Abstract: A method and apparatus for quantizing pixels in an image formed by a plurality of pixels, each pixel constituting an image signal representing optical density of the image at a location therein, and having an original optical density value selected from one of a set of `c` original optical density values that has a number of members larger than a desired output set of `d` optical density values, through a process of error diffusion. For an input image so comprised, initially, an image signal is initially modified in accordance with previously determined error. Thereafter, during the quantization step of the process, the threshold signal for quantization determination is dynamically adjusted in accordance with previous output quantization determinations to selectively control likelihood of whether the next pixel will exceed the threshold.

Abstract: A multifunction device having at least a facsimile function, a scanner and an image processing circuit is provided. The image processing circuit includes a circuit for applying a TRC correction to gray values derived at the scanner, before a halftoning circuit quantizes the gray values for printing. The TRC correction circuit includes at least two stored TRC correction functions that can be applied by the TRC correction signals. In making a call to transmit a document via the facsimile function to a called station, the exchange of signals required for establishing the facsimile connection includes identification of a preferred TRC correction function preparatory to printing at the called station printer. In accordance with the identification of a preferred TRC correction function, the image processing circuit operates on image signals derived at the scanner, to provide TRC correction of the image signals preparatory to printing at the destination printer.

Abstract: A method of decompressing a document image compressed with JPEG ADCT and a subsequent statistical encoding method, includes an iterative processing step, which filters the image to correct for compression/decompression artifacts, and subsequently checks the ADCT coefficients of the filtered image to determine whether the filtered image is a possible one, given the received original ADCT coefficients and Q-Table description. In such an arrangement, the iterative process step can be terminated at a preselected number of iterations based on the measured size of the statistical encoding prior to removing the statistical encoding.

Abstract: In a device for processing color images preparatory to printing, there is provided a method of reducing marking material coverage in text and line art areas of secondary colors including the steps of: a) determining the locations of text and line art color pixels having excessive marking material coverage; b) upon determining the locations of color pixels having excessive marking material coverage, processing separation pixels to turn OFF a predetermined portion of the separation pixels corresponding to color pixels having excessive marking material coverage; and c) to prevent artifacts from occurring in the pixel reduction step, processing a given area of separation pixels in an order which tends to randomize the turn OFF effect.

Abstract: A method for processing images for printing includes the steps of for each separation, making a pixel level determination of marking material coverage, based on the number of pixels within a given area that are turned on; if a determination is made that too much marking material will be placed within the given area, turning off a fraction of pixels in the area to reduce the amount of marking material that will be used for the given area; and to preventing artifacts from occurring in the pixel reduction step by utilizing a processing order through each given area which tends to randomize the turn off effect. Additionally, the results of the determination are compared for each separation, to determine that the turnoff result allows at least one corresponding pixel among each of the separations to be turned ON.

Abstract: Halftone screens are generated for each separation in accordance with the goal of avoiding overlapping whenever possible. Initially, the black separation is halftoned, generating a dot with a number of ON pixels and OFF pixels in accordance with the area density of the black separation. Next, a first color separation is halftoned, setting a number of the previous OFF pixels to ON. Then, if any white pixels remain, the second color separation is halftoned, setting a number of the previously OFF pixels to ON. After the second color separation is halftoned, if any OFF pixels remain, the third color separation is halftoned, setting a number of the previous OFF pixels to ON. If during the processing of the second and third separations, it is determined that no OFF pixels exist to be turned ON, second and third layers of color is started, respectively superimposed over the first layer and then, if required, superimposed over the second layer.

Abstract: A color printer, responsive to printer signals to deposit printer colorants on a medium in accordance with printer signals received, is calibrated by operating the color printer with printer signals selected to cause the printer to print color samples on the medium; measuring the color samples to determine a first colorimetric response of the printer to the printer signals using the first measured colorimetric response to generate a first mapping of colorimetric values to printer signals; using the first measured colorimetric response or a subsequent measured colorimetric response to generate at least one additional mapping of colorimetric values to printer signals; storing the first and additional mappings in a color conversion memory producing printer signals as a function of the first and additional mappings stored in the color conversion memory to convert color definitions from a first color space to the printer signals suitable for producing a corresponding response at the color printer.

Abstract: An input scanner is provided with a housing adapted for support on a level surface, having a first external surface supporting a platen at a first angle with respect to the level surface and a second surface adjacent to the first surface and forming an angle with the first surface forming a book supporting surface; a scanning element supported with the housing for scanning motion past the platen, the scanning element supporting a linear array of photosensitive elements substantially in parallel with the platen, for image acquisition during scanning motion past the platen; and a drive arrangement, coupled to the scanning element, to drive the scanning element in scanning motion. Optionally provided is an adjustable housing support, normally in a first condition supporting the housing in a fashion maintaining the first angle relationship between the platen and the level surface, and adjustable to a second position to bring the platen into a parallel relationship with the level surface.

Abstract: A method of producing a raster font from a contour font entailing the steps of deriving font metrics and character metrics of font characters in terms of arbitrary font units; scaling the font characters to a selected size and output resolution (pixels per unit length); altering the thickness of vertical and horizontal strokes of each character to a desired thickness, from the measured font metrics and character metrics, and including a difference applied to the thickness of the strokes by the printer process, to cause the strokes to be close to an integer number of pixels and thickness and to compensate for thinning and thickening which the printing engine might produce; bringing the leading and trailing edges of the characters to integer pixel locations, where such locations are based on and scaling the character between the leading and trailing edges proportionally therebetween, and producing a rasterized font from the altered contour font character.

Abstract: A method and apparatus for image-dependent color saturation correction in natural scene images in electronic documents is provided, wherein an input image is converted from its original color space definition to a luminance-hue-saturation color space, such as HSV space, where S has a strong correlation to perceived saturation. That saturation component of the signal is averaged over the image for at least a region of its input value range corresponding to brightness, and the determined average is compared to a threshold selected to represent desirable saturation level. If saturation is less than target saturation, a filtering function is selected, operable on the image to enhance saturation as a function of the average saturation and desired saturations. Otherwise, no change is made to the image.

Abstract: A method of improving the contrast in a natural scene image, in which the image is converted from an original set of color coordinates to an expression where one term has a relationship to overall image intensity. A global histogram of the image is derived for that term, which plots the populations of pixels at each possible level of intensity in the image. The signal describing the histogram is operated on with a filter having the characteristic of weakening strong peaks and valleys in the function, but not effecting flat portions of the signal. The filtered histogram signal is used for controlling the TRC mapping in a device at which the image is to be printed. Contrast is improved in areas likely to have the most image information, using the method described above, and further, dividing the image into a number of segments, each describable by a local histogram signal for that image segment. Each local histogram signal is compared to the global histogram, to determine which signals are flatter.

Abstract: A digital copier with mail preparation functions including a document input scanner deriving an electronic representation of an original document placed at a scanning position associated therewith; a document editor, responsive to operator command from a user interface to identify in, an original document an area thereof including an address; a document creator, for combining the image from the identified area with a pre-stored envelope image; a source of sheets and envelopes; means for selectively feeding sheets and envelopes from the source to a printer; the printer is controlled to create an image on the selected sheet or envelope in accordance with the created envelope image.

Abstract: A method of calibrating the response of the printer to an image described in terms of colorimetric values, including the steps of: a) setting printer parameters; b) deriving a printer response characteristic by printing a calibration test from device dependent printer signals stored in a device memory, the calibration image including a plurality of color patches, some of which may be repeated at a plurality of locations on the test image at spatially disparate locations selected to keep local printer non-uniformities from affecting both locations; c) measuring printer response characteristics in device independent terms; d) generating a memory mapping of device independent colors to printer responses for subsequent use in printing images defined in device independent terms.

Abstract: A method of altering the exposure in the reproduction of an electronically encoded natural scene image, including process steps of a) receiving an electronically encoded natural scene image, where the encoding is in terms of red-green-blue signals; b) converting the signals to a luminance-chrominance signal format, wherein at least one signal represents overall image intensity; c) comparing the intensity signal to a pair of preset threshold signals T.sub.light, T.sub.dark, respectively indicating satisfactory brightness and darkness of the image and producing a multi-state signal responsive to the comparison; d) if the signal state indicates that both thresholds are exceeded, or that neither threshold is exceeded, directing the electronically encoded image without alteration to further processing; e) if the signal state indicates that one of the pair of preset thresholds is exceeded, the original electronically encoded signal is processed in accordance with the equation:OutputI=InputI.sup..gamma.

Abstract: An image processing system for preparing a color document for printing, each discrete area or pixel in the image described by a signal having a number of possible states greater than can be rendered by a selected printer, in which each separation of the image is halftoned, with at least one of the separations processed with a non-periodic halftoning method, and at least one of the remaining separations processed with a periodic pattern. Preferably, in a printer printing with colorants approximating cyan, magenta, yellow and black, one of the non-yellow separations is processed with the non-periodic halftoning method.

Abstract: A method of decompressing a document image compressed with JPEG ADCT or the like method of compression includes: a) receiving encoded quantized transform coefficient blocks for the original image; b) removing any lossless encoding of the quantized transform coefficient blocks for the original image; c) multiplying each quantized transform coefficient in a block by a corresponding quantizing value from the quantization table to obtain a block of received transform coefficients; d) recovering the image by applying an inverse transform operation to the received transform coefficients; e) reducing high frequency noise appearing in the recovered image as a result of the lossy quantization process, while preserving edges, whereby the appearance of the recovered image is rendered more visually appealing; f) changing the filtered recovered image into blocks of new transform coefficients by the forward transform coding operation using the frequency space transform compression operation; g) comparing each block of new

Abstract: High addressability image signals, each representing a pixel in an image, where the signal has one of a relatively large number of signal levels, are directed through an error diffusion quantization process, for the conversion of the signal to one of a relatively small number of levels. Each signal is modified by a correspondingly weighted error correction term signal or signals from previously processed image signals, thereby generating a modified image signal. This modified image signal is compared to a threshold to derive a preliminary output signal having a smaller number of levels. The preliminary output signal is directed to an output if it has the same level as the previous output signal. If the preliminary output signal does not have the same level as the previous output signal, the preliminary output signal is directed to the output only if the previous output signal was one of a contiguous group of a preselected number of like level signals.

Abstract: A method for correcting color shifting produced by improper imaging, in a digital signal representation of a natural scene image including the steps of: determining the white point of an image; determining the black point in an image; calculating a color correction for the image as a function of the white point and the black point and applying the correction to each pixel in the digital signal representation of a natural scene image for printing.

Abstract: A method of altering the sharpness in the reproduction of an electronically encoded natural scene image, including process steps of: a) converting the signals to a luminance-chrominance signal format, wherein at least one signal represents overall image intensity; b) determining the maximum local contrast within the image; c) determining a filter function applicable to the image which increases maximum local contrast to a predetermined target value, and all other contrast to an amount proportional thereto; and d) applying the determined filter function to the image to increase sharpness thereof.

Abstract: A method of improving the appearance of an ADCT decompressed document image while maintaining fidelity with an original document image from which it is derived, the method including the decompression steps of: a) receiving the encoded quantized transform coefficient blocks for the original image; b) removing any lossless encoding of the quantized transform coefficient blocks for the original image; c) multiplying each quantized transform coefficient in a block by a corresponding quantizing value from the quantization table to obtain a block of received transform coefficients; d) recovering the image by applying an inverse transform operation to the received transform coefficients; e) i) adaptively selecting on a block by block basis a filter threshold, ii) detecting edges within the block and forming a mapping of the edges occurring, and iii) iteratively filtering for a predetermined number of times the image with a smoothing filter, the filtering operation controlled by the derived edge map so as not to oper