JP2898169B2 - Thermal gradation recording device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-tone printer which can be used as a hard copy device in the fields of computer graphics, video systems, and communications such as facsimile.

[0002]

2. Description of the Related Art A thermal recording system in which thermal recording is performed using thermal recording paper or a thermal transfer film is easier to colorize than an ink jet system or an electrophotographic system, and the apparatus can be configured in a small size. It is also widely used as a hard copy device for recording pictorial images because it is advantageous in terms of cost, maintenance, and the like.

A color printer using the thermal transfer method is a horizontal printer.
Using a thermal head in which heating elements are arranged in a row and an ink sheet coated in three colors of yellow (Y), magenta (M), and cyan (C), an image receiving paper is provided for each color by a three-color surface sequential method. It is common to record while rewinding,
The thermal sublimation transfer method and the concentrated heat transfer method capable of performing smooth gradation recording are excellent.

[0004] However, the method of performing density gradation recording in an analog manner by modulating the applied energy by an energizing pulse width or the like, as in both of these methods, has a problem that the recording density depends on the environmental temperature and is affected by the heat storage in the thermal head. And stable density reproduction is difficult at all times. This temperature dependency is an element that limits the improvement of image quality in developing these printers.

To cope with these problems, a correction coefficient of the energization pulse width is determined for each line so as to correct the influence of the environmental temperature and the recording density due to the heat storage of the head base and the heat storage of the heating element substrate. A gradation printer that corrects the energizing pulse width of the next line by using a coefficient
Publication).

FIG. 3 is a configuration diagram of a conventional gradation printer. In FIG. 3, reference numeral 301 denotes a thermal head having a large number of heating elements provided in a line on a heating element substrate; 302, a γ correction unit for converting density data into a corresponding applied pulse width; and 303, a correction coefficient for the applied pulse width. 305 is a head driving means for driving the thermal head 301 with multi-step pulse widths, 305 is a pulse width integrating means for integrating the pulse width for one line, and 306 is a heating element of the thermal head 301 The heat storage amount predicting means for predicting the heat storage amount of the substrate, 307 is a temperature detecting means for detecting the temperature of the head base of the thermal head 301, 308 is the head base temperature detected by the temperature detecting means 307 and the heat storage amount predicting means 306. This is a coefficient determining means for calculating a temperature compensation coefficient from the predicted heat storage amount of the heating element substrate.

In thermal transfer recording or thermal recording, there is a nonlinear relationship between applied energy and recording density called a γ characteristic, and the γ correction means 302 is necessary for recording the density corresponding to the input data. Output energizing pulse width data. The pulse width correction unit 303 is configured to output the energization pulse width data corrected by multiplying the energization pulse width data output by the γ correction unit 302 by the correction coefficient given by the coefficient determination unit 308.

[0008]

Here, in temperature correction in gradation recording, the density correction accuracy is raised to a level corresponding to a gradation step, and recording is performed at any environmental temperature.
It is required that the density of each gradation step can be accurately reproduced. In general, a gradation printer capable of recording a full-color image requires at least 64 gradations (6 bits), and currently 256 gradations (8 bits) are the majority. This is largely due to the fact that the input digital RGB data is predominantly 8 bits, and there is a background that human beings can recognize as 256 colors each color as full color.

Therefore, it is necessary to perform multi-step processing of 8 bits or more for energization pulse width data in the gradation printer. In a conventional gradation printer, to perform temperature correction,
When the coefficient determining means 308 is at the reference base temperature and at the reference heat storage amount of the heating element substrate, it takes a value of 1, and the pulse width correcting means 3
Numeral 03 obtains corrected energization pulse width data by multiplying the energization pulse width data output by the γ correction means 302 by a correction coefficient that decreases monotonously with respect to both the base temperature and the heat storage amount. .

Here, considering the case where such a correction process is not performed, in order to secure the final 256 gradations, the thermal head 301 needs to be supplied with 8-bit energizing pulse width data.
Need to be driven. Therefore, assuming that the input energization pulse width data and the correction coefficient are 8 bits and the corrected energization pulse width data is the upper 8 bits of the result of multiplying the input energization pulse width data and the correction coefficient, respectively, the change of the minimum 1 bit of the correction coefficient The difference in the energized pulse width data whose amount has been corrected is two gradations out of a maximum of 256 gradations.

