JPH026158A - Evaluation of nondefective or defective print by thermal printer - Google Patents

Abstract

PURPOSE:To evaluate a nondefective or defective print picture surface automatically and objectively by setting the density selecting level of the picture data of the print surface in two shown in L and E and displaying the quantity of a print by the ratio of the number of points higher than the high level L to the number of points higher than the low level H. CONSTITUTION:The number of the dots of a printer takes various values such as 4.75/mm, 16/mm, etc., but a density histogram is not represented by a diagram A or B typically according to the number of dots, and there is often trouble in which any diagram must be applied. In this case, the histogram is shown in the type of the diagram A when print density is lowered slightly, and shown in the type of the diagram B when print density is increased slightly. Consequently, proper print density is determined experimentally, and thermosensible paper may be compared mutually through printing by various thermosensible paper in the density or printers compared mutually by using the same thermosensible paper in the density.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for evaluating the quality of prints by a thermal printer.

(Prior Art) For printing with a thermal printer, thermal transfer carbon tape or thermal paper may be used. When using thermal paper, the quality of the print depends not only on the characteristics of the printer but also on the quality of the thermal paper. Therefore, in order to improve the quality of prints, it is necessary to consider not only the printer but also the thermal paper. However, no matter which side is considered, a means of objectively quantifying the quality of the print is needed.

In the printing method using a thermal printer, a print pattern is expressed by an array of dots, and the principle of pattern display is the same as that of halftone dot printing.

Therefore, the quality evaluation superiority of halftone dot printing can be used to evaluate the quality of prints. Conventionally, a visual method has been used to evaluate halftone dot printing. This involves printing at a constant density using halftone dots, magnifying the fixed area with a microscope, observing each halftone dot, and counting the number of halftone dots, missing halftone dots, etc.
It calculates the ratio to the total number of halftone dots within a certain area.
It was very time-consuming, and when classifying individual halftone dots into good and bad, the subjectivity of the person making the judgment inevitably came into play, making objective evaluation difficult. For this reason, a device that automatically and objectively evaluates the quality of halftone printing
Proposed by No. 794. This proposed device stores image data of an enlarged image of the printed surface in an image memory, and binarizes the data of each pixel in the image memory into two types, one with halftone dots and one without halftone dots, according to a predetermined determination level. In the enlarged image of the print surface made up of this binarized data, search for the position where halftone dots should be, specify multiple pixel points within a predetermined area including that position, and then Compare the number of points that can be obtained with the set value,
When the set value is not met, the operation of determining a defective halftone dot is performed for each position where the above halftone dot should be, and the total number of halftone dots determined to be defective halftone dots is counted. Halftone printing can be evaluated by calculating the ratio of the number of defective halftone dots to the total number. When the individual halftone dots in halftone dot printing are enlarged, they are usually perfectly circular, but there are some halftone dots that are partially missing.

When the brightness signals of the enlarged image of halftone dot printing are binarized and displayed as a video image, complete and incomplete halftone dots are clearly displayed. If you take , specify 9 or 16 points in the grid pattern within that area, and make sure that if the halftone dots are complete, you can get a signal indicating that there is a halftone dot from all of those points, then you can detect the missing halftone dots. In other words, the number of signals with halftone dots is less than 9 or 16. Therefore, if there are fewer than 9 or 16 halftone dots, it cannot be determined that the halftone dots are defective.

When the above-described halftone evaluation method is used to evaluate the print screen of a thermal printer using thermal paper, there is a problem in that it is time-consuming because special printing is required.

(Problem to be Solved by the Invention) The present invention improves the device proposed in the above-mentioned Japanese Patent Application No. 60-67794 to provide an automatic and objective method that can be applied to the quality evaluation of printed image surfaces by thermal printers. This is an attempt to obtain an evaluation method.

(Means for solving the problem) A histogram of the density of the coloring surface is created using a video signal of an enlarged image of the coloring surface of thermal paper that has been colored to a constant density using a thermal printer, and the peaks on the low density side that appear in this histogram are Select one density H corresponding to the valley between and the peak on the high density side, and another density H between the high density end of the histogram and the density I, and select the density H from the video signal. Area Nh of 8 or more and area N of density 1 or more
l was calculated, and the quality of the print was evaluated based on the value of the ratio between the two. In some cases, the two peaks may not appear in the histogram. In such a case, a histogram of the density of the coloring surface is created from a video signal of an enlarged image of the coloring surface of the thermal paper that has been colored to a constant density by a thermal printer, and the histogram shows a single peak. The half-value width or standard deviation value of the peak is calculated, and the calculated value is used as an evaluation value of print quality.

