JPH0681233B2 - Multi-gradation recording method - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention is a multi-layered system in which one pixel is composed of a plurality of dot matrices and a pseudo gradation image is obtained by the area ratio of mark dots recorded in the matrix. Regarding recording method.

[Technical background of the invention and its problems]

In the fusion-type thermal transfer recording method, in which heat-meltable ink is heated by a thermal head to melt or soften the ink and transfer recording is performed on recording paper, the density expression by ink transfer is
Since it is "1" or "0", gradation expression by area modulation, which is so-called binary area gradation, is generally performed.

However, according to this method, the number of gradations that can be represented when one pixel is represented by a matrix of n × n image points is only n ² +1 including the background density level of the recording paper. Therefore, for example, only 17 gradations can be expressed with a matrix size of 4 × 4. However, in order to obtain an image that is natural to the eyes, it is generally said that the resolution of color image points is 4 dots / mm or more and the number of gradations is 64 or more. In order to satisfy this with the binary area modulation method, it is necessary to use a thermal head having an 8 × 8 matrix size and a heating element density of 32 dots / mm or more. However, the limit of currently feasible thermal heads is 16 dots / mm, and it is currently difficult to realize thermal transfer recording with a resolution of 32 dots / mm.
Therefore, it is extremely difficult to obtain a smooth density gradation by the binary area gradation.

Therefore, in order to solve this, ink with different densities should be
A method of obtaining multi-gradation by using a combination of image dots having different densities and image dot arrangements using ink ribbons laminated in layers (JP-A-57-
193377) or an ink ribbon in which inks having different densities are sequentially applied in the longitudinal direction to sequentially superpose recording image points from low density inks to high density inks (JP-A-59-
No. 55768) has been proposed. However, all of these methods have drawbacks such as unstable ink transfer and long printing time.

[Object of the Invention]

The present invention has been made under such circumstances, and an object of the present invention is to provide a multi-gradation recording method capable of extremely smooth gradation expression without lowering the resolution.

[Outline of Invention]

According to the present invention, one pixel is composed of an n × n dot matrix, a fixed pattern is set in the matrix, and the dot formation energy of the mark dots forming the fixed pattern is multivalued so that the pseudo gradation is obtained. In the multi-gradation recording method in the thermal transfer recording method for obtaining the above described, the fixed pattern has a shape including at least a part of a pattern in which a plurality of dots are arranged in an L shape.

〔The invention's effect〕

According to the present invention, since a multi-gradation image is obtained by multi-valued image formation energy of a fixed pattern, it is possible to obtain a larger number of gradations than conventional even with a small matrix size. It is possible, and the gradation characteristics are extremely smooth. Further, since the same number of gradations as the conventional one can be expressed with a smaller matrix size than the conventional one, it is possible to increase the number of gradations and at the same time, the resolution thereof.

Further, according to the present invention, since gradation expression is performed by changing the image forming energy of the mark dots forming a specific fixed pattern, the most preferable pattern for thermal transfer recording can be selected. In this case, since the fixed pattern based on the L shape is used as the fixed pattern, the ink can be remarkably spread in the space portion inside the L-shaped refraction portion. Therefore, it is possible to obtain gradation characteristics having a wide density dynamic range and excellent linearity.

Example of Invention

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram for explaining the expansion of the density dynamic range when an L-shaped pattern is used as an embodiment of the present invention.

That is, FIG. 7A shows a concentrated pattern which is commonly used when the dither method is applied to the thermal transfer recording system, and FIG. 8B shows a stripe-shaped pattern which extends in the vertical direction (sub-scanning direction). Further, FIG. 7C shows an L-shaped pattern according to this embodiment.

Now, when the energy for forming each mark dot of these patterns is gradually increased, the melted area of the ink is expanded, and the area of each fixed pattern is expanded as indicated by the broken line and the alternate long and short dash line, respectively. In high-speed thermal transfer recording, image points that are slightly elongated in the sub-scanning direction are generally formed due to a heat storage phenomenon. Therefore, the image points widen according to the number of image points continuous in the sub-scanning direction. In other words, if the amount of change in the amount of energizing energy is the same, it means that the dynamic range of the more expressible concentration is expanded. In addition, since the matrix is generally square, if the pattern shown in FIG. 1A is used in the case of a small matrix size, when the energizing energy amount is increased, the so-called "matrix" of the adjacent matrix is recorded. A bridging phenomenon occurs, which causes density jumps and impairs the smoothness of gradation expression. Further, since the bridging phenomenon occurs randomly, there is also a problem that the image quality is significantly deteriorated due to the noise caused by the bridging.

In this regard, with the L-shaped pattern shown in FIG. 1A, due to the heat accumulation phenomenon of the thermal head or the ink ribbon in the dot formation in the vicinity of the intersection of each dot row in the main scanning direction and the sub scanning direction, Since the spread of the image points due to the transferred ink is added to the area surrounded by the dot rows in the scanning direction and the sub-scanning direction, compared with the patterns shown in FIGS. 1A and 1B, The dynamic range in which the density can be expressed can be expanded.

