Color calibration alarm for use in an image-rendering device

Abstract: This invention relates to a color calibration alarm apparatus and method for use in an image-rendering device. The alarm apparatus, and associated method, make use of a sensor device that compares printed or measured color values with expected or ideal color values. If the measured values differ sufficiently from the ideal color values, the alarm apparatus signals to the user that a calibration should be performed. The printed or measured color values are obtained from a test patch that is printed, preferably, on a break page between print jobs. The alarm device is placed at the output tray of an image rendering device in one embodiment that may also be a separate stand alone hand-held unit in other embodiments where it is manually used.

Description: BACKGROUND OF THE INVENTION This invention relates to a color calibration alarm apparatus and method for use in an image-rendering device. The alarm apparatus, and associated method, make use of a sensor device, a comparing device and a latching device to facilitate comparison of printed or measured color values with expected or ideal color values at an appropriate time. If the measured color values differ sufficiently from the ideal color values, the alarm apparatus signals to the user that a calibration should be performed. The printed or measured color values are obtained from a test patch that is printed, preferably, on a break page between print jobs. The alarm device is placed at the output tray of an image-rendering device but may also be implemented as a separate stand-alone hand-held unit. While the invention is particularly directed to the art of color calibration alarms for use in image rendering devices, and will be thus described with specific reference thereto, it will be appreciated that the invention may have usefulness in other fields and applications. For example, the invention may be used in any image-rendering device where calibration of the system to achieve a desired output is required. By way of background, many color calibration systems are known. Some of these known systems are simple and elegant while others are more involved and require special color measuring equipment A common feature of these known techniques, however, is that such techniques typically require the user or other individual to decide the time at which the calibration should be carried out. The problem with this approach is that, if a user waits until the color prints are perceptively and obviously of insufficient quality, then there may well have been a number of other previous prints made of sub-optimal quality. On the other hand, if calibrations are conducted on a regular schedule, many of the calibrations may be unnecessary -- thus wasting valuable resources. It would therefore be desirable to have a reliable system for indicating a proper time in which to conduct a calibration. In this regard, it would be advantageous to have a color calibration alarm that only reports to the user that a color calibration is necessary as opposed to a system that also reports the color detected and/or conducts the calibration In this way, such a system could be adapted for use in a variety of different printing environments. US 5,877,787 describes an apparatus for recalibrating a multicolor imaging system. Input color values control amounts of colorants to be applied to a substrate by an imaging system. A subset of input color values is selected such that one or more different color patches is formed by application of a combination of at least two different colorants on the substrate. Color values are measured for each of the different color patches and compared to the reference color values representing a calibrated condition of the imaging system. An error value is calculated A latching device for selectively latching an output of a comparing device is not disclosed. US 4,888,636 describes an image reproducing system. A reading device can read test charts as well as an original image and generates image signals representing the one of the test chart and original image thus read. A correcting circuit corrects the image signals and an image forming apparatus forms an image on the basis of the corrected image signal. A discriminator discriminates a reproduction condition on the basis of the image of the test chart when formed by the image forming apparatus and thus produces a discrimination signal. The correction characteristic, used by the correcting circuit, is selected in accordance with the discrimination signal. A latching device for selectively latching an output of a comparing device is not disclosed. The present invention contemplates a new and improved color calibration alarm for use with image rendering devices that resolves the above-referenced difficulties and others. SUMMARY OF THE INVENTION It is the object of the present invention to improve color calibration with regard to the aspect of providing a simple and reliable system for indicating to the user that it is useful and/or necessary to conduct a color calibration to maintain a sufficient color quality of the printed output. This object is achieved by providing a color calibration alarm apparatus according to claim 1 and a method for rendering color images according to claim 7. Embodiments of the invention are set forth in the dependent claims. Further scope of the applicability of the present invention will become apparent from the detailed description provided below. DESCRIPTION OF THE DRAWINGS The present invention exists in the construction, arrangement, and combination of the various parts of the device, and steps of the method, whereby the objects contemplated are attained as hereinafter more fully set forth, specifically pointed out in the claims, and illustrated in the accompanying drawings in which. Figure 1 is