Ink model generation mechanism

<u>FIELD OF THE INVENTION</u>

0001The invention relates to the field of printing systems, and in particular, to performing ink usage estimation for a printing system.

<u>BACKGROUND</u>

0002Some print systems estimate ink usage assuming a constant volume for ink drops ejected from the printhead. However, ink volumes ejected by the printhead tend to vary over time and during printing due to changes in the print environment or conditions of the ink or printhead. Accordingly, ink estimates that assume constant ejection amounts are inaccurate. Determining accurate ink model parameter estimates and computing actual ink drop sizes for a printer are complicated processes that may take large amounts of time to perform.

0003Performing those determinations typically requires printing a range of print jobs while measuring ink volumes and ink drop counts for each print job. Further, these determinations apply only to the specific print mediums, print settings and printers that are to be evaluated. Because these processes are arduous, efficient mechanisms to determine accurate ink model parameter estimates and computing ink drop sizes are desired.

<u>SUMMARY</u>

0004In one embodiment, a printing system is disclosed. The printing system includes at least one physical memory device to store drop size logic and one or more processors coupled with at least one physical memory device to execute the drop size logic to generate drop size data associated with a printing system based on ink deposition data for a print medium and ink drop count data.

<u>BRIEF DESCRIPTION OF THE DRAWINGS</u>

0005A better understanding of the present invention can be obtained from the following detailed description in conjunction with the following drawings, in which: <ul id="ul0001" list-style="none" compact="compact"><li><figref idref="f0001"><b>Figure 1</b></figref> is a block diagram of one embodiment of a printing system;</li><li><figref idref="f0002"><b>Figures 2A</b></figref><b>&amp;2B</b> illustrate block diagrams of embodiments of a print controller;</li><li><figref idref="f0004"><b>Figure 2C</b></figref> illustrates another embodiment of an ink model logic and drop size logic implemented in a network;</li><li><figref idref="f0005"><b>Figure 3</b></figref> illustrates one embodiment of ink model logic;</li><li><figref idref="f0006"><b>Figure 4</b></figref> is a flow diagram illustrating one embodiment of an ink model computation process;</li><li><figref idref="f0007"><b>Figure 5</b></figref> illustrates one embodiment of drop size logic;</li><li><figref idref="f0008"><b>Figure 6</b></figref> illustrates one embodiment of a graph of uncalibrated drop fractions as a function of gray level;</li><li><figref idref="f0009"><b>Figure 7</b></figref> is a flow diagram illustrating one embodiment of a drop size computation process; and</li><li><figref idref="f0010"><b>Figure 8</b></figref> illustrates one embodiment of a computer system.</li></ul>

<u>DETAILED DESCRIPTION</u>

0006A mechanism for determining ink model parameter estimates and using the estimates to compute drop sizes is described. In the following description, for the purposes of explanation, numerous specific details are set forth to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without some of these specific details. In other instances, well-known structures and devices are shown in block diagram form to avoid obscuring the underlying principles of the present invention.

0007Reference in the specification to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of the phrase "in one embodiment" in various places in the specification are not necessarily all referring to the same embodiment.

0008<figref idref="f0001"><b>Figure 1</b></figref> is a block diagram illustrating one embodiment of a printing system 130. A host system 110 is in communication with the printing system 130 to print a sheet image 120 onto a print medium 180 via a printer 160 (e.g., print engine). Print medium 180 may include paper, card stock, paper board, corrugated fiberboard, film, plastic, synthetic, textile, glass, composite or any other tangible medium suitable for printing. The format of print medium 180 may be continuous form or cut sheet or any other format suitable for printing. Printer 160 may be an ink jet, electrophotographic or another suitable printer type having a well-defined association with the amount of marking material deposited in each individual printer picture element (pel).

0009In one embodiment, printer 160 comprises one or more print heads 162, each including one or more pel forming elements 165 that directly or indirectly (e.g., by transfer of marking material through an intermediary) forms the representation of picture elements (pels) on the print medium 180 with marking material (e.g., ink, paint, toner, polymers and other materials suitable for printing) applied (e.g., deposited) to the print medium. In an ink jet printer, the pel forming element 165 is a tangible device (e.g., an ink jet nozzle) that ejects the ink drop 170 (e.g., marking material elements) onto the print medium 180 and, in an electro-photographic (EP) printer the pel forming element may be a tangible device that determines the location of toner particles printed on the print medium (e.g., an EP exposure LED or an EP exposure laser).

