Abstract: Multiple input patches are received on an output media, which patches are characterized by print density representing a document processing system's response to different input grayscale values over a potential response space. Values associated with the print density of each input grayscale value are measured. Reference Engine Response Curves are determined from the measured print density values and input gray scale values. A variance data representative of a difference between each measured print density value and a respective reference Engine Response Curve is determined. The variance data is transformed into individual components. Based at least on one selected individual component, a set of calibration compensating Tone Reproduction Curves is determined. The determined calibration compensating Tone Reproduction Curves are applied to input grayscale values.

Abstract: Aspects of color of a halftoned image are controlled or adjusted. A method for adjustment can include determining a color description of a color of an area or window associated with a target halftoned pixel, determining a desired adjustment to the color associated with the target pixel, determining a color change value based on the desired adjustment and the color description associated with the target pixel, combining the color change value with at least one value of the target halftoned pixel, thereby generating at least one combined target pixel value and quantizing the at least one combined target pixel value. For instance error diffusion and/or rank-ordered error diffusion is used to perform the quantization. Color adjustments can be based on user preference and/or calibration compensations between original and target devices.

Abstract: A test target is written in a non image zone at set time intervals. The test target is sensed. At least one of frequency, amplitude and phase of banding, which is inherent in a printing device, is determined based on the sensed test target. At least one banding compensation parameter based at least on one of the determined frequency, amplitude and phase of banding is determined. Characteristics of producing an image based on the determined banding compensation parameter are adjusted to compensate the banding inherent in the printing device.

Abstract: A color correction method includes for each of a plurality of color separations of a digital image, establishing a tone reproduction curve in the form of a vector. The vector is a function of a plurality of basis vectors. The basis vectors account for colorant interactions between a primary colorant with which the color separation is to be rendered and at least one secondary colorant with which at least a second of the plurality of color separations is to be rendered. The vector includes modified input values corresponding to input values for the color separation which vary, depending on the input values of at least the second color separation. For a pixel of interest in the digital image, a modified input value for the color separation which corresponds to the input value of the given color separation is identified from the vector.

Abstract: A color transformation method which accounts for colorant interactions includes establishing a plurality of tone reproduction curves (TRCs), for one or more of the color separations forming a digital image. Each TRC accounts for colorant interactions between a primary colorant with which the first color separation is to be rendered and at least one secondary colorant with which at least a second of the plurality of color separations is to be rendered. The TRCs include input values and their corresponding modified input values. In a given TRC, the input values of the second and optionally other color separations are fixed. For a pixel of the digital image having a given input values for the first and second color separation one or more of the TRCs are selected which bound the fixed input value for the second color separation and a modified input value is determined therefrom.

Abstract: A watermark is provided for use with images or image portions, such as saturated text. The watermark is provided as a modulation to the optical density of a public image or image portion wherein both modulated and unmodulated portions of the public image or image portion have an optical density that is beyond a threshold optical density beyond which the human visual system has a low sensitivity to optical density variations. Alternatively, the modulation is made at such a low amplitude as to be difficult to perceive by the human visual system. The modulation may be applied via an overprinting operation. Alternatively the modulation may be applied to image data prior to printing.

Abstract: Image object adjustment is achieved without lookup tables or templates. Cross sections of image objects are modeled. Parameters of the modeled cross-section are adjusted in accord with a desired effect. For example, a width of the modeled cross section is change. The changed cross section model is sampled to determine a new value for a target pixel. For instance, vector windows are applied to a target pixel. If a candidate image object is included in the vector window, a cross section thereof is modeled as a rectangle. A parameter of the model, such as a width, is adjusted. Area sampling of the adjusted model can be used to determine a new value for the target pixel. Accuracy can be increased by blending information associated with a plurality of vector windows.

Abstract: A method for encoding high resolution data to a form having a reduced number of bits can include predefining a plurality of high-output-resolution output patterns, associating respective output-resolution output patterns of the plurality with respective encoded resolution bit patterns, receiving a block of input-resolution input data, determining a respective difference between a pattern of the received block of input data and the respective output-resolution output patterns, selecting a respective output-resolution output pattern associated with a lowest respective difference to be a representative output pattern for the received block of input data and encoding the received block of input-resolution input data as the respective encoded resolution bit pattern associated with the selected respective representative high-output-resolution output pattern. A system includes a library of output patterns in association with encoded resolution bit patterns, a block analyzer, a block selector and an encoder.

Abstract: Spatially dependent colorant interaction effects are identified and isolated from other aspects of spatially dependent colorant appearance nonuniformities. A decorrelating function for compensating for the identified spatially dependent colorant interaction effects is determined. Spatially dependent single colorant compensating functions for compensating for the other aspects of the spatially dependent colorant appearance nonuniformities may also be determined. Image data is processed through the decorrelating function, thereby generating colorant values that are compensated for spatially dependent colorant interaction effects. Optionally, image data is also processed through the spatially dependent single colorant compensating functions, thereby generating colorant values that are compensated for both aspects of colorant appearance nonuniformities. The two kinds of compensating functions may be determined, calibrated and/or stored at different spatial and temporal frequencies or resolutions.

Abstract: A target pixel is processed according to a blended combination of two or more error diffusion techniques. For example, the two or more techniques may include a standard error diffusion technique and rank ordered error diffusion. Additionally, or alternatively, a quantization resolution is selected for the target pixel based on information regarding the pixel. For example, a quantization resolution is selected based on a relative position of the target pixel or based on a value of the target pixel and/or values of pixels neighboring the target pixel.

Abstract: A method for avoiding objectionable moiré in a color image can include identifying a problematic excitation angle associated with a problematic excitation in a marking process or in the color image and selecting a set of at least two halftone screens for rendering at least two separations of the color image wherein the set of screens is selected to avoid including significant screen fundamental, harmonic and beat frequencies at angles closer than about 1 degree of the identified problematic excitation angle. Halftoning the color image according to the selected set of screens avoids objectionable moiré associated with the problematic excitation.

Abstract: A method of adjusting a TRC of an image is provided. The method involves receiving an image at an input resolution, resampling the image to a processing resolution if the imput resolution and the processing resolution are not same, processing the image using rank-ordered error diffusion, and resampling the processed image to a desired output resolution for the image if the processing resolution and the output resolution are not same.

Abstract: One aspect of the invention provides a method of halftoning an image which involves determining a quantization error for a selected target pixel of an image, selecting a diffusion mask, the mask relating to the target pixel and pixels neighboring thereto, receiving a first pair of neighboring pixel values for a first pixel pair including a first neighboring pixel and a second neighboring pixel, and receiving a second pair of neighboring pixel values for a second pixel pair including a third neighboring pixel and a fourth neighboring pixel. The method further involves determining a ranking order of the first, second, third and fourth neighboring pixels by comparing pixel values of the first, second, third and fourth neighboring pixels, and diffusing error to at least one of the first, second, third and fourth neighboring pixels based on the determined ranking order of the first, second, third and fourth neighboring pixels.

Abstract: Disclosed herein is an image processing method for producing enhanced halftone edges, particularly suited to those edges which only lie upon the background as apposed to those edges which abut other halftone screens. It utilizes a step of defining border pixels and a step of halftoning those border pixels in a different manner than the halftoning applied to the interior region of the tint or image segment. The preferred halftone for the border pixels will be related to the interior halftone by some number of common spatial frequency harmonics.

Abstract: Engine response curves (RCs) can be used for streak compensation for printed documents. A feedback control paradigm can be included to effect RC compensation. Singular Value Decomposition (SVD) can be used to represent each RC in the collection of spatial RC data as a linear combination of basis vectors. RCs are approximated by selecting the first few basis vectors, the approximation aiding in noise rejection and reducing computation in the controller by reducing dimensionality of the RC data from gray levels to the number of SVD bases selected. An optimal subset of RCs is selectable from the set of approximated RCs by clustering the SVD weights, the clustered SVD weights producing TRCs that span all engine response RCs generated by a printer.

Abstract: A method for halftoning a color image, the color image including a plurality of color separations, includes parsing the color image into image objects; examining each image object to determine its color content; for each color separation: determining a dominant color of the image object, wherein a dominant color of an image object is determined in accordance with a predetermined relationship based on a desired output image characteristic; selecting a halftone screen property to optimize for the desired output image characteristic; and selecting a halftone screen having the halftone screen property that is optimized for the dominant image object color and the desired image output characteristic; and halftoning the image object using the selected halftone screens. Using this method, halftone screens can be optimized based on screen angle, screen offset, screen frequency and dot shape.

Abstract: Compensation for rendering device non-uniformities is provided for halftoned images. A spatially dependent tone reproduction curve (TRC) provides compensation values. Pixel location information is used to access TRC values. For example, the values are modification values. The modification values are added to the pixel values to generate combined values. Quantization is applied to the combined values to prepare compensated image data for rendering. For example, Rank Ordered Error Diffusion is applied to the combined values. The combined values may include diffused error from previously processed pixels. Gray values may be estimated for the respective pixels. The estimated gray values may be used to access compensation information from a TRC that is both spatially and gray value dependent. Mathematical basis decomposition is used to reduce TRC memory requirements.

Abstract: A method for minimizing boundary effects when switching between halftone screens on a scanline, includes selecting a first halftone screen having a first fundamental frequency and a first angle for printing pixels of a first type; and selecting a second halftone screen having a second fundamental frequency and a second angle for printing pixels of a second type, wherein the second frequency and second angle are harmonically matched to the first frequency and first angle, wherein at least one pixel of the second type is adjacent to a pixel of the first type. In one embodiment, the first and second frequencies are selected to have a substantially zero frequency beat. In another, the first and second frequencies are selected to have a substantially high frequency beat.

Abstract: A method of measuring and controlling high frequency banding, the method includes creating a test pattern, sensing the test pattern with optical sensors, determining a beat frequency based on the sensed test pattern, and determining the frequency, phase and amplitude of high frequency banding based on the beat frequency. An exemplary embodiment of a feedback control method for controlling high frequency banding includes creating a test pattern, sensing the test pattern with optical sensors, measuring high frequency banding and adjusting the imaging parameters based on the measured high frequency banding in order to decrease the extent of high frequency banding. Moreover, an exemplary embodiment of a system for measuring high frequency banding includes an image marking device having a receiving member, optical sensors arranged on the receiving member, and a controller that is functionally coupled to the optical sensors and to the marking device.

Abstract: A method for sharpening the corners of digital image data within an anti-aliasing image path so as to overcome corner rounding when displayed or printed. The method comprises stepping a window across the image data and comparing that windowed data to templates or performing Boolean logic and arithmetic operations on the image data. Upon determining a match or a corner detection, pixel values are substituted in the identified pixel locations to achieve a clustering of the substituted pixel values about the corner structure producing a corner-enhanced digital image. Filtering and sampling are then performed according to an anti-alias operation to the corner-enhanced image to produce an anti-aliased corner enhanced image. The data substitution will achieve a localized clustering or “ear” of toner/ink, or in the alternative for inside corners the localized clustered absence of toner/ink. The result of this clustering is a sharpening of the corners so that they display or print as intended by the bitmap.