JP2006076253A - Evaluation method and apparatus for printout image - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an evaluation method for a printout image wherein a dot gain characteristic generated in the printout image printed by a printer can be simply evaluated by the use of a predetermined dither pattern, and to provide an apparatus. <P>SOLUTION: The printout image printed by the printer is read by a resolution higher than a resolution of the printer. A predetermined measurement block included in the read readout image is divided in units of pixels. A colored region of the measurement block included in the divided readout image is distinguished in units of pixels. An area of the distinguished colored region is measured in units of pixels. A colored area ratio of each measurement block is calculated on the basis of the measured area of the colored region in units of pixels. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a print image evaluation method and apparatus for evaluating a print image printed by a printing apparatus, and in particular, easily provides dot gain characteristics generated in a print image printed by a printing apparatus using a predetermined dither pattern. The present invention relates to a printed image evaluation method and apparatus that can be evaluated.

  In general, a dither method using a predetermined dither pattern is used to express multi-tone with an electrophotographic printer based on binary output. Here, in order to perform accurate gradation expression, it is necessary to generate an optimal dither pattern.

  Incidentally, it is known that in electrophotographic printers, a so-called dot gain is generated in which toner protrudes from an ideal dot region during toner adhesion and fixing processes. Due to this dot gain characteristic, the black area ratio of the printed image may be higher than the theoretical value and darkly printed.

  The dot gain characteristics vary depending on the printer engine, and a certain dot gain is affected by the dither pattern. Therefore, even if the number of black dots is theoretically the same, it is printed at a different density depending on the dither pattern used. End up.

  Therefore, in order to perform accurate gradation expression with an electrophotographic printer, it is possible to accurately grasp the dot gain characteristics for each engine of the printer and to grasp the detailed dot gain occurrence state corresponding to each dither pattern in a short time. It is necessary to do so.

  Conventionally, as a method for grasping in detail the dot gain occurrence state, a method using a microscope image obtained by enlarging a printed image with a microscope is known. However, in the method using a microscopic image, the field of view is narrow, and it is difficult to grasp in a short time the dot gain occurrence status corresponding to a large number of dither patterns for statistical processing.

  Therefore, a technique using a read image obtained by reading a print image with a high-resolution scanner instead of the microscope image has been studied.

  However, in order to examine the dot gain occurrence status of a print image using a read image read by a high resolution scanner, a predetermined value corresponding to the resolution of the printer, that is, the dot of the print image, is read from the read image read by the high resolution scanner. The unit dither pattern must be extracted as a measurement block.

  In order to examine the dot gain occurrence status, it is necessary to accurately measure the density of the extracted measurement block, that is, the black area ratio.

  By the way, as what can calculate the evaluation value corresponding to the subjective rough feeling of an image with the size of dots, such as a halftone dot, what was indicated in patent documents 1 is known. .

The apparatus described in Patent Document 1 uses an apparatus for calculating an objective evaluation value of an image expressing shading by a halftone dot or the like in order to perform multi-tone expression. From the image information of the image data obtained, the dot center is obtained from the center of gravity of the dot, the size of the pixel is estimated from the center interval, the average density within the pixel centered on the center of gravity is calculated from the average value of the reflectance, and the average The dot size is specified by converting the density into the dot area ratio.
JP-A-11-225228

However, in the device disclosed in Patent Document 1, in specifying the dot size, the center of the dot is estimated, the pixel size is estimated, the average density is calculated based on the average reflectance, and the dot density is calculated from the average density. Dot estimation is performed by area ratio conversion, and there is a problem in that high-precision information cannot be obtained due to information deterioration due to the addition of estimation and conversion intermediate processing.
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a print image evaluation method and apparatus capable of easily evaluating dot gain characteristics generated in a print image printed by a printing apparatus using a predetermined dither pattern. And

  In order to achieve the above object, the invention of claim 1 is a print image evaluation method for evaluating a print image printed by a printing apparatus using a predetermined dither pattern. The image is read by the image reading unit at a resolution higher than the resolution of the printing apparatus, the predetermined measurement block included in the read image read by the image reading unit is divided into pixels by the division processing unit, and is divided by the division processing unit Pixels determined in pixel units by the determination unit in the measurement block included in the read image, the areas of the color regions determined by the determination unit are measured in pixel units by the measurement unit, and pixels measured by the measurement unit The color area ratio of the measurement block unit is calculated by the calculation means based on the area of the unit color region.

