Patent Description:
This invention relates to a coffee grinder, and to a method for controlling a grinder.

Coffee drinks are popular beverages in many parts of the world and have been consumed for thousands of years. A "coffee drink," as used herein, refers to a liquid that is prepared using coffee beans and water, often for consumption as a beverage. <FIG> shows a basic coffee brewing process <NUM> for preparing a coffee drink from roasted coffee beans. At S11, roasted coffee beans are ground into small pieces. Then, the ground coffee beans (coffee grounds) are placed in contact with hot water in a manner that allows the compounds in the coffee beans to be extracted into the water (S12). The solid grounds are separated from the liquid portion that ends up in the coffee drink (S13).

Numerous methods and devices exist for placing the ground coffee beans in contact with hot water (S12) and separating the remaining solid grounds (S13) to produce coffee drinks. Devices include, for example, percolators, vacuum pots, the French press, drip coffee makers, and espresso makers. <CIT> relates to a machine for brewing a beverage such as coffee which includes a chamber and a piston assembly disposed in the chamber. The chamber is operable to receive a liquid such as water and a flavor base such as ground coffee, and to allow the beverage to brew from a mixture of the liquid and the base. The piston assembly is operable to filter a solid such as spent coffee grounds from the brewed beverage by moving in a first direction, and to force the filtered beverage out of the chamber by moving in a second direction. By modifying or automating some or all steps of the French press brewing technique, such a machine may control one or more of the brewing parameters with a level of precision that yields brewed coffee having a uniform taste from cup to cup. Furthermore, such a machine may brew the coffee with a speed that renders the machine suitable for use by establishments that serve significant amounts of coffee. <CIT> relates to a machine for brewing a beverage such as coffee which includes a chamber and a piston disposed in the chamber. The piston is operable to move to a first position to allow the chamber to receive a liquid and a flavor base such as ground coffee, to remain in the first position for a time sufficient for the beverage to brew, and to move to a second position to dispense the beverage by forcing the beverage out of the chamber. By modifying some or all steps of the French press brewing technique, the machine can typically control coffee-brewing parameters with a level of precision that yields brewed coffee having a uniform taste from cup to cup and can typically brew the coffee with a speed that renders the machine suitable for use by establishments that serve significant amounts of coffee.

<FIG> illustrate methods for preparing (S12 and S13) a coffee drink from the ground coffee beans using, respectively, a French press and an Aeropress® (Aerobie®, Inc. <FIG> illustrates the principles for preparing (S12 and S13) espresso from ground coffee beans. In the French press device <NUM> of <FIG>, ground coffee beans (grounds) <NUM> and hot water <NUM> are mixed in a container <NUM>, e.g., a glass cylinder. The grounds <NUM> and hot water <NUM> are allowed to steep for a period of time. A plunger <NUM> that includes a mesh filter <NUM> is then pushed down through the liquid, catching the grounds <NUM> and holding them at the bottom of the container <NUM>. The coffee drink <NUM> in the container <NUM> is above the filter <NUM>, separated from the grounds <NUM> that are at the bottom.

In the AeroPress® device <NUM> of <FIG>, a filter <NUM> is positioned over openings <NUM> at the bottom of a cylindrical holder <NUM>. The grounds <NUM> and hot water <NUM> are mixed together and allowed to steep over the filter <NUM> for a period of time. Then, a plunger <NUM>, which makes an airtight seal with the cylindrical holder <NUM>, is used to force the liquid <NUM> (which is a coffee drink) through the filter <NUM> into a receiving vessel <NUM>. The grounds <NUM> are held above the filter <NUM>. The French press device <NUM> and AeroPress® device <NUM> differ in that pressure is applied in the AeroPress® to force the liquid past the ground coffee beans as it exits the cylindrical holder.

To make an espresso drink, as shown in <FIG>, the grounds <NUM> are first compacted together to form a "puck" <NUM>. Hot water <NUM> is then forced under high pressure through the contained puck <NUM> into a receiving vessel <NUM>, to make the espressotype coffee drink <NUM>. A wide variety of devices have been devised to make espresso coffee drinks <NUM>.

In the process for preparing coffee, as shown in <FIG>, the roasted coffee beans are first ground (S11). The fineness or coarseness of the grind of the roasted coffee beans affects the flavor of the coffee drink obtained in S12 and S13, and the coarseness of the grind is typically matched to the method that will be used to brew the coffee. Brewing methods in which the coffee grounds are exposed to heated water for a relatively long period of time generally use a coarse grind. If the grind for such methods is too fine, then too much surface area of the coffee beans will be exposed to water for too long a time, and the resulting coffee will be over-extracted, producing a bitter taste. On the other hand, if the brewing method used exposes the ground coffee beans to the heated water for a short period, too coarse a grind will result in weak, tasteless coffee.

Additionally, because coffee beans are grown and roasted under a wide variety of conditions, each batch of roasted coffee beans may require different conditions to prepare high quality, flavorful coffee. Properly adjusting the fineness of the coffee grinds and other brewing parameters to achieve the desired flavor generally requires trial and error, and often a trained "barista. " A way to predictably reproduce the desired coffee flavor without spending significant time and effort is desired.

In the following description, <NUM> inch corresponds to <NUM>. Preparation of coffee drinks has remained largely an art in the sense that efficient and accurate reproduction of a desired flavor is extremely difficult. Generally, it requires a trained person (e.g., a barista) with a refined palate to taste a coffee drink and make another cup that has the same flavor, especially with a different batch of beans. While many people make and drink coffee drinks as part of their daily routine without much thought or complaint, even an average coffee drinker would admit that some coffee drinks taste better than others. The inventive concept disclosed herein allows a coffee drinker to reproduce the flavor of a model coffee drink in the convenience of his own home, without having to travel to a remote coffee shop or spending a lot of time. This reproducibility is achieved by characterizing a model coffee drink with a set of brew parameters and making those parameters available to people who make coffee.

In one aspect, a method for preparing a coffee drink having consistent taste characteristics includes characterizing a coffee drink with a set of brew parameters that are specific to batch of roasted coffee beans. As will be disclosed in more detail below, brew parameters include grind size, ratio of water to grounds, packing pressure (for espresso coffee drinks), water temperature, dwell time, extraction pressure, and agitation time, among others. A small portion of the roasted batch of beans may be used for the characterization to determine the brew parameters, with the assumption that the same characterization applies to the "batch" of beans that came from the same source (e.g., field) and were roasted together. The brew parameters may hence be used with portions of the batch that were not directly characterized.

