JPH0747317B2 - Thermal printer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention converts an image information signal obtained from an original image by a novel gradation adjustment method to form a recorded image having excellent gradation reproducibility. The thermal printer that can do.

More specifically, the present invention can be obtained from various original images (including continuous tone images such as monochrome or color photographs, video images, etc., which are all intended to be reproduced on recording paper. The same applies hereinafter). The image information signal is subjected to conversion processing under a new gradation adjusting mechanism, and an image composed of pixels having color density corresponding to the density of the original image is formed on the recording paper based on the gradation-converted output signal. The present invention relates to a thermal printer that can be used.

(Prior Art) When an image is reproduced on a recording sheet by an image forming apparatus such as a copying machine from an original image having a continuous tone like a photograph, a photosensitive paper is used as the recording sheet but an analog processing (exposure) of the original is performed. ), An image having continuous tone corresponding to the original is formed (silver salt photographic recording). On the other hand, in a thermal printer device that records an image on plain paper instead of photosensitive paper, it is not possible to form an image by analog processing, it is difficult to reproduce continuous gradation, and in the case of color image formation, color balance adjustment is performed. And so on is not easy.

For this reason, efforts are being made to improve the reproducibility of gradation in printer devices. The formation of an image in a thermal printer is an image obtained by photoelectrically scanning an original image having continuous tones such as photographs in the same manner as the method of converting continuous tones into halftone dots in photoengraving in printing. The information signal is processed, and an image is formed on a recording sheet by a distribution of pixels having a color density corresponding to the original image by the signal.

However, in the currently used printer devices, the gradation adjustment method that processes the image information signal obtained from the original image for gradation reproduction is unscientific, so satisfactory gradation reproducibility is obtained. The current situation is that it has not been done.

As is well known, the gradation characteristics depend on the color density display performance of pixels, and in the case of a thermal printer, as a method of displaying the color density of pixels, there is a method of changing the pixel coverage by the size of dots (size modulation method). , A method of changing the coverage of pixels by the number of specified (the same size) dot arrangement (density modulation method), and further, a sublimation dye was used for those using image recording materials (inks) of the same color density. As seen in a thermal printer, there is a method (direct density gradation display method) that can directly change the density of the pixel itself. However, when copying the original image with a thermal printer,
For the color density value of a predetermined sample point on the original image, the coverage of dots corresponding to this on the duplicate image,
That is, no particular consideration has been made on what the color density value of a pixel should be (hereinafter, simply referred to as a pixel (in) density value), and how to obtain such a pixel density value. Depends solely on the experience and intuition of the operator and the subjective judgment of the equipment designer. Especially regarding the characteristics of the pixel density value, which is extremely important for reproducing the gradation,
At present, the operator uses the data accumulated in the memory in the printer device, which is determined by the device manufacturer in advance based on experience, intuition, and a limited number of materials based on fixed conditions.
Therefore, in the case of a non-standard color original that the device manufacturer did not assume, adjustment is not easy to form a desired recorded image, and it is possible to maintain the image quality level and stabilize the image quality. It is difficult and lacks the flexibility to change or modify the image quality arbitrarily.

(Problems to be Solved by the Invention) The cause of the above-mentioned problems in the conventional printer apparatus is the first cause when an image with a final pixel distribution is formed from a document image such as a continuous tone image. The idea is for the process of gradation conversion of an image that plays an important role in stages. In other words, the conventional way of thinking about gradation conversion was not that "it must be performed based on a scientifically rational gradation conversion means", but that it depended solely on experience and intuition. .

The present inventor pays attention to such a situation, and in order to ultimately rationalize an image forming process and form a recorded image with excellent quality, a rational image gradation conversion technique must be established. Based on the basic recognition that

(Means for Solving the Problems) If the present invention is outlined, the present invention relates to a thermal printer for forming a recorded image corresponding to a document image on a recording sheet based on an image information signal obtained from the document image,
The image information signal of the previous period is formed with a basic density value (x) of an arbitrary sampling point on the original image (difference between the density value at the sampling point and the density value at the brightest portion H on the same image). In order to correlate with the pixel density value (y) at the position corresponding to the sample point in the recorded image, for example, the following relational expression (1)
The present invention relates to a thermal printer having a gradation adjusting mechanism that performs processing as defined by the above.

