receives and collects light reflected by the original, and a real-size full-color sensor 6 into which a light image is input by the rod array lens. The rod array lens 5, the real-size full-color sensor 6, and the halogen exposure lamp 10 in combination constitute an original scanning unit 11 which is movable in the direction of an arrow Al whereby the original is scanned. The color-separated image signals obtained through scanning over each scan line are input to a sensor output signal amplifier circuit 7 so as to be amplified to a predetermined voltage level. The amplified signals are input through a signal line 501 to a video processing unit 12 and are processed by this unit in a manner which will be detailed later. In order to ensure a high fidelity of signal transmission, the signal line 501 is constituted by a coaxial cable. Another signal line 502 is intended for transmitting driving pulses for driving the real-size full-color sensor 6. All the pulses necessary for driving the full-color sensor 6 are produced in the video processing unit 12. Numerals 8 and 9 denote, respectively, white and black boards for use in white-level correction and black-level correction which will be explained later. More specifically, the white and black boards 8 and 9 are adapted to be illuminated by the halogen exposure lamp 10 and are suitably processed thereby forming signals of predetermined levels which are used in white-level correction and black-level correction of the video signal. A reference numeral 13 designates a control unit having a microcomputer. The control unit 13 performs various controls: namely, control of display and key-input on the control panel 20 through a BUS 508; control of operation of the video processing unit 12; control of the stepping motor driving circuit for driving a stepping motor 14 which drives the scanning unit 11 through the signal line 502 in response to position signals representing the position of the scanning unit 11 detected by position sensors S1, S2 and transmitted through signal lines 509, 510; control of the state of the halogen exposure lamp 10, as well as the quantity of light from the same, by means of an exposure lamp driver which in turn is controlled through the signal line 504; and all types of control necessary in the color reader unit 1 including the control of a digitizer 16, control of internal keys and control of display units. The color image signals read by the exposure scanning unit 11 during the scanning operation are input to the video processing unit 12 through the amplifier circuit 7 and the signal line 501, and undergo various processings conducted in this unit 12 as will be explained later. The thus processed color image signals are sent to the printer unit 2 through an interface circuit 56. A description will be made hereinunder as to the color printer 2. The color printer 2 has a scanner 711 which includes various parts such as a laser output unit for converting the image signals from the color reader 1 into light signals, a polygon mirror 712, e.g., an octagonal mirror, a motor (not shown) for rotationally driving this polygonal mirror, and an f/ lens (image-forming lens) 713. A reference numeral 715 designates a photosensitive drum. The laser beam emitted from the laser output unit is reflected by the polygon mirror 712 onto the surface of the photosensitive drum 715 thereby to raster-scan the surface of the photosensitive drum 715, whereby a latent image corresponding to the original image is formed on the surface of the photosensitive drum 715. The color printer 2 further has a primary charger 717, a whole exposure lamp 718, a cleaner unit 723 for collecting residual toner particles which have not been used in the image transfer, and a pre-transfer charger 724. The primary charger 717, whole exposure lamp 718, cleaner unit 723, and the pre-transfer charger 724 are arranged around the photosensitive drum 715. A reference numeral 726 designates a developing unit capable of developing the electrostatic latent image formed on the surface of the photosensitive drum 715. The developing unit 726 includes developing sleeves 731Y, 731M, 731C and 731Bk which are adapted for conducting development upon direct contact with the photosensitive drum 715 toner hoppers 730Y, 730M, 730C and 730Bk for preserving toner particles and a screw 732 for conveying the toner as the developer. These parts of the developing unit 726 are arranged around the axis P of rotation of the developing unit. When an yellow toner image is to be formed, the development is conducted in the illustrated position by means of the yellow toner, whereas, when a magenta toner image is to be formed, the developer unit 726 is rotated about the axis P in the drawings so as to bring the developing sleeve 741M into contact with the photosensitive drum 715. Development in other colors, i.e., cyan and black, can be conducted in the same manner. The toner image formed on the photosensitive drum 715 is transferred to a paper by means of a transfer drum 716. A reference numeral 719 designates an actuator plate for detecting the position of the transfer drum 716. More specifically, a position sensor 720 is adapted to produce a signal representing that the transfer drum 716 has been brought to the home position, as it is brought to a position near the actuator plate 719. The color printer 2 further has transfer drum cleaner 725, a paper retaining roller 727, a charge eliminator 728 and a transfer charger 729. These parts 719, 720, 725, 727 and 729 are arranged around the transfer roller 716. The copy paper sheets are fed selectively from paper cassettes 735, 736 by means of paper feed rollers 737, 738. The feed and convey of the printing paper sheet are controlled by means of timing rollers 739, 740 and 741. The paper sheet which has been fed by the feed rollers is guided by a paper guide 749 and is wound on the transfer drum 716 with its leading end gripped by a later-mentioned gripper so as to be sent to an image-forming process. A reference numeral 550 designates a drum motor which drives the photosensitive drum 715 and the transfer drum 716 in such a manner that these drums rotate in synchronism with each other. A reference numeral 750 designates a separator claw for separating the copy paper sheet from the transfer drum 716 after completion of formation of the image. A numeral 742 denotes conveyor belts for conveying the copy paper sheet after separation from the transfer drum 716. A numeral 743 designates an image fixing unit for fixing the image on the copy paper sheet which has been conveyed by the conveyor belts 742. The image fixing unit 743 has a pair of heat-pressing rollers 744 and 745. A description will be made hereinunder as to the control unit 13 of the reader unit, with specific reference to Fig. 2. (Control Unit) The control unit includes a CPU 22 which is a microcomputer. The control unit is adapted for performing various types of control such as the control of the video processing, control of the lamp driver 21 for effecting exposure and scanning, control of the motor driver 15, control of the digitizer 16 and the control of the control panel 20. These controls-are performed through signal lines (BUSes) 508, 504, 503 and 505 and in accordance with programs stored in the ROM 23 and RAMs 24 and 25, so as to obtain desired copy of the image. The RAM 25 is backed-up by a series of batteries 31 which ensures non-volatile nature of this memory. The signal line 505 is constituted by a line which is ordinarily used for the purpose of serial signal transmission. The signals transmitted through this signal line are input by the operator through the digitizer 16, in accordance with the protocol between the CPU 22 and the digitizer 16. More specifically, signals input through the signal line 505 are, for example, instruction