In another aspect, brew parameters for a batch of coffee beans may be stored in a database and associated with an identifier assigned to the particular batch of coffee beans. A user can use the identifier to access the brew parameters that are stored. For example, the user may enter the identifier affixed to a bag of coffee into a website to retrieve the brew parameters. Alternatively, the user may use a portable device (e.g., a smartphone) to read the identifier that is encoded on the bag of beans and obtain brew parameters.

In some embodiments, the brew parameters are encoded directly onto a bag of beans so that a user can read the code to obtain the brew parameters. In other embodiments, a software would receive input from the user regarding the type of coffee maker he is using or the type of drink he wants to make (e.g., a cappuccino) and provide brew conditions that are obtained using the brew parameters. "Brew conditions" include parameters other than brew parameters that affect the brewing, such as settings for particular grinders in the market and recipes that may be used to make the desired drink. The "brew conditions" are determined based on the brew parameters that characterize the beans.

The specific taste characteristic of brewed coffee is the result of the total dissolved solids ("TDS") that dissolve from the ground roasted coffee beans into the water. Another component that affects a coffee drink's taste characteristic is the type and quantity of compounds extracted that manifest as TDS. For example, hotter water and longer steep times will tend to release more chlorogenic acid lactones and phenylindanes, while cooler water and shorter steep times will tend to release more acidic compounds. The taste is affected by the quantity of TDS compared to the amount of water (the "TDS ratio") and also the chemical composition of the TDS. The TDS ratio and chemical composition are influenced by the characteristics of the roasted coffee beans themselves and the process used for preparing coffee, i.e., the process used for extracting the TDS. The characteristics of the roasted coffee beans can be influenced by factors such as the growing conditions and roasting conditions that can be difficult to reproducibly control. However, for a given batch of roasted coffee beans, if the process for preparing the coffee - which is an aqueous extraction process for the TDS - can be reproduced, the same taste characteristics for coffee resulting from the batch of roasted coffee beans can be reproduced.

<FIG> depicts a brew parameter generation process <NUM> in accordance with an embodiment of the inventive concept. As shown, the brew parameter generation process <NUM> includes selection of a "model coffee drink" for a batch of beans (S32). The "model coffee drink" is the drink which has the flavor that consumers would want to replicate. During the model coffee drink selection process of S32, batches of coffee beans are subjected to tests and characterized to determine which of the various sets of parameters produces the "perfect" coffee flavor. This determination may involve a trained professional or a tasting panel that tastes coffee drinks made with different brew parameters and votes on or selects the best drink. Another way for making this determination is to allow the purchasers of the roasted coffee beans to submit brew parameters, and then to have members of the community vote for their favorite flavors, for example through a social network or an online voting software. Since the brew parameters used to produce each coffee drink is known, the brew parameters that were used to produce the drink that received the most number of votes can be easily identified. Yet another way to determine the brew parameters of a "good coffee drink" involves chemical analysis. This process may take the form of analyzing for a few ingredients in the coffee, for instance by determining caffeine level, acrylamide level, pH, or the content of any specific chemical identified as contributing positively or negatively to the desired result. Testing by chemical analysis may also take the form of determining overall results, such as the total amount of TDS, or a spectrographic result of the TDS and comparing to known amounts/spectrographs for coffee with desirable properties. The inventive concept is not limited to any particular way of selecting the "model coffee drink.

Once the "model coffee drink" is selected, its properties are translated to brew parameters (S34) that will allow consumers to replicate its flavor. The aqueous extraction process for extracting the TDS from roasted coffee beans into a coffee drink is controlled by a set of brew parameters, which include the following:.

The brew parameters listed above are not intended to be exhaustive, and the inventive concept disclosed herein is not limited to any particular combination of brew parameters. For example, in some embodiments, the following parameters may be included in the brew parameters:.

Each brewing method requires managing the set of parameters that are relevant to the particular device. For example, for espresso extractions, the primary parameters necessary to control are the grind, pack ratio, temperature, dwell and pressure. These brew parameters result in the extraction time and volume, and the resulting quantity and chemical composition of the TDS. This relationship can be expressed as the following relationship (<NUM>): <MAT>.

For an AeroPress® extraction, the primary parameters necessary to control are the grind, ratio, temperature, agitation, dwell, and pressure. These primary parameters result in the extraction time, and the resulting quantity and chemical composition of the TDS. With an Aeropress® as compared to espresso, there is no "puck" so the pack is not relevant. However, the agitation time is important. For an Aeropress ®, the relationship can be expressed as follows: <MAT>.

For a French press, the primary variables are grind, ratio, temperature, agitation and dwell. With a French press no pressure is applied and also there is no "puck," so no pack pressure is required, and the relationship can be expressed as follows: <MAT>.

Traditionally, coffee brewers have treated the brew variables as an informally managed group. This is largely because the grind, i.e. particle size distribution of the ground roasted coffee beans, has been impractical to measure, and thus needed to be determined via trial and error and validated each time by tasting the result. At the same time, the grind has a high impact on the resulting taste characteristics of the coffee. Thus, of all the variable parameters in the brewing process, the ability to accurately measure and control the grind has a great effect on the quality of the coffee.

With the ability to measure grind accurately, it becomes possible to treat grind as the main primary parameter, and fix the remainder of the primary parameters based on the grind to produce predictable results in the secondary group and consequently create consistent characteristics from the extraction. A novel method for determining particle size distribution for ground roasted coffee beans is described below with respect to <FIG>, <FIG> and <FIG>. In the method, an ordinary camera, such as a camera attached as part of a smart phone, is used to photograph (or generate a bitmap of) a small amount of coffee grounds distributed on a calibration grid. The photograph (bitmap) is then processed to determine the particle size distribution of the grounds. This method is practical to implement, and thus grind can be reproduced, making reproducible taste characteristics of the coffee possible.

An example of encoded brew parameters may look like the following:.

These brew parameters, which are for use with an Aeropress® device, includes the settings a user can use to produce a coffee drink that tastes like the "model flavor" that was selected by the model determination process described above. In this particular example, the grind brew parameter indicates that to reproduce the selected flavor, <NUM>% of the grind particles have a size of <NUM> or less (within a standard deviation of <NUM>).

The brew parameters affect each other, such that when one parameter changes, one or more of the other parameters may be adjusted to "work with" the change and obtain the same result. For example, if the grind is too coarse, the water temperature and/or dwell time can be adjusted (e.g., increased) to compensate for the coarseness and achieve the same desired flavor. Similarly, if the grind is too fine, the water temperature and dwell time can be adjusted (e.g., decreased) accordingly to compensate for it.

Once the brew parameters are determined in S34, the brew parameters are made available to consumers (S36). In one embodiment, the brew parameters are encoded and associated with the batch of beans. For example, where the beans are packaged into onepound bags, the brew parameters may be encoded and affixed to the packaging. In one embodiment, the brew parameters for different types of coffee makers may be printed on a sheet of paper or sticker and affixed to a bag of coffee beans. A user who purchases the coffee beans would automatically receive the brew parameters for reproducing the "model coffee drink" using those beans.