0010The pel forming elements may be grouped onto one or more printheads. The pel forming elements 165 may be stationary (e.g., as part of a stationary printhead) or moving (e.g., as part of a printhead that moves across the print medium 180) as a matter of design choice. The pel forming elements 165 may be assigned to one of one or more color planes that correspond to types of marking materials (e.g., Cyan, Magenta, Yellow, and blacK (CMYK)).

0011In a further embodiment, printer 160 is a multi-pass printer (e.g., dual pass, 3 pass, 4 pass, etc.) wherein multiple sets of pel forming elements 165 print the same region of the print image on the print medium 180. The set of pel forming elements 165 may be located on the same physical structure (e.g., an array of nozzles on an ink jet print head) or separate physical structures. The resulting print medium 180 may be printed in color and/or in any of a number of gray shades, including black and white (e.g., Cyan, Magenta, Yellow, and blacK, (CMYK)). The host system 110 may include any computing device, such as a personal computer, a server, or even a digital imaging device, such as a digital camera or a scanner.

0012The sheet image 120 may be any file or data that describes how an image on a sheet of print medium 180 should be printed. For example, the sheet image 120 may include PostScript data, Printer Command Language (PCL) data, and/or any other printer language data. The print controller 140 processes the sheet image to generate a bitmap 150 for transmission. Bitmap 150 may be a halftoned bitmap (e.g., a calibrated halftone bit map generated from calibrated halftones, or uncalibrated halftone bit map generated from uncalibrated halftones) for printing to the print medium 180. The printing system 130 may be a high-speed printer operable to print relatively high volumes (e.g., greater than 100 pages per minute).

0013The print medium 180 may be continuous form paper, cut sheet paper, and/or any other tangible medium suitable for printing. The printing system 130, in one generalized form, includes the printer 160 that presents the bitmap 150 onto the print medium 180 (e.g., via toner, ink, etc.) based on the sheet image 120. Although shown as a component of printing system 130, other embodiments may feature printer 160 as an independent device communicably coupled to print controller 140.

0014The print controller 140 may be any system, device, software, circuitry and/or other suitable component operable to transform the sheet image 120 for generating the bitmap 150 in accordance with printing onto the print medium 180. In this regard, the print controller 140 may include processing and data storage capabilities. In one embodiment, measurement module 190 is implemented as part of ink model and ink drop size systems to obtain measurements of the printed medium 180. The measured results are communicated to print controller 140 to be used to generate ink model parameter data, as well as generate drop size data. The measurement module 190 may be a stand-alone process communicably coupled to printing system 130 or be integrated into the printing system 130.

0015According to one embodiment, measurement module 190 may be a sensor to take measurements of printed images on print medium 180. Measurement module 190 may generate and transmit print image measurement data. Print image measurement data may be color response (e.g., RGB, optical density, etc.) data corresponding to a printed image that is either raw or processed. In one embodiment, measurement module 190 may comprise one or more sensors that each or in total take measurements for printed markings produced for some or all pel forming elements 165. In-line ink volume sensing devices to monitor the amount (e.g., volume or mass) of ink used for printing is another type of device which may be included in measurement module 190.

0016In another embodiment, measurement module 190 may be a camera system, in-line scanner, densitometer or spectrophotometer. In a further embodiment, print image measurement data may include map information to correlate portions (e.g., a pel or plurality of pels) of the print image data to the corresponding pel forming elements 165 that produced the portions of the printed images.

0017<figref idref="f0002"><b>Figures 2A</b></figref><b>&amp;2B</b> illustrate embodiments implementing print controller 140. <figref idref="f0002"><b>Figure 2A</b></figref> illustrates a print controller 140 (e.g., DFE or digital front end), in its generalized form, including ink model logic 220, drop size logic 230, and ink estimation logic 240. <figref idref="f0003"><b>Figure 2B</b></figref> illustrates an embodiment in which print controller 140 includes drop size logic 230 and ink estimation logic 240, while ink model logic 220 are coupled externally. In either embodiment, the separate components may represent hardware used to implement the print controller 140. Alternatively, or additionally, the separate components may represent logical blocks implemented by executing software instructions in a processor of the printer controller 140.