  The invention according to claim 2 is the invention according to claim 1, wherein the measuring means extracts a boundary line between the colored area and the white area in the pixel and performs linear approximation passing through a plurality of points on the boundary line. And measuring the area of the colored region.

  According to a third aspect of the present invention, in the second aspect of the invention, the area value of the colored region measured by the measurement unit is normalized and stored in the storage unit corresponding to all the pixels in the measurement block. The calculating means calculates the colored area ratio for each measurement block by dividing the sum of the area values of all the pixels in the measurement block stored in the storage means by the number of pixels in the measurement block. Features.

  According to a fourth aspect of the present invention, there is provided a print image evaluation apparatus for measuring a density of a print image printed by a printing apparatus using a predetermined dither pattern, wherein the print image printed by the printing apparatus is displayed on the printing apparatus. An image reading unit that reads at a resolution higher than the resolution, a division processing unit that divides a predetermined measurement block included in the read image read by the image reading unit in units of pixels, and the read image that is divided by the division processing unit Determining means for determining the colored area of the measurement block included in the pixel unit, measuring means for measuring the area of the colored area determined by the determining means in pixel unit, and colored in pixel unit measured by the measuring means And a calculating means for calculating a colored area ratio in units of the measurement block based on the area of the region.

  According to the present invention, a print image printed by a printing apparatus is read at a resolution higher than the resolution of the printing apparatus, a predetermined measurement block included in the read image is divided into pixel units, and the divided image is divided. The color area of the measurement block included in the read image is determined in pixel units, the area of the determined color area is measured in pixel units, and the color area ratio of the measurement block unit based on the area of the color region in the measured pixel unit Therefore, the dot gain characteristic generated in the print image can be easily and appropriately evaluated.

  Hereinafter, a printed image evaluation method and apparatus according to the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a block diagram showing an embodiment of a print image evaluation apparatus according to the present invention.

  The print image evaluation apparatus reads an evaluation target print image with an image reading device (scanner) having a resolution higher than the resolution of the printing apparatus that printed the evaluation target print image, and evaluates the print image based on the read image thus read. Perform an evaluation.

  That is, a dither method using a predetermined dither pattern is used to express multi-tone in an electrophotographic printer based on binary output, but in an electrophotographic printer, an ideal process for toner adhesion and fixing is used. It is known that so-called dot gain that protrudes from the dot area occurs, and in order to perform accurate gradation expression with this electrophotographic printer, the dot gain characteristics for each engine of the printer are accurately grasped, and each It is necessary to accurately grasp the detailed dot gain occurrence state corresponding to the dither pattern.

  Therefore, in this print image evaluation apparatus, a print image printed by an electrophotographic printer using a predetermined dither pattern is read by a scanner having a resolution higher than the resolution of the electrophotographic printer, and the print image is based on the read image. Evaluate the occurrence of dot gain.

  According to such a configuration, for example, when a print image printed by an electrophotographic printer having a resolution of 600 dpi is read by a flat bed scanner having a high resolution of 3200 dpi, one dot of the print image is about 28 pixels (5.3). An image enlarged to (5.3 pixels) is obtained, and by using this read image, it is possible to evaluate the dot gain occurrence state of the printed image.

  The print image evaluation apparatus 100 shown in FIG. 1 includes an image input unit 10, an image memory unit 20, an image division processing unit 30, and a density measurement processing unit 40.

  Here, the image input unit 10, for example, prints a print image including a plurality of measurement blocks in units of dither patterns printed using a predetermined dither pattern with an electrophotographic printer (hereinafter simply referred to as a printer) having a resolution of 600 dpi at 3200 dpi. A read image read by a high-resolution flat bed scanner (hereinafter simply referred to as a scanner) is input. The read image input to the image input unit 10 is stored in the image memory unit 20.

  When the image is read by the scanner, the print image is scanned as a gray level (8-bit) multi-valued image.

  The image division processing unit 30 divides the measurement block of the high-resolution read image stored in the image memory unit 20 for each pixel (dot) corresponding to the resolution of the printer that printed the print image for evaluation of the print image. Perform the process.