In another embodiment, the brew parameters are encoded and affixed or printed onto the packaging of the coffee beans. A user would scan the code using a scanner or a code reader (which may be implemented as an application for a smartphone) to obtain the encoded brew parameters. The parameters could also be encoded on an RFID or NFC device.

In one embodiment, the selection of the model coffee flavor (S32) is done for a number of categories, such as "strong and robust," "medium body," and "light and smooth," with a model coffee drink (and its brew parameters) selected for each category.

In yet another embodiment, the brew parameters are stored in a database and accessed by the users. Each batch of beans that is characterized is assigned an identifier. For each coffee bean batch identifier, brew parameters for different types of coffee makers (e.g., French press, Aeropress®, espresso) are entered for the different flavor categories into a database. The brew parameter database may include other data, such as a list of commonly used coffee makers and any brew parameter adjustments to be used with each of the different-brands and models. Also, if professional tasters were used to determine the "model coffee drink," instead of agreeing on one set of best brew parameters, the parameters most liked by each professional taster could be stored separately and identified. This way, with experience, someone making the coffee would know which taster's selection he usually prefers and choose the brew parameters associated with that taster's model drink. Additionally, the database may include dates and timetables so that, if the brew parameters change over time, for instance as the roasted beans become less fresh, corrected brew parameters can be accessed.

In addition to the brew parameters associated with each brew condition, a related table of settings, for instance for particular devices, may be stored (e.g., in a look-up table).

Additionally, the identifier may be linked to other information related to the batch of roasted coffee beans, such as, for example, varietal, origin, batch and roast dates, additional descriptive content (i.e. color and size of beans), "use by" dates, additional recommendation regarding the roasted coffee beans, suggested brew methods and these information may be stored or linked to the brew parameter database. The database can be updated as needed.

<FIG> depicts an embodiment of a parameter-based coffee replication process <NUM> in accordance with the inventive concept. In this process <NUM>, the coffee bean identifier is obtained (S41). The identifier can be input by the user or read by the machine, depending on the encoding method used. For instance, a barcode, QR code (Quick Response Code), RFID Tag (Radio Frequency Identification), or URI (Uniform Resource Identifier) code identifier could be read by a scanner, or a code number printed on the coffee bean package could be manually input into a web-based application. In addition to the identifier, other information that will narrow down the set of parameters in the database may be requested and received (S43). This additional information may pertain to the type of grinder and/or coffee maker that is being used (e.g., Aeropress®, standard drip, French press, espresso) and/or the desired flavor category (strong, medium, light). Using the identifier and the optional additional information, the correct set of brew parameters are found in the database (S45). The database may be accessed via a network or stored locally. Upon retrieving the set of brew parameters for reproducing the flavor of the model coffee drink using the consumer's coffee maker, the brew parameters are retrieved and provided, for example to the user (S46). The brew parameters may be provided to the user as an easy-to-follow, step-by-step instruction.

The parameter-based coffee replication process <NUM> may be implemented as a software or firmware residing in different machines. For example, the software may be implemented as an application for a smartphone that can be downloaded. The software may also be implemented as a web-based application in which the user interacts with a web-based interface. The software may also be implemented, in total or partially, as part of an automatic coffee grinding and/or brewing device, and used to run the device as described below.

<FIG> depicts an embodiment of the inventive concept that includes a "smart" coffee grinder <NUM> that is configured to carry out a parameter-based grinding process <NUM> that is depicted in <FIG>. The smart coffee grinder <NUM> is configured to receive a user request about the type of coffee drink that is desired, retrieve the brew parameters (specifically, the grind parameter), and produce coffee grinds that meet the brew parameter requirement. As shown, the smart coffee grinder <NUM> includes a grinder <NUM> for grinding the beans, a grind control unit <NUM> for controlling the particle size of the coffee grind, and a processor <NUM>. The smart coffee grinder <NUM> is also able to communicate with a consumer via a interface unit <NUM>. The user interface unit <NUM> may be built into the smart coffee grinder <NUM> or be in communication with (via hard wire or wirelessly) a separate user interface unit (e.g., smartphone, tablet, laptop, desktop, PDA). The user interface device is able to receive user input as well as output information to a user and typically includes a visual and/or audio devices. The smart coffee grinder <NUM> also has a data interface <NUM> through which it accesses the brew parameter database. The data interface <NUM> may be a port configured to receive a memory device that stores the brew parameters, or a network connectivity port that allows database access via a network.

In one embodiment, the grind control unit <NUM> may be implemented using the particle size determination method that is described below with respect to <FIG>, <FIG> and <FIG>. Where the method that is described below is used, the grind control unit <NUM> includes a camera <NUM> positioned over a calibration grid <NUM> that has calibration marks. The processor <NUM> obtains the brew parameters for the user's desired coffee drink in the manner shown in <FIG>, for example from the database mentioned above. The processor <NUM> extracts the grind size parameter from the brew parameters, and adjusts the setting and grind time of the grinder <NUM> to achieve the prescribed grind size. The processor <NUM> may be programmed to translate the brew parameters to certain settings for the grinder <NUM>. After the initial grind, a sample of the coffee ground is sprinkled on the calibration grid <NUM> and imaged with the camera <NUM>. Distortion corrections may be made in accordance with the method of Appendix A and the particle size distribution of the grind is determined. If the particle size distribution is within the grind size parameter of the brew parameters for the desired drink, the grinding is complete. If, on the other hand, more grinding is needed, the grinder <NUM> is turned back on at an adjusted setting that is likely to get the grind to the correct particle size. A sample of the re-ground coffee grinds is then sprinkled on the calibration grid <NUM>, the particle size distribution is determined again, and the iterative grinding cycle continues until the desired particle size is reached.

The smart coffee grinder <NUM> may be equipped with a local memory <NUM> that stores the coffee bean identifier and the grind settings associated with that identifier. Hence, if a user wants to make the same type of coffee drink for several days using the same bag of coffee, the smart coffee grinder <NUM> would not have to repeat the entire process of <FIG> each time.

<FIG> depicts the parameter-based grinding process <NUM> that may be executed by the smart coffee grinder <NUM> in accordance with the inventive concept. The smart coffee grinder <NUM> reads the coffee bean identifier (S5010), optionally receives input from the consumer regarding brew preferences and conditions (e.g., the desired flavor category) (S5020), and retrieves the correct set of brew parameters from the database (S5030). It identifies the grind parameter from the brew parameters, and sets the grinder <NUM> to a setting and runtime that would achieve the desired particle size of the grind (S5040). After the grinding process is complete, the grind control unit <NUM> checks the grounds (S5050) to see if the particle size is within the target range defined by the brew parameters. Initially, the smart coffee grinder <NUM> may set the grinder to produce grounds that are slightly coarser than what is ultimately desired, so that the second round of grinding can recompute the grind parameter to fine tune the grounds (S5060) and obtain grinds that are within target particle size. Once the target particle size is reached, the grounds are provided to the user (S5070).