<Relational expression (1)> However, x: basic density value of an arbitrary sample point X on the original image. That is, a value obtained by subtracting the density value at the brightest portion H on the image from the density value at an arbitrary sample point X on the image.

y: the pixel density value of the pixel point Y corresponding to the sample point X on the recorded image to be formed.

y _h : Pixel density value set for the pixel in the brightest portion H of the recorded image to be formed.

y _s : Pixel density value set in the pixel of the darkest portion S of the recorded image to be formed.

α: reflectance of recording paper.

β: Surface reflectance of the image recording material.

The ratio k: (density threshold of recorded image to be formed) / (density threshold of original image).

Respectively.

Hereinafter, the constitution of the present invention will be described in detail.

In the recorded image formed by the thermal printer,
The basic constituent elements that make up the recorded image are density values in pixels (this is the proportion covered by the number and size of dots in the pixels on the recorded image formed as described above, or the use of sublimable dyes). If it is present, the ratio of the density of the pixel itself is shown) and the surface reflection density of the image recording material (ink, pigment), of which the human visual sense is, for example, 1 of the size of the halftone dot area in the printed image. As can be seen from the fact that the difference in% can be easily identified as the density difference, the pixel density value having the same relationship with the size of the halftone dot area is extremely important as an image forming means. That is, how to set the pixel density value is very important.

Further, in connection with the above, when a recorded image is to be formed by a thermal printer, the quality content of the original image varies, and the image forming process also has various characteristics. There is a background such as that image quality evaluation criteria are not uniform, and these complicated and unstable factors must be overcome.

Therefore, when converting an original image such as a continuous tone image into an image having a halftone by a thermal printer, the density value (y _h ) of the pixel block of the brightest portion (H)
And the density value (y _s ) of the pixel block of the darkest part (S) can be arbitrarily selected, and the gradation of the image from the brightest part (H) to the darkest part (S) can be rational and It is absolutely necessary to provide a hand that can be easily adjusted and managed.

Based on such an idea, a method for adjusting a gradation applied to the gradation adjusting mechanism of the thermal printer according to the present invention has been devised, more specifically, a floor defined by the relational expression (1). This is a key adjustment method (hereinafter, also referred to as “main adjustment method”).

The gradation adjusting method of the present invention is based on the numerical values of the reflectance of the recording paper and the surface reflectance of the image recording material (ink, pigment), and the image desired to be placed at H and S of the recorded image to be formed. While arbitrarily selecting the density value, the image density value (y) of the pixel block (Y) corresponding to the position formed on the print image formed from the basic density value (x) of the arbitrary sample point (X) on the original image. ).

In the relational expression (1) of the present invention, there is a numerical value by a densitometer for measuring the basic density value (x) (for example, a person image of a positive color film has a density value of 0.2 to 2.70). ), And y _n [the pixel density value set in the pixel block of the brightest part (H)] and y _s [pixel density value set in the pixel block of the darkest part (S)] are numerical values (for example, If you use 5% or 95%.), Y
The [pixel density value recorded in the pixel block (Y) corresponding to an arbitrary sample point (X) on the original image] is calculated as a percentage value. In operating the relational expression (1), this point may be taken into consideration and modified and used. When measuring the above-mentioned basic density value (x), the density is measured by a color densitometer (transmissive type, reflective type, dedicated type,
Any concentration measuring means such as a common type) may be used.

In the gradation adjusting method of the present invention, the basic density value (x)
Is not limited to the numerical value obtained by the densitometer, and the original image may be photoelectrically scanned to detect an electric signal (current or voltage value) corresponding to the x value, and the y value may be calculated based on the electric signal. Needless to say, it's good. That is, x
Any value may be used as long as it is in some sense correlated with the basic density value of the original image.

Equation for obtaining the above-mentioned pixel density value (y) (1) are commonly found concentrations formula (photographic density, optical density), i.e. _{D = logI o / I = log1} / TI o; the amount of incident light I: reflection Light amount or transmitted light amount T = I / I _o ; Derived from reflection or transmittance.

Applying this general formula for the density D in the case of image formation will be as follows.

Where A: unit area dn: area covered by dots in the nth pixel in the unit area α: reflectance of recording paper β: surface reflectance of image recording material (ink, pigment) .

The present invention uses the density formula (D ') relating to the image formation in addition to the basic density value (x) at an arbitrary sample point on the original image such as the continuous tone image and the pixel block on the recorded image corresponding to the basic density value (x). The relational expression (1) is derived so that the theoretical value and the actually measured value approximately match with each other by incorporating a request for associating with the pixel density value (y).

