The subject of the inventions is a method of printing on a surface of a sphere and an apparatus for printing on a surface of a sphere, used to apply images recorded by omnidirectional 360 cameras, which allow the recording of images in all directions simultaneously.

The image recorded by such a camera represents/describes the light which reaches the camera from all direction at a given instance of time, when the image (light, photo) was taken. Such an image represents the stream of light which passes through a certain surface (usually a sphere) surrounding camera. Image capturing is typically done using one or multiple electronic light sensitive sensors which can record the amount (intensity) of light in three ranges corresponding to three primary colours (red, blue and green).

Due to the fact that an omnidirectional image represents a stream of light, the image is not recorded on a flat surface, like in typical photo cameras, but on a sphere. As a consequence an image registered in this manner cannot be printed using traditional printing devices, such as laser or inkjet printers, since they are adapted to printing on flat surfaces.

An image is a collection of pixels which represent the amount and colour (wavelength) of light which was fixed or recorded by a photo camera device. In case of digital photography image is a coliection of pixels described in a colour space described by RGB (red, green, blue) components. This model results from the properties of human eye, where an impression of any colour may be caused by mixing three light beams in specific proportions. The RGB space uses additive colours, where the lowest values mean complete black, and the highest - white.

For printing, colours are described using a CMYK palette of four basic colours (cyan, magenta, yellow and black). The final colours in the CMYK method are obtained by combining each the primary colours in proportions from 0% to 100%. CMYK inks are dyes which transmit (or scatter) light, so they are combined not by mixing, but by application by layers, which is why the resulting colour may have from 0% to 400% of colour (that is component colours). Colours created using CMYK should be viewed as layers of coloured, light transparent film.

Conversion of an image generated by a digital device in an RGB space to a CMYK palette colour is performed by special software which edits and processes the recorded image and prepares the material for printing.

The invention concerns a method for the application of a print which represents an omnidirectional image on the surface of a spherical medium, which may be a ball made of plastic, laminate or another printable material.

In the currently available solutions, in order to print an omnidirectional image, in addition to converting an image from the RGB space to CMYK it was necessary to represent the location of the recorded light intensity (image colour point) on the surface of a sphere to a corresponding location on a flat printout surface in accordance with the required mapping. For this purpose cartographical mappings are used, which allow the stretching, mapping or representation of a spherical geometry, such as: cylindrical representation, azimuth representation, stereographic representation, pseudoconic representation, Mollweide representation, Lambert representation and others.

Should any mapping of a sphere onto a plane is used, an omnidirectional image recorded on a sphere is distorted in various manners after printing. Another method of printing an omnidirectional image is direct printing of an image on a ball. In the solutions known and used so far an image on a sphere-like surface is obtained by using:

- water transfer printing

- pad printing

- combined method, using a computer printer, application for appropriate selection of the drawing areas on the pattern, and a cutting plotter.

A spherical image created during a 3D spatial printing using drop on powder (CJP, Colorjet Printing)

THE ONLY currently available on the market technology which enables the representation of a photo on a sphere, however with two significant limitations

- very low quality of the presented image,

- restriction in the size of the printed element (sphere) to the limit size of the 3D printer (depending on the model the maximum diameter is approx. 30 cm)

When using currently available devices and technologies a spherical image may be fixed by the use of technology combining 3D powder printing with the colouring of the powder using during printing (a 3D spatial powder printing, that is CJP (Color Jet Printing)). However, this is a complicated, and multi-stage industrial manufacturing technology, which is currently not being developed due to the development of much more effective and easier to control 3D printing process - e.g. PolyJet technology (models are based using acrylic resin which is hardened with ultraviolet radiation in layers with a thickness of multiple μηη). In the CJP (ColorJet Printing) technology, the creation of a model consists of selective binding of powder using a special, colour binder placed using printing heads similar to the ones in inkjet printers. The process of application and binding of individual layers is repeated until the entire model is finished. A colour image (in this case a photo image on a sphere) is created by binding a properly coloured powder, layer after layer. An image thus created has a very low quality (low contrast, very soft colours and a coarse surface).

All the methods listed above have very important defects compared to the subject of the invention, which practically prevent the effective mapping of the photo on the sphere's surface.

Water transfer printing (hydrographic) is performed by transferring onto items of an image which was printed earlier using flexographic printing on a special, organic transfer film. The graphics are transferred by the immersing the decorated item in water, on the surface of which the film with the printout has been placed earlier. It is a relatively simple technique, which enables obtaining extremely spectacular effects, however it has multiple restrictions. Water transfer may be used on all types of materials (from wood to glass), but requires special preparation of the surface (cleaning, polishing and spraying of special undercoat).

RESTRICTIONS

-due to the need of using a special flexographic printed transfer foil for the application, it is practically impossible to use an arbitrary created image. Very high costs of preparing polymer flexographic stencils in practice restrict the list of patterns which may be used in this decorative technology to proposals of designs prepared by specialised printing houses, which reuse specially designed stencils.

- due to a problem with the orientation of the applied drawing compared to the decorated item and due to numerous distortions which result from stretching and overlapping of fragments of the water transferred drawing film, effective decoration of items with this method may be performed solely using wallpaper patterns (e.g. patterns of wood, fibre, camouflage, animal skin etc.)