<FIG> depicts an embodiment of the inventive concept that includes a "smart" coffee maker <NUM> that is configured to carry out a parameter-based coffee making process <NUM> that is depicted in <FIG>. In some embodiments, the smart coffee maker <NUM> may incorporate the smart coffee grinder <NUM>. Specifically, the smart coffee maker <NUM> includes a scale <NUM> for weighing the coffee beans and/or water, a grinder <NUM> for grinding the coffee beans, a grind size control unit <NUM> for determining the grind size, a water receiving and heating unit <NUM>, an extraction unit <NUM> where the grind and the water are placed in contact, and a coffee drink receiving unit <NUM>. Where the brew parameters specify the water amount in terms of volume, the water receiving unit <NUM> may have marks that indicate water volume. The smart coffee maker <NUM> includes a processor <NUM> coupled to a local memory <NUM> and a data interface <NUM> that may be configured with network connection capability. The network connection capability is useful for accessing the database described above.

<FIG> illustrates the parameter-based automated coffee making process <NUM> that may be executed by the smart coffee maker <NUM> in accordance with an embodiment of the inventive concept. The smart coffee maker <NUM> reads the coffee bean identifier (S6010), optionally receives input from the consumer regarding brew preferences such as the desired flavor category (S6020), and retrieves the correct set of brew parameters from the database (S6030). It identifies the grind parameter from the brew parameters, obtains the correct amount (weight) of coffee beans (S6035), places the coffee beans in the grinder <NUM> set to a setting and runtime that would achieve the desired particle size of the grind (S6040). After the grinding process is complete, the grind control unit <NUM> checks the grounds to see if the particle size is within the target range defined by the brew parameters, as described in reference to <FIG>, for example using the technique described below with respect to <FIG>, <FIG> and <FIG>. Once the desired particle size is achieved, the grounds are poured into the extraction unit <NUM> (S6060). Water is measured, e.g. with the scale <NUM>, to obtain the amount prescribed by the brew parameters (S6045) and heated to the prescribed temperature (S6050). The water and the grounds are combined (S6060) in the extraction unit <NUM> and placed in contact (with agitation, in some devices) for the amount of dwell time prescribed by the brew parameters. The grounds are separated from the liquid portion of the coffee drink (S6070) to produce the coffee drink.

Once the coffee is brewed, the software can, optionally, request and incorporate feedback regarding the coffee (not shown). This feedback may be, for example, a chemical analysis of either specific chemicals or of the resulting coffee in total, to compare to results of a chemical analysis described above, such as to provide a cross-check on the resulting coffee. This feedback may also be, for example, provided by the users. For example, as the community gains experience with a roast batch they may provide variations on the brew parameters to achieve different results. These updates can be published and rated by other members of the community.

<FIG> illustrates an example operation of a parameter-based automated coffee preparation process <NUM> in accordance with the inventive concept. The particular example is for use with a French Press device, although the process can be adapted for any type of device. In this automated coffee preparation process <NUM>, there are five nodes: node <NUM> (<NUM>) for weighing and grinding beans, node <NUM> (<NUM>) for weighing and heating water, node <NUM> (<NUM>) for loading the extraction unit, node <NUM> (<NUM>) for extraction, and node <NUM> (<NUM>) for plunge control. Each node is controlled by a control unit <NUM>. The nodes may be different parts of an integrated unit such as the smart coffee maker <NUM> described above, or separate units that can communicate with the control unit <NUM>, for example wirelessly (e.g., via Bluetooth). For example, node <NUM> may be at a grinder, node <NUM> may be at a kettle, and nodes <NUM>, <NUM>, and <NUM> may be at a free-standing French Press device.

The control unit <NUM> controls the nodes independently in a coordinated manner. The control unit <NUM> has access to the brew parameter database, and retrieves the parameters for each node from the database. It then sets the node parameters according to the retrieved parameters (S760) and initiates the node operation (S770). The node operations are then performed (S780) in a coordinated manner, such that the steps of the process happen in the right order. With each step, the control unit <NUM> confirms that the operation has been completed before moving on to the next step (S790). There is a timer built into or read by the control unit <NUM> so that the control unit <NUM> can set the runtimes for various processes (e.g., grinding, agitating) according to the brew parameters.

The method of determining the particle size distribution of ground coffee beans using an image is described with respect to <FIG>, <FIG> and <FIG>.

The method entails generating or otherwise obtaining an image (e.g., a bitmap) that includes the small particles of the ground coffee beans and a calibration pattern, wherein the dimensions of the calibration pattern are known. The image may be produced, for example, using any conventional camera to image the small particles positioned on or around a calibration pattern. Where particle size is small (e.g., in the order of <NUM>-<NUM> inches), corrections are made to account for distortions caused by the camera lens.

In one embodiment of the method that is disclosed, the particle size of the ground coffee beans is determined using a calibration pattern that includes marks of known dimensions. The calibration pattern and the particles are imaged together, with the assumption that the same distortions will apply to both the calibration pattern and the particles. Using the known dimensions of the calibration pattern, a transformation is generated for removing the distortion effects and converting the image to a corrected image that is free of distortion effects. The transformation is then applied to determine particle size distribution from the corrected image.

Advantageously, any camera (or other device capable of producing a bitmap) can be used to record the bitmap, and specialized imaging or recording equipment is not required. Furthermore, because the calibration pattern and particles are recorded together in a single image, the camera, lens and other image parameters do not need to be known to correct for distortions and extract accurate particle sizes. Capturing the particles and the calibration pattern together in one image eliminates the need to record additional, separate calibration images to obtain a set of parameters to correct for distortions before recording the measurement image. In the method that is disclosed, the information necessary to accurately determine the sizes of the ground coffee beans is embedded in a single image.

<FIG> illustrates an embodiment of a method for determining particle size. After the particles to be measured are distributed on a calibration pattern, for example calibration grid <NUM> (<FIG>), the camera <NUM> is used to capture a digital image (e.g. record a bitmap) of the particles on the calibration grid <NUM> (step S810). The image generation may include preparation of the image to facilitate object recognition, for example by applying image processing techniques (including, but not limited to noise reduction and/or thresholding and/or filtering) to improve the clarity/definition of the image. Any suitable noise reduction techniques may be used.