  The density measurement processing unit 40 acquires an image corresponding to each pixel of the electrophotographic printer subjected to the division processing by the image division processing unit 30 from the image memory unit 20, and evaluates the dot gain occurrence state based on the image. Concentration measurement processing is performed.

  FIG. 2 is a diagram for explaining an example of a measurement block employed in this embodiment.

  As shown in FIG. 2, in this embodiment, it is assumed that the printer performs printing using an 8 × 8 dot dither pattern, and therefore the measurement block is set to 8 × 8 dots.

  In addition, since the dot gain of the measurement block of 8 × 8 dots is influenced by the peripheral blocks, the same measurement block having a width of 4 dots around the measurement block of 8 × 8 dots is added to add this effect. A repetitive block using the dither pattern is provided.

  Then, an 8 × 8 dot measurement block and its surrounding repeated blocks are included as a 16 × 16 dot basic block 200, and the printer prints a print image with the 16 × 16 dot basic block 200 as one unit.

  Further, in this embodiment, in order to simultaneously evaluate the dot gain occurrence status in a plurality of measurement blocks, as shown in FIG. 3, 32 × 32 basic blocks of 16 × 16 dots shown in FIG. This is a large block 300, and cross-shaped reference point markers 301, 302, 303, 304 for specifying the position of the measurement block are drawn around the four corners of the large block 300. Between 302, 303, and 304, a division marker 310 that is used in a division process for dividing an image of a measurement block in pixel units (dot units) is drawn.

  Here, in this embodiment, the cross-shaped reference point markers 301, 302, 303, 304 and the division marker 310 are drawn using a line segment having a line width of 2 dots and a line length of 64 dots, respectively. The line width interval is drawn with 6 dots.

  When the print image is evaluated using the print image evaluation apparatus of this embodiment, for example, the large block 300 having the reference point markers 301, 302, 303, 304 and the division marker 310 around the periphery shown in FIG. As shown in FIG. 4, 10 × 7 are arranged to form one screen, and this screen is printed on a surface of, for example, A4 paper by a printer to form a print image for dot gain evaluation.

  When evaluating the dot gain using this print image, this image is read by a high-resolution scanner, and this read image is input to the image input unit 10 shown in FIG. 1 and stored in the image memory unit 20.

  FIG. 5 is a flowchart for explaining the processing of the image division processing unit 30 shown in FIG.

  The image division processing unit 30 shown in FIG. 1 first specifies the position of the measurement block in each large block 300 from the reference point markers 301, 302, 303, 304 included in the read image stored in the image memory unit 20. A reference point for extraction is extracted (step 501).

  Here, the extraction of the reference point uses the Steger method which is not easily affected by the luminance change of the read image. That is, the reference point markers 301, 302, 303, and 304 are determined from the distribution of density changes in the read image, and the reference point markers 301, 302, 303, and 304 are determined from the determined reference point markers 301, 302, 303, and 304. The coordinates of the crossing point are extracted as a reference point.

  Next, a skeleton line is extracted based on the division marker 310 drawn between the reference point markers 301, 302, 303, and 304 (step 502).

  Here, the division marker 310 is discriminated using the Steger method based on the distribution of the density change of the read image, similarly to the reference point markers 301, 302, 303, and 304. The center of the division marker 310 is calculated by linear approximation by the least square method.

  Next, based on the reference point extracted in step 501 and the skeleton line extracted in step 502, a division process for dividing the measurement block in units of pixels (dots) is performed (step 503), and this process is terminated.

  FIG. 6 is a flowchart showing details of the division processing in step 503 shown in FIG.

  In the division process shown in FIG. 6, first, one large block is selected from a plurality of large blocks based on the reference point extracted in the step of FIG. 5 (step 601).

  Next, one basic block is selected from a plurality of basic blocks in the selected large block (step 602), and measurement blocks included in the selected basic block are extracted (step 603).

  Then, the coordinates of the dividing points for dividing the extracted measurement block for each pixel (dot) are calculated based on the skeleton line extracted in step 502 of FIG. 5 (step 604).