(Function) The state of color development when color is developed on thermal paper by a thermal printer varies depending on the number of dots per mm.

In the case of a thermal printer with a small number of dots, the individual dots are lined up independently from each other on the coloring surface, but in the case of a thermal printer with a large number of dots at the same average density, each dot connects with each other and covers the entire paper surface. covered. For this reason, it is difficult to control printers with a large number of dots and printers with a small number of dots using a single print image evaluation method. In the present invention, evaluation methods are provided for cases in which the number of dots is small and for cases in which there are many dots.

If you create a density appearance frequency curve (histogram) by level-selecting the enlarged video signal of a screen printed at a constant density, you will see two peaks as shown in Figure 2A in the case of a printer with a small number of dots. For printers with a large number of dots, the dots will be in the shape of a single mountain as shown in Figure 2B. In the histogram with the smaller number of dots, the peak on the low density side shows the brightness distribution of the fabric in the uncolored part of the thermal paper, and the peak on the high density side shows the density of the colored part 5) fabric. Ideally, the peaks on the low concentration side and the center on the high concentration side should form an emission line spectrum with sharp peaks, but if you look closely at the paper used to make it, it has a concentration distribution that can be seen. , the colored part also has a considerable density distribution.

In the case of halftone dot printing, the binarization of whether or not the ink sticks to the paper for each halftone dot is done at the printing stage, and the density distribution within each halftone dot is not very large. Therefore, in the histogram of Fig. 2A, the peak on the high density side has a relatively narrow peak shape, and the valley at the boundary with the density distribution of the fabric paper clearly appears, so the density of the valley is set at the binarization selection level. As a result, we were able to separate the parts of the halftone dots with and without ink and measure the degree to which the halftone dots deviated from the circular shape.

However, in the case of a thermal printer, when looking at one dot, the temperature is highest at the center of the dot, and the temperature decreases toward the outer periphery.This temperature distribution determines the area of the coloring area, and the area around the coloring area has a clear border. The density gradually decreases to the level of dough, as if the smearing is spreading. Therefore, rather than individual dots having missing parts as in halftone printing, the overall shape of the colored dots is distorted due to microscopic differences in the way heat spreads, and the density gradient area at the dot boundary becomes wider. The quality of the print screen as a whole is determined by how it differs from dot to dot.

Therefore, when the number of dots is small, the print screen can be evaluated by the shape of the peaks on the high density side in FIG. In other words, it is good if the peak is biased toward the high concentration side, as shown in allflM in Fig. 3, and a concentration distribution like b+lI+Bit is good because there are large variations in concentration between and within dots. In the present invention, in order to quantify this determination, two density selection levels are set for the image data on the print surface, as shown in FIG. 2, A and H. (and not the printer dot)
The print quality is displayed as the ratio of the number of points of high level L or higher to the number of points.

Next, in the case of a printer with a large number of dots, the density histogram becomes as shown in Figure 2B, because even if the print is relatively light, the spread of the colored areas overlaps each other and almost completely covers the thermal paper fabric. Therefore, the density distribution of the thermal paper fabric and the density distribution of the dot portion do not separate to form a mountain, and the histogram is considered to have a single mountain shape. In this case, the method of quantifying the shape of individual dots in some way as in the case of halftone printing cannot be applied, and the two-step density selection method as described above when the number of dots is small is also appropriate. isn't it. In the present invention, the half width, standard deviation, etc. of the histogram are used as evaluation values. It goes without saying that the half-width is small (it also means that the density unevenness of the printed screen is small).

(Example) FIG. 1 shows an example of an apparatus for carrying out the method of the present invention. 1 is the main body of the microscope with an imaging device, 2 is the imaging device, and 3 is the microscope body with an imaging device.
Monitor CR that displays a mirror image or the contents of the image memory as described below
It is T. The sample stage 4 of the microscope is equipped with a fine movement device in the X and y directions and a rotation device around the Z axis. 5 is a computer (CPU) for data processing, 6 is an image memory, 7 is a keyboard for setting various parameters and inputting operation commands, 8 is a CRT for display, and 9 is a printer for outputting evaluation results, etc. .