Any technology for capturing or generating two-dimensional or three-dimensional images may be used in step S810, including techniques that utilize photographic (i.e., visible light), ultrasound, x-ray, or radar. The inventive concept is not limited to any particular way of capturing the bitmap. The calibration pattern, such as calibration grid <NUM>, usefully includes a background and calibration marks. For example, the calibration marks of calibration grid <NUM> are the outlines of squares having consistent dimensions x and y, which are drawn with lines of a substantially constant thickness and repeated at a consistent interval w in rows and columns. For example, <FIG> shows a calibration grid <NUM> with calibration marks <NUM> that are the outlines of squares having consistent dimensions x and y, which are drawn with lines of a substantially constant thickness and repeated at a consistent interval w in rows and columns. The dimensions of the calibration marks are known (e.g., by measuring the physical pattern). The calibration marks can be of any dimensions that provide enough information for producing a corrected image that allows accurate measurement in the desired particle size range.

The calibration pattern, for example calibration grid <NUM>, is most useful if the main color or shade of the background has a high contrast to the color of the particles to be measured and the color of the calibration marks. It is also useful to have the color of the calibration marks be different than the color of the particles whose size is to be determined. For example, if the particles are brown or black, the background may be white and the calibration patterns may have a blue hue. In general, any material may be used for the calibration pattern, and it may be useful if the surface of the calibration pattern is impervious to the material of the particles, so that the particles do not damage the calibration pattern. In one example, the calibration pattern is a pattern printed on a sheet of paper and the particles of the ground coffee beans are sprinkled on it. A digital image of the calibration pattern may be obtained by the user and printed at home.

The smallest particle size of the coffee grounds that can be determined using the technique disclosed herein depends on a number of factors, one of which is the ratio between the smallest measurable object's pixel coverage and the calibration mark's pixel coverage. There also should be enough camera resolution to capture one or more calibration marks and enough particles of the sample to gather statistics. The camera that is part of an iPhone ® that is currently available in the market would allow determination of particle size as small as <NUM> × <NUM>-<NUM> inches. In one embodiment, the dimensions of the calibration marks depend on the digital resolution of the camera and the size of the smallest particle to be measured. For example, for a camera having a resolution of <NUM> × <NUM> pixels, a square of <NUM> pixels by <NUM> pixels is needed to measure a particle with a diameter of <NUM> × <NUM>-<NUM> inches, and a calibration pattern that is <NUM> pixels per side (i.e., surrounds an area of <NUM>,<NUM> pixels) is used.

Patterns may include repeating squares of a grid, and also patterns other than the repeating squares may be used for the calibration patterns. However, using a regular pattern that is mathematically easy to model, e.g., that includes orthogonal lines, for the calibration patterns may simplify the processing of the recorded image. Additionally, the calibrations mark uses maximum use of the color that has a high contrast to the color of the particles whose size is being determined. A pattern such as a "checkerboard" pattern, for example, may not work as efficiently because half of the boxes would be dark and, where the particles are dark, too many of the particles would lie on the dark areas where there is not much contrast between the particles and the surface they are on.

At step S820, the image of calibration grid <NUM> is corrected to remove distortions. One of the problems of using imaging for determining particle size is that various distortions in the recorded image will lead to inaccuracies in the size determination. These distortions are particularly deleterious when trying to make accurate measurements of small particles, in the size ranges of, for example, <NUM>-<NUM> inches. Such distortions can be the result of imperfections in lens geometry or alignment, which may cause, for example, straight lines to be captured in the image as non-straight lines. Distortion can also be the result of perspective distortion, which occurs when the camera's optical axis is not perpendicular to the center of the object being imaged, causing parallel lines to appear non-parallel in the image. As particle sizes are determined using the dimensions of the calibration marks, distortion in the image of the calibration marks will likely result in error in size determination. Hence, distortions in the calibration marks are corrected before particle size determination is done. At the end of step S820, a "corrected image" is produced that includes the distortion-free calibration marks and the original (uncorrected) image of the particles.

In one approach to removing distortions in step S820, calibration marks are extracted from the image. A domain filtering technique may be used for this extraction. For example, where the calibration marks are blue, a technique that uses a chroma range to extract patterns in the blue hue range may be used (the background of the calibration pattern is a different color from the marks). The result is a calibration mark object array that is built by extracting contours from the blue portions of the image. The calibration mark object array is used to generate a uniform scale that is useful for mapping the image, as in orthophotographs. This generation of a uniform scale is an ortho-transformation, which may be reused with the same calibration pattern repeatedly once it is generated.

At step S830, particle sizes of ground coffee beans are determined using the corrected image of the calibration pattern. This process entails extracting the particles from the corrected image using domain filtering. For example, domain filtering may be accomplished using a chroma range to extract the particles that are known to be in the brown/black color range. A particle object array is generated by extracting contours of the particles from the processed image. Each element of the particle object array can then be measured to determine particles dimensions, for example the extent (diameter), area and circularity of each particle. From these measurements, a size distribution of the measured particles is obtained. In measuring the particle sizes, the calibration pattern acts as a dimensional reference.

As mentioned above, the dimensions of the calibration marks in the physical world (as opposed to in the image) are known. Optionally, the accuracy of the calibration mark distortion correction used in S820 can be cross-checked by measuring the calibration marks in the corrected image and calculating the discrepancy from known sizes of the calibration marks in the calibration pattern.

As step S840, the measurements of the particle object array are characterized. A size distribution histogram, an area distribution histogram, volume distribution histogram, minimum, maximum and standard deviations and distribution peak analysis may be used to determine a set of size parameters that characterize the size and shape of the particles of the ground coffee beans. A "set" of size parameters, as used herein, is intended to mean at least one size parameter.

In some cases, the particle size determination may be made with the objective of processing (e.g., grinding) the particles to achieve a desired size. In these cases, there may be a profile of target particles that is available, and the profile may be defined in terms of the set of size parameters that is used in step S840. Based on a comparison of the measured parameters (result of step S840) against the profile of the target particles, one may determine what action needs to be taken to bring the two profiles closer. This determination may be made automatically by a processor or by a person. Where the determination is made automatically, the processor may indicate to an operator (e.g., visually and/or by sound) that further grinding would bring the measurement closer to the target profile.

When brewing coffee as shown in <FIG> and <FIG>, a user who desires to make coffee of a certain flavor may obtain the profile of target coffee grinds, i.e., the grind size, that he knows would produce the flavor he wants when used with a specific setting in his coffee maker. Such user could sprinkle some coffee grinds on the calibration <NUM> and use the above method to obtain the set of size parameters that characterize his grinds, then compare the size parameters to the target profile. For example, if the set of parameters indicate that measurement distribution for his grinds is centered on <NUM> inch and the target profile is for <NUM> inch, the user would know that he ground the beans too fine and that he needs to restart with a coarser preparation.