Therefore, in the gradation adjustment from the original image such as the continuous gradation image to the recorded image by the pixel distribution of the present invention, the gradation adjustment is performed by correlating the basic density value (x) and the pixel density value (y). It covers all things.

It should be understood that the correlation between x and y in the relational expression (1) is an example, and the present invention is not limited to this. That is, appropriate changes can be made without departing from the scope of the present invention.

The feature of the gradation adjustment of the present invention is that, no matter what quality image the original image such as continuous gradation has, the y _h and y _s are expressed as shown in the relational expression (1), Alternatively, it is possible to extremely easily know what kind of gradation characteristic the recorded image due to the distribution of pixels to be created should have, by arbitrarily selecting the values of α and β. .

"This adjustment method" can be used by transforming this,
For example, the values of y _h and y _s , and α and β are arbitrarily selected,
In addition, if the original image density area such as a color photographic image having continuous gradation and the density area of the recorded image due to the pixel distribution are different, a well-known gradation compression method is adopted, that is, (recorded image density area) / The k value, which is the ratio value of the (original image density range), may be appropriately selected, and the image adjustment may be performed by the “main adjustment method”.

That is, according to the present invention, the relational expression (1) is used when a recorded image is formed with a pixel distribution based on an image information signal obtained by photoelectrically scanning an original image such as a continuous tone image.
The value of y _h , y _s , k defined by By appropriately changing the value of, it is possible to perform image gradation conversion and gradation correction (or change) with extremely high flexibility.

To describe this in detail, it should be noted that the user (worker) has the following degrees of freedom when applying the “main adjustment method”.

<Part 1>: Use the relational expression (1) for the purpose of forming an image faithful to the original image. That is, the relational expression (1) is applied by primarily considering that the same visual sensory images as observed by the human eye are obtained. In the present invention, such a tone adjustment attitude is described by the term "(image) tone conversion".

<Part 2>: Use the relational expression (1) so as to change or modify the manuscript image from the technical need of image formation, the artistic demand, or the needs of the ordering side. That is, the relational expression (1) is applied, primarily considering that a visually perceptual image itself observed or observed with the human eye is obtained as a corrected or changed image. Such a tone adjustment attitude is described in the present invention by the term “(image) tone correction (or change)”.

The gradation adjustment work according to the present invention, specifically, the gradation conversion and gradation correction (or change) described above is performed by the relational expression (1).
This can be easily performed by appropriately changing the values of y _h , y _s , k, and E.

In that case, it goes without saying that the relational expression (1) or the terms, numerical values, and coefficients contained therein may be appropriately processed, deformed, guided, omitted, etc. as long as they do not impair the rationality in the gradation conversion of the image. Nor.

When forming a multicolor image, for example, when a color original is reproduced by an ink jet printer, color separation well known in the field of printing, that is, reflected light from the color original is reflected in blue (B) and green (G). ), The image information signal is obtained by spectrally splitting into red (R), the image information signal for each color is processed by the gradation adjusting mechanism using the relational expression (1), and an image is formed based on this processing information. You can do it. Alternatively, a reference color component (eg, yellow ink)
Y value, that is, a reference gradation characteristic curve (By calculating the y value and plotting the y value with respect to the x value, a gradation characteristic curve similar to the halftone gradation characteristic curve in the printing technique is obtained. .) And the gradation characteristic curves of other color components can be rationally determined by multiplying the y value of the reference color component by an appropriate adjustment value based on the gray balance ratio of each ink. Therefore, it suffices to form an image using these image information.

Y value for each color component determined as described above,
That is, the gradation characteristic curve for each color component is expressed by the relational expression (1).
Of course, it is a rational characteristic curve as defined by
The interrelationship between the characteristic curves relating to gradation and color tone is also rational and appropriate.

Basically, in the method of adjusting the gradation of an image in the gradation adjusting mechanism using the relational expression (1), whether the gradation conversion (or correction, change, etc.) is direct or indirect. According to the method, a continuous gradation image having a linear density gradation characteristic curve is immediately converted into a gradation image based on pixel distribution, and the gradation is first converted in the continuous gradation image, and this gradation conversion is performed. There is a method of converting into a recorded image by pixel distribution through a continuous tone image (here, since the tone conversion has already been performed, the term conversion is used for distinction).
Further, depending on whether or not the density range is compressed in any of the above-described methods, a method of directly converting the density range of continuous tone into a density range of pixel distribution without compression and a density range of pixel distribution are supported. There is a method of performing it through a density range compressed original image. In practice, the one suitable for the work environment is selected from the image gradation conversion methods obtained by the combination of these basic methods.