- items to which figures are transferred using the described technology have to be made of water-resistant material due to the need for immersion in water

- the image transferred to the item being overprinted should be fixed by spray-painting with a transparent lacquer, which additionally complicates the technological process. Pad printing is an indirect printing method, which is a derivative of intaglio printing, consisting of application of printer's ink using a soft, smooth pad. An appropriately shaped pad enables printing on uneven and irregular surfaces. By selecting printer's ink it is possible to print on surfaces (profiles) such as plastic, rubber, glass, metal etc.

For printing with this technique the following are needed: pad printing machine, matrix (polished metal or polymer plate with engraved or etched pattern), pad and ink.

RESTRICTIONS

- printing is not possible with tonal transitions and combining colours (necessary e.g. when printing photos) due to relatively large ruling and raster dot size

- difficult process of preparing matrices for print which requires special process equipment (imagesetter, matrix etching station)

- technology which is completely unprofitable for printing single items

- may in practice be used only for large print runs

- impossible to transfer accurate (high resolution) graphics and tonal transition graphics (such as photos) onto the surface of a sphere.

A spherical image prepared with a combined method - using currently available devices and technologies, such as a computer printer, application for appropriate distribution of image areas on a pattern, and a paper cutting plotter enables one to present a spherical image by placing graphics on a polyhedron as close to a sphere as possible. By using a special application which enables the modification of a recorded spherical photo file, fragments of images are transposed in a manner which enables printing the image on paper and cutting the drawing by using a cutting shape defined in the software. At the end the cut element is assembled by using special locks (cuts to the paper which enable the connecting of individual edges), as a consequence creating a spatial polyhedron which approximates a sphere.

Creation of a printout with the aforementioned technique is very difficult and time-consuming, it also requires good manual dexterity, access to special software and to a paper cutting plotter. The shape finally obtained is not a sphere, but a polyhedron which approximates a sphere. The essence of the invention, which is a method of printing over a surface of a sphere by moving a printing head along the surface of a sphere, which consists of the print being applied by a printing head over a helix, from the first pole of the sphere to the second pole of the sphere.

It is advantageous when the first pole of the sphere is the bottom pole, and the second pole of the sphere is the upper pole

It is also advantageous when the print is applied by the printing head to a surface of a sphere in the form of sequentially printed great circles.

It is also advantageous when the printing head prints the great circles which pass through both poles of the sphere.

It is also advantageous when the printing head prints in sequence the great circles which are at a maximum distance from the previously printed great circles.

It is particularly advantageous, when the printing head prints the first great circle, then the great circle spaced 90 degrees from the first great circle, then subsequently the two great circles at a 45 and 135 degrees angle to the first great circle, then subsequently four great circles at a 22.5, 67.5, 112.5 and 157.5 degree angles to the first great circle, then the remaining surface of the sphere.

In the solution according to the invention an omnidirectional image could have been already transformed using one of the aforementioned sphere mappings. In this case it is advantageous when the printing head prints the image around the sphere, whereas the omnidirectional image in a cylindrical projection is divided into strips, with a width that depends on the distance between the strip and the equator of the sphere. The farther from the equator towards the sphere poles, the narrower are the applied strips. The image of the strips (layout of colours in the image) then controls a printing head which applies the image to the surface of the sphere being printed, using droplets of ink or toner, in accordance with the layout of colours in the image strips.

According to the invention the print is applied on the sphere surface using a printing unit in the form of a sphere holder and a print head. The essence of the printing unit consists of the sphere being placed on a rotary support which rotates the sphere, and the printing head is located in the sphere surface area.

It is advantageous when the rotary support is a mandrel which rotates around its lengthwise axis, and an element with two arms is placed on the base, with a swinging half-ring installed at the end of the arms on swivels, whereas the swivel rotation axes are located in the ball's equatorial plane, whereas on the half-ring a slider with a moving arm is installed, at the end of which a printing head is installed.

It is also advantageous when the rotary support is a system or rollers installed on the base, electrically powered in order to ensure that the sphere rotates, and the printing head is installed in a fixed manner on the base.

It is also advantageous when the rotary support is a system of powered rollers installed in the base and in the casing of the pressure system, used to rotate the sphere.

It is also advantageous when the image is applied on the surface of the sphere by a raster placement of pixels or by a random placement of the pixels.

It is moreover advantageous when the head for the printing of images on the surface of the sphere is a writing implement, advantageously a pen. The use of the solution presented in the invention enables the following technical and utility effects:

overprinting of the sphere surface without needing to use any mapping which distorts the omnidirectional image,

precise placement of the print on the sphere surface, uniform printing of the entire sphere surface,

high quality of the printed image obtained by the high contrast and sharpness of the print, which result from the contours of fragments of the printed image do not overlap,

short time needed to print the image on the sphere surface, synchronisation of the reciprocal movement of the printing head and the printed sphere,

printing over a sphere with any radius,

continuity of sphere surface printing by synchronisation of the sphere rotation and the operation of the printing head.

