JP2693825B2 - Recording quality evaluation method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for evaluating recording quality in a laser beam printer, a facsimile machine, a copying machine, etc. The present invention relates to a recording quality evaluation method capable of quantitatively evaluating density unevenness and resolution.

[Conventional technology]

Up to this point, the quality evaluation and inspection for printing and drawing by printers etc. were mainly conducted by visual sensory inspection, but quantitative evaluation of inspection is necessary to perform more reliable inspection. There is. For this reason, evaluation methods that have taken into consideration quantitative evaluation have hitherto been disclosed in, for example, JP-A-60-175
It depends on what is disclosed in Japanese Patent No. 187 and Japanese Patent Laid-Open No. 63-19084. In the case of these publications, the characters printed on the recording paper or the rectangular black solid pattern are captured and processed as an image by a TV camera or the like, and the contrast between the characters and the recording paper, the print width, the sharpness, The unevenness and blurring of the contour are evaluated by the width of the pixel and the edge width. As described above, most of the evaluation methods used so far are those that evaluate the reproducibility of characters.

On the other hand, regarding the basic elements in the print quality and the drawing quality, the density inspection device using a densitometer disclosed in JP-B-63-36264 and JP-A-62-277509 are disclosed. A known method for evaluating unevenness in density due to variations in density difference has been known.

[Problems to be solved by the invention]

However, even if a TV image is used for evaluation in order to eliminate the deficiency in the visual sensory test, that is, the variation in the evaluation due to individual differences and unstable physiological conditions, the influence of illumination fluctuation in the density test and the drawing Problems such as the fact that the detection of density unevenness is not taken into consideration are still left. In recent years, with the development of OA, not only character printing but also image drawing are frequently performed, but with such a tendency, the evaluation and inspection of the recording quality of output devices also become strict. However, with respect to items such as density, density unevenness, and resolution, it is the actual situation that evaluation by visual sensory inspection is still performed.

An object of the present invention is to prevent density fluctuations and ambient light from affecting the density quality and density unevenness on recording, density variations,
Furthermore, it is to provide a recording quality evaluation method capable of quantitatively evaluating the resolution.

[Means for solving the problem]

The above-mentioned object is to simultaneously image a recording paper on which a plurality of black solid patterns are recorded as a scattered state and a density reference containing white and black arranged near the recording paper in the same visual field, and As a ratio of the two-dimensional image data corresponding to the black solid pattern to the two-dimensional image data corresponding to the density reference, the relative density of each black solid pattern with respect to the density reference is evaluated, and the black solid pattern is compared with each other. After the variation in the density between the two is evaluated, the density uniform pattern on the recording paper by the same output device is imaged and stored as a multi-valued two-dimensional image, which is orthogonal to the two-dimensional image data corresponding to the pattern. This is achieved by evaluating the density unevenness in the same direction as any of the above two directions based on the brightness projection distribution from each of the two directions.

Further, in evaluating the resolution, after the density, density unevenness, and density variation were evaluated, the line density on the recording paper by the same output device was gradually narrowed in each of two orthogonal directions. A black-and-white line pattern is captured and then stored as a multi-valued two-dimensional image, and the resolution is evaluated based on the brightness projection distribution from each direction parallel to the black-and-white line for the two-dimensional image data corresponding to the pattern. Is achieved in.

[Action]

This is to more quantitatively evaluate the recording quality of items such as density, density unevenness, and resolution for the same output device. First, regarding the density as the most important item, the ratio of the multi-valued two-dimensional image data corresponding to the density reference including at least white and black to that corresponding to the black solid pattern recorded by the output device is used to determine the black solid with respect to the density reference. The relative density of the pattern can be obtained without being affected by illumination fluctuations or ambient light. At that time, if the absolute density of the density reference is known, the absolute density of the black solid pattern can also be easily obtained.

In addition, when a uniform density pattern is recorded on recording paper, uneven density generally appears in a specific direction in a streak pattern. Therefore, for multi-valued two-dimensional image data corresponding to the uniform density pattern, the specific direction If the brightness projection distribution is obtained, the density unevenness can be detected as the position of the streak portion is manifested. By differentiating the brightness projection distribution, the density unevenness is quantitatively obtained from the density difference between the striped portion and the surroundings and the width of the striped portion.

Furthermore, if a black-and-white line pattern in which the line-to-line density becomes narrower gradually is recorded on the recording paper and the brightness projection distribution in the black-and-white line direction is calculated for the corresponding multi-valued two-dimensional image data, the line-to-line density The resolution can be quantitatively evaluated by how much the distribution value changes with respect to the change.

〔Example〕

 The present invention will be described below with reference to FIGS. 1 to 9.