As a typical example, the basic density area of a continuous tone image (original image) having a linear density gradation characteristic curve in FIG. 1 (a) is proportionally compressed to obtain a density area compressed original image, which is then transmitted. FIG. 2B shows an example in which a recorded image is converted according to the pixel distribution.
A gradation image of a continuous gradation image (original image) having a linear density gradation characteristic curve is simultaneously converted, and at the same time, the density region is compressed to obtain a density region-compressed original image, and this image is proportionally An example of converting and creating an image by pixel distribution will be shown.
In FIGS. 1A and 1B, D _o is the density value of the original image which is a continuous tone image.

DR _o ... Basic density range of the original image that is a continuous tone image. this
The density value obtained by subtracting the density value at the brightest point (the extreme point of the highlight portion; H) from the density value at the sample point (X) on the document in DR _o becomes the basic density value (x).

D' _o ... Density value of a density range compressed document image obtained by proportionally compressing a density range of a document image of continuous tone by the value of k.

DR ' _o ... density range The density range of the compressed original image.

D ″ _o ... The density value of a continuous tone image obtained by converting the tone of a continuous tone original image by the “main adjustment method” and compressing the density range.

DR " _o ... The density range of a continuous tone image in which the original image of continuous tone is subjected to tone conversion by the" main adjustment method "and the density region is compressed.

D _p ... Pixel density value of recorded image due to pixel distribution.

DR _p ... The density range of the recorded image due to the distribution of pixels.

P ... A gradation characteristic value based on the quality evaluation standard of the formed recorded image. The value of P is compared with the value of y to assess the consistency of the two.

H: Brightest point on document image (pole of highlight part) S ... Darkest point on document image (pole of shadow part) M ₁ ... Point at intermediate density of document image (intermediate density point) M ₂ shows density points at which a pixel density value of 50% is located in the formed recorded image, and the same applies to the following examples and description.

〔Example〕

Hereinafter, the thermal printer of the present invention will be described in more detail based on examples, but it goes without saying that the present invention is not limited to the following examples unless it exceeds the gist of the present invention.

An embodiment of the thermal printer of the present invention will be described with reference to the drawings (FIGS. 2 to 4).

FIG. 2 is a block diagram of the thermal printer of the first embodiment of the present invention.

As shown in FIG. 2 (a), the thermal printer of the present invention converts transmitted light or reflected light of an original image into R (red),
The detection unit 1 that is spectrally read into G (green) and B (blue), and the output signal of the detection unit 1 into Y (yellow), M (magenta), C (cyan), and K (black) color separation signals. A color separation unit 2 for conversion, a gradation adjustment unit 3 for processing the color separation signal so as to obtain an appropriate gradation image by using the above-described “main adjustment method” of the present invention, and this gradation adjustment unit 3 The output stylus (head) of the printer is changed on the basis of the output signal of (1), and the output section 4 transfers the ink to the recording sheet in accordance with the change.

Here, the detection unit 1 is a photomultiplier or a solid-state image sensor (CCD).
Such as detecting the transmitted light or reflected light of each part of the document 5,
The R, G, B, and USM signals as current values are output, and these signals are converted into voltage signals in the A / V converter 6.

The color separation unit 2 includes the R, G, and
B and USM voltage signals are logarithmically calculated and converted to concentration,
In the basic masking (BM) 8, the black (K) component is separated from this concentration, and further the Y, M and C components are separated. Next, in the color correction (CC) section 9, R,
Controls the Y, M, and C components for each original color of G, B, and Y, M, and C, and UCR / UCA for the block components of the original.
UCR (under color removal) or UCA (under
In color addition), the ratio expressed by three types of inks Y, M, and C and the ratio expressed by K (black ink) are determined. After these Y, M, C, and K components have been obtained, the tone adjustment unit 1
1, the pixel density value in the pixel block of each color component from Y, M, C, K, that is, ye ′, me ′, c indicating the effective area ratio of each color component
Convert to e ′, ke ′. The gradation adjustment unit 11 has an algorithm of “main adjustment method” inside, applies the “main adjustment method” to each of Y, M, C, and K, and the ye ′, me ′, ce ′, k
Find e ′.

The gradation adjustment unit 11 has a "main adjustment method" algorithm as software and a general-purpose computer that has an A / D, D / A I / F (interface), and an electric circuit that implements the algorithm as a logic with a general-purpose IC. Circuit, electric circuit including ROM holding the operation result of algorithm,
It can take various forms such as a PAL that embodies the algorithm as an internal lodge, a gate array, and a custom IC.

The effective surface area ratio corresponding to the color density information of each color component obtained by the gradation adjusting unit 11 is input to the color channel selector 12, and the color channel selector 12 sets ye ′, me ′, c
Output e ', ke'. This output is A / D converted by the A / D converter 13.
It is converted and input to the output unit 4. In the output section 4, the dot control section is formed by the known thermal printing means.
A pulse signal corresponding to the image information signal from 14 is applied to the thermal head 16, and recording is performed on the recording paper 17. In this embodiment, the multicolor ink film 18 as shown in FIG.

FIG. 3 is a block diagram of the thermal printer of the second embodiment of the present invention. The one shown in FIG. 3 uses a TV signal as an image information signal of a document image. The Y, M, C, and K component signals of the TV signal are input to the gradation adjustment unit 11 having the "main adjustment method", and the A / D conversion device 21 converts the digital signal through the color channel selector 12. Then, this digital signal is sent to a data storage device 22 such as a semiconductor memory, the address is determined and stored for the required number of pixels, a start pulse is applied to the address counter 24, and a reference clock is sent to the address counter 24. The address counter 24 sends the first address to the data storage device 22, the data at that address is sent back from the data storage device 22, and this data is sent to the grayscale data comparison circuit 25. At this time, the count of the data counter 26 is set to 0, and the data sent back from the data storage device and the data counter 26
The data from the data storage device 22 is equal to or larger than the data (count 0) from the data counter 26, and the shift register circuit 27 is set to 1 Signal of 0 is sent to the shift register circuit 27 if smaller. Then, when the address counter 24 finishes counting the total number n of the heating resistors R ₁ , R _2, ..., Rn of the thermal head, _one data transfer pulse is sent to the latch circuit 28. Also, at the same time as sending the first data pulse, the heating pulse is applied to the gates G ₁ , G ₂ ..., Gn.
Send to.

Thereafter, similarly, each time the address counter 24 finishes counting n, the count of the data counter 26 is incremented by one, and the maximum color density is set to m.
Are counted m times, the number of data counters 26 and the data of each address sent back from the data storage device 22 are compared by the grayscale data comparison circuit 25 each time, and the data from the data storage device 22 is If it is greater than or equal to the number of counts from the counter 26, the shift register circuit 27
A signal of 1, and a signal of 0 if it is smaller. Then, when the address counter 24 finishes counting the total number n of the heat-generating resistors R ₁ , R _2, ..., Rn of the thermal head, _one data transfer pulse is sent to the latch circuit 28, and at the same time, the heating pulse is gated. Send to G ₁ , G ₂ , ..., Gn.

In this way, the heat-melting ink of the transfer paper 2 is placed between the thermal head 4 and the pressure roller 3 which are heated by the electric current flowing through the low heat-generating antibodies R ₁ , R _2, ..., Rn for a predetermined time. If the recording paper 1 is fed in the direction of the arrow at a speed V in close contact with 2 ', and the time required for the address counter 24 to count n is t, the length corresponding to the maximum color density is mvt. Dots are transferred, and dots with a length of vt are transferred in the area corresponding to the minimum color density, and dots with an integral multiple of vt are transferred according to each color density. As a result, area gradation recording can be performed by changing the color density per unit area (size modulation method) as shown in FIG.

FIG. 4 is a block diagram of the thermal printer of the third embodiment of the present invention.

In the figure, 15 ₁ to 15 ₃ are dot pattern generators, and 16 is a buffer memory. This example is a halftone reproduction method (density modulation method) generally called a dot pattern method in which M × N dots correspond to one pixel. Dot pattern generator 15 ₁ to 15 ₃
Selects and outputs a dot pattern including the number of "1" according to the level according to the density level of each primary color adjusted by the "main adjustment method". The buffer memory 16 is M ×
This is a buffer for absorbing a speed difference caused by making N dots correspond to one pixel, that is, a difference between the dot recording speed and the input speed of the image information signal.

It should be noted that FIG. 9B shows an example of a dot pattern when M = N = 4.

