An image forming apparatus includes an image forming section and a controller. The image forming section forms an image on a first sheet or a second sheet. The controller controls the image forming section. The first sheet is a blank sheet. The second sheet is a reused sheet. The controller refers to reference images each belonging to any of a plurality of categories to determine whether or not the image belongs to any of the categories. The controller directs the image forming section to form the image on the second sheet when determining that the image does not belong to any of the categories. The controller directs the image forming section to form the image on the first sheet and stores the image as a reference image when determining that the image belongs to any of the categories.

In an error diffusion process, a control device determines a dot value of a target pixel by using a gradation value of the target pixel, and an error value. The control device determines distribution error value by comparing a gradation dependent value with a first evaluated density value indicating a density of a first dot. The control device determines the distribution error value by using the first evaluated density value when the dot value of the target pixel indicates formation of the first dot and when the gradation dependent value is smaller than or equal to the first evaluated density value. The control device determines the distribution error value by using a modified evaluated density value greater than the first evaluated density value when the dot value indicates formation of the first dot and when the gradation dependent value is greater than the first evaluated density value.

The present invention provides an image processing apparatus which employs a dither method capable of printing a thin line of desired density without any break irrespective of printing conditions. The first threshold changing unit changes part of threshold values in a threshold matrix to generate a first threshold matrix so as to increase the number of dots to be printed in a specific pixel area. The second threshold changing unit changes part of threshold values in the threshold matrix to generate a second threshold matrix such that the number of dots to be printed in a specific pixel area is smaller than the case of changing a threshold value by the first threshold changing unit. A determining unit determines whether a threshold value in the threshold matrix is to be changed by the first threshold changing unit or by the second threshold changing unit.

An image processor performs: determining a dot value indicating a dot formation state, the determining including: in a case where a target pixel is not an edge pixel and a first dot forming condition is satisfied, setting the dot value to a value indicating forming a first dot; and in a case where a second dot forming condition is satisfied, setting the dot value to a value indicating forming a second dot; determining a distribution error value, the determining including: in the case where the target pixel is not the edge pixel and the first dot forming condition is satisfied, setting the distribution error value to a value corresponding to a density of the first dot; and in the case where the second dot forming condition is satisfied, setting the distribution error value to a smaller value than a value corresponding to a density of the second dot.

A halftone comprises a first halftone screen and a second halftone screen. The first halftone screen comprises a first plurality of amplitude modulated dots arranged according to a first plurality of rows, the first plurality of rows being orientated according to a first direction and comprising a first dot spacing. The second halftone screen comprises a second plurality of amplitude modulated dots arranged according to a second plurality of rows, the second plurality of row being orientated in a second direction and comprising a second dot spacing. The first direction and the second direction define an angle of 45 degrees or less and a ratio of the second dot spacing to the first dot spacing is less than one.

An example embodiment may involve causing a page of a document to be printed on a printing device, wherein the printing device is in an AM halftoning mode and prints the page using an AM halftone; displaying, on the display unit, a graphical user interface, wherein the graphical user interface includes a selectable option to switch the printing device from the AM halftoning mode to an FM halftoning mode; receiving an indication that the selectable option has been selected; possibly in response to receiving the indication that the selectable option has been selected, causing the printing device to switch from the AM halftoning mode to the FM halftoning mode; and causing the page of the document to be printed again on the printing device, wherein the printing device is in the FM halftoning mode and prints the page using an FM halftone.

A method for compensating tone value fluctuation in inkjet printing includes generating multi-bit halftone images of pixels on a computer during prepress screening for color separations with multiple tone values out of print image data, forwarding multi-bit halftone images to a control unit of an inkjet printing machine, and printing the multi-bit halftone on the machine, wherein encoded binary values of multi-bit halftone images correspond to ink drop sizes to be generated by the machine. The computer introduces additional binary values of multi-bit halftone images not corresponding to ink drop sizes in pixel positions of multi-bit halftone images where occurring tone value fluctuations are to be compensated for by modified ink drop sizes, causing additional binary values to be ignored by the machine in a regular print mode, and assigning additional binary values to modified ink drop sizes in a correction print mode.

A secure image for a security document is generated by performing a rasterization process for each of a plurality of mono-color base images using a plurality of different threshold functions. For each base image, the plurality of threshold functions cover different intensity regions and result in a complex rasterization pattern depending on the intensity of the input image. The resulting binary images obtained by the rasterization process are combined using offset printing with fluorescent inks of different colors, to result in a multi-color fluorescent output image including a plurality of different complex rasterization patterns.

A block configured with Nb pixels included in image data is classified into Nt groups, position information which is information indicating a position of the pixel configuring is created, a block gradation value is decided by a data amount smaller than a data amount required for representing gradation values of the Nb pixels based on the gradation value for each pixel configuring each group, for each of the Nt groups, dot arrangement which is information indicating the presence or absence of dot formation for each pixel configuring the block is temporarily decided based on the block gradation value, for each of the Nt groups as the target, the dot arrangement targeting the block is decided by using the temporarily decided dot arrangement and the position information, and it is determined whether or not the dot arrangement decided by the dot arrangement deciding unit is corrected by using an error diffusion method.

A method corrects color density unevenness during a printing operation on an inkjet printing machine having printing nozzles and a computer. The computer modifies the number or size of the drops to be applied to a printing substrate to attain nominal color density values after the processing of a rasterized print image. For different actual tone values, it is determined which target tone value is required to attain a nominal coloration by measuring a test image for every printing nozzle using a color measurement device, and, based thereon, an area coverage-dependent compensation profile is determined and saved on the computer to be applied in the printing operation to calculate the number and size of the drops on the computer.