Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
2002-10-30
2004-03-09
Nguyen, Thinh (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C347S043000
Reexamination Certificate
active
06702416
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to ink jet printing, and more particularly to printed media, a method of printing and an apparatus for providing images having grey levels of varying intensity, especially for printing on transparencies used to produce high quality medical images such as X-ray, ultrasound, nuclear medicine, magnetic resonance, computed tomography, positron emission tomography, and angiography. With grey levels is meant black/white and/or colour levels of varying intensity.
BACKGROUND OF THE INVENTION
In medical imaging, it is necessary to print images with a resolution of at least 300 dpi and to have 256 distinguishable grey levels, in order to be able to see enough details in the medical image.
In general, three methods exist to achieve a grey level in an image: area modulated printing, density modulated printing or combined area and density modulated printing.
In area modulated printing, grey levels are achieved by printing on certain places of a printing medium, and not printing on others. Ink with an infinite density is used. Light falling in on the medium passes through areas where nothing is printed, and is absorbed completely by the ink on the printed areas. Different methods are possible to print an image in this way: using one pixel with different dot-sizes, using different pixels with one dot-size or using different pixels with different dot-sizes.
U.S. Pat. No. 6,102,513 describes a method and apparatus for printing an output image on a receiver medium in response to an input image file defined by a plurality of pixels. Each pixel obtains a pixel value. The apparatus includes a print head with a plurality of nozzles. Each of the nozzles is capable of ejecting a plurality of ink droplets therefrom. The centres of ink droplets of different volumes are placed at the centre of a pixel on the receiver. In this way, ink spots of different diameters or sizes are symmetrically placed within pixels on the receiver.
It is very difficult to use an area-modulated printing method to obtain 256 grey levels on 300 dpi in a transparent image, because the printed dots need to be very small (smaller than 10 &mgr;m) in order to come below the Kanamori curve, which is a curve taking into account the non-linearity of the sensitivity of the human eye. If a plane with a first density lies within a plane with a second density, and the density difference between both lies under the Kanamori curve, then the plane with the first density is indistinguishable from the plane with the second density. Furthermore, the dots have to be placed very accurately. If it is desired to have a density of 3 with an infinite ink, an area of {fraction (1/1000)}
th
of the pixel should not be covered, as the relationship between density and transparency is given by T=10
−D
, D being the density and T being the transparency. This means that the droplets have to be placed with an accuracy of
1
1000
of the resolution. This is 2.7 &mgr;m for 300 dpi. If the accuracy is less (the distance between two dots is more than 2.7 &mgr;m for a 300 dpi image), stripes wil become visible.
A second method to obtain a grey image is density modulated printing, in which grey levels are achieved by printing dots of the same size, but with a different ink density. A different ink density is obtained by reducing the transparency of the ink for certain dots. Light passes more or less through the ink, depending on the density or the colour of the ink. Because it is impossible to have 256 heads each printing a different ink, the ink has to be mixed during printing. This can be done either before jetting, such as described e.g. in U.S. Pat. No. 5,606,351 or in U.S. Pat. No. 6,097,406, or on the medium.
In U.S. Pat. No. 6,042,209, continuous tone pixels are produced on a receiver by controlling the amount of ink delivered to the receiver in order to control the optical density of the pixels. All image pixels have equal areas on the receiver, regardless of the volumes of ink deposited. When a low optical density is desired, little ink is delivered; and when a high optical density is desired, more ink is delivered.
In U.S. Pat. No. 5,625,397, plural inks of the same dye, having different densities, are used in a dot-on-dot printing format. That way, a desired optical density level may be readily achieved.
In combined area and density modulated printing, the methods of both are combined.
WO 91/04864 describes a method to improve the printing quality of half-tone originals by means of printers of the type in which a number of dots are brought together in a cell. Each dot in the cell is controlled individually with respect to its size and/or its colour value. The above method has the disadvantage that not enough grey levels can be obtained for printing e.g. medical images.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a plurality of grey scale levels, preferably at least 256, the densities of which are equally spread over the total density range so as to meet the Kanamori curve, i.e. so as to provide a quantisation of the density values wherein increments between a first and a second density value corresponding with successive grey scale values correspond with the minimum perceptible density difference.
It is an object of the present invention to provide printer and a printing method capable of printing a plurality of grey scale levels, preferably at least 256, the densities of which are equally spread over the total density range so as to meet the Kanamori curve, i.e. so as to provide a quantisation of the density values wherein increments between a first and a second density value corresponding with successive grey scale values correspond with the minimum perceptible density difference.
It is an object of the present invention to provide printed media having printing with a plurality of grey scale levels, preferably at least 256, the densities of which are equally spread over the total density range so as to meet the Kanamori curve, i.e. so as to provide a quantisation of the density values wherein increments between a first and a second density value corresponding with successive grey scale values correspond with the minimum perceptible density difference.
The present invention provides a method of printing an image having super-pixels made of a combination of dots on a print medium, wherein each of the dots is independently controlled with respect to the size of each dot, the density of each dot, and an at least part overlap of at least two of the dots.
According to a preferred embodiment, at least two inks with different grey levels may be used.
The present invention also provides a method of selecting a plurality of grey scale levels of super-pixels made of a combination of dots on a print medium, the grey levels being determined by the size of each dot, the density of each dot and an overlap of at least two of the dots, wherein the selection is based on the Kanamori curve. Preferably the plurality of grey scale levels contains 256 grey scale levels. The selection may furthermore be based on stability. By stability is meant the resistance of each grey scale value to printing errors, e.g. the resistance of the density to the errors in the accuracy of placing each dot which makes up a super-pixel or of the control of the size of each dot or density of dot.
All methods of the present invention may be used for providing and selecting grey scale levels for printing medical images.
The present invention also provides an apparatus for printing an image having super-pixels, each super-pixel comprising a combination of dots to be printed on a print medium, the apparatus comprising means for independently controlling dots within a super-pixel with respect to:
1) a size of each dot,
2) a density of each dot, and
3) an at least part overlap of at least two of the dots.
The present invention also provides a printing medium comprising printed data, the printed data being represented by a plurality of super-pixels, each super-pixel comprising a plurality of printed dots,
AGFA-Gevaert
Hoffman, Warnick & D′Alessandro
Merecki John A.
Nguyen Thinh
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