0018Although shown as a component within of print controller 140, other embodiments may feature ink model logic 220 and drop size logic 230 included within independent devices, or combination of devices, communicably coupled to print controller 140. For instance, <figref idref="f0004"><b>Figure 2C</b></figref> illustrates one embodiment of ink model logic 220 and drop size logic 230 implemented in a network 280. As shown in <figref idref="f0004"><b>Figure 2C</b></figref><b>,</b> ink model logic 220 and drop size logic 230 are included within a computing systems 260 and 270, respectively, and transmit data to printing system 130 via a cloud network 290.

0019According to one embodiment, ink model logic 220 generates ink model parameter data for an unknown print medium based on uncalibrated ink deposition data for a reference print medium and uncalibrated optical density (OD) measurement data for the unknown print medium printed on a print system (e.g., printing system 130). In such an embodiment, the uncalibrated ink deposition data associated with the reference print medium is generated from reference ink model parameter data for the reference print medium and uncalibrated optical density measurement data for the reference print medium.

0020<figref idref="f0005"><b>Figure</b> 3</figref> illustrates one embodiment of ink model logic 220. As shown in <figref idref="f0005"><b>Figure 3</b></figref><b>,</b> ink model logic 220 includes ink deposition generation logic 310 and ink model generation logic 320. According to one embodiment, ink deposition generation logic 310 generates the uncalibrated ink deposition data associated with the reference print medium based on received reference ink model parameter data. In such an embodiment, the reference ink model parameter data comprises a one-time generation of ink model parameter data for the reference print medium.

0021In one embodiment, ink model parameter data (e.g., reference or unknown) comprises parameter estimates that are generated by applying an ink model, such as a Weibull ink model regression, to describe a functional relationship between OD and ink deposition data. Weibull cumulative distribution function (CDF) describes the probability that a real-valued random variable X with a given probability will be found at a value less than or equal to x (where x is a one possible value of the random variable X). Intuitively, it is the "area under the curve" function of the probability density function (PDF). Cumulative distribution functions are also used to specify the distribution of multivariate random variables. The Weibull CDF model that is employed uses two parameters.

0022In one embodiment, the Weibull CDF is modified to incorporate paper white and the solid area maximum optical density. This modified Weibull CDF will be described as simply "Weibull CDF". The forward Weibull CDF relates ink deposition to OD, while the inverse Weibull CDF relates OD to ink deposition. In one embodiment, ink deposition is represented by: <maths id="math0001"><math display="block"><mi>Ink</mi><mspace width="1ex" /><mi>Deposition</mi><mo>=</mo><mfrac><mrow><mi>Total</mi><mspace width="1ex" /><mi>Ink</mi><mspace width="1ex" /><mi>Mass</mi></mrow><mi>Area</mi></mfrac><mo>,</mo><mi>Total</mi><mspace width="1ex" /><mi>Ink</mi><mspace width="1ex" /><mi>Mass</mi><mo>=</mo><mstyle displaystyle="true"><munder><mo>∑</mo><mi>Area</mi></munder><mrow><mi>Drop</mi><mspace width="1ex" /><mi>sizes</mi></mrow></mstyle></math><img file="EP4040768A1_D0001.tif" /></maths>

0023In one embodiment, a four parameter Weibull ink model is implemented using OD = (p(3) *(1-exp^{((-(x/p(1))^p(2)))})+p(4). In such an embodiment, the two-parameter classical Weibull CDF function has been extended to four parameters to create an ink model. The two additional parameters allow the model to account for paper white and absolute paper referenced OD, where x = ink deposition mass per area, p(1) = ink mass per area scale factor, which is similar to the classical Weibull scale factor, and p(2) = slope factor.

0024This factor influences the shape of the function similarly to the classical Weibull slope factor, p(3) = maximum paper referenced OD and p(4) = paper white OD. Factors p(1) and p(2) are the parameters used in the classical two parameter Weibull CDF function. The p(1) scale factor adjusts the shape of the curve to modify how much ink deposition is required to achieve various ODs. Larger values for p(1) require more ink deposition to achieve the same OD.

0025In addition, since p(1) is similar to two-parameter classical Weibull slope, it indicates the point of the curve where the ink deposition corresponds to the OD level approximately 63% between the range defined by the paper referenced OD, parameter p(3) and the OD defined by p(4). The model provides a value for the maximum absolute OD for the ink/paper. This maximum OD will be given by the sum of the p(3) and p(4) parameters. This maximum OD would occur at infinite ink deposition.