Next, the usefulness of the "main adjustment method" applied to the gradation adjustment mechanism of the thermal printer of the present invention will be supplementarily described.

This is a supplementary explanation for facilitating the understanding of the present invention. Regarding the “main adjustment method”, which is a main element that establishes the image gradation adjustment mechanism according to the present invention, a working example (a relational expression of the present invention) The operation will be described in detail, focusing on (1) the operation and the significance of the result.

(B) Operation experiment of "main adjustment method" The following two experiments were conducted as a basic experiment to be incorporated in the gradation adjustment mechanism of "main adjustment method".

a) First of all, an ordinary simple calculator, that is, a product name Sharp Pythagoras EL509A (manufactured by Sharp Corporation) is used to operate the simple calculator while applying a desired numerical value to the "main adjustment method". (1) (2) (3), Table 2 and Table 3 were prepared for the gradation adjustment table of the image.

As a result, the time required for these operations was 3 hours, 2 hours, and 2 hours, including the inspection time of the calculation results.

b) The following experiment was also conducted.

Simple personal computer (NEC PC-9801-M
The desired software separately obtained in 2) is input as function data, and the basic density value (x) of the original image (continuous tone image) corresponds to the density value of the pixel on the recorded image (the relational expression (1) The work of adjusting to (y value) was performed.

As a result, naturally, the same numerical value as the result of the manual calculation using the above-mentioned simple calculator was obtained.

Moreover, in this experiment, the N88-BASIC attached to the personal computer was used to create the software for adjusting the gradation of the image input to the personal computer, without using any special software. However, it only took an hour to complete.

In addition, conversion or correction of the gradation of the target image can be performed by software that can directly input the measured values of the densitometer ranging from highlight (H) to shadow (S) of the original image instead of the basic density value of the original image. It was confirmed that can be done.

Using these software, on the original image, the desired density interval (for example, 0.00 to 1.00 in 0.05 increments, 1.00 to
It was possible to obtain the target pixel density value (y) by setting the value up to 3.00 in 0.10 steps and inputting the value to the personal computer.

Furthermore, by inputting the density values at a plurality of locations from the highlight to the shadow on the original image, it was possible to obtain the desired pixel density value (y) corresponding to them.

The above-mentioned software pixel density value (y) can be output independently or simultaneously for both a positive image and a negative image.

Next, the usefulness of Tables (1), (2) and (3), Tables 2 and 3 will be described.

[Table 1 (1) (2) (3)] Table 1 shows the range of ink material density (recorded image density range) and pixel density value when a monochrome image is created from an original image by an image forming apparatus. Is a list of how the pixel density value (y) at each sample point should be obtained in order to obtain an ideal gradation characteristic curve for gradation conversion.

In addition, even if the ink density is the same from the list (that is, the recording image density range in the leftmost column of Table 1 is the same), it is ideal when the use range of the maximum pixel density value is changed. It is possible to know how the halftone dot gradation characteristic curve changes, and what must be changed. In Table 1, (1), (2), and (3), the pixel density value in the column of pixel density value (%) is a value when E = 1, (α = 1.0, β = 0), and the others are It is a value at the E value shown in the table.
In this case, the E value was determined using α = 1.0 and β = value obtained from the ink density (printed image density area), that is, β = 10 ⁻ (printed image density area).

It should be noted that it is not possible to create a black-and-white image with a pixel distribution corresponding to 1: 1 from a document image such as a continuous-tone image, and to acquire techniques and methods that can arbitrarily adjust the gradation of the black-and-white image. It is also the basis of multicolor image formation.

[Regarding Table 2] Table 2 is similar to Table 1 in the case where the density of the image forming material (ink, pigment) changes when forming a monochrome image from the original image (that is, the recording image density range changes). In this case), the pixel density value (y) is used from 0% to 100%, and the contrast of the whole pixel is aside, and an image having the same image tone and similar image quality to the human visual sense is formed. This is a list of pixel density values (y) at each sample point necessary for that purpose.

In other words, when the assumption is ideal, the pixel density values of each sample point on the ideal gradation characteristic curve corresponding to the maximum density value of the image forming material (ink, pigment) used are listed. It is a thing.

[About Table 3] The basic conditions of Table 3 are the same as those of Table 2, but when the use range of pixel density values (5% to 95%) is used, 9 is a table showing what percentage of pixel density values should be set at sample points.

