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 method for modifying color density values in a dot-based printing system uses a control unit. The control unit implements the modification of the color density values after a raster image has been created and modifies the number and/or size of print dots to be applied to a printing substrate in order to attain pre-defined color density target values.

A color image processing device uses a dither pattern of blocks, each including a plurality of dots representing the gradations of each pixel of an image in a prescribed region. The dither pattern includes a plurality of dot groups stacked, each dot group including dots arranged in a direction where a printing element moves relative to a recording medium, and the beginning of each group is set off by one or more dots in the movement direction, and a halftone image including the pixels is recorded, using variations in density, with the growth order going either from the first dot of the uppermost row of the dither pattern to the last dot of the lowermost row, or from the first dot of the lowermost row to the last dot of the uppermost row.

A special-purpose image processor can convert an electronic file into a bitmap by generating printing halftone dots within the bitmap based on locations of colors within the electronic file, and generating non-printing dots within the bitmap. A printing apparatus can print the bitmap, by not print marking materials where the non-printing dots are positioned within the bitmap. The special-purpose image processor can generate the non-printing dots within the bitmap by increasing the size of the printing halftone dots until they contact one another, or generating printing lines that connect the printing halftone dots to each other within the bitmap. Also, the special-purpose image processor can generate, as each printing halftone dot, a higher frequency pattern of printing dots, where the non-printing dots are generated to have a lower frequency pattern relative to that higher frequency.

A raster image processor (RIP) for digital binary halftoning a continuous tone image (CT) by a threshold tile (TT) into a halftone raster image (RT) for a printing device capable of printing on a plurality of substrates (S.sub.1, S.sub.2, . . . , S.sub.M); wherein said processor comprises an input field in which information regarding a substrate is to be used; a memory having stored thereon a plurality of threshold tiles (TT.sub.1, TT.sub.2, . . . , TT.sub.N) for generating regularly tiled halftone dots; and a threshold selector which is capable to select said threshold tile (TT) of said plurality of threshold tiles (TT.sub.1, TT.sub.2, . . . , TT.sub.N) based on information supplied to the input field.

In an example method, a visually significant marking scheme is generated including a pattern of data marks and reference marks based on a received image to be printed, data information, and reference information. Data marks are generated based on the data information and the reference marks are generated based on the reference information. The image is printed including the data marks and the reference marks arranged based on the visually significant marking scheme onto the surface of the object.

An image forming apparatus includes: a scanning unit configured to form an electrostatic latent image on a photoconductor by scanning the photoconductor with one or more scanning beams in a main scanning direction based on an image signal, repetitively in a sub-scanning direction perpendicular to the main scanning direction; a generating unit configured to perform halftone processing on image data to generate the image signal; and a storage unit configured to store correction information. The correction information is set such that start positions of a plurality of scanning lines are linearly displaced to either a negative side or a positive side of the main scanning direction along the sub-scanning direction, in accordance with a direction of a first vector forming a smaller angle with the sub-scanning direction among two vectors in the halftone processing.

In an example, a machine-readable medium stores instructions which when executed by a processor cause the processor to determine a difference between a measured printed output and an expected printed output. Based on the difference, a first control instruction for controlling a drop size wherein the drop size is variable, and a second control instruction for controlling a dot density of a variable dot density may be determined.

A quantized value for a pixel of interest in an input image is derived by using a predetermined threshold value matrix. Then, based on a pixel value group in a predetermined reference area including the pixel of interest in the input image and a threshold value group corresponding thereto, directionality of correction is determined. Further, based on the pixel value group and the threshold value group, whether or not the pixel of interest satisfies a predetermined condition for changing the quantized value is determined. Then, based on both the determination results, the quantized value is corrected.

In an example, a method includes determining, using a processor, a first halftone screen comprising a plurality of cells. Each of the cells may contain a predetermined pixel cluster pattern, and a centre position of a cluster pattern within a first cell may be different to a centre position of a cluster pattern within a second cell.