This disclosure relates to advanced image signal processing technology including encoded signals and digital watermarking. One implementation is directed a printed object comprising: a substrate comprising a first area; a first colored ink or design printed within the first area, the first colored ink or design comprising a spectral reflectivity of less than or equal to 20% at or around 660 nm; a colored ink mixture printed over the first colored ink or design at a first plurality of spatial locations within the first area, the colored ink mixture printed such that the first area comprises a second plurality of spatial locations without the colored ink mixture, the colored ink mixture comprising opaque white ink and a first colorant, wherein the color ink mixture comprises a spectral reflectivity greater than the first colored ink or design at or around 660 nm, and wherein colored ink mixture comprises a spectral reflectivity less than the first colored ink or design in the range of 495 nm-570 nm; in which the first plurality of spatial locations is arranged in a pattern conveying an encoded signal, and in which the first colored ink or design and the colored ink mixture comprise a spectral reflectivity difference at or around 660 nm in a difference range of 8%-30%. Of course, other objects, methods, packages, labels, containers, systems and apparatus are described in this patent document.

A method for building a security image for a security structure of a security document from multiplexing color images, including selecting a marking method capable of producing sets of colors on the security document comprising different colors that can be displayed according to illumination/observation modes of the security structure, establishing a plurality of color sets that can be displayed by the security structure in a plurality of the different illumination/observation modes, distributing the color sets in a plurality of groups of color sets, establishing combinations of groups of color sets having at least one color set in common across the number of different illumination/observation modes, selecting a combination of a group of color sets based on the number of desired illumination/observation modes and the number of colors per color image, and determining the color images to multiplex by means of the combination of the group of color sets selected.

A watermark image may be generated that includes a first set of encoded pixels each of which is assigned a first transparency value and a second set of encoded pixels each of which is assigned a second transparency value, the second transparency level being different from the first transparency level. The encoded pixels may be distributed among a set of blank pixels such that each encoded pixel neighbors one or more blank pixels in the watermark image, and in particular at least two blank pixels in the watermark image. Herein, each blank pixel may be assigned the second transparency value. The watermark image may be overlaid and blended over a background source image to create an encoded source image. A decoder system may recover encoded information from the encoded source image.

This disclosure relates to advanced signal processing technology including signal encoding and image processing. One implementation describes an encoding system including a masking module. The masking module scales or eliminates signal encoding adjustments based on an image's luminance or chrominance values. Of course, other implementations, combinations and claims are also provided.

A method of printing authentication indicia by applying an at least amplitude-modulated halftone print in a detection zone to an object uses adjoining halftone cells, in each of which a halftone dot is printed from a matrix of printable halftone elements, individual tone values of the halftone print corresponding in each case to a halftone plane of a halftone mountain for a halftone dot. In this process, the assigned screen plane of the screen mountain is modified in the detection zone in a predetermined manner for a plurality of tone values of screen dots to be printed, so that a predetermined matrix image of the screen elements to be printed is assigned to it while the tone value of the print remains constant.

Disclosed are a quantum color image encrypting method based on modification direction and corresponding circuit, respectively providing quantum modular circuits design for a parallel adder, a parallel subtractor, a comparator, a cyclic shift add 1, and a cyclic shift subtract 1; and based on these modular circuits, circuit for implementing quantum color image steganography is provided. From the complexity analysis of implementing quantum circuit for color image steganography, it is seen that for a two-dimensional quantum color image with 2.sup.2n pixels and the R, G, and B channels of which are respectively represented by q number of quantum bits, the steganography algorithm is an efficient transformation method, and the circuit complexity is O(q.sup.2+n), which can hardly be achieved by classical geometric transformation. The disclosure is applicable for many practical image processing applications, e.g., transmitting secrete data via a public image; they all need an effective and secure steganography algorithm; besides, the present disclosure is significant in perfection and applications of image processing theories.

An image forming apparatus includes an image forming device that forms an image on a recording medium and circuitry that controls the image forming device. The image forming device forms an invisible image with an invisible material on the recording medium and forms a visible image with a visible material on the invisible image. Each of first and second adhesion amounts includes respective adhesion amounts of the visible material and the invisible material per unit area in a portion, in which the visible image is formed on the invisible image, of the composite image. The second adhesion amount is smaller than the first adhesion amount. The controller adjusts the amount of the invisible material included in the second adhesion amount to be smaller than that included in the first adhesion amount, to cause the image forming device to form the image according to the second adhesion amount.

A color chart is for evaluating printing quality of an image forming apparatus. The color chart includes identification information and a color evaluation patch. The identification information is on an image forming apparatus on which evaluation of printing quality is to be performed. The color evaluation patch includes a plurality of color patches for performing evaluation of printing quality on the image forming apparatus indicated by the identification information.

A method of verifying an authenticity of a printed item includes: photographing the printed item to obtain a photographic image of the printed item, retrieving reference data of the printed item, the reference data including a reference image of the printed item, determining a test noise parameter from the photographic image of the printed item, determining a reference noise parameter from the reference image, comparing the test noise parameter of the photographic image of the printed item to the reference noise parameter of the reference image, and determining an authenticity of the printed item from a result of the comparing. The determining the authenticity of the printed item from the result of the comparing may include establishing from the reference noise parameter of the reference image and the test noise parameter of the printed item.