Such an effect is more remarkable in the cross-shaped fixed pattern in which L-shaped shapes are combined. FIGS. 2 and 3 show an example in which a matrix size is 4 × 4 and a cross-shaped fixed pattern having 3 dots in the main scanning direction and 3 dots in the sub scanning direction is arranged in this matrix. .

That is, when the image forming energy of a fixed pattern expressed by a cross shape is increased in the order of 1, 3, 5 as shown in FIG. 2 (a), as shown in FIG. 2 (b), A series of image points extending in the vertical direction and the horizontal direction gradually becomes thicker. Along with this, the blank portion surrounded by the above-mentioned image point array is gradually filled up due to the increase in the softened area of the ink.

According to this embodiment, an effective area modulation action inside the L-shaped bent portion can be expected at four places, so that the dynamic range of expression density can be made wider.

Further, as shown in FIG. 3A, this fixed pattern is a pattern in which one dot of space dot is arranged so that the fixed patterns do not come into contact with each other even when the matrices are adjacent to each other. There is. Therefore, according to this pattern, as shown in FIG.
Independence between fixed patterns is maintained even when the image forming energy is sufficiently increased. In other words, the pixels become larger as the amount of energizing energy increases, but because there are space dots that do not energize between adjacent patterns, the ink adhesion is weak, and the recording paper caused by the separation of the ink ribbon and the recording paper. It becomes difficult for ink transfer to occur. Therefore, it is considered that the independence of the pattern is maintained.

Further, conventionally, when adjacent patterns were in contact with each other, a peculiar increase in the ink transfer area was observed in accordance with the image forming energy at that portion, and this increase was generally extremely rapid. For this reason, the linearity of the pixel density is often hindered as the image forming energy increases. However, according to the cross-shaped pattern as described above, since the thinnest portions of the patterns are close to each other, even if the patterns are connected to each other, the portion that increases the image area by the energizing energy is the closest portion. Since it is the center part of the cross pattern that is farthest from, the non-ink transfer part is reduced concentrically, and good image quality is maintained until the end.

Next, an example in which the present invention is applied to a recording device capable of expressing 39 gradations in a 4 × 4 matrix will be described.

FIG. 4 is a block diagram showing the configuration of this thermal recording device.

That is, a multi-gradation image signal input in the form of a digital signal from a scanner, an A / D converter, an image memory, a transmission system demodulation circuit, a decoding circuit, etc. (not shown) is processed by the multi-gradation signal processing circuit 1 to specify the printer specifications. And a signal having a form suited to the characteristics is subjected to signal processing and output. The signals processed by the multi-gradation signal processing circuit 1 are processed by the multi-value pattern table 2
Has been entered in.

The multi-valued pattern table 2 is for determining a fixed pattern and an implantation energy amount according to the concentration information held by the signal, and is specifically a ROM and is a main part of the present embodiment. This multi-valued pattern table 2
Is a ROM that generates a binary dither pattern of a table look-up type in the past, and sometimes includes a calculation for compensating for the thermal storage phenomenon of the thermal head. However, in this embodiment, this portion stores fixed pattern information and formation energy information of each mark dot as described later.

The matrix position designating circuit 3 is a circuit for designating the position on the matrix of the pattern in the matrix consisting of the image points required for digital recording or pseudo intermediate recording. Normally, in the case of a line printer, it is a dot counter in the main scanning direction. , Is interlocked with the line counter in the sub-scanning direction. In some cases, it may be linked with a clock for image signal input used in the multi-gradation signal processing circuit 1.

The fixed pattern information and the energization energy information from the multi-valued pattern table 2 are given to the thermal recording circuit 4. The thermal recording circuit 4 controls the energizing pulse width for each heating element of the thermal head. The energizing pulse output from the thermal recording circuit 4 is output to the thermal head drive circuit 5.

The thermal head drive circuit 5 is an IC circuit including a shift register, a latch, and a gate driver, and is mounted on the thermal head substrate.

The interlocking operation of the thermal recording circuit 4 and the thermal head drive circuit 5 is the same as the operation performed to compensate for the heat storage phenomenon in the conventional fusion thermal transfer recording, and is disclosed in, for example, JP-A-57-208283 and 59-59. As described in −98878 or the like, it is possible to change the energizing pulse width, change the voltage level of the energizing pulse, or to use these in combination.

By the way, the details of the stored contents of the multi-valued pattern table 2 which is the main part of the apparatus according to the above embodiment are shown in FIG. The pattern stored in the multi-valued pattern table 2 constitutes one pixel in a 4 × 4 dot matrix, and the pattern formed in this matrix is fixed.