0026Based on the Weibull CDF parameters, OD ink response data may be generated using uncalibrated ink deposition data. In other embodiments, the response data may be represented using CIE L*a*b* rather than OD. In such an embodiment, CIE L*a*b* is implemented to provide Delta E calculations. Alternate ink models, like the Weibull model described previously, can be used to describe the relationship between CIE L*a*b* and ink deposition. For example L* versus ink deposition can use the same equation, by modifying the definitions for p(3) and p(4) to use L* values instead of OD. The alternate model predicts decreased L* values with increased ink deposition x. A polynomial function, alone or combined with a Weibull like equation, can be used to describe a* and b* vs ink deposition.

0027Uncalibrated OD measurement data comprises OD response data measured from a print medium. In one embodiment, the OD response data comprises an OD versus digital count, where digital count is the gray level representing the pels in the bitmap 150. Uncalibrated ink deposition (or ink deposition) is defined as an average amount of ink deposited per printed device pel, where a pel is a picture element of the printer 160 (e.g., the printing device).

0028In a further embodiment, the amount of ink deposition changes as a function of digital count. In such an embodiment, the pels in bitmap 150 range from 0-255 for a typical 8-bit system. Additionally, the digital count is a control parameter of an output pel. In yet a further embodiment, an ink deposition curve is the ink deposition (e.g., amount of ink per area) defined over the range of all possible gray levels (e.g., 0-255). In such an embodiment, ink deposition is computed on an average basis to eliminate local variations due to halftoning using a set of discrete drop sizes. An area equal to the printed size of the halftone threshold array is a good region to use for the area calculation, since it defines the size of the fundamental halftone patterns. Ink drop sizes may be determined by analyzing the amount of ink used and counts of ink drops of each size, as will be discussed in more detail below.

0029According to one embodiment, the reference ink model parameter data may be generated from an uncalibrated OD measurement data for the reference medium and an uncalibrated ink deposition may be generated from measured drop sizes and halftone drop fractions generated for test print jobs (e.g., printed and measured at printing system 130, or another printing system)

0030Once the reference ink model parameter data has been received at ink model logic 220, the reference print medium is installed, and one or more test print jobs may be printed, at printing system 130. As a result, measurement module 190 measures uncalibrated OD measurement data of test data printed to the reference print medium. The uncalibrated OD measurement data for the reference print medium may then be received at ink model logic 220.

0031Uncalibrated ink deposition data for the reference print medium is generated based on the reference ink model parameter data and the uncalibrated OD measurement data for the reference print medium (see details further below). Subsequently, the process may be repeated with an unknown print medium being installed at printing system 130, and one or more test print jobs being printed to the unknown print medium.

0032Again, measurement module 190 measures uncalibrated OD measurement data for printed test data, this time for the unknown print medium. The uncalibrated OD measurement data for the unknown print medium may then be received at ink model logic 220. In one embodiment, ink model generation logic 320 generates the ink model parameter data (e.g., via the Weibull ink model regression) for the unknown print medium based on uncalibrated ink deposition data for the reference print medium using inverse Weibull ink model and the uncalibrated optical density (OD) measurement data for the unknown print medium.

0033<figref idref="f0006"><b>Figure 4</b></figref> is a flow diagram illustrating one embodiment of a process 400 for performing an ink model computation. Process 400 may be performed by processing logic that may include hardware (e.g., circuitry, dedicated logic, programmable logic, microcode, etc.), software such as instructions run on a processing device, or a combination thereof. In one embodiment, process 400 is performed by ink model logic 220.

0034According to one embodiment, process 400 begins at processing block 410, where ink model parameter data is received for the reference print medium. At processing block 420, the reference print medium is installed at printing system 130, where one or more test print jobs are printed on the reference print medium. At processing block 430, uncalibrated OD measurement data is received for the test print jobs printed on the reference medium (e.g., form measurement module 190).

0035At processing block 440, uncalibrated ink deposition data is generated for the reference print medium, based on the OD measurement data for the reference print medium and inverse ink model for the reference print medium. At processing block 450, an unknown print medium is installed at printing system 130, where one or more test print jobs are printed on the unknown print medium.

0036At processing block 460, uncalibrated OD measurement data is received for the test print jobs printed on the unknown medium. At processing block 470, ink model parameter data for the unknown print medium is generated based on the OD measurement data for the unknown medium and the ink deposition data for the reference print medium by using the inverse ink model for the reference print medium. At processing block 480, the ink model parameter data for the unknown print medium is transmitted. It should be understood that measurements and ink depositions for like digital count values are used to obtain matching sets of data to generate the ink model parameters for the unknown medium. By performing this, ink model parameter data for the unknown print medium has been determined efficiently and with minimal system resources. Ink model parameter data may be used to determine ink drop sizes and/or ink usage estimation in a print system 130.