First, the recording quality evaluation apparatus according to the present invention will be described. FIG. 2 shows an external structure of an example thereof together with a recording paper (sample) to be evaluated. As shown in the figure, the recording paper on which a predetermined pattern is recorded by an output device such as a printer is illuminated by the illumination device 2 as the recording paper 1 to be evaluated, and the predetermined pattern is multivalued by the TV camera 3. The image is captured as a three-dimensional image and then temporarily stored in the image processing device 5. The multi-valued two-dimensional image data corresponding to the predetermined pattern is the image processing device 5.
The image quality is internally processed so that the recording quality for the pattern is evaluated.
The monitor TV4 is provided for confirming the processing result of the image.

FIG. 3 shows a configuration of an example of the image processing apparatus. As shown in the figure, a CPU (connecting a display / printer) 5-4, an image input / output circuit (connecting a TV camera 3 and a monitor TV4) 5-1, an image memory (for storing multi-valued two-dimensional image data) 5- 2, a general-purpose input / output circuit 5-3, an arithmetic circuit 5-7, a program memory 5-6, a floppy disk controller 5-5 and the like.

First, in order to evaluate the degree of black density of a character or a drawing pattern recorded on a recording paper by an output device, a black solid pattern is recorded on the recording paper by the output device. ing. FIG. 4 (a) shows an example of the black solid pattern 6 recorded on the recording paper 1 to be evaluated, and the black solid pattern 6 is scattered at several places in order to evaluate the variation of the black density together. It is recorded as a state. The evaluated recording paper 1 on which such a black solid pattern 6 is recorded is temporarily stored after being imaged as a multi-valued two-dimensional image together with a separately prepared density standard, but FIG. Shows the density standard 7 in which black and white of the standard density are displayed. The density standard 7 may include white ash or gray black as an intermediate density color, but in any case, the black solid pattern 6 is imaged together with the density standard 7. FIG. 4 (c) shows a density reference image 7'and a black solid pattern image 6'simultaneously displayed on the same screen of the display. Multi-valued two-dimensional images corresponding to these images 7'and 6 ', respectively. The relative density of the solid black pattern 6 with respect to the reference density is quantitatively obtained from the data.

That is, if the values of the two-dimensional image data corresponding to the black part and the white part in the density reference 7 are f _a and f _b , respectively, and the value corresponding to the black solid pattern 6 is f _x , The relative concentration P _x is obtained as follows.

Here, what reduces the f _x, f _b respectively than f _a, it is hardly value of f _a is zero due lighting conditions, f _x, f _b
This is for offsetting. As a result, the relative density of the solid black pattern 6 can be quantitatively obtained without being affected by the illumination state or the like. For example, if P _x is 100%, the density of the black solid pattern 6 is the same as the white density on the density standard 7, and if it is 0%, it is the same as the black density on the density standard 7. is there. If it is 50%, the density of the black solid pattern 6 is judged to be between the white and black densities in the density standard 7. At that time, if the absolute densities of white and black in the density standard 7 are measured in advance by a Macbeth densitometer or the like, the black solid pattern 6
The absolute concentration of is also easily sought. FIG. 5 is a flow chart showing an example of the concentration evaluation process according to the present invention, in which the magnitude relationship between the appropriately set allowable concentration (corresponding to the lower limit of good concentration) and the measured P _x is shown. By the determination, the quality of the density of the black solid pattern 6 is determined. In addition to this density evaluation processing, the density can be comprehensively evaluated by determining variations in density among a plurality of black solid patterns scattered at several places.

Incidentally, the evaluation value of the density indicates the recording density of the output device, and the automatic density adjustment method can be considered as a method utilizing this. While the actually measured recording density does not reach the permissible density, the actual recording density is set to be equal to or higher than the permissible density by updating the recording data itself, the applied power, the toner amount, and the like in a stepwise manner. Further, it has been considered that a threshold value for binarizing the binarization target image is automatically determined based on the measured density.
Even if the brightness of the binarization target and the brightness of the background are not so different, the binarization target is determined by determining the threshold for binarization processing each time in consideration of the fluctuation of the lighting condition. It is intended to stably binarize an image. First, after the density standard including white and black as the reference density is imaged together with the image to be binarized and the threshold value is set as the relative density, the actual threshold value is determined from the threshold value by measuring the density with respect to those reference density values. If the value is determined, the binarization target image can be stably binarized by the threshold value that is finely settable.

