JPH044793B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a character/gradation image recording method,
In particular, in an image recording device that uses a thermal print head to perform color recording on thermal paper, a character and gradation image recording device that records a gradation image by combining color density and color area within one pixel. This paper relates to a method for recording characters and images using . Conventionally, in order to output images with text and gradation using thermal recording, the image was expressed by changing the color density in fine steps equal to the number of gradations by controlling the power applied to the heating element or the heating pulse width. However, the text is one of the gradation densities in the gradation image.
A method was used to record the concentration equal to the level. This method has the following problems, for example, when obtaining gradation images of six or more gradations, which are often used, and characters in all colors. That is, () Setting the heating conditions is complicated and difficult because control must be performed by combining the delicate coloring characteristics of the paper and the characteristics of the thermal print head. () It is difficult to obtain an image with stable gradation in response to changes in the environment (temperature, humidity). Further, for example, when the density of an image portion changes to become lower, the density of a character portion also becomes lower. () In order to obtain stable gradation images, paper with high smoothness is required. For example, Beck smoothness requires paper with a durability of 500 seconds or more (for general thermal printing, paper with a durability of about 200 seconds can be used). In order to eliminate these drawbacks, the present invention provides a plurality of heating elements corresponding to one pixel of an original image in a thermal print head arranged perpendicularly to the paper feeding direction, and a current passing through each heating element. Alternatively, in a character and gradation image recording device that changes the energization time, it is possible to use an image at a saturation density level to record characters, and use a density level lower than the saturation density to record a gradation image. Its characteristics are to make the recording of character parts clear and stable even under changes in the environment, and to improve the linearity of the proportional relationship between the gradation signal level of the gradation image part and the recording density level. The purpose is to This invention will be explained below. FIG. 1 is a structural block diagram of the gradation image recording apparatus used in the present invention, in which 1 is a thermal printing head, 2 is a heating element, 3 is a printing unit, 4 is a signal conversion section, 5 is a random number generation circuit section, 6 is a line buffer, 7 is a recording paper, 8 is a paper feeding device, and 9 is a print result. FIG. 2 shows the printing results of one printing unit 3 which gave gradations. In this embodiment, for one heating element 2, () does not generate heat (white), ()
Three levels are set: saturated density (black), and 1/2 density (halftone) of the saturated density. When setting the density to three levels, heating conditions can be easily and stably compared to achieving six or more density gradations for one printing unit 3 based on control of one heating element 2. It becomes possible to set. The Yule-Nielsen equation is shown below. D=-n log [1-a・(1-10 ^-d/n )] ...(1) D; Total reflection density a; Recording area ratio d; Reflection density of recorded part n; Depends on paper and resolution By using the Yule-Nielsen equation, the total reflection density of one printing unit 3 recorded in binary values of white and black can be determined from the relationship between the reflection density of the recorded portion and the recording area ratio. If the Yule-Nielsen equation is modified to find the total reflection density of one unit when recording is performed using three levels of density: white, black, and 1/2 density, the following equation can be derived. D=-n log [1-a・(1-10 ^d1/n )-b・(1-10 ^d2/n )]...(2) D: Total reflection density a: Recording area of saturated density (black) b: Recorded area of 1/2 density (halftone) d ₁ ; Reflection density of recorded part of saturated density (black) d ₂ ; Reflection density of recorded part of 1/2 density (halftone) n: Paper; Coefficients Dependent on Resolution The concentrations of each unit in FIG. 2 above are determined from equation (2) and are shown in Table 1, and the results are expressed on a number line and shown in FIG. 3.

[Table] However, in formula (2), d ₁ = 1.2, d ₂ = 0.6, n = 2
I asked for it as. In Figure 3, one printing unit 3 is (1 x 3)
Figure 4 shows the results of similar calculations for a (2x3) matrix, which is considered to be more general. In FIG. 4, L _c indicates the saturation density level used for character recording, and L _p indicates the density level used for gradation image recording. As shown in FIGS. 3 and 4, in the recorded density distribution of one printing unit 3, there is a large difference between the saturation density level and the next density level.
Concentration levels below that are clustered together. In other words, it is possible to easily separate the saturation concentration level from groups with lower concentration levels. Therefore, by utilizing this effect, it is possible to use the saturation density for recording characters, and to use groups of density levels lower than that for recording gradation images. Therefore, by using the saturation density level to record characters, it is possible to record with clear contrast and to be stable against environmental changes such as changes in paper type and temperature. Furthermore, as mentioned above, the density levels below the density level next to the saturation density exist closely together, so by selecting a density level suitable for the gradation signal level from among them, it is possible to widen the selection range. , it becomes possible to improve the linearity of the proportional relationship between the gradation signal level and the recording density level. Note that in the above embodiment, saturation density was used to record characters, and density other than saturation density was used to record gradation images, but in the case of recording gradation images, the highest density was set to saturation density. The following density levels may be determined in accordance with the number of gradations. As explained in detail above, the present invention uses pixels at a saturation density level to record characters, and uses pixels at a saturation density level or less to record gradation images using all combinations of saturation density, halftone, and white. By using pixels with a density level selected from low densities corresponding to the number of gradations, the number of patterns used for gradation images has been dramatically increased, making it possible to record text clearly and In addition to recording stably even under changes in the environment, the linearity of the proportional relationship between the gradation signal level of the gradation image part and the recording density level is good, so it is suitable for use in the recording section of terminals in gradation facsimile communication, for example. By applying this method, output results with good recording quality can be obtained. Further, the present invention can be applied to a recording unit of a terminal in a complex information communication system that uses character codes and gradation image data as information media. It also has the advantage that it can be applied to a document printing section in a document creation device that combines a Japanese word processor and a gradation image reading device.

[Brief explanation of drawings]

Fig. 1 is a block diagram of the configuration of the gradation image recording device used in this invention, Fig. 2 is a diagram showing an example of gradation expression patterns used in this invention, and Fig. 3 is a numerical representation of the calculation results obtained in Table 1. The diagram shown on the straight line, FIG. 4, is a diagram showing calculation results when one printing unit is expressed by a (2×3) matrix. In the figure, 1 is a thermal print head, 2 is a heating element, 3 is a printing unit, 4 is a signal converter, 5 is a random number generation circuit, 6 is a line buffer, 7 is a recording paper, 8 is a paper feeding device, and 9 is a print result It is.

Claims (1)

[Scope of Claims] 1. One pixel is constituted by a plurality of heating elements, and the coloring by the heating element is changed in at least three stages of white, halftone, and black, and the coloring area and coloring reflectance density by the heating element are changed. In a gradation recording method that expresses the gradation per pixel by combining and black dots, replace any one of the pairs with two halftone dots, set a new intermediate level between the basic gradation levels, and set the new intermediate level to the new intermediate level. The character/gradation image recording method is characterized in that, for items containing the pair, the replacement is repeated and new intermediate levels are sequentially set.