The image processing apparatus obtains a degree of variation in signal values of a plurality of pixels included in a region of a predetermined size that includes a pixel of interest of image data obtained by reading a document on which a halftone-processed image has been printed, obtains a feature amount indicating a brightness of the region. The apparatus updates a difference between the obtained feature amount and an index value corresponding to the obtained degree of variation in accordance with whether or not the difference is larger than a predetermined threshold, with respect to a plurality of index values respectively corresponding to a plurality of mutually different degrees of variation, decides a correction value of the pixel of interest using the updated difference and the index value, and corrects a value of the pixel of interest using the decided correction value.

The image processing apparatus of the present invention includes: a first memory configured to store a first threshold value matrix used for halftone processing; a second memory configured to store a second threshold value matrix that is a threshold value matrix used for halftone processing and whose size is larger than the first threshold value matrix; and at least one circuit, the at least one circuit causing processing below: performing halftone processing for image data by using the first threshold value matrix or the second threshold value matrix selected based on attribute information on the image data, and the first threshold value matrix includes threshold values whose maximum number of bits is N and the second threshold value matrix includes threshold values whose maximum number of bits is M (M<N).

In some examples, dynamic threshold based error diffusion may include determining whether a pixel associated with a pattern to be printed includes a lighter tone or a darker tone compared to an adjacent pixel. In response to a determination that the pixel associated with the pattern to be printed includes the lighter tone or the darker tone compared to the adjacent pixel, a firing threshold may be respectively increased or decreased to respectively decrease or increase a likelihood of printing of the pattern.

An image processing apparatus converts a multivalued image to a binary image, determines a character region and a non-character region in the binary image, extracts areas in units of a character from the character region, determines whether each of the areas is a character region or a non-character region, and extracts, for each of the areas determined to be the character region, a first representative color from the multivalued image included in the area, and generates a binary image corresponding to the first representative color. The apparatus decides a second representative color closest to a color of a target pixel by comparing the first representative color with the color of the target pixel, and changes the binary image of the area corresponding to the first representative color to a binary image of the decided second representative color.

A plurality of halftone processing units are provided for processing each of a plurality of pieces of image data corresponding to a plurality of divided images to generate dot data representing presence or absence of dot formation. At least two halftone processing units simultaneously perform at least a part of halftone processing for at least two pieces of image data. In the halftone processing, complex error diffusion method processing of matching at least a part of dot data obtained by performing halftone processing using an error diffusion method for an error diffused gradation value of each pixel of a divided image with a determination result of a dither method, is performed.

In the case of performing halftone processing using a threshold value matrix, the memory capacity for storing the threshold value matrix is reduced without reducing the image quality of an output image. An image processing apparatus that generates a halftone image by performing halftone processing using a threshold value matrix for each piece of image data of a plurality of color planes corresponding to color materials used for printing processing, and the number of bits of a threshold value in a first threshold value matrix for a color plane whose visibility is relatively low of the plurality of color planes is smaller than the number of bits of a threshold value in a second threshold value matrix for a color plane whose visibility is relatively high of the plurality of color planes.

In some examples, dynamic threshold based error diffusion may include determining whether a pixel associated with a pattern to be printed includes a lighter tone or a darker tone compared to an adjacent pixel. In response to a determination that the pixel associated with the pattern to be printed includes the lighter tone or the darker tone compared to the adjacent pixel, a firing threshold may be respectively increased or decreased to respectively decrease or increase a likelihood of printing of the pattern.

A look-up table for use in a printing system is created. The printing system prints an input image in a print color space. The look-up table is created by accessing a predetermined look-up table representing a mapping of color values of an input color space to ink-vectors of a print color space; applying a p-by-q halftone threshold matrix to each ink-vector of the predetermined look-up table to generate a p-by-q halftone cell for each ink-vector; and creating a further look-up table which maps, at least a sample of, the color values of input color space to the at least one halftone cell.

From among a plurality of elements included in a printing head and arrayed in a predetermined direction, a faulty element that is unable to form dots properly on a printing medium is identified. At least one of correction processing for increasing a value of multi-valued input image data corresponding to the faulty element and correction processing for decreasing a threshold in a quantization process for the faulty element is performed. Complementary dot data is generated for the faulty element by taking the dot data generated for the identified faulty element as dot data corresponding to an element near the identified faulty element in the predetermined direction.

An image processing apparatus includes at least one memory storing instructions and at least one processor executing the instructions to provide an input unit configured to input image data representing a color of an image, and information identifying high gloss and low gloss areas in the image, a first determination unit configured to determine, based on the image data, a recording amount of a printing material for forming the image on a recording medium, and a second determination unit configured to determine a dot arrangement of the printing material by halftone processing for the recording amount according to the information.