a block diagram of an image-rendering system incorporating the present invention; Figure 2 is an illustration of a more specific embodiment of an image-rendering device incorporating the present invention; Figure 3 is a block diagram of a calibration alarm according to the present invention; Figure 4 is a block diagram illustrating another feature of the present invention; Figures 5(a) and (b) are block diagrams illustrating still other features of the present invention; Figure 6 is a flow chart illustrating a method according to the present invention; and, Figure 7 is an example of a printed page including a test image according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings wherein the showings are for purposes of illustrating the preferred embodiments of the invention only and not for purposes of limiting same, Figure 1 provides a view of an exemplary image-rendering system incorporating the present invention. As shown, such an exemplary system incorporating the present invention includes a scanner 10, an image processing unit (IPU) 12, a user interface 14 and a print engine 18. The IPU 12 has incorporated therein suitable print control structure Also included in the system are a color calibration alarm device 100 and a display device 102. It should be recognized that, in a copier or reproduction apparatus as shown, a document is input by scanning pages of the document by the scanner 10 and providing the scanned image(s) of the document to the image processing unit 12. The image processing unit 12 prepares the images of the input document for printing and provides appropriate data to the print engine 18. The print engine 18 then prints an output document. The color calibration alarm device subsequently makes use of sensors and compares printed or measured color values with expected or ideal color values If the measured values differ sufficiently from the ideal color values, the alarm device 100 signals to the user through the display device 102, or through the user interface 14, that a calibration should be performed. More particularly, the color calibration alarm device detects the colors of a test image such as a test color patch and compares those measured colors with the stored expected or ideal colors. The test color patch is preferably of a light gray color and suitably positioned on the page for detection The test color patch could take any of a variety of configurations but preferably is of a form to facilitate convenient detection by the alarm device, such as the form of a rectangle. In addition, the test patch is also suitably located on the page to facilitate such convenient detection In this regard, the test patch is preferably printed in the same location on every page upon which it is printed. As will be appreciated, the alarm device only needs to be fully operative at specified times (i e when the test color patch is printed). As such, a measure signal is generated in the system to indicate to the alarm that the information detected and compared should be latched and displayed to the user to indicate whether a calibration is needed The measure signal, as described below, could be provided based on different criteria that are embedded in the control structure of the system including upon the detection of a printed test pattern as a part of the test image that precedes the actual test patch to be analyzed. The printed test pattern contemplated could take a variety of forms but preferably takes the form of a recognizable bar code or sequence of colors in a convenient arrangement Referring now to Figure 7, an exemplary printed page according to the present invention including a test image is shown More particularly, the page 700 has a test image 702 printed thereon The test image takes the form of a bar code test pattern 704 followed by a test color patch 706. It is to be appreciated that the illustrated test pattern is merely representative and the test color patch 706 would preferably be printed in gray (although not shown in gray). In addition, a variety of other color patches 706', 706", etc. could be printed for purposes of detection and analysis to replace and/or supplement the gray test color patch. The measure signal could also be provided upon the printing of a test color patch on break pages between print jobs, without the use of a test pattern. Further, the measure signal could be manually input to the system by the user. As shown in Figure 1, the color calibration alarm device is incorporated into an image rendering system However, it should be appreciated that the device may also be implemented in the form of a hand-held or stand-alone device In this case, it will be recognized by those skilled in the art that modifications to the alarm would be advantageously incorporated into such a device, as compared to an alarm that is incorporated within an image-rendering system. For example, as will be described in more detail below, the calibration alarm device makes use of ideal color values that are captured after calibration of the image-rendering device. Where the alarm is incorporated into an image rendering device, the data is simply stored within the system for convenient access by the alarm device However, if a hand-held or stand alone device is implemented, the ideal color value information would need to be communicated to the hand-held or stand alone device in some other manner, such as by measuring a color patch that has been identified by the user as the calibration standard. The system shown in Figure 1 is that of a copier or image reproduction system that uses a scanner However, it is to be appreciated that the invention may also find usefulness in connection with printers. In those cases, a scanner would not be necessary as the image would be provided directly to the image processing unit. Moreover, the invention is preferably implemented in