Next, in thermal transfer recording and thermal recording, as described above, there is a non-linear relationship between the energization pulse width data and the recording density, called a γ characteristic as shown in FIG.
Therefore, in the case of the maximum recording density D = 2.4, considering the nonlinear relationship between the energization pulse width data of the γ characteristic and the recording density shown in FIG. When converted to the density change amount, D = 0.
02 or more. This density change is a range that can be sufficiently recognized by humans, and when recording a uniform density, the fluctuation due to the correction of the energization pulse width data by the temperature correction is identified as a density change, which causes a deterioration in image quality. .

This is due to the correction accuracy, and the correction accuracy can be improved by increasing the corrected energizing pulse width data and the bit number of the correction coefficient. With the increase in the number, there arises a problem that the size of the multiplier is increased and the price is increased. Further, when the number of bits of the corrected energization pulse width data is increased, it is necessary to output finer energization pulse width data within the same time.
Each time the number of bits increases, the processing speed is required to be substantially doubled, and this speedup causes problems such as a significant increase in the circuit scale.

In view of the above, it is an object of the present invention to provide a thermal gradation recording apparatus capable of improving the accuracy of correction processing for energization pulse width data such as temperature correction with a simple configuration.

[0014]

In order to solve the above-mentioned problems, a thermal gradation recording apparatus according to the present invention comprises a thermal head in which heating elements made of resistors are arranged in a line, and input energizing pulse width data (k). bit, k is positive integers) n bits for (n 2 ^m as the lower m bits (m correction factor is a positive integer) and comparison means for comparing a predetermined value, the predetermined value of a positive integer) A predetermined value setting means for repeatedly setting a different value every 2 ^m lines, an adding means for adding the output of the comparing means to the upper (nm) bits of the correction coefficient, and an output of the adding means. A multiplying means for multiplying the input energizing pulse width data; and a head driving means for driving the heating element to energize for each line in multiple stages according to the output of the multiplying means.

[0015]

With the above construction, the n-bit correction coefficient for the input energization pulse width data is divided into upper (nm) bits and lower m bits, and the lower m bits are compared with the predetermined value output from the predetermined value setting means. The output of the comparing means is added to the upper (nm) bits of the correction coefficient by the adding means, and the higher (nm) bits to which the output of the comparing means is added and the input energizing pulse width data (k ) Is multiplied by the multiplication means to create new energization pulse width data.

[0016]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a configuration of a thermal gradation recording apparatus according to one embodiment of the present invention. In this embodiment, in particular, a sublimation type thermal transfer printer capable of gradation recording is used, and the number of bits of the input energization pulse width data a1, the correction coefficient b, and the predetermined value c are 8 bits (k = 8) and 10 bits (n = 10), 2
The case of bits (m = 2) will be described.

[0017] In FIG. 1, 101 a thermal head having an array of heating elements comprising a resistive element in a line shape, 102 predetermined value setting means repeatedly set for each 2 ^m line a predetermined value to different values of 2 ^m as, Reference numeral 103 denotes comparison means for comparing lower-order two-bit data b2 of the correction coefficient b with a predetermined value c;
04 is an adding means for adding the upper 8 bits of data b1 of the correction coefficient b and the output of the comparing means 102 to set a new correction coefficient d. 105 is multiplying the input energization pulse width data a1 by the new correction coefficient d. The multiplication means 106 is a head driving means for driving the thermal head 101 in accordance with the temperature-corrected energization pulse width data a2 output from the multiplication means 105.

Next, this embodiment will be described in detail with reference to FIG. First, a preset correction coefficient b (10 bits) is divided into upper 8 bits and lower 2 bits, and data b1 of the upper 8 bits is input to the adding means 104,
The bit data b2 is input to the comparing means 103. Table 1 shows a predetermined value c which is an output of the predetermined value setting means 102.
Is shown.

[0019]

[Table 1]

As shown in Table 1, the predetermined value c is repeatedly input to the comparing means 103 with four kinds of values of 0, 2, 1, and 3 every four line cycles as shown in Table 1. The comparing means 103 compares the input data b2 with a predetermined value c, and
If 2 is larger than the predetermined value c, 1 is output, and if data b2 is equal to or smaller than the predetermined value c, 0 is output. The addition means 104 outputs the output b of the comparison means 103 and the upper eight bits of the correction coefficient b
1 is input, each data is added, and the multiplication means 10
5 is output. The multiplying means 105 inputs the energizing pulse width data a1 (8 bits) obtained by converting the input image signal into data for energizing and driving the heating element, and the output d of the adding means 104, multiplies the respective data, and performs multiplication. Top 8 results
The energized pulse width data a2 with the corrected bit is output to the head driving means 106. Further, the thermal head 101
Each of the heating elements is driven by the head driving means 106 for an energization time corresponding to the corrected energization pulse width data a2 output from the multiplication means 105. Therefore, the duration of energization of each heating element in the thermal head 101 is varied, the heating energy of each heating element is multi-step, and multi-gradation recording can be performed for each pixel by using a sublimable dye.