  That is, as shown in FIG. 7, division markers 310-11, 310-12, 310-13, 310-14,..., 310-21, 310-22, 310-23, 310-24, ... are drawn, and skeleton lines 320-1, 320-12, 320-13, 320-14, ..., 320-21, 320-22, 320-23, 320-24, ... are extracted from these divided markers. Suppose that

  In this case, based on the extracted 320-11, 320-12, 320-13, 320-14,..., 320-21, 320-22, 320-23, 320-24,. Dividing lines 330-11, 330-12,..., 330-19, 330-21, 330-22,. Find the coordinates of the dividing points for each division.

  Next, it is checked whether all the basic blocks in the selected large block have been selected (step 505). If there is a basic block that has not been selected yet (NO in step 605), the process returns to step 602 to return to the next basic block. Select a block and repeat the same process.

  If it is determined in step 605 that all basic blocks have been selected (YES in step 605), it is then checked whether all large blocks have been selected (step 606). If there is a large block that has not yet been selected (NO in step 606), the process returns to step 601 to select the next large block and repeat the same processing. However, in step 606, all large blocks are selected. If it is determined that it has been selected (YES in step 606), this process ends.

  By such processing, it is possible to obtain the coordinates of division points for dividing all measurement blocks included in the read image in units of pixels (dots).

  FIG. 8 is a flowchart for explaining processing of the concentration measurement processing unit 40 shown in FIG.

  In the process of the concentration measurement processing unit 40 shown in FIG. 8, first, one measurement block is selected based on the reference point extracted in step 501 of FIG. 5 (step 801). Next, one coordinate of the division point of the selected measurement block is acquired from the image division processing unit 30 (step 802), and an image in pixel units is acquired from the image memory unit 20 based on the acquired coordinate of the division point. (Step 803).

  Next, black and white discrimination is performed to discriminate between a white area and a black area of the pixel unit image acquired from the image memory unit 20 (step 804).

  Then, based on the black and white discrimination, the area of the black region of the image in units of pixels acquired from the image memory unit 20, that is, the black area is calculated (step 805).

  This black area is calculated when, for example, the coordinates of the upper left vertex of the pixel unit image acquired from the image memory unit 20 are (i, j), and the area of the pixel unit image is “1”. As shown in FIG. 9, a plurality of points A, B, and C on the boundary between the white region and the black region of the pixel unit image are obtained, and a black area is obtained by linearly approximating the points A, B, and C. Is calculated.

  When the calculation of the black area of the image in one pixel unit is completed in this way, next, it is checked whether or not the black area of all the pixels in this measurement block, that is, 8 × 8 pixels has been calculated (step 806). ) If pixels that have not yet been calculated remain (NO in step 806), the process returns to step 802, the coordinates of the next division point in the measurement block are acquired, and the same processing is repeated thereafter.

  If it is determined in step 806 that the calculation of the black area of all the pixels in the measurement block has been completed (YES in step 806), the black area of all the pixels in the measurement block calculated in step 805 is determined. Based on the above, the black area ratio of this measurement block is calculated (step 807).

The black area ratio is calculated when the number of pixels in the measurement block is 8 × 8, the area of each pixel is “1”, and the black area of each pixel image is S1, S2,.
Black area ratio = ΣSi / 8 × 8
It can be calculated from

  When the calculation of the black area ratio for one measurement block is completed, it is next checked whether all the measurement blocks have been selected (step 808). If there are measurement blocks that have not yet been selected (NO in step 808). Returning to step 801, the next measurement block is selected and the same processing is repeated.

  If it is determined in step 808 that all measurement blocks have been selected (YES in step 808), the process ends.

  By such processing, the black area ratio of all measurement blocks included in the read image can be calculated.

  In this way, the black area ratio of each measurement block calculated by the density measurement processing unit 40 in FIG. 1 is output to a computer or the like (not shown) and used for dot gain evaluation or the like.

  FIG. 10 shows a comparison between a logical pattern of a certain measurement block and an image obtained from the read image.

  FIG. 10A shows a logical black image pattern by the dither pattern used for printing the measurement block, and FIG. 10B enlarges the print image printed by the same dither pattern. As shown.

  Here, the logical black area ratio of the logical black image pattern in FIG. 10A is 0.328. For the actual print image, the black area ratio calculated by the print image evaluation apparatus 100 of this embodiment is used. According to the above, 0.517 is obtained. Accordingly, it is possible to determine that the difference between the black area ratios is due to the dot gain, and thereby it is possible to grasp the dot gain characteristic corresponding to the dither pattern.

