Image processing device, color printing device, image processing method and medium recording image processing program

In order to prevent an operational amount of color conversion from increasing when resolution is changed since the operational amount of color conversion is increased when the conversion is performed such that resolution is enhanced in printing, resolution of color image data constituting pre conversion data is compared with resolution of color image data constituting post conversion data. As a result of comparison, when the resolution on the input side is lower, color conversion is previously performed and resolution is converted subsequently, when the resolution on the input side is higher, resolution is converted prior to color conversion. Thus where conversion of resolution and color conversion are executed, color conversion is performed on the side having a lower one of the resolutions whereby color conversion is performed in respect of fewer pixels and the processing can be optimized.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to an image processing device, a color
 printing device, an image processing method and a medium recording an
 image processing program accompanied by conversion of resolution and color
 conversion.
 2. Description of the Prior Art
 In printing a color image from an application in a computer system,
 conversion of resolution must be performed due to a difference in a
 resolution on a screen and a resolution in a printing device and data of
 RGB (red, green, blue) handled in a computer system is to be converted
 into data of CMY (cyan magenta, yellow) corresponding to ink colors of a
 printer.
 In this case, the conversion of resolution is not indispensable since there
 are cases where both resolutions coincide with each other or where
 coincidence of the resolutions does not pose a problem. Therefore, as a
 procedure of processings, color conversion is executed after having
 resolutions coincide with each other.
 According to the above-described conventional image processing device, when
 conversion is performed such that resolution is promoted, an original
 single pixel is converted into a plurality of pixels by which an
 operational amount of color conversion is increased since color conversion
 is carried out with respect to each pixel.
 SUMMARY OF THE INVENTION
 Therefore, it is an object of the present invention to provide an image
 processing device, a color printing device, an image processing method and
 a medium recording an image processing program capable of optimizing
 processings when conversion of resolution and color conversion are
 executed.
 According to an image processing device accompanied by conversion of
 resolution and color conversion of the present invention, color conversion
 is performed in a state of low resolution, more specifically, the device
 includes resolution comparing means for comparing a resolution of color
 image data constituting pre conversion data with a resolution of color
 image data constituting post conversion data, resolution converting means
 for converting the resolutions between the color image data constituting
 the pre conversion data and the color image data constituting the post
 conversion data, color converting means for performing a color conversion
 between a color representing space of the color image data constituting
 the pre conversion data and a color representing space of the color image
 data constituting the post conversion data, and conversion order
 controlling means for executing the color conversion before or after
 converting the resolution on a side having a lower one of the resolutions,
 based on a comparison result of the resolution comparing means.
 According to the present invention constituted as described-above, when the
 resolution converting means converts the resolutions between the color
 image data constituting the pre conversion data and the color image data
 constituting the post conversion data, the resolution comparing means
 compares the resolution of the color image data constituting the pre
 conversion data with the resolution of the color image data constituting
 the post conversion data and the color conversion is performed between the
 color representing space of the color image data constituting the pre
 conversion data and the color representing space of the color image data
 constituting the post conversion data on the side having a lower one of
 the resolutions before or after converting the resolutions under control
 of the conversion order controlling means. Needless to say, various
 methods can be substituted for the conversion order controlling means.
 The essence of the present invention resides in performing color conversion
 in a state of low resolution when conversion of resolution and color
 conversion are executed in which when the original resolution is low and a
 conversion of enhancing the resolution is performed, the color conversion
 is performed before converting the resolution and when the original
 resolution is high and a conversion of lowering the resolution is
 performed, the color conversion is performed after converting the
 resolution.
 Accordingly, the color conversion is performed in a state where pixels
 constituting the object of color conversion are few and accordingly the
 amount of processings can be reduced.
 The resolution comparing means compares the resolution of the color image
 data constituting the pre conversion data with the resolution of the color
 image data constituting the post conversion data, where the means is not
 necessarily limited to a means for automatically outputting the comparison
 result and may be a means capable of determining on which side the
 resolution is low or high as a result, accordingly, the means may be a
 changeover switch by manual operation.