The operator sets a test piece of thermal paper that has been colored to a certain density using a thermal printer on the sample stage 4, adjusts the focus while viewing the microscope image on the monitor CRT, and issues a start command using the keyboard 7. Then, the CPU 5 stores the light and dark video signals of the enlarged image of the test piece surface obtained by the imaging device 2 as 8-bit image data in the memory 6.
Store in. Thereafter, the CPU performs the following data processing on the data stored in the memory 6.

The CPtJ5 creates a density histogram using the data in the memory 6. In this case, the image data is normalized by setting the brightest point in the image data to 256. Since the image data is 8 bits on the upper side, it is divided into 256 stages, so a histogram can be created by counting the number of pixels at each stage. This histogram is displayed on the display CRT 8. This is the histogram shown in FIG. 2A or B, but in reality it contains fine irregularities as shown in FIG. 4. While viewing this histogram display, the operator changes the subsequent data processing method by the CPU depending on whether the histogram belongs to AI:g or B in FIG.

When the histogram changes to the shape shown in Figure 2, the CRT8
Using the histogram displayed, specify the density of the bottom of the two mountains and the density of point H in Figure 2 A, and the density of point L, which is exactly in the middle between the high-density side end of the histogram and point H, and tell the CPU 5 to specify the density. The number Nh of pixels with density H or higher and the number Nl of pixels with density H or higher are counted, and the ratio N e /N h is calculated. The larger the value of this ratio, the better the quality of the print screen. When the histogram takes the form shown in FIG. 2B, the CPU 5 calculates the half width of the histogram or the standard deviation assuming that the histogram is a Gaussian distribution.

There are various dot counts for printers, such as 4.75/mm and 16/mm, but depending on the dot count, the density histogram typically does not look like FIG. 2A or B, and it may be difficult to decide which one to apply. In such a case, if you lower the print density a little, you will get the type shown in Figure 2 A, and if you increase it a little, you will get the type shown in Figure 2 B. Therefore, determine the appropriate print density experimentally, and print with various types of thermal paper at that density. Try comparing thermal paper with each other,
Alternatively, mutual comparison of blinks may be performed using the same thermal paper at that density.

In the above embodiment, when the density histogram takes the form shown in FIG. 2A, the operator sets the density selection levels H and L.
I am looking at the histogram displayed on RT8,
This operational step can be automated. That is, C
Let PU perform density histogram smoothing processing,
With this smoothed histogram, the valley bottom concentration H and the average (E
The concentration may be calculated as 10H)/2.

(Effects of the Invention) According to the present invention, there is an advantage that a comparative evaluation of coloring patterns of thermal paper by a thermal printer can be quickly, objectively and quantitatively performed.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an example of an apparatus for carrying out the method of the present invention, and FIG. 2 is a density histogram of a printed surface with a constant density.
FIG. 3 is a diagram showing characteristics of density histograms of good printed surfaces and poor printed surfaces, and FIG. 4 is a diagram of actual density histograms. ■...Microscope, 2...Imaging device, 3...Monitor C
RT. 4... Sample stage, 5... CPU, 6... Image memory, 7... Keyboard, 8... CRT for display, 9...
・Printer. Agent Patent Attorney Kosuke Agata

Claims (2)

[Claims] (1) A histogram of the density of the coloring surface is created from the video signal of an enlarged image of the coloring surface of thermal paper that has been colored to a constant density by a thermal printer, and the peaks on the low density side and the peaks on the high density side that appear in this histogram are created. Select one density H corresponding to the valley between the peaks and another density L between the high-density end of the histogram and the density H, and calculate the area Nh above the density H from the video signal. A method for evaluating the quality of prints by a thermal printer, characterized in that an area Nl having a density L or higher is calculated, and a ratio between the two is used as an evaluation value. (2) A histogram of the density of the coloring surface is created from the video signal of an enlarged image of the coloring surface of the thermal paper that has been colored to a constant density by a thermal printer, and when the histogram shows one mountain, A method for evaluating the quality of prints by a thermal printer, characterized by calculating a half-value width or a standard deviation value, and using the calculated value as an evaluation value.