0037Referring back to <figref idref="f0002 f0003 f0004"><b>Figures 2A-2C</b></figref><b>,</b> drop size logic 230 is implemented to generate ink drop sizes for printing system 130. In one embodiment, drop size logic 230 uses the ink model parameter data received from ink model logic 220 to generate the drop size data. <figref idref="f0007"><b>Figure 5</b></figref> illustrates one embodiment of drop size logic 230, including ink deposition generation logic 510 and drop size generation logic 520.

0038Ink deposition generation logic 510 generates uncalibrated ink deposition data using (or based on) ink model parameter data and uncalibrated OD measurement data. In one embodiment, the uncalibrated OD measurement data is associated with OD measurements generated to calibrate print heads 162 of printer 160 (<figref idref="f0001">Figure 1</figref>). In a further embodiment, the uncalibrated ink deposition data is generated using an inverse of the Weibull ink model (or inverse ink model).

0039As discussed above, the Weibull ink model refers to OD and ink depositions using measured drop sizes e.g., OD = W(i) = M(ID^-1(i)), where W is the Ink Model W(i) as a function of ink deposition i, M(g) is the Measured OD as a function of gray level g and ID is the uncalibrated ink deposition as a function of gray level. Thus, the inverse Weibull may be used to determine the uncalibrated ink deposition from the uncalibrated OD vs gray level g (e.g., W^-1(OD) = ID(M^-1(OD)). This defines both the OD and Ink deposition ID relationships versus gray level, whereas the ink model does not include this relationship.

0040It should be clear that while the ink model is referred to as a Weibull ink model, the ink model can be any functional relationship which relates OD to ink deposition for a printer. The inverse ink model being an inverse relationship requires a single value to provide a one to one relationship between ink deposition and OD. This one to one relationship for inverse functions is commonly described by the horizontal line test.

0041In our application to derive the ink model for an unknown paper, we have W₁^-1(OD) = IDi(g). This employs the inverse of the ink model W₁ for the reference paper to generate a function vs gray level g to describe the ink deposition ID₁ for the reference paper. Measuring OD as a function of gray level g using the unknown paper to establish M₂, we then can derive an ink model W₂ for the unknown paper using the relationship W₂(i) = M₂(ID₁^-1(i)). This produces a function W₂, which describes the ink model for the unknown paper. Again, since we have inverse functions, we must require them to pass the horizontal line test to ensure that a one to one relationship exists. In the case of the Ink deposition function ID this is generally guaranteed by the halftone design which requires the stacking condition that always has a larger drop size for every pel as the gray level is increased. This produces a monotonically increasing level of ink deposition for increasing gray level which is known to meet the horizontal line test.

0042Drop size generation logic 520 generates drop size data based on the uncalibrated ink deposition data at ink deposition generation logic 510. According to one embodiment, drop size generation logic 520 uses the uncalibrated ink deposition (or UID) data and ink drop count data (e.g., uncalibrated drop fractions) to generate the drop size data. Ink drop count data comprises a number of drops that occur at each of the plurality of gray levels. Uncalibrated drop fractions may be received by drop size logic 230. Drop fractions represent the ratio of number of drops for a given drop size, relative to the total number of possible drops of all sizes. Drop fractions are expressed as a function vs gray level.

0043<figref idref="f0008"><b>Figure 6</b></figref> illustrates one embodiment of a graph of uncalibrated drop fractions as a function of gray level for a four-drop size halftone, where the drop fraction range is between zero and one. The drop fractions for each individual drop size, including none, must always sum to a value of one since drops must be one of four different drop sizes.

0044In one embodiment, the uncalibrated drop fraction data is generated based on analysis of an uncalibrated halftone. A calibrated halftone is a halftone that has been adjusted to achieve a target response and so an uncalibrated halftone has not been adjusted to achieve a target response. Uncalibrated drop fractions represent percentages of a halftone threshold array for a specific drop size at each digital count (DC) level, where digital count is the gray level representing the pels in the bitmap 150, which ranges from 0-255 for a typical 8 bit system. DC is a print system input control and print system input control may be represented as DC, percent dot, or gray level.