 Various methods can be adopted with regard to methods of the resolution
 converting means for converting the resolutions between the color image
 data constituting the pre conversion data and the color image data
 constituting the post conversion data. Further, the resolution in this
 case corresponds to a number of pixels of rasterized dot matrix data in
 which before rasterizing as in meta file, in a state of a command file
 having no pixels, a number of objects to be subjected to color conversion
 corresponds to a number of commands designating color. Therefore, in this
 case, in a broad sense, the side having a lower one of the resolutions
 designates color image data where colors are designated by commands before
 rasterizing.
 The color converting means performs color conversion between the color
 representing space of the color image data constituting the pre conversion
 data and the color representing space of the color image data constituting
 the post conversion data and various kinds of converting methods can be
 adopted. Generally, a color conversion table having component values of
 image data in a pre conversion color representing space is prepared and
 the color conversion table is referred. Naturally, in referring to the
 color conversion table, the operation can pertinently be changed as in
 utilizing interpolation calculation, utilizing a grey scale conversion in
 place of an interpolation calculation disclosed in Japanese Unexamined
 Patent Publication No. JP-A-7-30772 filed by the applicants or the like.
 The conversion order controlling means may execute color conversion from
 the side having a lower one of the resolutions before or after converting
 the resolution degree as a result in which, for example, a procedure of
 converting the resolution after previously performing color conversion and
 a procedure of performing color conversion after previously converting the
 resolution may be prepared and either one of the procedures may be
 selected.
 Various kinds of devices may be conceived as application examples where
 conversion of resolution and color conversion are executed. Therefore, it
 is an object of the present invention to provide a color printing device
 that is one application example.
 According to an aspect of the present invention, there is provided a color
 printing device for printing a color image in accordance with a
 predetermined record density, in which raster data in accordance with the
 record density is formed from color image data constituting pre conversion
 data and color conversion is performed from a color representing space of
 the color image data constituting the pre conversion data to a color
 representing space of a print ink for printing with the record density,
 wherein a resolution of the color image data constituting the pre
 conversion data is compared with a resolution at the record density and
 the color conversion is performed before or after converting the
 resolutions, on a side having a lower one of the resolutions.
 According to the color printing device printing dots at the predetermined
 record density, the raster data in accordance with the record density is
 formed from the color image data constituting the pre conversion data and
 the color conversion is performed from the color representing space of the
 color image data constituting the pre conversion data to the color
 representing space of the print ink printing at the record density.
 According to the present invention constituted as described-above, the
 resolution of the color image data constituting the pre conversion data is
 compared with the resolution at the record density and the color
 conversion is performed before and after converting the resolutions, on
 the side having a lower one of the resolutions.
 Therefore, according to the present invention, the processing can be
 optimized in the color printing device for printing color image by
 printing dots at the predetermined record density.
 More specifically, the present invention can be realized by a constitution
 in which in a computer adopting an operating system, the operating system
 controls data in correspondence with a pixel size designated by the
 application and data in correspondence with a pixel size of a printing
 device, a printer driver compares resolution of color image data
 constituting pre conversion data with resolution of color image data
 constituting post conversion data based on the information and the color
 conversion is performed on the side having a lower one of the resolutions
 based on the comparison result.
 Further, the present invention is not limited to such an output stage but
 is applicable also to an input stage. For example, even in the case where
 an image processing application reads image data via a peripheral
 equipment, there is a case where color conversion of converting color tone
 of a input device to that in a standard system, and conversion of
 resolution in accordance with a size of an image file to be handled, are
 executed. At this stage, the color conversion may be executed on the side
 having a lower one of the resolutions. That is, when the application reads
 color image data constituting pre conversion data, the color conversion is
 performed in a state having a lower one of the resolutions in comparison
 with color image data held inside. Further, even in the case where the
 color image data is transmitted via a communication network and is
 displayed on a display, the similar operation is performed and the present
 invention is naturally applicable to a color facsimile, a color copier, a
 color scanner, a digital still camera, a digital video camera and the
 like.