The density evaluation method has been described above. Next, the density unevenness evaluation method will be described. When evaluating the agricultural unevenness, the entire surface of the evaluated recording paper 1 is evaluated as shown in FIG. 6 (a), for example. The uniform density pattern 8 is recorded over the entire area. As the density of the pattern 8, a halftone density (for example, gray) is generally suitable. This is because the density unevenness is caused by the rotation unevenness in the paper feeding system and the like and appears as black or white streaks in the x direction or the y direction as shown in FIG. 6 (b). And when evaluating the white streaks at the same time,
This is because the halftone density pattern is appropriate.
The density unevenness has a great influence on the recording quality especially when printing the drawing and as the difference between the density and the surrounding and the width thereof increase. FIG. 7 shows an example of the density unevenness evaluation processing according to the present invention. This is a flow chart of. In this case, the uniform density pattern is captured and stored as a multi-valued two-dimensional image, and then the projection distribution is calculated by adding its brightness in the x direction or the y direction (bidirectional as necessary). There is. FIG. 6 (c) shows the x-direction projection distribution for the multi-valued two-dimensional image data corresponding to the density uniform pattern shown in FIG. 6 (b). As shown in FIG. 6 (c),
Since it is assumed that the density unevenness in this example is black, the distribution waveform shape in the projected distribution portion corresponding to the position where the density unevenness exists is concave, and the existence of black density unevenness is known from this. Contrary to the above, in the case of white density unevenness, the distribution waveform shape is convex, and the existence of white density unevenness is known from the existence thereof. The presence of density unevenness can be easily detected by a threshold value that is variably set. Whether or not the density unevenness is present is determined by removing noise from the projected distribution waveform and then performing differentiation processing. This makes it easy to evaluate.
FIG. 6 (d) shows a waveform in the case where the projection distribution waveform shown in FIG. 6 (c) is subjected to differential processing after noise removal, and a large waveform change appears around the concave portion peak point. It is like this. If the maximum amplitude width P and the peak-to-peak width L are introduced as parameters that characterize this waveform change, the value of P is the density difference from the surroundings of the density unevenness, and the value of L is the density unevenness of the density unevenness. Since they correspond to the spread widths respectively, the density unevenness can be quantitatively evaluated using the values of these parameters. If at least one of the parameters is equal to or more than the allowable value, it is determined as defective in the density unevenness evaluation. FIG. 6 (e) shows an example of the relationship between the values of those parameters and the judgment ranges of “good” and “defective”. If such a judgment range is specifically determined from visual experience, It is enough.

The above-described method for evaluating density unevenness can also be applied to the evaluation of scratches existing on the surface of an object. If there is a flaw that extends in a certain direction on the surface of the object, the brightness at that flaw will be different from that of the surroundings, so the degree to which the surface of the object is rotated by a certain amount relative to the TV camera In addition, if the density unevenness evaluation is performed by the differential processing, it is known that the flaw is present because a large waveform change appears in the differential processing waveform. After the presence of the flaw is detected, the extent of the flaw can be quantitatively evaluated from the values of P and L in a state where the relative rotational position of the object surface with respect to the TV camera is finely adjusted.

To further explain the method of evaluating the resolution, when evaluating the resolution, black and white line patterns 9 and 10 are formed on the recording paper 1 to be evaluated as shown in FIG.
n) is recorded as a gradually narrowed state such that w ₁ > w ₂ >...> wn. It is intended to evaluate the resolution depending on the line density to which adjacent white lines and black lines can be separated.
FIG. 9 shows a flow in an example of the resolution evaluation processing according to the present invention. In this case, the black and white line patterns 9 and 10 are imaged, and the projection distribution by brightness addition is obtained in the direction parallel to the black and white lines. For example, the brightness addition processing is performed in the x direction for the x direction black and white line shown in FIG. 8 (b).
As a result, an uneven waveform having an amplitude corresponding to the line density wi appears as a distributed waveform as shown in FIG. 8 (c). Depending on the brightness addition process, variations in brightness in the lines are absorbed, and the black-and-white line gap is obtained as an average.
In addition, the uneven waveform having the amplitude corresponding to the line density appears because the variation in the brightness in the line influences as the line density becomes smaller, which lowers the brightness addition value. It has become a thing. This situation is the same for the black and white lines in the y direction, but in any case, the line density wi and the corresponding amplitude width Pi are obtained as the relationship shown by the broken line in FIG. 8 (d). Is. Incidentally, w _x indicates the line density at which black and white lines cannot be separated.

Now, if the relationship between the line density change amount w and the amplitude width change amount p is expressed as a slope P / W, the smaller the slope P / W, the better the resolution. The resolution can be quantitatively evaluated based on such a concept of inclination. By setting an inclination of a certain magnitude as the quality determination threshold value, the quality of recording with respect to the resolution can be easily determined. By using such a resolution evaluation method in reverse,
The resolution of the imaging lens can be evaluated. It is only necessary to image the standard black-and-white line pattern sheet for resolution evaluation through the imaging lens to be evaluated and process the image data as described above.

