Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
2002-07-24
2003-12-23
Nguyen, Lamson D (Department: 2861)
Incremental printing of symbolic information
Ink jet
Controller
C358S506000
Reexamination Certificate
active
06666538
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a recording method of medical image and a medical image recording apparatus capable of producing a medical image which has such a high quality as to be fit for diagnosis as a transmission image and is of such a good image quality that it never produces reversing of density gradation when it is observed as a reflection image.
BACKGROUND OF THE INVENTION
In recent years, in X-ray radiography, in place of an SF system, a system for picking up a digital electrical signal of an X-ray image such as a computed radiography (CR) system or a system employing a flat panel X-ray detector (FPD) has appeared. With the spreading of what is called a digital X-ray image pickup apparatus, also a digital medical-use image recording apparatus for recording a medical image on the basis of an electrical signal obtained by a CR system or an FPD system is spreading.
A recording method which has now become the greatest mainstream is a silver halide laser writing method in which an image is formed through converting an electrical signal of an X-ray image obtained by a CR system or an FPD system into laser beam intensity variation and carrying out print and development processing on a conventional silver halide film. However, because the method uses a silver halide film in the same way as a conventional method, there is a problem that it is troublesome and costs much.
As regards a method not using a silver halide film, a thermal transfer method or a sublimation-type printer can be considered. However, in the case of a thermal transfer method, the ink of a recorded image is present on the uppermost surface of a film, which produces a trouble such that ink is easy to be transferred in handling. Further, in the case of a sublimation-type printer, sufficient density cannot be obtained and waste matter such as an ink ribbon is produced after image formation as in the case of a thermal transfer method.
Lately, an image recording apparatus employing an ink jet method has become versatile as a small-sized low-priced printer, which enables the great improvement of the resolution and quality of a recorded image. Therefore, by applying an ink jet recording apparatus to X-ray image formation, the above-mentioned trouble is to be solved, and it is expected that an ink jet image forming method capable of forming an X-ray image which is made of low cost and easy to observe by making the most of the advantage of an ink jet printer can be provided.
Now, it is a subject in an image recording apparatus of not only an ink jet method but also all other recording methods that, for a medical image used mainly in diagnosis, an extremely high image quality is required.
It is said that the number of gray levels in a simple X-ray radiograph required for diagnosis is 10 bits (=1024 gray levels), and further, the number of gray levels enabling sufficient diagnosis is 12 bits (=4096 gray levels). In the case where an image of multiple gray levels such as a medical image is expressed by an ink jet method, because the number of ink density levels is limited, it is necessary to make the gradation expression of a recorded image in a digital way. For example, there is a method in which one pixel of image data is composed of a matrix having a plurality of elements, for example, a dither matrix of 4×4 elements, and gradation expression of 4×4+1=17 gray levels is achieved by using so called a dither method with this dither matrix made a unit.
Further, by using a plurality of kinds of ink, for example 4 kinds of ink, having colors of the same hue but different densities respectively, the number of gray levels to be produced can be increased innumerably. However, actually it is general that gradation expression is made on the basis of an error diffusion method by selecting several to several tens of dither matrices out of all the dither matrices that are able to be produced and utilizing these several to several tens of dither matrices. As regards the literatures concerning an error diffusion method, for example, it is described in detail in ‘R. FLOYD & L. STEINBERG, “AN ADAPTIVE ALGORITHM FOR SPATIAL GRAY SCALE”, SID 75 DIJEST, pp. 36 to 37’. By using this method composed of a dither method combined with an error diffusion method, multiple gray scale expression of 12 bits is possible, and by selecting suitable dither matrices and using a suitable error diffusion algorithm, it is possible to obtain a smooth gradation characteristic.
However, the above-mentioned error diffusion method is what is called an area-modulation method, and has the defect that it makes the roughness (noise) of an image larger as the compensation against the advantage that it is capable of expressing multiple gray levels. Therefore, it is necessary to increase the number of dither matrices to the utmost, but because the number of densities of the ink having the same hue is limited, it is often used a method in which the number of gradations is increased by shooting ink drops of different densities approximately at the same position.
As described in the publication of the examined patent application H5-46744, it has been known an invention utilizing the fact that the reflection density in the case where high-density dots and low-density dots are formed in a superposed way at the same cell in a dot matrix is different from that in the case where high-density dots and low-density dots are formed at different cells respectively in the above-mentioned dot matrix. Further, there is a method in which multiple gray level expression is made by utilizing positively the difference in the recording density to be produced by varying the order of superposing as keeping constant the number of the high-density and low-density dots.
As described in the publication of the unexamined patent application H3-218851, there is a method in which recording is done first with high-density ink and successively with low-density ink superposed. It is a method utilizing the nature such that, in a reflection image, in the case where recording is made with low-density ink followed by high-density ink, it appears as if a large dot of high-density ink is shot, which increases graininess, but in the case of high-density ink followed by low-density ink, a dot appears not so large as that in the former case.
It has been known that the above-mentioned two methods are appropriate recording methods for recording a reflection image, but the effect of the above-mentioned methods could not be obtained for a transmission image. On the contrary, in the case where an image is recorded by an ink jet method, they have rather the defect that the gradation is reversed in a part of an image in accordance with the order of shooting ink drops of different densities. It is considered that a transmission image has a characteristic which is proper to a transmission image and there is a method appropriate for the recording of a transmission image which is different from that of recording a reflection image.
The phenomenon that gradation is reversed is a problem peculiar to an ink jet method; however, in the first place, to use both a transmission image and a reflection image has been regarded as difficult in various image recording methods such as a silver halide method, a thermal transfer method, and other methods. Among various reasons which can be cited, the most difficult reason is the difference in the density characteristic between a transmission image and a reflection image.
FIG. 5
is a drawing showing a typical reflection density vs. transmission density characteristic. The detail is described in ‘Yasushi Ohyama, “The relation between transmission density and reflection density of a photographic image layer”, Journal of Japan Photographic Society, 41(1), pp. 42 to 59 (1978)’. As regards this characteristic, it is not limited to a silver halide photography, but a similar tendency can be observed also in a recording apparatus of an ink jet method. The reason is that the structure of the recording medium is hardly different between i
Konica Corporation
Nguyen Lamson D
Squire Sanders & Dempsey
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