  Here, when a print image printed with a different dither pattern for each large block or each measurement block is used, dot gain characteristics corresponding to a plurality of dither patterns can be evaluated by one reading process.

  Further, by measuring the interval between the extracted skeleton lines, the printing distortion characteristic information of the printing apparatus can be acquired at the same time.

  The dot size of the basic block of the print image, the line width between the reference marker and the division marker, and the line width interval between the division markers are not limited to the above-described embodiments, and arbitrary values can be used.

  Further, the skeleton line from the division marker may be extracted based on the density change of the black and white binary read image without using the multilevel (gray level) read image.

  In addition, the density measurement processing unit may be configured to output the maximum value, average value, standard deviation, dot shape, and the like of the black area ratio as evaluation values in addition to the black area ratio for each pixel.

  Further, instead of the black area ratio for each pixel, a difference between the black area logical value and the actual measurement value may be calculated.

  In the above embodiment, a monochrome image is targeted. However, the present invention can be applied to a color image by performing similar processing for each color.

  The present invention is applicable to the evaluation of the dot gain occurrence situation in an electrophotographic printer. According to the present invention, the print image printed by the printing apparatus is read at a resolution higher than the resolution of the printing apparatus, and the density of each measurement block is measured in pixel units based on the read image. It becomes possible to easily and quickly evaluate the dot gain characteristics generated in a printed image by one reading.

It is a block diagram which shows one Example of the evaluation apparatus of the printed image which concerns on this invention. It is a figure explaining an example of the measurement block employ | adopted by this Example. It is a figure explaining an example of the large block employ | adopted by this Example, a reference point marker, and a division | segmentation marker. It is a figure explaining an example of the printing image employ | adopted by this Example. 3 is a flowchart for describing processing of an image division processing unit illustrated in FIG. 1. 6 is a flowchart showing details of the division process shown in FIG. 5. It is a figure explaining the calculation process of the division | segmentation point shown in FIG. It is a flowchart explaining the process of the density | concentration measurement process part shown in FIG. It is a figure explaining the black area calculation process shown in FIG. It is a figure which compares and shows the logical pattern of a certain measurement block, and the image obtained from the read image.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Image input part 20 Image memory part 30 Image division process part 40 Density measurement process part 100 Printed image evaluation apparatus

Claims (4)

In a print image evaluation method for evaluating a print image printed by a printing apparatus using a predetermined dither pattern,
A print image printed by the printing apparatus is read by an image reading unit at a resolution higher than the resolution of the printing apparatus;
A predetermined measurement block included in the read image read by the image reading unit is divided into pixel units by a division processing unit,
The colored area of the measurement block included in the read image divided by the division processing unit is determined in pixel units by the determination unit,
The area of the colored region determined by the determining means is measured in pixel units by the measuring means,
A method for evaluating a printed image, comprising: calculating a colored area ratio in units of measurement blocks by a calculation unit based on an area of a colored region in units of pixels measured by the measuring unit. The measuring means extracts a boundary line between a colored region and a white region in the pixel, and measures the area of the colored region by linear approximation passing through a plurality of points on the boundary line. The evaluation method of the printed image of 1. Normalizing the area value of the colored region measured by the measurement means and storing it in the storage means corresponding to all the pixels in the measurement block;
The calculation means calculates a colored area ratio for each measurement block by dividing the sum of the area values of all the pixels in the measurement block stored in the storage means by the number of pixels in the measurement block. The method for evaluating a printed image according to claim 2. In a print image evaluation apparatus that measures the density of a print image printed by a printing apparatus using a predetermined dither pattern,
Image reading means for reading a print image printed by the printing apparatus at a resolution higher than the resolution of the printing apparatus;
A division processing unit that divides a predetermined measurement block included in a read image read by the image reading unit into units of pixels;
A discriminating unit that discriminates a colored area of the measurement block included in the read image divided by the division processing unit in units of pixels;
Measuring means for measuring the area of the colored region determined by the determining means in units of pixels;
A printing image evaluation apparatus comprising: a calculation unit that calculates a colored area ratio of the measurement block unit based on an area of a colored region of the pixel unit measured by the measurement unit.

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