Finally, a case of comprehensively evaluating the recording quality with respect to the density (considering the degree of variation), the density unevenness, and the resolution will be described. FIG. 1 shows a flow of an example for the evaluation processing. Is. The order of evaluation is density, density unevenness, and resolution in order of importance. In this example, the pattern to be evaluated is selectively imaged from various patterns recorded on the same recording paper to be evaluated. If the evaluation is performed and evaluated, and it is determined to be defective in any of the evaluation determination processes, the subsequent evaluation process is not performed at that time. Various patterns are recorded on the recording paper to be evaluated by standard recording pattern data or standard recording patterns, whereby the recording quality at the output device can be quantitatively evaluated.

〔The invention's effect〕

As described above, in the case according to claims 1 to 3,
The density quality, the density unevenness, and the density variation on the recording are further affected by the illumination fluctuation and the ambient light, and the density variation according to claim 4,
In this case, the resolution can be quantitatively evaluated in addition to the density quality, density unevenness, and density variation.

[Brief description of the drawings]

FIG. 1 is a diagram showing a flow of an example of processing according to the present invention for comprehensively evaluating recording quality with respect to density, density unevenness and resolution, and FIG. 2 is recording quality evaluation according to the present invention. Diagram showing the external configuration of the device together with the recording paper to be evaluated,
FIG. 3 is a diagram showing a configuration of an example of an image processing apparatus as one component of the apparatus, and FIGS. 4 (a) to 4 (c) are black solid patterns and a density standard required for density evaluation. ,
Furthermore, a diagram for explaining those imaging conditions, FIG. 5 is a diagram showing a flow of an example of the density evaluation processing according to the present invention, and FIGS. 6 (a) to 6 (e) are for the density unevenness evaluation. FIG. 7 illustrates an example of the density unevenness evaluation process according to the present invention, which is a diagram for explaining a required density uniform pattern, a mode of existence of density unevenness, a processing result in the density unevenness evaluation process, and density unevenness quality determination. 8A, 8B, 8C, 8D, 8E, 8D, and 8C are diagrams for explaining the determination of resolution, the black-and-white line pattern required for resolution evaluation, the processing result in the resolution evaluation processing, and FIG. The figure is a diagram showing a flow of an example of the resolution evaluation processing according to the present invention. 1 ... Evaluated recording paper, 2 ... Illumination device, 3 ... TV camera, 5 ... Image processing device, 6 ... Black solid pattern, 7 ...
... density standard, 8 ... uniform density pattern, 9, 10 ... black and white line pattern.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A 61-208387 (JP, A) JP-A 1-279376 (JP, A) JP-A 60-125509 (JP, A) JP-A 59- 95549 (JP, A) JP 62-277509 (JP, A) JP 64-67344 (JP, A) JP-B 7-104934 (JP, B2)

Claims (5)

(57) [Claims] 1. A recording quality method for evaluating the recording quality of printing or drawing on a recording paper by an output device such as a printer, the recording paper having a plurality of black solid patterns recorded as a scattered state, The black and white patterns for the two-dimensional image data corresponding to the density reference are stored at the same time as the density reference including white and black arranged in the vicinity of the recording paper are simultaneously captured so as to be included in the same visual field. As the ratio of the corresponding 2D image data, the relative density of each black solid pattern with respect to the density standard is evaluated, and the variation in the density between the black solid patterns is also evaluated, and then it is transferred to the recording paper by the same output device. The density uniform pattern of the image is imaged and stored as a multi-valued two-dimensional image, and the brightness from two orthogonal directions with respect to the two-dimensional image data corresponding to the pattern is stored. Based on the shadow distribution, recording quality evaluation method as density unevenness same direction as either of the two directions is evaluated. 2. The recording quality evaluation method according to claim 1, wherein the density unevenness is evaluated based on the density difference between the surroundings of the density unevenness obtained from the brightness projection distribution subjected to the differential processing and the width of the unevenness. . 3. The recording quality evaluation method according to claim 1, wherein the density of the uniform density pattern is halftone. 4. After the recording quality evaluation method according to any one of claims 1 to 3 is carried out, the line density is gradually increased on the recording paper by the same output device in each of two orthogonal directions. After capturing the narrowed black and white line pattern, it is stored as a multi-valued two-dimensional image, and the resolution is evaluated based on the brightness projection distribution from each direction parallel to the black and white line for the two-dimensional image data corresponding to the pattern. Recording quality evaluation method. 5. The recording quality evaluation method according to claim 4, wherein the resolution is evaluated from the change of the distribution value with respect to the change of the line density, which is represented by the brightness projection distribution.