To date, color separation work such as creating print images is
Color correction by masking technology is of primary importance, and image gradation adjustment work basically depends on human experience and intuition, or a limited number of fixed subject materials. There is. Therefore, it is necessary to scientifically analyze the gradation adjustment of the image by standing on the side of the image to be reproduced such as the printed image or the image recorded by the printer.

The "main adjustment method" is capable of performing gradation adjustment work at the time of image formation by a rational method, and also shows the mutual relationship between the basic density value of the original image and the pixel density value of the formed image. The data shown in Tables 1 to 3 serve as useful basic data for scientifically examining various basic matters in the color separation work during image formation.

From each of these tables, what is the essence or principle that exists between the manuscript image and the color separation work, and what is important in order to reasonably match the essence or principle and practice? You can extract what you have to do.

(B) Application of “Main adjustment method” to correction (or change) of gradation Next, “Main adjustment method” is to convert image gradation (that is, distribution of high-fidelity pixels from continuous gradation original image). It is also effective not only in the conversion into a gradation image by the above) but also in the correction (or change) of the so-called gradation for correcting the recorded image itself. The correction (or change) of the gradation in such an image is performed, for example, when the position (M ₂ ) where the pixel density value is 50% is appropriately moved depending on the size of the reduction / enlargement ratio, especially in the highlight portion or the shadow portion. It is a necessary means for strongly expressing gradation.

For example, when the pixel density values of H and S of the formed image are fixed to specific values of 5% and 95%, the change in the reflection density (based on yellow ink) of the image forming material (ink, pigment) causes Alternatively, the pixel density value (y), which is an extremely important control point in image formation due to the distribution of pixels, due to changes in the reduction ratio and enlargement ratio of the recorded image formed from the original image.
The problem is how to move the set point (M ₂ ) at which is 50% to correct or change the gradation of the image.

Table 4 shows an example of basic materials useful for solving this type of problem.

It is possible to rationally move the position (M ₂ ) where the pixel density value is 50% by preparing multiple basic data according to the actual work needs. (Or change).

The density range of the recorded image in Table 4 (corresponding to DR _p in FIG. 1) is determined by the solid density of the yellow ink used (and the value of β is also determined based on this), and )
The number inside is Is the value of.

The number in the upper left () in each space (frame) in the table is the basic density value (x) at the sample point, and the lower right number is the pixel density value (y) corresponding to each basic density value. Indicates.

However, the usable range of the pixel density value was 5% to 95%.
The calculated values shown in Table 4 are extremely important when managing the position of the pixel density value (y) of 50%.

For example, when creating an image with a reduction / enlargement ratio of 100% from a color original using film made by E company, the recorded image density range is 0.9%.
5. When the ε value is 1.12638, it is assumed that an image having a desired image quality is formed. Next, a gradation characteristic curve for obtaining a recorded image based on the distribution of pixels is created based on the calculated values in Table 4 (that is, the basic density value (x) of the original image is plotted on the horizontal axis and the pixel density is plotted on the vertical axis. A gradation characteristic curve is created by taking the value (y). Next, change the reduction / enlargement ratio for the reference color component, and move the position of the pixel area ratio of 50% to the S side for reduction, and move it to the H side for enlargement to form an image. To do.

The image quality of the test image thus obtained is compared with the image quality of the image (the image of the reference component) in which the desired image quality is obtained. Select a test image that has the same image quality as the image quality of the latter pixel distribution and, for example, reduce it to 1/2. If the density range of the image to be formed is 0.85 and the ε value is enlarged to 1.16449,200%, it is formed. The density range of the image is 1.10 and the ε value is 1.
It is assumed that it is 05958. Then, these gradation characteristic curves are created, and based on the intersection with the straight line where the pixel density value (y) on the curve becomes 50%, sample points of the density value of the original image (in practice, the original image Pixel density value (y) to sample points on the gray scale for work standards
You can know that you can enter 50%. The reason why the pixel density value (y) of 50% is selected as the sample point is that it is convenient for checking the recorded image by the pixel distribution after the color separation work. Therefore, as another method, sample points are selected as points 2/8 and 4/8 of the density range of the original image, and the percentage of the image density value corresponding to them is calculated from the gradation characteristic curve, and based on this, Color separation work may be performed.
By using Table 4 in this way, it is possible to rationally correct (or change) the image at the same time as converting the gradation of the image.