signals for appointing coordinates or regions in editorial operations such as shifting and synthesis of images, instructions for selecting a copy mode, instructions for determining the magnification, and so forth. The signal line 503 is adapted to transmit signals from the CPU 22 to the motor driver 15 for giving instructions concerning the scanning speed, scanning distance and scanning direction. Upon receipt of the instructions from the CPU 22, the motor driver 15 delivers predetermined pulses to the stepping motor 14 thereby operating the motor so as to attain the desired movement of the scanning unit. The serial I/Fs 29, 30 may be ordinary ones which may be realized by, for example, by serial I/F LSIs such as Model 8251 available from INTEL Co., Ltd. Although not shown in the drawings, similar circuits are also provided in the digitizer 16 and the motor driver 15. Fig. 3 shows the protocol of the interface between the CPU 22 and the motor driver 15. Sensors S1 and S2 are provided for detecting the position of the original exposure scanning unit 11 (see Fig. 1). More specifically, the sensor S1 detects that the original exposure scanning unit is in the home position where the white-level correction of the image signal is conducted. On the other hand, the sensor S2 detects that the original exposure scanning unit is on the leading end of the image. This position is used as the original reference position. (Printer Interface) Referring to Fig. 2, signals ITOP, BD, VCLK, VIDEO, HSYNC and SRCOM (511 to 516) are signals for the interface between the color printer unit 2 and the reader unit 1. The image signal VIDEO 514 as read by the reader unit 1 is transmitted to the color printer unit 2 in accordance with the above-mentioned signals. More specifically, the signal ITOP is a synchronizing signal for attaining synchronism in the direction of feed of the image. This direction will be referred to as "sub-scan direction", hereinafter. The signal ITOP is produced once for each color in the transmission of signals corresponding to one frame of image. Thus, in case of transmission of four-color image constituted by yellow, magenta, cyan and black, four pieces of signals ITOP are produced in the transmission of one frame. This signal is timed to be in synchronism with the rotations of the transfer drum 716 and the rotation of the photosensitive drum 715 so that the leading end of the copy paper sheet wound on the transfer drum 715 may be aligned with the image on the leading end of the original when the toner image on the photosensitive drum 715 is transferred to the copy paper sheet at the nip between both drums 715 and 716. To this end, the signal ITOP is input as an interruption 511 to the CPU 22 in the controller 13. The CPU 22 performs control of the image in the sub-scan direction for the purpose of. for example, edition, in accordance with the ITOP interruption. A synchronizing signal BD 512 is produced once per each rotation of the polygonal mirror 712, i.e., per each raster scan so as to attain synchronism of signals in the direction of the raster scan. This direction will be referred to as "main-scan direction", hereinafter. The reader unit 1 produces image signals upon reading the original, and the thus obtained image signals are delivered to the printer unit 2 in a line-by-line fashion in synchronism with the synchronizing signals BD. A symbol VCLK 513 is a synchronizing clock signal for delivering an 8-bit digital video signal to the color printer unit 2. For instance, the 8-bit digital video signal is transmitted through flip-flops 32 and 35, as shown in Fig. 4B. A horizontal synchronizing signal HSYNC 515 is a signal for attaining synchronization of signals in the direction of the main scan and is produced in synchronization with the VCLK 513 in accordance with the signal BD. The signal HSYNC has the same period as the signal BD. More strictly, the video signal VIDEO is produced in synchronization with the horizontal synchronizing signal HSYNC 515, for the following reason. The signal BD is generated in synchronization with the rotation of the polygon mirror 712, so that this signal inevitably contains jitter components produced by the motor for driving the polygon mirror 712. Therefore, if the signal VIDEO 514 is produced in synchronization with the signal BD, the signal VIDEO 514 inevitably contains jitter components. To overcome this problem, the signal VIDEO 514 is generated in synchronization with the horizontal synchronizing signal HSYNC 515 which in turn is generated in accordance with the signal BD in synchronization with the synchronizing clock VCLK which does not contain any jitter component. The signal line SRCOM is a semi-double signal line for by-directional serial signal transmission. As shown in Fig. 4C, a command CM is delivered in synchronization with an 8-bit serial clock SCLK which is delivered in a period between successive synchronizing signals CBUSY (command busy) which are delivered from the reader unit. In response to this command CM, the printer unit transmits a status signal ST in synchronization with an 8-bit serial clock produced in a period between successive SBUSY (status busy) signals. The timing chart in Fig. 4C shows that a status signal "3CH" is sent back in response to a command "8EH". Thus, instructions from the reader unit to the printer unit, e.g., appointment of color mode and selection of cassette, as well as information concerning the status of the printer, e.g., jamming of paper, absence of paper, wait.and so forth, are transmitted through this signal line SRCOM. Fig. 4A is a timing chart illustrating the timing of transmission of signals constituting a four-color image, in accordance with the signals ITOP and HSYNC. A signal ITOP 511 is produced once per each rotation or every other rotations of the transfer drum 716. More specifically, an yellow image, a magenta image, a cyan image and a black image are delivered from the reader unit 1 to the printer unit 2 in the periods 1 ○, 2 ○, 3 ○ and 4 ○, respectively, whereby the four color images are superposed so as to form a full color image on the transfer paper. Assuming here that the original image of A-3 (420 mm long) is to be read at a density of 16 pee/mm in the direction of feed, the horizontal synchronizing signal HSYNC is produced 6720 times (420 x 16 = 6720). The signal HSYNC also is delivered to the clock input of a timer circuit 28 in the controller circuit 13. When a predetermined number of signals HSYNC has been counted, an interruption HINT 517 is delivered to the CPU 22. The CPU 22 conducts various controls of image such as extraction or shift of image in the direction of feed, in response to the interruption HINT 517. The operation of the video processing unit 12 shown in Figure 5 is fully described in the specification of European Patent No. 0292212. In apparatus of the kind with which the present invention is concerned, various color correction methods have been proposed and used. For instance, it is well known to conduct masking correction in which color correction is performed by computing the following first degree equation for each color component video data Y i , M i and C i . In a method known as "inking", the minimum values Min(Y i , M i , C i ) of the color component data Y i , M i , C i are computed and black toner is added by treating the minimum values as black level. An under-color removal (UCR) is also known in which the amounts of the respective color toners are reduced corresponding to the amount of the black component added. Fig. 6 shows the arrangement of circuits for the masking correction, inking and UCR operations. This circuit arrangement has the following features: (1) Two masking matrix systems are used, and switching therebetween can be executed at a high speed by switching of the level of a signal line between "1" and "0". (2) Switching between a mode which employs UCR and a mode which does not employ UCR is conducted at a high speed by switching of the level of a signal line between "1" and "0". (3) There are two systems of circuit for determining the amount of inking, and switching therebetween is conducted at a high speed by switching of the level of a signal line between "1" and "0". Before the commencement of the reading of the image, any desired first matrix coefficient M 1 and second matrix coefficient M 2 are set though a BUS connected to the CPU. In the described embodiment, the following coefficients M 1 and M 2 are set in registers 87 to 95 and registers 96 to 104, respectively. Numerals 111 to 122, 135 and 131 denote selectors each being adapted to select "A" and "B", respectively, when the level of the S terminal thereof is "1" and "0", respectively. Therefore, the matrix coefficients M 1 and M 2 , are selected by setting the switching signal MAREA 564 at "1" and "0", respectively. Numeral 123 also designates a selector which provides one of outputs a, band c in accordance with a truth table shown in Fig. 6B, in response to selection signals C 0 and C 1 (566, 567). The selection signals C 0 , C 1 and C 2 correspond to the color signals to be output. Namely, color-corrected Y, M, C and Bk color signals are obtained by setting the selection signals C 0 , C 1 and C 2 as (C 0 , C 1 , C 2 ) = (0,0,0), (0,,0,1), (0,1,0) and (1,0,0), respectively. A color-corrected monochrome signal is obtained by setting the selection signals C 0 , C 1 and C 2 as (C 0 , C 1 , C 2 ) = (0,1,1). If the selection signals C 0 , C 1 and C 2 areset as (C 0 , C 1 , C 2 ) = (0,0,0) while the MAREA is set as MAREA = "1", the contents of the registers 87, 88 and 89, i.e., (a Y1 , -b M1 , -C C1 ) are obtained as the output (a,b,c) of the selector 123. On the other hand, the black component signal 574, which is computed as Min(Y i , M i , C i ) from the input signals Y i , M i , C i , is subjected to a primary conversion which is conducted by 134 in accordance with a formula Y = ax - b (a and bare constants), and is input to the B inputs of subtractors 124, 125 and 126 through the selector 135. For the purpose of the under-color removal, the subtractors 124 to 126 execute computations of Y = Y i - (ak - b), M = M i - (ak - b) and C = C i - (ak - b), respectively. The results of the computations are input to the multipliers 127, 128 and 129 for the masking computations. The selector 135 is controlled by a signal UAREA 565 which is capable of conducting a high-speed switching between a mode which employs the under-color removal (UCR) and a mode which does not employ the UCR, by switching of its level between "1" and "0". Each of the multipliers 127, 128 and 129 receives at its A input the signal (a Y1 , -b M1 , -C C1 ) and at its B input the signal [ Y i - (ak - b), M i - (ak - b), C i - (ak - b)] = [Y i , M i , C i ]. Therefore, as will be seen from his figure, an output Yout = Y i x (ay 1 ) + M i x (-b M1 ) + C i x (-C C1 ) is obtained at the output Dout, on condition of C 2 = 0 (select Y or M or C), whereby an yellow video data after masking color correction and under-color removal is obtained. Similarly, outputs Mout = Y i x (-ay 2 ) + M i x (b M2 ) + C i x (-C C2 ) and Cout = Y i x (-ay 3 ) + M i x (-b M3 ) + C i x (C C3 ) are obtained at the output Dout. The color selection is controlled by the CPU 22 in accordance with the table shown in Fig. 16B by suitably setting the values (C 0 , C 1 , C 2 ) in the sequence of development performed by the color printer. The registers 105 to 107 and 108 to 110 are monochrome image forming registers and are obtained by weighted addition of the colors in accordance with the formula of MONO = k 1 Y i + ℓ 1 M i + m 1 C i . The switching signals MAREA 564, UAREA 565 and KAREA 587 are for conducting, respectively, the high-speed switching between the masking color correction coefficient matrixes M 1 and M 2 , the high speed switching between the mode which employs UCR and the mode which does not employ the UCR, and the high-speed primary switching of the black component signal which is delivered from the Dout through the signal line 569 and the selector 131. More specifically, the KAREA 587 conducts a high-speed switching between Y = ck - d and Y = ek - f (c, d, e and f are constant parameters) for a given value K = Min (Y i , M i , C i ). it is therefore possible to apply different masking coefficients to different areas of a single image or to vary the amount of UCR and amount of inking according to areas. This arrangement,therefore, can be used for synthesizing images derived from different image input sources of different color-separation characteristics or a plurality of images of different black tone levels, as in the described embodiment of the invention. The area signals MAREA UAREA and KAREA 564, 565, and 587 are produced by an area signal generating circuit 51 (see Fig. 2) which will be detailed hereinunder. The principle of generation of the area signal MAREA 564, UAREA 565 and KAREA 587 will be explained with reference to Figs. 7 A to 7G. The term "area" is used to mean, for example, a region which is hatched in Fig. 7E. This area can be determined by generating a signal AREA at a timing shown in Fig. 7E in each scanning period in a region between A and B as measured in the direction of the sub-scan. Each area can by appointed by the digitizer shown in Fig. 1. Figs. 7A to 7D show an arrangement which enables a multiplicity of area signals to be formed in a programmable manner by the CPU 22. With this arrangement, therefore, it is possible to provide a variable number of area signals at variable timings and with variable lengths. In this arrangement, each area signal is constituted by one bit of a RAM which is accessible by the CPU 22. For instance, a pair of RAMs 136, 137 (Fig. 7D) each having n bits are used for the purpose of generating n-pieces of area signals AREA0 to AREAn. Thus, area signals AREA0 and AREAn as shown in Fig. 8B can be obtained by setting "1" in the bit 0 at the addresses x 1 and x 3 of the RAMs, while setting "0" in bits 0 at all other addresses. On the other hand, "1" is set in the bit n at addresses 1, x 1 , x 2 and x 4 , while "0" is set in bit n at all other addresses in the RAM. Then, by sequentially reading the data from the RAM in synchronization with clocks based on the signal HSYNC, data "1" is read at each of the addresses x 1 and x 3 as shown in Fig. 7C. The thus read data are input to J and K terminals of the J-K flip-flops 148-0 to 148-n shown in Fig. 7D so that a region signal such as AREA0, i.e., the area signal, is produced by a toggle operation, i.e., an operation which changes the output level from "0" to "1" and vice versa when CLK is input white "1" is read from the RAM. If data "0" is set in all addresses, the area signal is not generated so that no area is set. Fig. 7D shows the arrangement of this circuit having the RAMs 136 and 137. These two RAMs 136 and 137 are used alternately in such a manner that, while a line data is being read from the RAM 136, data for setting the area is set by the CPU into the other CPU 22 (see Fig. 2), thereby attaining a high-speed switching of the area length. For instance, when an area hatched in Fig. 7F is appointed, the RAMs A and B are switched from A to B, from B to A, from A to B and then from B to A. This operation will be explained in more detail with reference to Fig. 7D. When data (C 3 , C 4 , C 5 ) are set as (C 3 , C 4 , C 5 ) = (0, 1, 0), the output from the counter which counts in synchronization with VCLK is delivered as an address data to the RAM 136 through a selector 139 (Aa). At the same time, a gate 142 is opened white a gate 144 is closed so that the RAM 136 is used in the reading mode to allow data to be read therefrom, whereby n-bit data are input to the J-K flip-flops 148-0 to 148-n, whereby a region signal AREA0 to AREAn is generated in accordance with the value set in the RAM 136. Meanwhile, writing of the data by the CPU to the RAM B is conducted through an address BUS A-Bus and data BUS D-Bus, in accordance with an access signal R / W . The generation of the region signal on the basis of the data set in the RAM B 137 is conducted in the same manner, by setting the data (C 3 , C 4 , C 5 ) as (C 3 , C 4 , C 5 ) = (1, 0, 1). Meanwhile, data is written by the CPU into the RAM A 136. These two RAMs will be referred to as A-RAM and B-RAM, respectively, while the data C 3 , C 4 , C 5 will be collectively referred to as AREA control signal (ARCNT). The AREA control signal C 3 , C 4 , C 5 are generated through the I/O port of the CPU. Fig. 7G illustrates a table which contains correlations between the bits and the names of signals. <Color Conversion> The circuit arrangement for color conversion will be explained hereinunder with reference to Fig. 8. The term "color conversion" is used to mean a replacement of an input color component data (Y i , M i , C i ) of a specific density or color component ratio with another color. Practically, this operation is conducted for changing. for example, the red color of hatched area of the original shown in Fig. 8C into, for example, blue color. The respective color data (Y i , M i , C i ) input to this circuit are first delivered to averaging circuits 149, 150 and 151. The mean pixel numbers are set through a CPU BUS from an operation or control panel which will be described later. Practically, the mean pixel numbers are set in window comparators 156 to 158 through the CPU BUS. The setting of the mean pixel number is conducted in relation to the width between a comparison upper limit and a comparison lower limit. When the width is small, the mean pixel number is set to be large in order to avoid erroneous detection which may otherwise be caused by, for example, presence of a half-tone image. Conversely, when the width is large, the mean pixel number is set to be comparatively small, in order to avoid erroneous detection of,for example, fine lines. The average data from the averaging circuits are input to an adder 155 which computes (Y i + M i + C i ) and delivers the same to the B inputs of the dividers 152, 153 and 154. The outputs from the averaging circuits also are input to the A inputs of these dividers, whereby color ratios including the yellow ratio ray = Y i /(Y i + M i + C i ), magenta ratio ram = M i /(Y i + M i + C i ) and the cyan ratio rac = C i /(Y i + M i + C i ) are derived through signal lines 604, 605 and 606, respectively, and are input to the window comparator 156 to 158. These window comparators 156 to 158 are adapted to produce outputs of "1" level on conditions that the values of the color ratios fall within a ranges between the upper and lower limits (y u , m u , C u ), (y ℓ , m ℓ ,c ℓ ). Namely, outputs "1" are obtained from the respective window comparators on conditions of y ℓ ≤ ray < y u , m ℓ ≤ ram < m u and c ℓ ≤ rac < c u . The CPU judges that the input color is the very one which has been expected, when all of these three conditions are met. When all of these three conditions are met, a 3-input AND gate 165 produces an output of "1" level. This output is input to the S 0 input of a selector 175. When the level of the signal output from the I/O port of the CPU and carried by a signal line CHGCNT 607 is "1", the adder 155 produces an output When the same signal is "0", the adder produces an output 603 = 1. Therefore, when the level of the above-mentioned signal is "0", the dividers 152, 153 and 154 directly deliver the signals received by their A inputs. Thus, color density data rather than the desired color component ratio are set in the registers 159 to 164. The selector 175 mentioned above has four input lines and one output line. The inputs 1, 2 and 3 of the selector 175 receive the Y, M and C components as the color data of the color to be obtained after the color conversion. Meanwhile, the input 4 receives the data V in which has been obtained by conducting masking color correction and UCR in the read original image data. Thus, the input 4 is connected to the output Dout shown in Fig. 6A. The switching input S 0 takes a level "1" when the color detection is "true", i.e., when a predetermined color is detected, otherwise a level "0". A symbol S 1 is an area signal CHAREA0 615 produced in the area generating circuit shown in Fig. 7D. This signal takes "1" level for the data within an appointed area and "0" for the data which are out of the area. Thus, the color conversion is conducted only when this signal S 1 is set at "1". The inputs S 2 and S 3 (C 0 and C 1 ) 616 and 617 are the same as the signals C 0 and C 1 shown in Fig. 16A. The color printer performs formation of an yellow image, magenta image and cyan image conditions of (C 0 , C 1 ) = (0, 0), (C 0 , C 1 ) = (0, 1) and (C 0 , C 1 ) = (1, 0), respectively. Fig. 8B shows the truth table for the selector 175. The color component ratios to be obtained after the color conversion or the color density data to be obtained after the color conversion are set in registers 166 to 168 by the CPU. In the area where y', m' and c' are color component ratios, since the CHGCNT 607 has been set to "1", the output 603 of the adder 155 represents (Y i + M i + C i ) which is input to the B inputs of the multipliers 169 to 171. In consequence, the selector inputs 1, 2 and 3 receive, respectively, signals (Y i + M i + C i ) × y', (Y i + M i + C i ) × m' and (Y i + M i + C i ) × c', whereby color conversion is executed in accordance with the truth table shown in Fig. 9B. In contrast, when y', m' and c' are color component density data, the CHGCNT is set as CHGCNT = "0", so that the signal 603 takes "1" level. Therefore, the inputs 1, 2 and 3 of the selector 175 directly receive the data (y', mm', c') thereby causing a color conversion through replacement of the color component density data. As explained before, the area signal CHAREA0 615 allows the region length and region number to be set freely. It is therefore possible to apply the color conversion only to a plurality of regions r 1 , r 2 , r 3 . It is also possible to conduct a high-speed and real-time color conversion in a plurality of regions with a plurality of colors, e.g., from red to blue in the region r 1 , from red to yellow in the region r 2 and from white to red in the region r 3 , by using a plurality of circuits shown in Fig. 8A. Namely, a plurality color detection and conversion circuits of the same construction as that explained above are prepared, and a selector 230 selects the desired output from among the outputs A, B,C and D of these circuits in accordance with signals CHESEL0 and CHSEL1 and the thus selected output is delivered through an output 619. The area signals CHAREA0 to CHAREA3 applied to the respective circuits, as well as CHSEL0 and CHSEL1,are generated by the area generating circuit 51 as shown in Fig. 7D. <Gamma Conversion Circuit> Fig. 9 shows a gamma conversion circuit which is used for the purpose of controlling the color balance and the color densities of-the output image in the described system. The gamma conversion basically relies upon data conversion by means of an LUT (Look-Up Table). The data contained in the LUT can be rewritten in accordance with input from the control unit. Writing of data in the RAM 177 constituting the LUT is conducted as follows. By setting the level of the signal on the selection signal line RAMSL 623 at "0", the selector 176 selects the B input so that the gate 178 is closed while the gate 179 is opened, whereby the BUSes ABUS and DBUS (address data) leading from the CPU 22 are connected to the RAM 177, thus enabling wiring or reading of data into and from the RAM 177. Once the conversion table is formed, the RAMSL is set to "1" so that the video input from the Din 620 is input to the address input of the RAM 177 so that addressing can be done by the video data, whereby the desired data is input through the open gate 178 to the magnification control circuit of the next stage. At least two types of gamma characteristics (A and B in Fig. 9B) are provided in the gamma RAM for five color types of yellow, magenta, cyan, black and MONO. As in the case of the operation explained in connection with Fig. 6, the switching of each color is executed in terms of the data C 0 , C 1 ,C 2 (566, 567, 568). In addition, as shown in Fig. 9C, the area A is provided with a gamma characteristic A, while the area B is provided with a gamma characteristic B, in accordance with an area signal GAREA 626 generated by the area generating circuit (see Fig. 7), whereby both areas of different gamma characteristics form corresponding images in a single print. Thus, the gamma RAM has two types of magnification characteristics A and B which are switchable at a high speed for independent regions. Obviously, high-speed switching between three or more magnification characteristics is obtainable by increasing the type of the magnification characteristic. The output Dout 625 in Fig. 9A is connected to the input Din 626 of a magnification control circuit of the next stage. As will be seen from the drawings, the described gamma conversion RAM is constructed to enable the conversion characteristics to be changed for independent colors. The contents of the RAM can be rewritten by the CPU in relation to the operation of liquid-crystal touch panel key on the control panel. <Procedure of Gamma Conversion> Assume here that a density adjusting key e or f on a standard picture P000 (see Fig. 11 ) is touched by the operator. If the key touched by the operator is the key e, the setting is shifted to the left as from -1 to -2, as will be seen from Figs. 9D and 9E. The characteristics set in the RAM 177 also is shifted correspondingly from -1 to -2, from -2 to -3, from -3 to -4 and so on. When the key touched by the operator is the key f, the characteristics are shifted as from +1 to +2, from +2 to +3, from +3 to +4 and so forth, thus rewriting the content of the RAM 177. Thus, the whole table (RAM 177) for the Y, M,C, Bk or MONO can be rewritten by touching the key e or the key f on the standard picture mentioned above, whereby the density of the image can be changed without causing any change in the color tone. Fig. 15 shows a picture P 420 displaying a color balance control function in <color create> mode. The function enables the data for the independent colors Y, M, C and Bk only within the area of the RAM 177, so as to enable the color balance to be controlled. For instance, when it is desired to change the color tone of the yellow component, the black display belt on the picture P 420 is extended upward in response to pressing of a touch key y 1 so that the conversion characteristic is changed in the y 1 direction as indicated by -Y in Fig. 9F, whereby the density of the yellow color component is increased. Conversely, when the touch key y 2 is pressed, the characteristic is shifted in the direction y 2 , whereby the density of the yellow color component is decreased. Thus, the color balance function enables the color tone to be changed through a change in the density of each color component. The free color mode, which is set through the picture P 361 in Fig. 14 (free color mode in ,area appointing. mode) can be realized by rewriting the gamma conversion RAM in a manner which will be described later. The free color mode is a mode which has a function for producing an image of a single hue with gradation, as in the case of production of a black monochromatic copy image with gradation by a monochromatic copying apparatus from a full-color original image. The free color mode employed in this embodiment, however, enables a free selection of the single hue of the single hue image in converting the original color image into a monochromatic or single hue copy image, as one of its critical features. A description will be made hereinunder as to how the free color mode is realized, with reference to Fig. 16A. The description will be made on an assumption that the user wishes to obtain a copy image in the hue of blue color from an original image. The desired hue can be conducted by appointing the corresponding color on the original through the picture P 360 shown in Fig.14 to enable the apparatus to read the color, or by appointing the hue which has been registered in the picture P 360 of Fig. 14. The graph appearing on the right side of Fig. 16A shows the color component data (Y s , M s , C s ) of the color having the desired hue (light blue in this case) appointed through the picture P 362 or P 364 of Fig. 14. From this graph, it is understood that the desired hue (light blue) has a component ratio of Y s : M s : C s = 1 : 2 : 4. The graph on the left side of Fig. 16A shows gamma characteristics which are set in the MONO gamma RAM in the formation of yellow, magenta and cyan images, for the purpose of enabling conversion of image in hues of component ratios as shown by the right-side graph while preserving the gradation of the original image. Representing the maximum value among Y s , M s and C s by MAX, the gamma characteristic functions GY(x), GM(x) and GC(x) for the yellow, magenta and cyan are formed in the following manner. GY(x) = X· Y s MAX GM(x) = X· M s MAX GC(x) = X· C s MAX where, MAX is not equal to 0. The free color mode is realized by subjecting the thus obtained MONO gamma RAMs to gamma conversion while changing the gamma characteristics for yellow, magenta and cyan colors, respectively. In fact, the following condition is obtained for all MONO values X so that the formed image has the same ratio with respect to yellow, magenta and cyan, thus realizing the same hue. GY(x):GM(x):GC(x) = x· Ys MAX : x· Ms MAX : x· Cs MAX = Ys : Ms : Cs Fig. 6B shows the color components of the color in which the image is formed in the free color mode from an original having a black portion (MONO = 255) and a red portion (MONO = 160). It will be seen that the image of the portion of high MONO value on the original is formed with a high density, whereas the image of the portion of low MONO value is formed in a low density, while keeping the same hue. This method, however, does not enable free selection of density of the image of desired portion of the original image. Actually, it is often experienced that the density is controlled in such a manner that the image of the black portion of the original image is formed with reduced density of the desired hue, while the image of the red portion is formed with increased density of the desired hue. To this end, the described embodiment is so designed as to enable the density level to be varied over 17 levels, i.e., from level 1 to level 17, by manipulating the density control key a on the picture P 363 or P 364 of Fig. 14 (free color mode in <area appointing> mode). In accordance with the selected density level, the gamma curve (see Fig. 18A) of the color component having the greatest proportion (referred to as "main color component") is changed as shown in Fig. 18C. The standard level of the density is the level 9. When this density level has been selected, the gamma curve of Fig. 18C coincides with the gamma curve of Fig. 18A. The gamma characteristic function GMAIN i of the main color component is determined by the following formula for each of the constants M i (M 0 to M 17 ) (M s = 255) given for the respective density levels. In this embodiment, the upper limit is set to be 255 because the gamma RAM produces an 8-bit output (0 to 255). According to the present invention, the inclination of the gamma curve of the main color component is varied in accordance with the density level and the inclinations of other color components also are varied in accordance with the inclination of the gamma curve of the main color component so as to maintain the predetermined ratios. Fig. 18D shows a gamma curve as obtained when the example of Fig. 18A is changed to the density level 4. It will be seen that the image of the black portion of the original is formed in the same hue with reduced density, while maintaining the ratio of Y : M : C = 1 : 2 : 4. Figs. 18E shows the gamma curve as obtained when the example of Fig. 18A is varied to the density level 15. In order to maintain the constant value of the color component ratio, the control is conducted such that, when the main color component has reached the upper limit (255 in this case) and maintained constant, other color components also are set at constant levels. With this density level, it is possible to convert the red component of the original into a color of the same hue but having a higher density. Needless to say, the ratio of the output data of Y : M : C = 1 : 2 : 4 is maintained for all MONO input values. It is also possible to effect the density control by pointing, on the picture P 365 of Fig. 14 (free color mode in <area appointing> mode), the portion of the image which the user wishes to convert into the same density as the color (Ys, Ms, Cs) having the desired hue which has been appointed through the picture P 362 or P 364 in Fig. 11. Practically, this is conducted by reading the MONO value (reference MONO value) of the point pointed on the original, and setting the gamma curves of the respective color components in the MONO gamma RAMs such that Ys, Ms and Cs are output when the read MONO value is input. When the reference MONO value is comparatively small, the gradient is large as shown in Fig. 18E, whereas, when the reference MONO value is large, the gradient becomes small as shown in Fig. 18D. As explained before, the free color mode can be realized by three image forming operations for Y,M and C. However, when the image formation of Bk color is required due to simultaneous use of another operation mode, the gamma curve for the Bk color should be set such that 0 is output for all input values. Fig. 19 is an illustration of the control section of the color copying apparatus of the described embodiment. The control section 401 has various keys including a reset key 401 for resetting the operation mode to the standard mode, an enter key 402 for setting a later-mentioned registration mode or a later-mentioned service mode, a ten-key device 404 for inputting numerical data such as the number of copies to be produced, a clear/stop key for clearing remaining number of copies and stopping continuous copying operation, and keys 405 on the touch panel key for setting various modes and the state of the printer 2. A key 407 is a center shift key which is used for shifting an image to the central position in a later-mentioned shift mode. A key 408 is an original recognition key which is used for automatically detecting the size and position of the original in advance of the copying operation. A key 406 is a protector key which is used for appointing a later-mentioned projector mode. A key 409 is a recall key for recovering the conditions set for the preceding copying operation. A key 410 is a memory key for reading various set values programmed beforehand and for setting various values in memories (M1, M2, M3, M4). A key 411 is a registration key for allowing data to be registered in the respective memories. Fig. 20 is a view schematically showing the appearance of the digitizer 16. The digitizer 16 has entry keys 422, 423, 424, 425, 426 and 427 for setting later-mentioned operation modes. The digitizer 16 also has a coordinates detection plate 420 which is used in appointing any desired region on the original or in setting magnification. The appointment of the coordinates values is conducted by a point pen 421. The data input through these keys, as well as the coordinates data, are exchanged between the digitizer 16 and the CPU 22 through the BUS 505 and are stored in the RAM 24 and the RAM 25. <Explanation of Standard Picture> Fig. 11 illustrates a standard picture. The standard picture P000 is put on display when neither the copying operation nor the setting operation is conducted. This picture is presented for the purpose of enabling setting of various operation factors such as the magnification, selection of paper type and density control. The left lower corner portion of the picture is adapted for giving an instruction for effecting so-called real-form magnification changing operation. For instance, when a touch key a (contraction) is touched, the change in the size and the magnification are displayed as shown in the picture P010. Similarly, when a touch key b (enlargement) is touched, the size and the magnification are displayed as in the case of the contraction. In the copying apparatus of the described embodiment, the original image size can be increased in three stages and reduced also in three stages. The operator can reset the operation to the real-size mode (100% magnification), by touching a touch key h(real size). The user can also select one of an upper cassette and a lower cassette by pressing a touch key c on the center of the display. It is also to set an APS (Automatic Paper Select) mode in which a cassette containing copy papers of a size which best matches for the original size is selected automatically. This mode can be selected by pressing a touch key d. Keys e and f on the right portion of the display are keys for controlling the density of the print image. Instructions given through these keys are valid even during copying. A touch key g is for displaying a picture which illustrates a guide menu explaining how to operate touch keys and how to operate the copier, as a guidance for the operator. The operator therefore can operate the system without difficulty, upon consultation with the display of this guide menu. The guide menu is provided not only for the standard picture but also for various operation modes for the purpose of explaining these modes. The states of setting of various modes are displayed on the black beltlike strip area on the top portion of the display, so as to enable the operator to confirm the states of setting of moves thereby to avoid any wrong operation. A message display area provided under the stripe portion displays the state of the color copier as shown in the picture P 020, as well as suitable messages for informing the operator of any erroneous operation. In order to give messages concerning jamming of paper-and shortage of toners, the shape of the printer unit is displayed on the whole display area and a sign is displayed to visdally indicate the portion of the printer where the jam is taking place, as well as which one of color toners is to be supplied. <Explanation of Area Appointing Mode> When the area appointing. (area designation) mode M 300 has been selected, the user can appoint one or more areas on the original. One of three modes, i.e., trimming mode M 310, masking mode M 320 and image separation mode M 330, can be adopted for each of the appointed areas. The trimming mode M 310 is a mode in which only the image portion within the appointed area is copied. The masking mode M 320 is a mode id which the copy is produced such that the appointed area is covered by a white blank. The image separation mode M 330 is further divided into a color mode M 331, a color conversion mode M 332, a paint mode M 333 and a color balance mode M 334. The operator can select any one of these four modes. When the color mode M 331 has been selected, the