Now, further details will be provided about the distortion correction step S820 of <FIG>, and particularly about the generation of a transformation matrix for converting the original, distorted image to a distortion-free corrected image. The actual position of the calibration patterns is known from the physical, real-world calibration pattern. So, a comparison of the two (i.e., the actual position and the position in the image) can be used to determine a transformation matrix (or any other scalar) that converts the imaged calibration pattern back to the actual calibration pattern. This transformation matrix for the calibration pattern shows how to convert the image to real world measurements, and vice versa. The transformation matrix may be extrapolated across the set of pixels and applied to either the whole image or to a selected portion of the image in which, again using a chroma range extraction, just the particles are shown (obtained in step S830). After application of the transformation matrix to the image, a partially-corrected image that is less distorted (and perhaps substantially free of perspective or geometric distortions) is obtained. This approach generates a correction factor to each calibration mark to correct for distortion.

<FIG> depicts another approach <NUM> for distortion correction. Unlike the first approach using the empirically-generated transformation matrix, this second approach entails correcting the image for lens distortion and perspective distortion. Using the calibration mark object array described above and regions of the image referenced by the calibration mark object array at steps S910 and S920, distortion coefficients are obtained. For example, a method described in the calibration method of <NPL> may be used. The method described in Zhang uses a checkerboard pattern to obtain calibration parameters that can be used in subsequent photographs. For the inventive concept disclosed herein, however, the calibration pattern extracted from the image as described above is used. The calibration result obtained will include the lens distortion parameters as k<NUM> and k<NUM>.

The technique proposed by Zhang uses the camera to observe a planar pattern shown at a few (at least two) different orientations. The pattern can be printed on a laser printer and attached to a "reasonable" planar surface (e.g., a hard book cover). Either the camera or the planar pattern may be moved and it is not necessary for the details of the motion to be known. The proposed approach lies between the photogrammetric calibration and self-calibration because 2D metric information is used rather than 3D or purely implicit one. Both computer simulation and real data have been used to test the technique. The technique described herein advances 3D computer vision from laboratory environments to the real world.

Constraints on the camera's intrinsic parameters are provided by observing a single plane. A 2D point is denoted by m = [u,v]T. A 3D point is denoted by M = [X, Y, Z]T. The symbol ~ denotes the augmented vector by adding <NUM> as the last element: m̃= [u, v, <NUM>]T and M̃ = [X, Y, Z, <NUM>]T. A camera is modeled by the usual pinhole: the relationship between a 3D point M and its image projection m is given by: <MAT> where s is an arbitrary scale factor; (R, t), called the extrinsic parameters, is the rotation and translation which relates the world coordinate system to the camera coordinate system; and A, called the camera intrinsic matrix, is given by: <MAT> with (u<NUM>, v<NUM>) the coordinates of the principal point, α and β the scale factors in image u and v axes, and γ the parameter describing the skewness of the two image axes. The abbreviation A-T is used to represent (A-<NUM>)T or (AT)-<NUM>.

The model plane may be assumed as being on Z = <NUM> of the world coordinate system. The ith column of the rotation matrix R will be denoted as ri. From Equation (<NUM>), we have: <MAT>.

The symbol M is still used to denote a point on the model plane, but M = [X, Y]T since Z is equal to <NUM>. In turn, M~ = [X, Y, <NUM>]T. Therefore, a model point M and its image m is related by a homography H: <MAT>.

As is clear, the <NUM> × <NUM> matrix H is defined up to a scale factor.

Given an image of the model plane, a homography can be estimated. Denoting the homography by H = [h<NUM> h<NUM> h<NUM>], from Equation (<NUM>), we have <MAT> where λ is an arbitrary scalar. Using the knowledge that r<NUM> and r<NUM> are orthonormal, the following constraints are obtained: <MAT> <MAT>.

These are the two basic constraints on the intrinsic parameters, given one homography. Because a homography has <NUM> degrees of freedom and there are <NUM> extrinsic parameters (<NUM> for rotation and <NUM> for translation), <NUM> constraints are obtained on the intrinsic parameters. The parameter A-TA-<NUM> actually describes the image of the absolute conic. A geometric interpretation will now be provided.

The model plane, under the convention used herein, is described in the camera coordinate system by the following equation: <MAT> where w = <NUM> for points at infinity and w = <NUM> otherwise. This plane intersects the plane at infinity at a line, and we can easily see that <MAT> and <MAT> are two particular points on that line. Any point on it is a linear combination of these two points, i.e., <MAT>.

Computing the intersection of the above line with the absolute conic, and knowing that by definition, the point x∞ (the circular point) satisfies x∞T x∞ = <NUM>, i.e., <MAT>.

The solution is b = ± ai, where i<NUM> = -<NUM>. That is, the two intersection points are <MAT>.

Their projection in the image plane is then given, up to a scale factor, by <MAT>.

Point m̃∞ is on the image of the absolute conic, described by A-T A-<NUM>. This gives <MAT> requiring that both real and imaginary parts be zero yields (<NUM>) and (<NUM>).

The details on how to effectively solve the camera calibration problem will now be provided. An analytical solution will be presented, followed by a nonlinear optimization technique based on the maximum likelihood criterion. Finally, both analytical and nonlinear solutions will be provided, taking lens distortion into account.

Consider the following Equation (<NUM>):
<MAT>.

Noting that B is symmetric and defined by a 6D vector <MAT>.

Let the ith column vector of H be hi = [hi1, hi2, hi3]T. Then, we have <MAT> with <MAT>.

Therefore, the two fundamental constraints (<NUM>) and (<NUM>), from a given homography, can be rewritten as <NUM> homogeneous equations in b, as shown below in Equation (<NUM>): <MAT>.

If n images of the model plane are observed, by stacking n such equations as (<NUM>), the result can be expressed as: <MAT> where V is a <NUM>n x <NUM> matrix. If n ≥ <NUM>, generally, a unique solution b defined up to a scale factor is obtained. If n = <NUM>, the skewless constraint γ = <NUM>, i.e., [<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>]b = <NUM>, can be imposed and added as an additional equation to Equation (<NUM>). (If n = <NUM>, two camera intrinsic parameters, e.g., α and β, may be solved assuming u<NUM> and v<NUM> are known (e.g., at the image center) and γ = <NUM>. The solution to Equation (<NUM>) is well-known as the eigenvector of VTV associated with the smallest eigenvalue (equivalently, the right singular vector of V associated with the smallest singular value).