a xerographic printing environment wherein a xerographic print engine is utilized to render images in copying and/or printing applications. Still further, it is to be appreciated that the invention will find application in both digital and analog printing and/or reproduction/copying environments In this regard, the environment described in connection with Figure 2 is a digital reproduction environment utilizing an exemplary xerographic print engine; however, application of the invention is not so limited. In a more detailed example, a schematic elevational view showing an exemplary electrophotographic printing machine incorporating the features of the present invention therein is shown in Figure 2 As alluded to above, it will become evident from the following discussion that the present invention is equally well-suited for use in a wide variety of printing systems including ionographic printing machines, ink jet printers, and discharge area development systems, as well as other more general non-printing systems providing multiple or variable outputs such that the invention is not necessarily limited in its application to the particular system shown herein In addition, as shown, a color calibration alarm device 100 is shown to be positioned near the output of the image-rendering device In this exemplary embodiment, the alarm device 100 is connected to the image processing unit 12, the user interface 14 and the display 102 More particularly, with reference to Figure 3, the color calibration alarm device 100 includes a sensor device 302, a memory device 304, a comparing device 306, a latching device 308, and a display device 102. As implemented, the sensor device 302 preferably comprises a plurality of sensors These include a red sensor 302-1, a green sensor 302-2, and a blue sensor 302-3. As to the sensors themselves, any suitable form of sensor that accomplishes the objectives of the present invention could be used. More particularly, a simple sensor configuration that has the capability to sense three color component measurements will suffice. The sensors could include light emitting diodes (LEDs) and associated photocells that cooperate to detect light reflected from the test color patches used to implement the invention, as is well known in the art. Suitable and appropriately positioned filters may also be advantageously used to distinguish the various colors of light. Likewise, the memory device comprises a plurality of set point memories. Included in the plurality are a red set point memory 304-1, a green set point memory 304-2, and a blue set point memory 304-3. These memories may take a variety of forms but preferably store sufficient color information so that a suitable comparison between the stored color and the measured color as detected by the sensors may be accomplished. The contents of each of the set point memories include digital representations of a single color value or a range of color values, the capturing of which will be described in greater detail in connection with Figure 5 below. In the preferred form, the output of each sensor is connected to an analog to digital converter 305 and then fed to a digital comparator. The comparator 306-1 is connected to the converted output of the red sensor as well as the red set point memory. The comparator 306-2 is connected to the converted output of green sensor 302-2 as well as green set point memory 304-2. Last, the comparator 306-3 is connected to the converted output of blue sensor 302-3, as well as the output of blue set point memory 304-3. The comparators and any associated hardware and software may take any suitable form to accomplish the objectives of the invention With respect to comparisons that are accomplished within the system, it should be recognized that the ideal, or set-point, values stored in the memories are preferably stored in digital format Therefore, a range or plurality of acceptable ideal color values may be stored and suitably compared to the measured color value. In the case of storing of a range of color values as opposed to simply storing a plurality of color values, comparisons may be accomplished by determining if the measured color value falls between a stored upper limit and stored lower limit (e.g determining if the measured value is less than the upper limit and if the measured value is greater than the lower limit). As an alternative, the desired range can be realized by storing a single captured color value and specifying the acceptable limits on the desired range relative to that value, e.g., plus (+) or minus (-) 3 If either type of range storage is used, the comparator preferably includes or has associated therewith suitable mechanisms and/or modules to conduct any necessary arithmetic computations As an alternative to storing a range or a plurality of values, a single ideal color value can be stored and comparisons can be accomplished by only using the most significant bits of the ideal single color value and the measured single color value being compared. The impact of comparing the most significant bits is that an effective range of colors, although somewhat limited due to the nature of truncation, is compared without storing such a range and without implementing an iterative process. In the preferred embodiment, the digital outputs of each of the digital comparators are supplied to an OR gate 306-4 Such digital outputs, notwithstanding the manner in which the comparisons are accomplished, preferably indicate whether or not the measured value is sufficiently close to the ideal color value or values stored in the set-point memories. It should be appreciated also that an alternative form of the invention includes use of an analog comparator, thus necessitating the removal of the analog to digital converters 305 and the addition of digital to analog converters at the output of the memories 