0045To determine the uncalibrated drop fractions, an uncalibrated multibit threshold array may be analyzed to determine a number of drops (e.g., drop count) that occur at each DC or gray level. Thus, uncalibrated drop fractions are the number of drops in the threshold array for one drop size (e.g., small, medium, large and none) divided by the total number of drops for the one drop size in the threshold array, which is determined for each different drop size at each DC level.

0046The total number of drops for a single drop size is defined by the size of the threshold array. The total number of drops for a single drop size is the product of the number of rows and the number of columns in the threshold array. For example, at DC level 100, if we have 10000 small drops and the array is 256x256, the uncalibrated small drop fraction is 10000/(256*256) or 0.153. The uncalibrated drop fraction for the none drop size is not necessary to compute. It can be used for verification since the sum of all uncalibrated drop fractions including none must be equal to one (100%). Uncalibrated drop fraction may be determined for each color plane based on the uncalibrated multibit threshold corresponding to each color plane.

0047In one embodiment, UID=W^-1(OD_measured), provided inverse Weibull function = W^-1; measured OD = OD_measured; unknown drop sizes = DS_small, DS_medium and DS_large; Gray level = g; and uncalibrated drop fractions for small, medium and large drops: UDF_small(g), UDF_medium(g), and UDF_large(g). In a further embodiment, the ink model and the OD measurement data are for matching conditions. In other words, the ink model used must be for the same paper, halftone and ink set that was used to measure the OD. Ink models described previously for a reference print medium or unknown print medium maybe used. Thus, assuming a four-drop size system (e.g., none, small, medium and large): <maths id="math0002"><math display="block"><mtable columnalign="left"><mtr><mtd><mrow><mi>Ink</mi><mspace width="1ex" /><mi>deposition</mi><mspace width="1ex" /><mi>per</mi><mspace width="1ex" /><mi>pel</mi></mrow><mo>=</mo><mfenced><mi>UDF</mi><mo>_</mo><mi>small</mi><mfenced><mi mathvariant="normal">g</mi></mfenced><mo>*</mo><mi>DS</mi><mo>_</mo><mi>small</mi></mfenced><mo>+</mo><mfenced><mi>UDF</mi><mo>_</mo><mi>medium</mi><mfenced><mi mathvariant="normal">g</mi></mfenced><mo>*</mo><mi>DS</mi><mo>_</mo><mi>medium</mi></mfenced><mo>+</mo></mtd></mtr><mtr><mtd><mfenced><mi>UDF_large</mi><mfenced><mi mathvariant="normal">g</mi></mfenced><mo>*</mo><mi>DS</mi><mo>_</mo><mi>large</mi></mfenced><mo>;</mo></mtd></mtr></mtable></math><img file="EP4040768A1_D0002.tif" /></maths> and <maths id="math0003"><math display="block"><mi>Ink</mi><mspace width="1ex" /><mi>deposition</mi><mspace width="1ex" /><mi>per</mi><mspace width="1ex" /><mi>area</mi><mo>=</mo><mi>Ink</mi><mspace width="1ex" /><mi>deposition</mi><mspace width="1ex" /><mi>per</mi><mspace width="1ex" /><mi>pel</mi><mo>/</mo><mi>Area</mi><mspace width="1ex" /><mi>of</mi><mspace width="1ex" /><mi>pel</mi></math><img file="EP4040768A1_D0003.tif" /></maths>

0048Based on the above, drop size generation logic 520 determines best fit drop sizes to obtain an ink deposition per area that equals the uncalibrated ink deposition. In one embodiment, generation logic 520 determines the best fit drop sizes by performing a drop size regression. In such an embodiment, a least squares regression process is performed to solve the set of linear equations and obtain the unknown drop sizes.

0049Using the regression process, ink depositions are determined for each gray level. Based on a set of 256 (e.g., 0-255) simultaneous linear equations of uncalibrated ink deposition values, three equations are implemented to define three unknown drop sizes. Thus, approximately eighty-five (e.g., (256/3) sets of three different drop sizes may be determined, enabling an understanding of how drop sizes change across the tonal range (e.g., assuming an 8-bit halftone). Employing higher bit depth halftones permits obtaining a larger set of drop size estimates by employing the regression process for each pattern of the halftone. For example, a 14 bit halftone enables deriving drop sizes at each gray level for an 8 bit imaging path.

0050In yet a further embodiment, drop size generation logic 520 is also implemented to determine drop sizes for printer characteristics other than gray levels since drop sizes may vary depending on such conditions. In such an embodiment, drop size generation logic 520 may determine drop sizes for printer characteristics of print system 130, such as patch sizes, printhead voltages (PHV), printhead temperatures, jetting frequencies, number of jetting nozzles, other system temperatures, and/or etc.

0051<figref idref="f0009"><b>Figure</b> 7</figref> is a flow diagram illustrating one embodiment of a process 700 for performing a drop size computation. Process 700 may be performed by processing logic that may include hardware (e.g., circuitry, dedicated logic, programmable logic, microcode, etc.), software such as instructions run on a processing device, or a combination thereof. In one embodiment, process 700 is performed by drop size logic 230.

0052According to one embodiment, process 700 begins at processing block 710, where ink model parameter data is received. As discussed above, the ink model parameter data may be received from ink model logic 220. At processing block 720, the uncalibrated OD measurement data is received. In one embodiment, the uncalibrated OD measurement data is generated by print engine calibration.

0053At processing block 730, uncalibrated ink deposition data is generated using the uncalibrated OD measurement data and ink model parameter data (e.g., via inverse Weibull). At processing block 740, the drop size data is generated based on the uncalibrated ink deposition data (e.g., via a regression using drop fractions). At processing block 750, the drop size data is transmitted. In one embodiment, the transmitted drop size data may be displayed at a graphical user interface (GUI) 250 at print controller 140.

0054At decision block 760, a determination is made as to whether one or more changes to characteristics of print system 130 has been detected. If so, control is returned to processing block 720 where the process is repeated for updated uncalibrated OD measurement data generated in response to the change in the print system 130 characteristics. Otherwise, control remains at decision block 760 until a change to characteristics of print system 130 has been detected.

0055Referring to <figref idref="f0002 f0003 f0004"><b>Figures 2A-2C</b></figref><b>,</b> ink estimation logic 240 is implemented to provide an estimation of ink that is to be used to produce a print job. In such an embodiment, ink estimation logic 220 generates estimated ink usage data by computing a sum of ink usage data for each of a plurality of drop sizes generated by each pel forming element 165. In a further embodiment, ink estimation logic 220 uses histograms generated for each color plane (e.g., CMYK), as well as the drop size data and drop fractions, to estimate the print job ink usage. By performing this, ink drop size and/or ink estimation is determined accurately, efficiently and with minimal system resources. Ink drop size data may be used to evaluate and determine ink usage estimation in a print system 130.

0056<figref idref="f0010"><b>Figure 8</b></figref> illustrates a computer system 1000 on which printing system 130, print controller 140, ink model logic 220, drop size logic 230 and/or ink estimation logic 240 may be implemented. Computer system 1000 includes a system bus 1020 for communicating information, and a processor 1010 coupled to bus 1020 for processing information.

0057Computer system 1000 further comprises a random access memory (RAM) or other dynamic storage device 1025 (referred to herein as main memory), coupled to bus 1020 for storing information and instructions to be executed by processor 1010. Main memory 1025 also may be used for storing temporary variables or other intermediate information during execution of instructions by processor 1010. Computer system 1000 also may include a read only memory (ROM) and or other static storage device 1026 coupled to bus 1020 for storing static information and instructions used by processor 1010.

0058A data storage device 1027 such as a magnetic disk or optical disc and its corresponding drive may also be coupled to computer system 1000 for storing information and instructions. Computer system 1000 can also be coupled to a second I/O bus 1050 via an I/O interface 1030. A plurality of I/O devices may be coupled to I/O bus 1050, including a display device 1024, an input device (e.g., an alphanumeric input device 1023 and or a cursor control device 1022). The communication device 1021 is for accessing other computers (servers or clients). The communication device 1021 may comprise a modem, a network interface card, or other well-known interface device, such as those used for coupling to Ethernet, token ring, or other types of networks.

0059Embodiments of the invention may include various steps as set forth above. The steps may be embodied in machine-executable instructions. The instructions can be used to cause a general-purpose or special-purpose processor to perform certain steps. Alternatively, these steps may be performed by specific hardware components that contain hardwired logic for performing the steps, or by any combination of programmed computer components and custom hardware components.