That is, the density area is divided into three areas of 0 to 11 gradation levels, 12 to 23 gradation levels, and 24 to 38 gradation levels, and an L-shaped pattern is provided in the first area and a second area is provided. Is a cross-shaped pattern with a size of 3 × 3 dots, which is a combination of two L-shaped patterns sharing one corner dot,
Area includes L-shaped pattern and is 4 in total.
Information for forming mark dots is stored in each storage location so that a substantially L-shaped pattern composed of × 4 dots is assigned. Further, the image forming energy of each dot forming the fixed pattern is changed in 5 steps according to the density level as shown in the figure, and by combining these, 39 gradations can be expressed as a whole, Information on the injection energy amount of each dot (the amount represented by the numbers 1 to 5 in the figure) is stored in the storage location corresponding to each density.

As shown in FIG. 5, as the size of the fixed pattern arranged in the matrix, various size patterns can be applied with the matrix size as the upper limit. As long as the pattern shape is a shape including at least a part of a pattern in which a plurality of dots are arranged in an L shape, and the size of the pattern is within the pixel matrix size, it is the same as in FIG. 1 regardless of the size of the fixed pattern. The effect of is obtained.

Further, the pattern of the third region in FIG. 5 includes an L-shaped pattern in the vicinity of the intersection region of each dot row in the main scanning direction and the sub scanning direction. Further, in the L-shaped pattern included in the pattern of the third region, there is no dot located at the intersection of each dot row in the main scanning direction and the sub scanning direction, but there is a dot adjacent to the intersection. This dot does not interrupt the dot row near the intersection. Therefore, due to the thermal storage phenomenon of the thermal head or the ink ribbon in the dot formation near the intersection of each dot row, the spread of the image point is added to the area surrounded by the dot rows in the main scanning direction and the sub scanning direction. The same effect as described with reference to FIG. 1 can be obtained.

The solid line in FIG. 6 shows the tone density characteristics of the image recorded using the apparatus of this embodiment. The dotted line in the figure is shown as a comparative example, and the first pattern consisting of one dot, the second pattern extending only in the sub-scanning direction, and the L-shape extending in the main scanning direction and the sub-scanning direction. The third pattern and the third pattern are used respectively.

As is clear from this figure, the dynamic range of the present example has a wider dynamic range at a low concentration level than that of the comparative example, and as a result, the overall dynamic range is expanded. Further, the linearity of the density characteristic is greatly improved by expanding the dynamic range in the low density region as described above. In addition, in the case of the present embodiment, good image quality without roughness can be obtained in the entire density region.

As described above, according to the present embodiment, it is possible to increase the number of gradations from the conventional 17 gradations to 39 gradations even with a 4 × 4 matrix, and it is also possible to suppress a decrease in resolution due to this.

The present invention is not limited to the above embodiment. For example, the basic idea of the present invention includes various patterns shown in FIG. In this case, even if the pattern is for the high density area, the fixed pattern is at least one of the mark dot rows extending in the vertical direction or the horizontal direction.
It is desirable that the mark dot rows extending in one direction form at least one space dot at the outermost peripheral position of the matrix. This is because an irregular bridging phenomenon between adjacent patterns can be suppressed.

Further, the present invention is not particularly limited to the 4 × 4, 3 × 3 matrix and can be applied to the case of using other matrix sizes, but in order to further enhance the effect of the present invention, 2 <n A matrix size of ≤6 is desirable.

As described above, the present invention can be variously modified and implemented without departing from the scope of the invention.

[Brief description of drawings]

FIG. 1 is a view for explaining the effect of a fixed pattern according to an embodiment of the present invention in comparison with a fixed pattern of a comparative example, and FIG. 2 is a fixed pattern according to another embodiment of the present invention and its injection. FIG. 3 is a schematic diagram showing energy and its action, FIG. 3 is a schematic diagram for explaining the effect of the fixed pattern, and FIG. 4 is a block diagram showing a configuration of a thermal recording apparatus according to still another embodiment of the present invention. FIG. 5 is a schematic diagram showing stored contents of a multi-valued table in the apparatus, FIG. 6 is a characteristic diagram showing characteristics of recording density with respect to injection energy amount of the apparatus, and FIG. 7 is a fixed pattern according to the present invention. It is a schematic diagram which shows various examples. 1 ... Multi-gradation signal processing circuit, 2 ... Multi-valued pattern table,
3 ... Matrix position designation circuit, 4 ... Thermal recording circuit,
5 ... Thermal head drive circuit.

Claims (3)

[Claims] 1. A pseudo floor by forming one pixel by an n × n dot matrix, setting a fixed pattern in the matrix, and multi-valued dot forming energy of mark dots forming the fixed pattern. In the multi-gradation recording method in the thermal transfer recording method for obtaining tones, the fixed pattern has a shape including a pattern in which a plurality of dots are arranged in an L shape in at least a part thereof. 2. The multi-gradation recording method according to claim 1, wherein the fixed pattern has a cross shape. 3. The fixed pattern is such that a mark dot row extending in at least one direction of a mark dot row extending in a vertical direction or a horizontal direction forms at least one space dot at an outermost peripheral position of the matrix. The multi-gradation recording method according to claim 1, wherein: