Abstract: An apparatus for dithering a signal such as a pixels of an image having multiple address dimensions. A predetermined number of least significant bits of a first address of the pixel are used to index a one-dimensional dither array. Indexing the array produces a first dither value. A predetermined least number of significant bits of a second address of the pixel are combined with the first dither value to index a second one-dimensional dither array. The indexing of the second array produces a final dither value that can be used to dither the pixels.

Abstract: In an image scaling method and apparatus that uses adaptive edge enhancement, a plurality of sets of gradient threshold values and enhancement threshold values correspond respectively to predetermined enhancement modes. The enhancement mode corresponding to a mean pixel value for a one-dimensional pixel array that includes a center pixel to be updated and neighboring pixels of the center pixel is determined so that one of the sets of gradient threshold values and enhancement threshold values corresponding to the selected enhancement mode can be selected. After a sharpness value is computed by adding together absolute values of differences between values of the center pixel and each of the neighboring pixels, one of the enhancement threshold values in the selected set is selected by comparing the sharpness value with the gradient threshold values in the selected set.

Abstract: Halftone-dot image data in a position space is converted into data in a frequency space by fast Fourier transform unit, and data including low-frequency noise components whose frequency is lower than the fundamental frequency component of halftone dots is extracted from the data in the frequency space by a low-pass filter. The extracted data including the frequency noise components is inversely converted into image data in the position space by an inverse fast Fourier transform unit. Pixels of the halftone-dot image data in positions which correspond to pixels including the noise components in the inversely converted image data are corrected by a corrector such that the noise components will be reduced. The correcting process is in the position space, and can simply be carried out.

Abstract: An apparatus and method of reducing impulse noise using a median filter involve selecting a pixel of median.sub.-- value from a plurality of pixels, comparing a reference range, determined by adding or subtracting an offset value to or from the selected median.sub.-- value, with a mid.sub.-- pixel among the plurality of pixels, to determine whether the input image signal has impulse noise and generate a noise coefficient depending on the presence of impulse noise, calculating a correlation between the luminance component of a pixel and the color component thereof depending on the noise coefficient, and cross-fading the pixel of median.sub.-- value and the mid.sub.-- pixel depending on the correlation.

Abstract: A dithering device converts a multi-gradation image into a binary image by comparing, in sequence, values of pixels forming the multi-gradation image with threshold values of corresponding elements forming a dither matrix. For determining the element corresponding to the pixel, the dithering device uses an array representing a relationship between a first group of positions of the elements to be used currently and a second group of positions of the elements to be used next. By referring to the array, the dithering device determines the position of the element from the second group based on the position of the element in the first group so as to compare the next pixel with the threshold value of the determined element.

Abstract: A non-causal error diffusion technique that is capable of gray image signals into binary image signals to prevent the occurrence of visible correlated patterns and/or artifacts. In the non-causal error diffusion method, transformation errors produced when great gray level sets of image signals for a certain pixel are transformed into reduced gray level sets of image signals are reflected to the image signals for pixels at non-causal locations with respect to the certain pixel.

Abstract: A method and a system for color converting an HT image according to a desired color conversion. The method includes the steps of dilating the HT image to form a dilated HT image, converting the original HT image and the dilated HT image to CT images, color converting the CT image from the original HT image to form a converted CT image, and then using the CT images as a guide to interpolate between the dilated and the original HT images.

Abstract: A system and method for reducing noise using recursive noise level estimation. The system and method for noise reduction substitute a target pixel in a processing window with a weighted average of a plurality of neighboring pixels according to the degree of similarity between thc target pixel and the neighboring pixels. The similarity is based on the noise level affecting the image and the local brightness of the processing window. The filter is based on fuzzy logic and filters out noise without smoothing the image's fine details. The filter uses a human visual system (HVS) response to adjust brightness.