appointed area can be copied in any of nine colors: namely, 4-full-color, 3-full-color, Y, M, C, Bk, RED, GREEN, and BLUE. The free color mode M 335 makes it possible to select, within the designated or appointed area, a mono-color image in a color other than the seven mono-colors which have been registered beforehand. The color conversion mode M 332 is a mode which conducts the copying operation while replacing a portion of the appointed area having a color falling whithin a predetermined density level with any other desired color. When the paint mode M 333 has been selected, a copy is obtained in which the appointed area is uniformly "painted" with any desired color. The color balance mode 334 is a mode which performs adjustments of densities of Y. M, C and Bk colors in the appointed area, thereby to produce a copy in which the appointed area is printed with a color balance (color tone) which is different from that of the image portions other than the appointed area. A description will be made hereinunder as to the practical way for operating the apparatus in the area appointing mode M 300, with specific reference to Fig. 11. The user first presses the area appointing key 424 on the digitizer 16, so that the content of the liquid crystal display is changed to a picture P 300. The user places the original on the digitizer 16 and points the desired area by means of the point pen 421. When two points in the area are presses by the point pen 421, the content of the display is changed to a picture P 310. If the area has been appointed correctly, the user presses the touch key a on the picture P 310. Then, the user selects one of the trimming mode, masking mode and the image separation mode which are displayed in the picture P 310 and presses a key corresponding to the selected mode. If the trimming mode or the masking mode has been selected, the user presses the touch key a on the picture P 320 so that the process proceeds to a next step for appointing the area. On the other hand, if the mode selected on the picture P 320 is the image separation mode, the content of the display is changed to a picture P 330 which enables the use to select one from the four modes: namely, the color conversion mode, paint mode, color mode and the color balance mode. For instance, if the user wishes to print the image in the appointed area in 4-full-color consisting of Y. M. C and Bk, he presses the touch key a (color mode) on the picture P 330 so as to select the 4-full-color mode from the nine color modes, thus completing the operation for appointing printing of the appointed area in 4-full-color. If the user has pressed the key b on the picture P 330, the content of the display is changed to P 340 which enables the user to appoint a point in the appointed area having the color information which is to be converted by means of the point pen. The color conversion is effected in accordance with this color information. The color range to be subjected to the color conversion can be varied as desired by means of a conversion range appointing key which is on the center of the picture P 341. The term "conversion range" is used to mean the range of the color information which is regarded as being the same as the color information of the appointed point. When a touch key b is pressed, the range of conversion is widened so that the conversion is effected to include also regions which have different density levels and hues. On the other hand, when a touch key c is pressed, the range of conversion is narrowed so that the conversion is effected to include only the region having the appointed density level and hue. If this point is pointed correctly, the user presses the touch key a of the picture P 341, so that the display proceeds to a picture P 370. The picture P 370 is intended for allowing the user to appoint the color to which the color of the point appointed on the picture P 340 is to be converted i.e., the color to be obtained after the color conversion. In this case, the user can select one from four types of color, i.e., standard color, designated colors, registerd colors and white, as the color after the conversion. When a standard color is to be selected as the color to be obtained after the conversion, the user presses the touch key a on the picture P 70 so as to appoint one of standard colors displayed on the picture P 390. These colors are: yellow, magenta, cyan, black, red, green and blue. Thus, the standard colors are color informations peculiar to the copying apparatus. In the illustrated embodiment, the standard colors have ratios as shown in Fig.17 so that the print image is formed with a medium level of color density. It is, however, quite natural that the user wishes to increase or decrease the color density from the previously set density. In such a case, the user an appoint any desired density of the color after the conversion, by pressing a density appointing key on the center of the picture P 390. If the user has pressed the key c (designated color) on the picture P 370, the content of the display is changed to a picture P 380. The user then appoints a point having a color information to be obtained after the conversion by means of the point pen, in the same manner as the appointment of the color coordinates of the color information before the conversion. If the user wishes to vary only the density without changing the color coordinates, he presses the density control key a on the center of the picture P 381 thereby to set the density of the color to be obtained after te conversion at any desired level. When the desired color is not found on the original nor in the list of the standard colors, the user can effect the color conversion by making use of the color information which is registered through the process of the later-mentioned color registration mode. To this end,the user presses the touch key c on the picture P 370 and then presses the touch key of the No. corresponding to the color number to be used, from among the colors registered through the picture P 391. It is possible to change only the density of color without changing the ratios of the color components, also in this mode. When the touch key c (white) is pressed on the picture P 370, the effect same as that produced by the operation in the masking mode M 310. When the user wishes to appoint the paint mode M 33 in the image separation mode M 330, he presses the touch key c on the picture P 330 so that the content of the display is changed to a picture P 370. Then, the painting color is appointed in the same manner as that of the procedure which is conducted in the color conversion mode M 332 after the display of the picture P 370. When the user wishes to print only the appointed area in a desired color balance (color tone), he presses a touch key d (color balance), so that the content of the display is changed to a picture P 350 which enables the user to control the densities of color components, i.e., yellow, magenta, cyan and black, by means of an up/down key. In the picture P 350, the states of appointment of the density levels are indicated by black bar graphs together with a gradation or scale. When a touch key e is pressed on the picture P 330 so as to appoint the free color mode, the display is changed to a picture P 361 which enables the user to select whether an appointed color or a registered color is to be used as the color of the MONO color. Namely, when the user has pressed the key a to select the appointed color, the display is changed to a picture P 362 and the user appoints, by means of the point pen, a point on the image to be copied having the desired mono-color information. The display then proceeds to a picture P 363. In this state, if the user wishes to effect a mono-color copying through varying only the density while maintaining the hue of the