The recording of one line is completed by the above-described operation, the input energizing pulse width data a1 and the correction coefficient b of the next line are input again, and the predetermined value setting means 102 corresponds to the recording line as shown in Table 1. The given value c is input to the comparing means 103 again.

Here, the effects of the present invention will be described based on specific examples. First, the input energization pulse width data a1 is 80
H (8 bits) (the subscript H represents a hexadecimal number), and the correction coefficient b is 202H (10 bits). As shown in equation (1), the correction coefficient b is such that the upper one bit is an integer part and the lower nine bits are
The bit is set so as to represent a value after the decimal point, and 202H is 1+ (1/256).

202H = 1.0000000010 (binary notation) = 1 + (1/256) (1) When the above-described specific example is calculated using a decimal number, the input energization pulse width data a1 is 128 and the correction coefficient b is ( 1+ (1/256) as shown in the equation (1), and the result of the multiplication becomes 128.5 as shown in the equation (2).

128 × {1+ (1/256)} = 128.5 (2) Here, in the conventional example, even if the number of bits of the correction coefficient is increased to increase the correction accuracy, the corrected energization Since the pulse width data a2 is 8 bits, it is impossible to take a value of 128.5. Therefore, the value after the decimal point is rounded up or down and recorded at a value close to 128.5, and the accuracy of such correction is reduced.

However, in this embodiment, the lower 2 bits 2H of the correction coefficient b are compared with predetermined values shown in Table 1 in the comparing means 103, and the output of the comparing means 103 is 1 in the first and third lines. And the second and fourth lines are 0.
Therefore, the outputs of the multiplying means 105 in the first to fourth lines are 80H, 81H, 80H, and 81H, and when viewed on the fourth line, a pseudo intermediate value between 80H and 81H, that is, 128 shown in the equation (2) .5 is equivalent to recording. Thus, the corrected energizing pulse width data a
Since there is no need to increase the number of bits of 2, the correction accuracy can be improved without significantly increasing the circuit scale and increasing the configuration of the multiplying means 105 due to the speeding up of data transfer to the head driving means 106. Can be improved.

As described above, the present embodiment uses the comparing means 103 and the adding means 104 which are simpler in configuration than the multiplying means 105, thereby enabling correction by 8 bits × 8 bits shown in the conventional example. The correction accuracy can be improved as compared with the correction processing for calculating the energized pulse width data.

Here, in this embodiment, the comparing means 103 and the adding means 104 are embodied as a hardware configuration. However, when a microcomputer or the like is used, it is needless to say that these processes can be easily embodied as software. .

Further, in the present embodiment, the predetermined value c has four types of 2 bits, but may be 1 bit, 3 bits or more. Further, the value of the predetermined value c may be set as 3, 1, 2, 0 or 2, 0, 1, 3 in order from the first line, for example, and is not limited to the present embodiment.

[0029]

As described above, according to the thermal gradation recording apparatus of the present invention, a correction coefficient is applied to input energization pulse width data, such as temperature correction for accurately reproducing the gradation level density. When performing the multiplication and correction processing, it is not necessary to increase the number of bits of the corrected energization pulse width data a2. It is possible to obtain a great effect that the correction accuracy can be improved without increasing the configuration of the means.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a thermal gradation recording apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing a non-linear relationship called a γ characteristic between energization pulse width data and recording density;

FIG. 3 is a diagram showing a configuration of a conventional gradation printer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 101 Thermal head 102 Predetermined value setting means 103 Comparison means 104 Addition means 105 Multiplication means 106 Head driving means

Claims (1)

(57) [Claims] 1. A thermal head in which heating elements formed of resistors are arranged in a line, and a correction coefficient of n bits (n is a positive integer) for input energization pulse width data (k bits, k is a positive integer) comparison means (the m positive integer) low order m bits compare with a predetermined value, the predetermined value setting means repeatedly set for each 2 ^m line said predetermined value to different values of 2 ^m as the comparison means Is output to the higher (n-
m) adding means for adding to the bits, multiplying means for multiplying the output of the adding means by the input energizing pulse width data, and setting a time for energizing the heating element according to an output of the multiplying means for each line. A thermal gradation recording apparatus, comprising: a head driving means for driving in multiple stages.