Once b is estimated, values in camera intrinsic matrix A can be calculated. Once A is known, the extrinsic parameters for each image may be computed. Using Equation (<NUM>), for example, the following may be obtained: <MAT> <MAT> <MAT> <MAT> with λ = <NUM> / ∥A-<NUM>h<NUM>∥ = <NUM> / ∥A-<NUM>h<NUM>∥. Due to the presence of noise in data, the so-computed matrix R = [r<NUM>, r<NUM>, r<NUM>] does not satisfy the properties of a rotation matrix.

Suppose there are n images of a model plane and m points on the model plane. Suppose also that the image points are corrupted by independent and identically distributed noise. The maximum likelihood estimate can be obtained by minimizing the following functional:
<MAT>
where <IMG> (A, Ri, ti, Mj) is the projection of point Mj in image i, according to Equation (<NUM>). A rotation R is parameterized by a vector of <NUM> parameters, denoted by r, which is parallel to the rotation axis and whose magnitude is equal to the rotation angle. R and r are related by the Rodrigues formula. Minimizing Value (<NUM>) is a nonlinear minimization problem, which may be solved with the Alevenberg-Marquardt Algorithm. It uses an initial guess of A, {Ri, ti|i = <NUM>. n} which can be obtained using the technique described above.

The solutions above do not consider lens distortion of a camera. However, a desktop camera usually exhibits significant lens distortion, especially radial distortion. Now, first two terms of radial distortion will be discussed. It is likely that the distortion function is dominated by the radial components, and especially by the first term.

Let (u, v) be the ideal (distortion-free) pixel image coordinates, and (<IMG>, <IMG>) the corresponding real observed image coordinates. The ideal points are the projection of the model points according to the pinhole model. Similarly, (x, y) and (<IMG>, <IMG>) are the ideal (distortion-free) and real (distorted) normalized image coordinates, <MAT> <MAT> where k<NUM> and k<NUM> are the coefficients of the radial distortion. The center of the radial distortion is the same as the principal point. From <MAT> <MAT>.

Estimating Radial Distortion by Alternation. As the radial distortion is expected to be small, one would expect to estimate the other five intrinsic parameters, using the technique described above reasonably well by simply ignoring distortion. One strategy is then to estimate k<NUM> and k<NUM> after having estimated the other parameters, which will give the ideal pixel coordinates (u, v). Then, from Equations (<NUM>) and (<NUM>), we have two equations for each point in each image: <MAT>.

Given m points in n images, we can stack all equations together to obtain in total 2mn equations, or in matrix form as Dk = d, where k = [k<NUM>, k<NUM>]T. The linear least-squares solution is given by <MAT>.

Once k<NUM> and k<NUM> are estimated, one can refine the estimate of the other parameters by solving Equation (<NUM>) with m̂(A, Ri, ti, Mj) replaced by Equations (<NUM>) and (<NUM>). We can alternate these two procedures until convergence.

The convergence of the above alternation technique may be slow. A natural extension to Equation (<NUM>) is to estimate the complete set of parameters by minimizing the following functional:
<MAT>
where m (A, k<NUM>, k<NUM>, Ri, ti, Mj) is the projection of point Mj in image i according to Equation (<NUM>), followed by distortion according to Equations (<NUM>) and (<NUM>). This is a nonlinear minimization problem, which is solved with the Levenberg-Marquardt Algorithm. A rotation is again parameterized by a <NUM>-vector r, as disclosed above. An initial guess of A and {Ri, ti | i = <NUM>. n} can be obtained using the technique described above. An initial guess of k<NUM> and k<NUM> can be obtained with the radial distortion solutions described above, or simply by setting them to <NUM>.

At step S930, the lens distortion parameters k<NUM> and k<NUM> are then used on the original image to obtain an image that is corrected for lens distortion. Alternatively, instead of using the image, a particle object array that describes the particle's geometries, may be corrected. The lens distortion parameters k<NUM> and k<NUM> are used to correct the image for lens distortion using the following equations (<NUM>) and (<NUM>).

Let (xcorrect, ycorrect) represent the correct locations in the image if there were no distortion due to the lens. Then: <MAT> <MAT> where r<NUM> = (xcorrect -u<NUM>)<NUM> + (ycorrect - v<NUM>)<NUM>, and u<NUM> and v<NUM> are principal points (i.e., the intersection points of the cameral optical axis and image plane).

The lens distortion can then be corrected by warping the recorded bitmap with a reverse distortion. For each pixel in the corrected image, its corresponding location is mapped in the distorted image using equation (<NUM>) and (<NUM>) above. The section below titled Geometric Image Transformations describes how the two-dimensional image coordinates and the three-dimensional world coordinates are related by a camera's intrinsic parameters (e.g., focal lens, principal points, distortion coefficients) and extrinsic parameters (rotation and translation matrix). For each integer pixel coordinates in the destination (corrected bitmap), trace back to the source (recorded bitmap) and find the corresponding float coordinates, using the surrounding integer pixels to interpolate the float coordinates. Bilinear interpolation may be used in this process.

In Summary, the lens-distortion correction procedure proposed here, part of which incorporate Zhang's technique, is as follows:.

At step S940, correction for perspective distortion may be achieved using the four corner points of a rectangular calibration mark to solve the homology H using the following process:
Suppose we have a point in world coordinates <MAT> and we write this in homogeneous coordinates as <MAT>.

Similary, the corresponding point in image coordinates is <MAT>, and we write this in homogeneous coordinates as <MAT>.

The relationship between these two can be expressed in the following equation: <MAT> where <MAT> is the Homography we want to solve.

Expanding both sides of the equation using matrix multiplication, we get: <MAT> <MAT> <MAT>.

Plug in the third equation to the first two, we get two equations from this pair of points: <MAT> <MAT>.

Since there are eight unknowns in H, we need <NUM> pairs of points to solve H. We write the eight equations in matrix form: <MAT>.

Thus, for each image suffers from the projective distortion, we pick four points in this image, and given the world coordinates of these four points, we are able to solve H.

The "k" in the above equation is a scalar for the homogeneous representation of the two-dimensional coordinates, different from the lens coefficients k1, k2. Four points (e.g., four corners where the shape is rectangular) of multiple calibration marks may be used to account for nonuniformity of distortions. The starting point for perspective correction in this approach is not the original image, but the corrected image where lens distortion effects have been removed. The homography H is determined using four points from a set of calibration marks identified in the image corrected for lens distortion, and then is applied to the corrected image to determine a bitmap (the corrected, or true-size, bitmap) that has been corrected for both lens and perspective distortion.

A perspective distortion usually occurs when the camera's optical axis is not perpendicular to the center of the object. Using the image of particles captured on a gridpatterned background, multiple (e.g., five) pairs of orthogonal lines in the scene may be used to find the homography to correct the perspective distortion. This correction will often make parallel lines in the physical world also parallel in the image, orthogonal lines in the physical world also orthogonal in the image, squares in the physical world have unit aspect ratio in the image, and/or circles in the physical world circular in the image.