It should be noted that the correction (or change) of the gradation of the image is not limited to the reduction and enlargement ratio of the image formed by one person, the intention of the orderer, the type of the target image in the color original, the purpose of use of the formed image, the recording In some cases, the whiteness of the paper and the density of the image recording material (ink) may have to be used. In any case, Table 4 can be used to reasonably support the various color separation work. Standard, can be standardized.

Further, according to the present invention, the gradation of the image in the highlight portion or the shadow portion can be corrected (or changed) in the same manner, and special measures are taken for the color fog in the highlight portion of the color original. Can be removed automatically without any.

[Effects of the Invention] The present invention has the following excellent effects.

1) Correlation between the density of a document image such as a continuous tone image and the pixel density value of a recorded image (image recorded by pixel distribution) to be formed, which is the most basic matter for image formation. Conventionally, the decision was made by the irrational method of exclusively based on the experience and intuition of the operator or a limited number of fixed-case data. However, this can be replaced by a rational and simple determination method. When converting an original image such as a continuous tone image into a recorded image based on the distribution of pixels, the most important requirement is how to control the tone (conversion, correction or change of tone). Not only that, but the color tone of the image is directly deeply related, so that the present invention enables rational management of gradation and color tone. In other words, a thermal printer that adopts the "main adjustment method" in the gradation adjustment mechanism can systematically and reasonably systematize color separation work and gradation conversion work, and simplify the work. The effect is extremely large.

2) By adopting "this adjustment method" in the gradation adjustment mechanism of the thermal printer, the printer device can be rationalized and simplified, the manufacturing cost can be reduced, and the operation is simplified and clarified. It is possible to greatly improve the performance of the thermal printer by extremely reducing the number of redoing work and saving the consumption of consumables.

3) By the gradation adjustment mechanism using the "main adjustment method", the quality evaluation standard of the recorded image based on the pixel distribution can be rationally and simply separated from the image information of the original image. That is, the "main adjustment method" is capable of scientifically and objectively defining the highlight and shadow of the original image and the density gradation characteristic curve from the shadow to the highlight, and radically streamlining the present printer mechanism. can do.

4) By adopting "this adjustment method", education of engineers required with the sophistication of printer equipment,
Training can be carried out effectively, and unnecessary labor in daily work can be saved to secure time for new creative research and development.

[Brief description of drawings]

FIG. 1 (a) shows an example in which a density image of a document image is converted into a recorded image with a pixel distribution through a document image, and FIG.
FIG. 6 is a diagram showing an example of converting a document image into a recorded image having a pixel distribution via a gradation-converted density region compressed document image. FIG. 2 is a block diagram showing a first embodiment of the thermal printer of the present invention. FIG. 3 is a block diagram showing the second embodiment, and FIG. 4 is a block diagram showing the third embodiment.

Claims (6)

[Claims] 1. A thermal printer for forming a recorded image having a halftone of one color or multiple colors on a recording sheet based on image information of the original image, wherein the thermal printer gradations the image information of the original image to the halftone. As a gradation adjusting mechanism for conversion, the basic density value (x) of an arbitrary sample point on the original image is converted to a pixel density value (y) of a corresponding point on the recorded image by the following <relational expression (1)>. A thermal printer having a conversion mechanism. <Relational expression (1)> However, x: basic density value of an arbitrary sample point X on the original image. That is, a value obtained by subtracting the density value at the brightest portion H on the image from the density value at an arbitrary sample point X on the image. y: the pixel density value of the pixel point Y corresponding to the sample point X on the recorded image to be formed. y _h : Pixel density value set for the pixel in the brightest portion H of the recorded image to be formed. y _s : Pixel density value set in the pixel of the darkest portion S of the recorded image to be formed. α: reflectance of recording paper. β: Surface reflectance of the image recording material. The ratio k: (density threshold of recorded image to be formed) / (density threshold of original image). Respectively. 2. The thermal printer according to claim 1, wherein the recorded image having a halftone is a dot density modulated image formed by a dither matrix. 3. The thermal printer according to claim 1, wherein the recorded image having a halftone is a dot-size modulated image formed by changing a recording dot diameter. 4. The thermal printer according to claim 1, wherein the recorded image having a halftone is formed by changing the density of the recorded dots themselves. 5. A multi-color recorded image, a plurality of print heads,
The thermal printer according to claim 1, which is obtained by a plurality of ink films corresponding thereto. 6. The thermal printer according to claim 1, wherein a recorded image having multicolor halftones is obtained by a single print head and an ink film in which multiple colors are repeatedly arranged. .