304-1, 304-2, and 304-3. In the analog case, the sensors feed analog outputs directly to an analog comparator. The digital representation of the color values stored in the set-point memories is then converted to an analog form by the digital to analog converters and also provided to the analog comparator. The output of the comparator is, consequently, a difference between two analog signals If the difference is within an acceptable range, then no signal is provided for calibration. If, however, the difference is outside of an acceptable range, then calibration would be required Threshold devices are preferably employed to accomplish these determinations. In either the digital or analog environments, the output of the OR gate 306-4 is provided to the latch 308 which is connected to the display device 102. Alternatively, the output of the latch could be supplied to the UI for display to the user The latch 308 is also provided with a measure signal and a clear signal. In this regard, the latch is operative to latch the information provided from the OR gate when the measure signal is present The measure signal is provided to the latch in ways that are more particularly described below Of course, the clear signal is preferably manually provided by the user at such time as the information in the latch is no longer useful for operation of the device Referring now to Figure 4, a preferred manner in which to provide a measure signal to the latch 308 is shown. A pattern detection logic module 402 is provided with converted outputs of various sensors so that the measure signal is only provided upon detection of a particular pattern, either bar code or color pattern More specifically, a red sensor 404, a green sensor 406, and a blue sensor 408 all have outputs that are connected to analog to digital converters 410. The converted outputs are then provided to the pattern detection logic module 402. The pattern detection logic module generates a measure signal to be provided to the latch shown in Figure 3 if the outputs of the sensors indicate that a predetermined pattern is detected It should be recognized that the sensors 404, 406 and 408 may be of the same or different form as the sensors illustrated in Figure 3. In some embodiments, it may be advantageous to utilize the same set of sensors for both the purposes of Figure 3 and Figure 4 to reduce hardware requirements for the system. Referring now to Figure 5(a), a preferred configuration for capturing ideal color values in each set point memory is shown. The capturing of ideal color values, or set points, can be accomplished by detecting sensor values for a test color patch just after calibration is carried out. To accomplish this, as shown, a sensor 500 detects a color in analog form that is then provided to an analog to digital converter 502 The digital output of the converter is then preferably provided to a range generator module 503, which then provides the range information generated therein to the set point memory 504 (which could be any of the set-point memories illustrated in Figure 3) for storage. For example, the range generator module 503 adds a predetermined incremental value to the captured color value to obtain an upper limit on the desired range and subtracts a predetermined incremental value from the captured color value to obtain the lower limit on the desired range. The upper and lower limits are then provided to the set point memory As referenced below, the comparisons can then be accomplished using this information. To accommodate the above referenced option of storing all values of a range, a more rudimentary process involves the actual calculation of all such values in the desired range by the range generator module 503, which values are then provided to the set point memory. As an alternative to the range generator module 503, as shown in Figure 5(b), the captured value could simply be directly stored in the set point memory 504 and the incremental values could be stored either separately in a register module 504' within the set point memory or elsewhere in the system. With this stored information, the comparator, or its associated arithmetic modules/mechanisms, calculates the range of acceptable color values each time a comparison process is conducted Of course, if only a single captured color value is stored, there is no need to generate range information. In this case, the embodiment illustrated in Figure 5(b), modified to exclude the incremental value storage register, could be implemented. As such, the captured color value is stored directly in the set point memory Of course, this technique of capturing color is used only when a capture signal is generated and provided to the set point memory The capture signal is preferably provided by the image processing unit at the instruction of the user. It should also be recognized that the sensor 500 may be of the same or different form as the sensors illustrated in Figures 3 and 4. In some embodiments, it may be advantageous to utilize the same set of sensors for the purposes of Figures 3, 4 and 5 to reduce hardware requirements for the system. Referring now to Figure 6, an exemplary method according to the present invention is shown. Initially, the image rendering device is calibrated (step 602) Then, ideal color values, or set points, are captured (and stored as values or ranges) by the device for each of the red, green and blue memories as shown and described in connection with Figures 5(a) and (b) (step 604). Once these steps are accomplished, the system is now ready for rendering images. In this regard, at an appropriate time, a rendering process is initiated (step 606) For each page printed, it is determined whether a test pattern and color patch should be printed on the page (step 608). This determination is based on the control parameters that are set in the system. For example, a test pattern and at least one color patch may be printed on the break page of each print job. In that case, the determination in step 608 would depend on whether a break page was being printed or not. If a test pattern and color patch(es) are to be printed on the page, the test pattern and color patch(es) are retrieved from an appropriate storage location within the system (step 610) for the printing process Whether or not the test pattern or color patch(es) are to be printed, the page is printed (step 612) The page then passes by the color calibration alarm and a determination is made as to whether a test pattern was detected by the alarm device (step 614) If so, a measure signal is generated (step 616). Whether or not a test pattern is detected, the sensors also detect the colors on the page that are passing by the sensors (step 618) At this point, a comparison between the measured color values and the ideal color values that were captured in step 604 is made (step 620). A determination is then made as to whether a measure signal is present (step 622). If not, the process is ended (step 624). If, however, the measure signal is present, the result of the comparison of the test color patch(es) and the ideal color values in step 620 is latched (step 626). Then, the contents of the latch are displayed (step 628). The user consequently has an indication from the system as to whether calibration needs to be conducted In this regard, if the measured color values detected by the color calibration alarm are not sufficiently close to the ideal color values, then calibration is required. This is indicated to the user through the user interface or simply by the lighting of an LED on the image-rendering device. If, however, the measured color values are within an acceptable range of the ideal color values, then no calibration is needed This, too, can be indicated to the user via the user interface or by simply not lighting the LED. It should be recognized that the method described in connection with Figure 6 will vary slightly depending upon the precise configuration and operation of the system into which the present invention is implemented. For example, for a copier device, the test pattern and color test patch could be generated by copying an image containing the test pattern and ideal color test patch. Or, if no test pattern is printed, then the steps involving generation and detection of the test pattern are not required. In addition, those skilled in the art will appreciate that the method could be impacted if the color calibration alarm device 100 is implemented in a hand-held or stand alone type unit. It will also be understood by those of skill in the art that the invention described herein may be implemented using suitable hardware and software techniques. However, such hardware and software techniques may vary depending on the environment of use and implementation requirements for a given system

Claims: A color calibration alarm apparatus for indicating a proper time to conduct calibration useful in an image rendering device, the apparatus comprising: a sensor device (302) operative to detect color of a test image (702) to obtain at least one measured color value; a memory device (304) having stored therein at least one ideal color value; a comparing device (306) operative to compare the at least one measured color value to the at least one ideal color value; a latching device (308) operative to selectively latch an output of the comparing device; a pattern detection device for generating a measure signal when a predetermined pattern is detected whereby the latching device (308) is responsive to said measure signal so as to selectively latch the output of the comparing device only when the measure signal is present; and a display device (102) operative to display the latched output thereby reporting to a user of the image rendering device that a color calibration is necessary. The apparatus as set forth in claim 1 wherein the sensor device (302) comprises a plurality of sensors (302-1, 302-2, 302-3), each corresponding to a separate color. The apparatus as set forth in claim 1, wherein the memory device (304) comprises a plurality of set point memory modules (304-1, 304-2, 304-3), each module having stored therein one of a separate ideal color value and a range of the separate ideal color values. The apparatus as set forth in claim 1 wherein the comparing device (306) comprises a plurality of comparators (306-1, 306-2, 306-3), outputs of which are input to a combining logic (306-4). The apparatus as set forth in claim 4, wherein the combining logic (306-4) is an OR gate. The apparatus as set forth in claim 1 wherein the pattern detection device is a logic module (402) having sensors (404, 406, 408) connected thereto which are operative to detect the predetermined pattern. A method for providing a color calibration alarm indicating a proper time to conduct calibration for use in an image rendering device for rendering color images, the method comprising the steps of: capturing an ideal color; selectively rendering a test image; detecting a predetermined pattern; generating a measure signal when the predetermined pattern is detected; detecting colors of at least one test color patch (706) in the test image (702) to obtain measured color values; comparing the measured color values to the ideal color to obtain comparison results; combining the comparison results into an overall measurement; latching the overall measurement only if the measure signal is present; and, displaying the latched result thereby reporting to a user of the image rendering device that a color calibration is necessary.

Inventors: HARRINGTON STEVEN J, HARRINGTON, STEVEN J.
Applicants: XEROX CORP, XEROX CORPORATION
Application year: 2001
Main classification: H04N1
IPC codes: H04N1, B41J5, G06T1, B41J29