The subject of the invention, in an example implementation, which is not limiting, was presented in diagrams on a figure, on which, to better present the invention, the apparatus for the printing of the sphere surface was presented first.

On fig. 1 the unit is presented in the first version of the implementation, on fig. 2 the unit was presented in the second version of the implementation, on fig. 3 subsequent phases of printing the image were presented, on fig. 4 the method of printing an image in cylindrical projection on the sphere surface, and on fig. 5 a unit in the second version of the implementation with a second set of pressure rollers is presented.

In the apparatus for overprinting of the surface of the sphere 1 , in the form of a sphere 1 holder 2 and a printing head 3, the sphere 1 is mounted on the base 4 on a rotary support 5, which rotates the sphere 1, and the printing head 3 is located on the zone of the sphere 1 surface.

There are versions of implementation shown on fig. 1 where the rotary support 5 is a mandrel which rotates around its lengthwise axis, and an element with two arms 6 is placed on the base 4 ₍ with a swinging half-ring 9 installed at the end of the arms 7 on swivels 8, whereas the swivel 8 rotation axes are located in the sphere's 1 equatorial plane, whereas on the half-ring 9 a slider 10 with a moving arm 11 is installed, at the end of which a printing head 3 is installed. In the second version of implementation, shown on fig. 2 the rotary support 5 is a system of powered rollers 12 installed in the base 4, which rotates the sphere 1 , whereas the printing head 3 is placed in the base 4.

In the second version of implementation, shown on fig. 5 the rotary support 5 is placed on the base 4 and in the case of the roller 12 pressure system 13 a system of powered rollers 12 to rotate the sphere 1 , whereas the printing head 3 is installed in the base 4.

There are versions of the implementation when the image is applied on the surface of the sphere 1 by a raster placement of pixels or by a random placement of the pixels.

There are moreover versions of the implementation where the head for the printing of images on the surface of the sphere 1 is a writing implement, advantageously a pen.

In the first version according to fig. 1 the sphere 1 is intended for printing, placed on the base 4 on a rotary support 5. During the rotation of the printed sphere 1 the head printing head 3 moves from the pole of the printed sphere 1 towards the equator, applying a helical print on the surface of the sphere 1. The rotation of the sphere 1 with the movement of the moving part of the half-ring 9 is selected in a manner which ensures that every fragment of the sphere 1 was printed over exactly once. The unit enables the printing of the sphere 1 with varying diameters, due to the placement of the printing head 3 on a moving arm 1 1. The sphere 1 is mounted on a support 5, which enables its placement ensuring that its centre is located in the axis of rotation of the half-ring 9.

In another version of the implementation, according to fig. 2, the printing head 3 is placed in an immovable manner on the base 4. Directly in the zone of the head 3, on the system of rollers 12 the sphere 1 intended for printing is placed. The system of rollers 12 enables the rotation of the sphere 1 in a manner which allows the printing head 3 to overprint every fragment of the sphere 1. The printed sphere 1 is held in the apparatus by its own weight.

In another version of implementation, shown on fig. 5 the sphere 1 is pressed by a second set 13 of rollers 12.

A special process of printing control is implemented by an electrical control device, which enables the rotation of the sphere 1 during the printing in a manner that ensures that every fragment of the sphere 1 is printed over only once.

An integral part of the solution according to the invention is a method for controlling the printing device. In accordance with the method according to the invention an omnidirectional image is transformed to a continuous strip of image data in the form of a helix line, for the solution presented in the first version of implementation, or to a series of rings subsequently printed over the surface of a specially rotated sphere 1.

For both versions of implementation a continuous strip of image data represents subsequent image pixels placed over the sphere 1 surface (in the form of dots of ink, toner etc.), which narrows at the beginning and at the end is printed as a helical line from the one pole, to the other pole of sphere 1 , whereas the narrowing of the image data strip at the beginning and at the end means that less pixels are placed in this area (less dots of ink, toner etc.).

Omnidirectional images are frequently recorded/stored in an equidistant cylindrical projection.

in case of a print of an image recorded/stored in a equidistant cylindrical projection the image is divided into strips of varying width (thickness). The width of a given strip (number of image pixels) depends on the distance of the given strip from the sphere 1 equator. The farther from the equator, the lower width of the strip. Finally the strips taken from the image are scaled to a continuous strip, which widens at the beginning and narrows at the end. In the second version the surface of the sphere 1 is transected by a plane along the line which connects the poles of the sphere 1. This operation results in prints on the sphere's 1 great circle. By changing the longitude of the transecting plane multiple subsequently printers great circles of the sphere 1 are obtained, as shown on fig. 3.

The great circle with the latitude of 0° is printed first - fig. 3a. The great circle with the latitude of 90° is printed second, with the exception of two fragments printed earlier when printing the great circle with the latitude of 0° - intersections of the 0° and 90° circles - fig. 3b. Two great circles at 45° and 135° angles to the first great circle are printed afterwards, then great circles at 22.5°, 67.5°, 1 12.5° and 157.5° angles to the first great circle are printed, fig. 3c, fig. 3d, then the remaining area of the sphere 1 - fig. 3e.