 Naturally, examples of implementing the thought of the present invention
 are not limited to those described above but according to an aspect of the
 present invention, there is provided a method of image processing
 accompanied by conversion of resolution and color conversion, the method
 including, a step of comparing a resolution degree of color image data
 constituting pre conversion data with a resolution of color image data
 constituting post conversion data, a step of converting the resolutions
 between the color image data constituting the pre conversion data and the
 color image data constituting the post conversion data, a step of
 performing a color conversion between a color representing space of the
 color image data constituting the pre conversion data and a color
 representing space of the color image data constituting the post
 conversion data and a step of controlling a conversion order such that the
 color conversion is executed before or after converting the resolutions,
 on a side having a lower one of the resolutions, based on a comparison
 result of the resolutions.
 That is, the present invention is not necessarily limited to a substantial
 device but is effective also as a method thereof.
 In the meantime, when an example of implementing the thought of the
 invention is a software of an image processing control program, the
 present invention is naturally present and utilized also on a record
 medium recording such a software. Of course, the record medium may be a
 magnetic record medium or a photomagnetic record medium and any record
 medium to be developed in the future can be regarded quite similarly.
 Further, the same goes with unquestionably in respect of a copying stage
 of a firstly copied product, a secondly copied product and the like. In
 addition thereto, in respect of a software, the present invention is
 invariably utilized even in the case where the method of supplying the
 software is not provided by the above-described record media but is
 provided by utilizing a communication network. In that case, the side of
 providing software by utilizing a communication network functions as a
 device of providing the software and utilizes the present invention
 similarly and invariably.
 Further, the thought of the present invention remains unchanged even in the
 case where a portion is constituted by a software and other portion is
 realized by a hardware and the present invention may be of a mode where a
 portion thereof is stored in a record medium and is pertinently read as
 necessary.

DESCRIPTION OF THE PREFERRED EMBODIMENTS
 An explanation will be given of embodiments of the present invention in
 reference to the drawings as follows.
 FIG. 1 shows by a block diagram an example of a specific hardware
 constitution of a color conversion device according to one embodiment of
 the present invention.
 In FIG. 1, an image input device 10 outputs grey scale color representing
 data to an image processing device 20 by photographing a color image or
 the like, the image processing device 20 performs a predetermined image
 processing including conversion of resolution and color conversion in
 respect of the data and outputs the data to the image output device 30 and
 the image output device 30 displays an original color image.
 In this case, a scanner 11, a digital still camera 12, a video camera 14,
 or the like correspond to a specific example of the image input device 10;
 a computer 21, a hard disc 22 and a computer system comprising a key board
 23, a CD-ROM drive 24, a floppy disc 25, a modem 26 and the like
 correspond to a specific example of the image processing device 20, as can
 be seen in FIG. 2(a), and a printer 31, a display 32 or the like
 corresponds to a specific example of the image output device 30, also seen
 in FIG. 2(a). Incidentally, the modem 26 is connected to a public
 communication network, connected to an outside network via the public
 communication network and can introduce by downloading software or data
 from a file server 27. Accordingly, not only the floppy disc or the CD-ROM
 or the like constitutes a record medium but a communication network is
 naturally included in a record medium.
 When the scanner 11 as image input device 10 outputs grey scale data of,
 for example, RGB (red, green, blue) as grey scale color representing data
 and further, the printer 31 as the image output device 30 necessitates as
 an input data binary data of CMY (cyan, magenta, yellow) or CMYK added
 with black as grey scale color representing data, a specific role of the
 computer main body 21 as the image processing device 20 is to convert grey
 scale data of RGB into binary data of CMY. Further, referring to both FIG.
 1 and FIG. 2(a), when an image of a bit map system is drawn by using the
 key board 23, a mouse 13 or the like, the image is processed as grey scale
 data of RGB, in the case of the display 32, data is displayed by using it
 as it is and in the case of the printer 31, a processing of converting the
 data into binary data of CMY is similarly carried out. Incidentally, a
 similar operation is performed also in the case where an image of a draw
 system is drawn.