To summarize the perspective distortion correction process detailed above, the process entails the following steps:.

The lens distortion correction and the projection distortion correction mayb e tested separately and cascaded, so that Shepard's interpolation may only be done once.

The method illustrated in <FIG> and <FIG> may be implemented in a processing device. As discussed with respect to <FIG>, once the camera <NUM> captures the image, the data processing of the image can occur using a processor directly connected to the camera <NUM>, alternatively, the image data may be transmitted to a separate processor.

This section will now talk about some known image transformation functions that may be used to correct and manipulate the image of the particle. More specifically, the functions in this section perform various geometrical transformations of 2D images. They do not change the image content but deform the pixel grid and map this deformed grid to the destination image. In fact, to avoid sampling artifacts, the mapping is done in the reverse order, from destination to the source. That is, for each pixel (x, y) of the destination image, the functions compute coordinates of the corresponding "donor" pixel in the source image and copy the pixel value: <MAT>.

In case the forward mapping is specified as 〈gx, gy〉 : src → dst, the functions described below first compute the corresponding inverse mapping (fx, fy) : dst → src and then use the above formula.

The actual implementations of the geometrical transformations, from the most generic Remap and to the simplest and the fastest Resize, need to solve two main problems with the above formula.

This function calculates an affine matrix of 2D rotation. Some parameters used for this process are as follows:.

The function calculates the following matrix: <MAT> where <MAT> <MAT>.

The transformation maps the rotation center to itself. If this is not the target, the shift should be adjusted.

This function calculates the affine transform from <NUM> corresponding points. Some parameters used for this process are as follows:.

The function calculates the <NUM> × <NUM> matrix of an affine transform so that: <MAT> where <MAT>.

This function calculates a perspective transform from four pairs of the corresponding points. Some parameters used for this process are as follows:.

The function calculates a matrix of a perspective transforms so that: <MAT> where <MAT>.

This process retrieves a pixel rectangle from an image with sub-pixel accuracy. Some parameters used for this process are as follows:.

This function extracts pixels from src at sub-pixel accuracy and stores them to dst as follows: <MAT> where <MAT> and <MAT>.

The values of the pixels at non-integer coordinates are retrieved using bilinear interpolation. When the function needs pixels outside of the image, it uses replication border mode to reconstruct the values. Every channel of multiple-channel images is processed independently.

This function retrieves the pixel rectangle from an image with sub-pixel accuracy.

This function extracts pixels from src: <MAT> where the values of the pixels at non-integer coordinates are retrieved using bilinear interpolation. Every channel of multiple-channel images is processed independently. While the rectangle center must be inside the image, parts of the rectangle may be outside. In this case, the replication border mode is used to get pixel values beyond the image boundaries.

This function remaps an image to a log-polar space.

This function transforms the source image using the following transformation:.

The function emulates the human "foveal" vision and can be used for fast scale and rotation invariant template matching, for object tracking and so forth. The function cannot operate in-place.

This function applies a generic geometrical transformation to the image.

This function transforms the source image using the specified map: <MAT> where values of pixels with non-integer coordinates are computed using one of available interpolation methods. mapx and mapy can be encoded as separate floating-point maps in map<NUM> and map<NUM> respectively, or interleaved floating-point maps of (x, y) in map<NUM>, or fixed-point maps created by using ConvertMaps function. The reason one might want to convert from floating to fixed-point representations of a map is that they can yield much faster (~2x) remapping operations. In the converted case, map<NUM> contains pairs (cvFloor(x), cvFloor(y)) and map<NUM> contains indices in a table of interpolation coefficients. This function cannot operate in-place.

To shrink an image, it will generally look best with INTER_AREA interpolation, whereas to enlarge an image, it will generally look best with INTER_CUBIC (slow) or INTER_LINEAR (faster but still looks OK).

This function applies an affine transformation to an image.

The function warpAffine transforms the source image using the specified matrix: <MAT> when the flag WARP_INVERSE_MAP is set. Otherwise, the transformation is first inverted with InvertAffineTransform and then put in the formula above instead of M. The function cannot operate in-place.

The function is similar to GetQuadrangleSubPix but they are not exactly the same. WarpAffine requires input and output image have the same data type, has larger overhead (so it is not quite suitable for small images) and can leave part of destination image unchanged. While GetQuadrangleSubPix may extract quadrangles from <NUM>-bit images into floating-point buffer, has smaller overhead and always changes the whole destination image content. The function cannot operate in-place.

This function applies a perspective transformation to an image. Parameters useful for this function include the following:.

This function transforms the source image using the specified matrix: <MAT> if CV_WARP_INVERSE_MAP is not set <MAT> otherwise
Note that the function cannot operate in-place.

While some of the embodiments are described in terms of a method or technique, it should be understood that the disclosure may also cover an article of manufacture that includes a non-transitory computer readable medium on which computer-readable instructions for carrying out embodiments of the method are stored. The computer readable medium may include, for example, semiconductor, magnetic, opto-magnetic, optical, or other forms of computer readable medium for storing computer readable code. Further, the disclosure may also cover apparatuses for practicing embodiments. Such apparatus may include circuits, dedicated and/or programmable, to carry out operations pertaining to embodiments.

Examples of such apparatus include a general purpose computer and/or a dedicated computing device when appropriately programmed and may include a combination of a computer/computing device and dedicated/programmable hardware circuits (such as electrical, mechanical, and/or optical circuits) adapted for the various operations pertaining to the embodiments.

Claim 1:
A coffee grinder comprising:
a grinder (<NUM>) for grinding coffee beans;
a grind control unit (<NUM>) for controlling a ground size of the ground coffee beans, the grind control unit (<NUM>) including a camera (<NUM>) positioned over a calibration grid (<NUM>) having a calibration mark; and
a computer processor (<NUM>) connected to the grind control unit (<NUM>),
wherein the computer processor (<NUM>) is configured to:
receive an identifier for the coffee drink, retrieve the correct set of brew parameters from a database (S5030), identify a grind parameter from the brew parameters, wherein the grind parameter includes at least a desired particle size of the grind, and carry out the following iterative grinding cycle until the desired particle size of the coffee grounds is reached:
set the grinder (<NUM>) to a setting and runtime that would achieve the desired particle size of the grind (S5040),
complete grinding process, and
check the grounds (S5050) using the grind control unit (<NUM>) to see if the particle size is within a target range defined by the brew parameters,
whereby during the first iteration, the processor may alternatively set the grinder to a setting and runtime that achieved a slightly coarser particle size than the desired particle size.