0060Elements of the present invention may also be provided as a machine-readable medium for storing the machine-executable instructions. The machine-readable medium may include, but is not limited to, floppy diskettes, optical disks, CD-ROMs, and magneto-optical disks, ROMs, RAMs, EPROMs, EEPROMs, magnetic or optical cards, propagation media or other type of media/machine-readable medium suitable for storing electronic instructions. For example, the present invention may be downloaded as a computer program which may be transferred from a remote computer (e.g., a server) to a requesting computer (e.g., a client) by way of data signals embodied in a carrier wave or other propagation medium via a communication link (e.g., a modem or network connection).

0061The following clauses and/or examples pertain to further embodiments or examples. Specifics in the examples may be used anywhere in one or more embodiments. The various features of the different embodiments or examples may be variously combined with some features included and others excluded to suit a variety of different applications. Examples may include subject matter such as a method, means for performing acts of the method, at least one machine-readable medium including instructions that, when performed by a machine cause the machine to perform acts of the method, or of an apparatus or system according to embodiments and examples described herein.

0062Some embodiments pertain to Example 1 that includes a system comprising at least one physical memory device to store drop size logic and one or more processors coupled with the at least one physical memory device to execute the drop size logic to generate drop size data associated with a printing system based on ink deposition data for a print medium and ink drop count data.

0063Example 2 includes the subject matter of Example 1, wherein the drop size data is generated by performing a drop size regression.

0064Example 3 includes the subject matter of Examples 1 and 2, wherein the drop size regression determines a best fit of drop sizes for a plurality of gray levels to determine an ink deposition per area equal to the ink deposition data.

0065Example 4 includes the subject matter of Examples 1-3, wherein the ink drop count data comprises a number of drops that occur at each of the plurality of gray levels.

0066Example 5 includes the subject matter of Examples 1-4, wherein generating the ink deposition data comprises applying an inverse of ink model parameter data to an optical density data.

0067Example 6 includes the subject matter of Examples 1-5, wherein the drop size data is generated based on a plurality of print system characteristics.

0068Example 7 includes the subject matter of Examples 1-6, wherein the print system characteristics comprise at least one of gray levels, patch sizes, printhead voltage and printhead temperature.

0069Example 8 includes the subject matter of Examples 1-7, wherein the ink estimation logic further transmits the drop size data.

0070Example 9 includes the subject matter of Examples 1-8, further comprising a graphical user interface to display the drop size data.

0071Some embodiments pertain to Example 10 that includes a method comprising generating drop size data associated with a printing system based on ink deposition data for a print medium and ink drop count data.

0072Example 11 includes the subject matter of Example 10, wherein the drop size regression determines a best fit of drop sizes for a plurality of gray levels to determine an ink deposition per area equal to the ink deposition data.

0073Example 12 includes the subject matter of Examples 10 and 11, wherein the ink drop count data comprises a number of drops that occur at each of the plurality of gray levels.

0074Example 13 includes the subject matter of Examples 10-12, wherein generating the ink deposition data comprises applying an inverse of ink model parameter data to an optical density data.

0075Example 14 includes the subject matter of Examples 10-13, wherein the drop size data is generated based on a plurality of print system characteristics.

0076Example 15 includes the subject matter of Examples 10-14, wherein the print system characteristics comprise at least one of gray levels, patch sizes, printhead voltage and printhead temperature.

0077Some embodiments pertain to Example 16 that includes at least one computer readable medium having instructions stored thereon, which when executed by one or more processors, cause the processors to generate drop size data associated with a printing system based on ink deposition data for a print medium and ink drop count data.

0078Example 17 includes the subject matter of Example 16, wherein the drop size data is generated by performing a drop size regression.

0079Example 18 includes the subject matter of Examples 16 and 17, wherein the drop size regression determines a best fit of drop sizes for a plurality of gray levels to determine an ink deposition per area equal to the ink deposition data.

0080Example 19 includes the subject matter of Examples 16-18, wherein the ink drop count data comprises a number of drops that occur at each of the plurality of gray levels.

0081Example 20 includes the subject matter of Examples 16-19, wherein generating the ink deposition data comprises applying an inverse of ink model parameter data to an optical density data.

0082Whereas many alterations and modifications of the present invention will no doubt become apparent to a person of ordinary skill in the art after having read the foregoing description, it is to be understood that any particular embodiment shown and described by way of illustration is in no way intended to be considered limiting. Therefore, references to details of various embodiments are not intended to limit the scope of the claims, which in themselves recite only those features regarded as essential to the invention.