 FIG. 2(a) shows processings carried out inside of the computer main body
 21. As shown by FIG. 2(a), in the computer main body 21, an operating
 system 21a is operated and a printer driver 21b and a video driver 21c
 corresponding to the printer 31 and the display 32 are integrated.
 Meanwhile, execution of processings of an application 21d is controlled by
 the operating system 21a and the application 21d carries out a
 predetermined image processing in cooperation with the printer driver 21b
 and the video driver 21c as necessary.
 In the case of the scanner 11, read heads are formed at predetermined
 intervals and read resolution is determined in correspondence with the
 interval between the read heads. Meanwhile, in respect of the application
 21d, although it is generally, known to hold data by having the resolution
 of the data coincide with display resolution of the display 32, a
 processing where the resolution of the data is always made to coincide
 with the resolution of the display 32 may be performed while holding the
 data virtually.
 Print data formed by the application 21d is inputted to the printer driver
 21b via the operating system 21a and the printer driver 21b converts the
 print data into image data of a format requested by the printer 31. The
 conversion corresponds to the above-described processing of converting
 grey scale data of RGB into binary data of CMY. Further, the video driver
 21c writes display image data formed by the application 21d to a
 predetermined memory for screen and displays at the display 32 via a
 hardware circuit.
 The image data formed by the printer driver 21b is a dot matrix data
 comprising binary data of CMY and the data is transmitted to the printer
 31. FIG. 3 shows the outline constitution of the printer 31 and the
 printer 31 includes as major constituent parts, print heads 31a formed
 with ink inject holes of respective colors in the vertical direction, a
 print head drive unit 31b for driving to inject color printing ink from
 predetermined ones of the ink inject holes in the print heads 31a, a print
 head digit moving motor 31c for reciprocating the print heads 31a in the
 digit direction, a paper feed motor 31d, print buffers in addition thereto
 and the like and is provided with a printer controller 31e performing a
 general control. That is, the dot matrix data correspond to an arrangement
 of the ink inject holes in the print heads 31a as well as correspond to
 the scanning range of the print heads 31a in the digit moving direction
 and when the print heads 31a is moved in the digit direction by the print
 head digit moving motor 31c, the print head drive unit 31b has the color
 printer ink injected from the predetermined ones of the ink inject holes
 in correspondence with the dot matrix data by which printing is performed.
 In this case, the ink inject holes of print heads 31a do not constitute
 immediately a pixel size but a distance between centers of actually
 printed dots is calculated as a pixel size in view of a control operation
 by the paper feed motor 31d and the print head digit moving motor 31c
 while using such ink inject holes.
 Although according to the embodiment, as an application example of the
 color conversion device, the above-described printing system combined with
 the computer and the printer is pointed out, a system performing
 conversion of resolution and color conversion in respect of input data is
 sufficiently applicable. For example, as shown by FIG. 4, the system may
 be a printer system 33 including a printer 33a connected via a modem 33c
 to a communication network 33b such as a telephone network or the like for
 printing image data by receiving it or the like. Alternatively, the system
 may be a television system 34 including television 34b capable of
 receiving general image broadcast by being connected to a communications
 network 34a, which prints a color image supplied from the network as shown
 by FIG. 5. Further, the system is applicable to various ranges of devices
 such as a color copier or a color facsimile.
 Next, an explanation will be given of the print processing that is
 performed from the computer 21 to the printer 31. FIG. 6 and FIG. 7 show a
 procedure in the case where the application 21d performs printing. The
 application 21d executes the print processing while mutually cooperating
 with the operating system 21a and the printer driver 21b. That is, when
 the application 21d requests printing to the operating system 21a at step
 S110, the operating system 21a starts the printer driver 21b at step S120
 and the application 21d and the printer driver 21b cooperate to execute
 setting of a form or the like at step S130. Thereafter, the application
 21d outputs print data to the operating system 21a in a predetermined
 format in correspondence with the form at step S140 and accordingly, the
 printer driver 21b forms the data by receiving the output of the print
 data and outputs it at step S150.