mono-color, he can select the free color mode and to obtain a copy of the desired density of the same hue, by pressing the density control key a on the picture P 363. When an OK key b is pressed on the picture P 363, the display proceeds to a picture P 365. The use can input, by means of the point pen, the position of the reference color information which he wishes to convert into the same density as the density of the color information appointed through the picture P 362, whereby a free color mode is executed to produce a copy image of the desired density. Conversely, when the user has pressed the touch key b to select the registered color, the display proceeds to a picture P 364 to enable the user to use the color information of the desired one of a plurality of registered colors. Conversion of the density alone, i.e., conversion without changing the hue, can be effected also in this case. As the OK key on the picture P 364is pressed, the display proceeds to a picture P 365 which enables the user to select the free color mode in which the user can make the density of the standard color appointed on the picture P 365 coincide with the registered color appointed on the picture P 364. <Explanation of Color Creation Mode> Referring to Fig.18 , the color creation (create) mode M 400 is further devided into six types of mode: namely, a color mode M 410, color conversion mode 420, paint mode M 430, a sharpness mode M 440, a color balance mode M 450 and a free color mode M 460. The user can appoint one or more of these five modes. It is recalled that the area appointing mode M 330 described before also has the color mode M 331, color conversion mode M 332, paint mode M 333, the color balance mode M 334 and the free color mode M 335. The sole point of difference between these modes in the color creation mode M 400 and those of the area appointing mode M 300 resides in that, in the color creation mode M 400, the effects of these modes are applied to the whole area on the original, unlike the area pointing mode in which the effects are produced only on selected area. Other portions of these modes are the same as those of the corresponding modes in the area appointing mode M 300. The description therefore is omitted as to these five modes: namely, the color mode M 410, color conversion mode M 420, paint mode M 430 and the color balance mode M 450. The sharpness mode M 440 is mode for enabling the sharpness of the image to be adjusted. This can be conducted by, for example, effecting an edge stressing on the character images or by controlling the rate of smoothing effect on halftone image. The practical manner of setting of the color create mode will be explained hereinunder with reference to Fig. 37. When the color create mode key 425 on the digitizer 16 is pressed, the content of the liquid crustal display proceeds to a picture P 400. If the user presses the touch key b (color mode) on the picture P 400, the display proceeds to a picture P 410 which enables the user to select the color mode to be copied. When the monochrome color mode other than 3- and 4-full-color modes is selected, the content of the display is further changed to a picture P 411 which enables the user to select either one of negative and positive. When the user has pressed the touch key c (sharpness) on the picture P 430, the content of the display is changed to a picture P 430 which enable the use to adjust the sharpness of the copy image. If the user wishes to strengthen the sharpness, he presses the strengthening touch key i so that the amount of edge stressing is increased as explained before, so that minute lines such as those of characters are printed clearly. Conversely, when the user wishes to weaken the sharpness, he presses a weakening touch key h so that the smoothing is effected on the peripheral pixels so as to increase the smoothing effect, whereby defects such as moire inevitably produced when halftone image is copied can be suppressed. The operations in the color conversion mode M 420, paint mode M 430 and the color balance mode M 450 are not described because they are materially the same as those in the area appointing mode. The color copying apparatus of this embodiment is constructed to allow a manual feed of the copy paper besides the paper feed from the upper and lower paper cassettes. The manual paper feed appointing mode M 730 is a mode for allowing the user to feed a copy paper manually. When the user wishes to use the apparatus in so-called APS (Automatic Paper Select) mode, the user can appoint the size of the paper to be manually fed, by using this function. The described embodiment enables the user to convert various types of original such as mono-color and full-color images into a desired color having a desired gradation, whereby a copy of the desired color and the desired gradation can be output.

Claims: Image processing apparatus comprising: input means for inputting image data representing individual density levels of colour components of the pixels of an original image; area pointing means (CPU 22, 50, RAMS 136, 137) for generating area signals (AREA 0-AREAn) defining an area within said original image; hue appointment means for appointing a desired hue; and converting means (51) for converting image data within an area appointed by said area appointing means into converted image data representing the desired hue; characterised in that said converting means are arranged to convert the density levels of the colour components of each pixel of the original image within said appointed area so that the density ratios between pixels of different hues in the original image within said appointed area are preserved between corresponding pixels in the converted image so as to preserve the gradation of the original image. Apparatus according to claim 1, wherein said converting means comprise a random access memory (177) into which can be written a look-up table (LUT) which defines the gamma characteristics which enable the conversion from the input image data to the converted image data to be carried out with the preservation of gradation. Apparatus according to claim 2, wherein the random access memory is a part of a gamma conversion circuit (176, 177, 178) adapted to control the colour balance and the colour densities of an output image. Apparatus according to either of claims 2 and 3, wherein where the colour component data of the desired hue is Ys, Ms, Cs and the colour component ratio of the desired hue is Ys:Ms:Cs, the gamma characteristic functions GY(x), GM(x) and GC(x) for yellow, magenta and cyan are set in the random access memory as GY ( x ) = X . Y s MAX GM ( x ) = X . M s MAX GC ( x ) = X . C s MAX where MAX is not equal to zero and is the maximum value of Y s , M s , C s , and GY(x):GM(x):GC(x) = Ys:Ms:Cs. Apparatus according to claim 1, wherein said area appointing means and said hue appointing means include common operating means for appointing the area and the desired hue. Apparatus according to any preceding claim, wherein said input means is a flat-bed scanner. Apparatus according to claim 6, wherein said flat-bed scanner consists of plural line sensors. Apparatus according to claim 1, wherein said hue appointing means appoints the desired hue by appointing a desired portion on the original image. Apparatus according to claim 5, wherein said common operating means comprises a digitizer. Apparatus according to any preceding claim, further comprising image formation means for forming a visible image on a medium in accordance with the converted image data.

Inventors: HONMA TOSHIO, KADOWAKI TOSHIHIRO, KATO KOICHI, OHNISHI TETSUYA, SUZUKI YASUMICHI, HONMA, TOSHIO, KADOWAKI, TOSHIHIRO, KATO, KOICHI, OHNISHI, TETSUYA, SUZUKI, YASUMICHI
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1988
Main classification: H04N1
IPC codes: H04N1