 The flow chart of FIG. 8 shows the processing in which the printer driver
 21b receives the print data from the operating system 21a and performs
 printing at step S150.
 Now, referring to FIG. 2(a), the printer driver 21b is constituted by a
 rasterizer 21b1 where the application 21d cuts out a scanning range of the
 print heads 31a in the printer 31 from image data formed by a
 predetermined screen unit, a color conversion unit 21b2 for converting
 grey scale data of RGB into grey scale data of CMY in reference to a color
 conversion table with respect to each pixel of the dot matrix data, a grey
 scale converting unit 21b3 for converting the grey scale data of CMY into
 binary data and a resolution comparing unit 21b4 for inquiring a pixel
 size designated by the application 21d in accordance with a function in
 respect of the operating system 21a and comparing the pixel size with a
 pixel size of the printer 31. Incidentally, the printer driver 21b is
 constituted by software and respective constituent elements are also
 constituted by software. Further, these elements scan the print heads 31a
 in respect of the printer 31 in accordance with a procedure shown by FIG.
 8 and outputs print data of printable dot matrix data.
 That is, at step S210, the operation inquires a pixel size designated by
 the application 21d to the operating system 21a, compares it with a pixel
 size of the printer 31 and determines which resolution is larger. For
 example, a general resolution of the display 32 is a resolution of 72 dpi.
 There are cases where the application 21d handles data in accordance with
 the resolution of the display 32. There are cases where when the
 resolution of the scanner 11 is 300 dpi, data is handled internally in
 accordance with 300 dpi and a display is performed on the display 32 in a
 state in which the resolution is converted into 72 dpi. The application
 21d outputs print data by designating a pixel size regardless of the
 resolution of the display 32 and accordingly, the printer driver 21b
 inquires the pixel size.
 When the pixel size designated by the application 21d is known, the pixel
 size is compared with a pixel size of the printer 31. Although depending
 on designation of print mode, when the resolution of the printer 31 is 600
 dpi, the resolution on the side of the application 21d, that is, the
 resolution of color image data constituting pre conversion data is lower.
 When the resolution of color image data constituting pre conversion data
 is lower than the resolution of color image data constituting post
 conversion data, in order to match the resolutions for printing, as shown
 by FIG. 9, an original 1 dot pixel is converted into 4 dots. Accordingly,
 when color conversion is performed before converting the resolution, one
 operation of color conversion is needed and when color conversion is
 carried out after converting the resolution, four operations of color
 conversion are needed.
 Therefore, in order to reduce an amount of calculation, when the resolution
 of color image data constituting pre conversion data is lower than the
 resolution of color image data constituting post conversion data at step
 S210, the processing of color conversion is previously executed at step
 S220. That is, the determination per se at step S210 constitutes
 resolution comparing means and a branched processing in accordance with
 the result of determination constitutes conversion order controlling
 means.
 FIG. 10 indicates three-dimensional color representing space having
 component values of RGB gray scale data formed by the application 21d as
 coordinates where grey scale data of CMY in correspondence with a color
 conversion table are recorded in correspondence with lattice points
 present at predetermined intervals. That is, the color conversion table is
 a three-dimensional table of (R, G, B) arranged to be able to read
 univocally respective data of CMY with grey scale data of RGB as component
 values. However, the file per se is provided with a four-dimensional file
 structure that is referred to by four of arrangement variables such that
 three data of (C, M, Y) can be taken out for one set of (R, G, B) .
 Incidentally, such a color conversion table is recorded on the hard disc
 22.
 FIG. 11 shows the principle of calculation in respect of eight point
 interpolation calculation. When a cubic body comprising 8 points of
 lattice points surrounding coordinates P having RGB grey scale data as
 component values, is assumed in a pre conversion color representing space,
 when a converted value at a k-th apex of the cubic body is designated by
 notation Dk and the volume of the cubic body is designated by V, a
 converted value Px at an inner point P of the cubic body can be
 interpolated by the following equation by weighting in accordance with
 ratios of volumes Vk of illustrated eight small rectangular
 parallelepipeds divided by P point.
 ##EQU1##
 Accordingly, 8 of the lattice points surrounding the coordinates are
 specified and calculation is executed for each of grey scale data of CMY
 at each lattice point. Further, step S220 constitutes the color converting
 unit 21b2.
 After performing the color conversion, at step S230, the resolution is
 converted into the resolution of the printer 31. The concept of the
 converting operation is shown by FIG. 12 where calculation is performed
 with respect to which pixel in an image range in correspondence with the
 pre conversion resolution (range designated by solid lines of figure) an
 image range in correspondence with the post conversion resolution (range
 designated by broken lines of figure) corresponds to. When one pixel after
 conversion is within one pixel of resolution before conversion, the same
 color is succeeded as it is and when one pixel after conversion ranges
 over two pixels of the resolutions before conversion, the respective color
 components are succeeded in proportion to area ratios of the ranged two
 pixels. The same is applicable in the case where one pixel after
 conversion ranges over four pixels of resolutions before conversion. Such
 a conversion processing of a resolution to the printer resolution is not
 naturally limited to this example and can be changed pertinently.
 Incidentally, step S230 constitutes resolution converting means.
 By contrast, assume a case where the pixel size designated by the
 application 21d is smaller than the pixel size of the printer 31. Although
 depending on designation of printing mode, the operation corresponds to
 the case where the resolution of the scanner 11 is 600 dpi and the
 application 21d handles data in accordance with the resolution and the
 resolution of the printer 31 is 300 dpi. When the resolution of the pre
 conversion color image data is higher than the resolution of the post
 conversion color image data in this way, if the resolutions are intended
 to match for printing, as shown by FIG. 13, original 4 dots of pixels are
 converted into 1 dot of pixel. Accordingly, when the color conversion is
 performed before converting the resolution, 4 times of color conversion is
 needed and when color conversion is performed after converting resolution,
 one time of color conversion is needed.
 Accordingly, at step S240, the resolution is converted into the resolution
 of the printer before color conversion and color conversion is performed
 at a successive step S250.
 Incidentally, although according to the example, data which the application
 21d outputs via the operating system 21a, is a dot matrix data, it may be
 something like meta file. Meta file is a command file describing
 information of figure such as whether a figure is square or circular and
 in respect of the command file, the rasterizer 21b1 in the printer driver
 21b carries out also a processing of forming a dot matrix data in
 accordance with the resolution of the print heads 31a. The side having a
 lower resolution may be regarded as a side having smaller information
 source to be converted by color conversion and accordingly, even with the
 side having a low resolution of a meta file, when color conversion is
 executed before converting the resolution of the printer, color conversion
 for each pixel is not needed. Further, according to the case of a meta
 file, colors are designated by a figure drawing command and accordingly,
 only color designating portions in the figure drawing command are changed.
 When conversion to the printer resolution and color conversion have been
 finished by a predetermined procedure as described above, at step S260, a
 binarizing operation referred to as half tone is carried out in order to
 form data which the printer 31 can print at step S270. Although an
 explanation has not be given of a specific method of grey scale conversion
 represented by the binarizing operation, a well-known method such as error
 diffusion method, dithering utilization or the like may be applied which
 is, for example, explained also in Japanese Examined Patent Publication
 No. JP-B-7-30772 filed by the applicants. Thereafter, when the print data
 is outputted to a print buffer of the printer 31 at step S270, printing
 can be performed at a high speed since the color conversion has been
 performed by fewer calculation processings.
 In this way, the resolution of color image data constituting pre conversion
 data is compared with resolution of color image data constituting post
 conversion data at step S210, as a result of comparison, when the
 resolution on the input side is lower, the color conversion is previously
 performed at step S220 and the resolution is converted at step S230. When
 the resolution on the input side is higher, the resolution is converted at
 step S240 and thereafter, color conversion is performed at step S250.
 Thus, the color conversion is carried out on the side where the resolution
 is low when both of the conversion of resolution and the color conversion
 are conducted whereby color conversion is performed with respect to fewer
 pixels and the processing can be optimized.