JPH076783B2 - Densitometer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention includes all continuous-tone original images (monochrome or color film originals, etc. to be reproduced on a recording medium such as recording paper). The present invention relates to a densitometer that is useful when creating a halftone dot duplicate image (a copy of a document image such as a print image or a printer image).

More specifically, according to the present invention, when a duplicate image is created from a continuous-tone original image, the density information value of a desired sample point (pixel) on the original image and halftone dots of corresponding points on the duplicate image are used. The present invention relates to a densitometer that displays gradation intensity values such as area% values.

(Prior Art and Problems Thereof) Printing is a representative field of producing a halftone dot duplicate image.

At present, one of the important issues in platemaking in the printing field is
For image conversion processing such as color separation and halftone printing, more specifically, a basic image for gradation conversion from a continuous tone original image (for example, a color film original) to a halftone dot printed image. Although the density value is obtained as information, this basic image information has a scientific and rational relationship with the evaluation of the image quality of the printed image, which is the product, and the adjustment and management of the image information during gradation conversion work. That is not available. That is,
The relationship between the density value of the original image and the gradation intensity value (halftone dot area% value) when the density value is converted into gradation depends exclusively on the experience and intuition of the plate-making operator. is the current situation.

In other words, even if the density value as the image information of the original image is measured with a densitometer, the plate making design performed thereafter is entirely based on human experience and intuition. The reality is that the work can't be standardized reasonably today and it has reached the present day.

In today's platemaking work, it is possible to create highly diversified print images while increasing the efficiency of use of expensive advanced photolithography equipment such as scanners, saving consumable materials, and shortening platemaking time. There is a strong demand for eliminating operational mistakes.

In order to meet the above-mentioned needs and demands, a platemaking company has introduced a press scanning system, has adopted a pre-soft proofing system using an expensive CRT before color separation, or has a proof print to be submitted to the customer. )
Some efforts have been made, such as doing in-house proofs (called in-school) before doing, but it is not very effective,
At present, they are forced to introduce expensive equipment and unnecessary work procedures.

The fundamental reason for the problems in the above-mentioned plate making operation is the gradation conversion processing technique of an image that converts a continuous-tone original image into a halftone dot print image. The image gradation conversion processing technology is not established as a scientific and rational technology.

The above-mentioned point, even in the case of the printing field, is said to be based on human experience and intuition for all image gradation conversion techniques when producing duplicate images with printer devices, copy devices, etc. It's not too much to say. That is, the fact that the gradation conversion processing technology for images in the density area has not been scientifically and rationally performed is not limited to the plate making work in the printing industry alone, but also for halftone dot reproduction images. It is common to the technical fields related to production.

(Problems to be Solved by the Invention) The present invention has been made in view of the above-described limitations of the conventional technique, and relates to improvement of a densitometer as a useful tool for gradation conversion work. That is, the density value at an arbitrary sample point (pixel) on the continuous-tone original image measured by the densitometer is used to produce a halftone dot reproduction image of a desired image quality (gradation characteristic). The present invention is intended to rationalize the above-mentioned gradation conversion work of an image by providing a mechanism and a function capable of converting the gradation strength value of 1 to 3 and displaying the gradation strength value.

As described above, continuous gradation is defined as halftone.
There are various fields in which the gradation conversion is performed to produce a duplicate image, but in these fields, the density information value (the density value measured by a normal densitometer is used as the primitive information (basic image information) of the image processing. In a broad sense, it refers to the amount of information correlated with the density. The same shall apply hereinafter) is obtained from a continuous tone original image. Therefore, the densitometer of the present invention is not limited to the field of printed images, but is widely useful when trying to rationalize the gradation conversion work when producing duplicate images.

An object of the present invention is not only to display the density information value, but also to process the density information value by a new gradation conversion expression and display the gradation strength as well. It is to provide a useful densitometer when making.

(Means for Solving the Problems) The present invention can be summarized as follows. In the densitometer of the present invention, which is useful as a work guide when creating a halftone dot reproduction image from a continuous tone original image, The total (i) displays the density information value at an arbitrary sampling point on the original image, and (ii) on the duplicate image obtained by processing the density information value at the sampling point by the following <relational expression (1)>. A densitometer, which displays the gradation intensity value (y) of.

<Relational expression (1)> However, x: a basic density information value obtained by subtracting the density information value in the brightest portion H on the same image from the density information value at any sample point on the original image.

y: Gradation intensity value at a point on the duplicate image corresponding to an arbitrary sample point on the original image.

yh: A desired gradation intensity value set in the brightest portion H on the duplicate image.

ys: Desired gradation intensity value set in the darkest part S on the duplicated image.

α: Surface reflectance of a recording medium for recording a duplicate image.

β: Surface reflectance of an expression medium for expressing a duplicate image.

k: arbitrary coefficient.

Respectively.

Hereinafter, the technical configuration of the present invention will be described in detail.

As described above, the present invention provides a densitometer that is normally used when producing a duplicate image such as a printed image, and displays a density information value and a floor area such as a halftone dot area% value that guides the production work of the duplicate image. The feature is that the tonal intensity is displayed.

In the present invention, the gradation intensity value is calculated by the <relational expression (1)> theoretically obtained by the present inventors.

Therefore, first, the <relational expression (1)> will be described.

The above-mentioned <relational expression (1)> was born in the process of obtaining the density formula in plate making / printing from the density formula (optical density, photographic density) generally accepted,
It is rational.

The above-mentioned <relational expression (1)> can be arbitrarily changed or modified in terms of numerical values and personality of each item of the <relational expression (1)> as long as it conforms to the gist of the present invention. ,processing,
It does not prevent simplification.

For example, the above <relational expression (1)> is replaced by the following <relational expression (2)>
It may be modified as follows.

y = yh + E (1-10 ^- kx) (ys-yh) (2) where E = 1 / (1-β) <Relational expression (2)> is the α value of <relational expression (1)>. A 10
This corresponds to 0% (surface reflectance).

The inventors of the present invention have confirmed that <Relational Expression (1)> is extremely effective in gradation conversion work when producing a printed image, and a patent application has already been filed for this point. Japanese Patent Application No. 62-148912, U.S. Pat. No. 4,811,108).

The operational characteristics of the <relational expression (1)> will be described by taking a case where a halftone dot print image is produced as a duplicate image as an example.

When a printed image is produced, in the <relational expression (1)>, the x value is the basic density value (the density value at an arbitrary sample point on the original image is subtracted from the density value at the brightest portion H on the same image). Density value), yh is a halftone dot area percentage value of a desired size set in the brightest portion H of the print image, and ys is a halftone dot area percentage of a desired size set in the darkest portion S of the print image Where y is the reflectance of the printing paper and β is the surface reflectance of the printing ink, the y value is the halftone dot area percent value on the printed image at the point corresponding to any sample point on the original image ( Gradation intensity value).

In the production of a print image, since the density range value (dynamic range) of the print image is generally different, the k value of the <relational expression (1)> is taken into consideration in consideration of compression of the density range.
It is effective to use the ratio of (density range value of print image) / (density range value of original image). However, the k value is not limited to the above value.

When the y value is plotted against the x value, y = yh at the brightest point and y = ys at the darkest point.
A curve connecting between .about.ys, that is, a halftone dot gradation characteristic curve (gradation conversion characteristic curve) is formed.

The halftone gradation characteristic curve is a work curve for converting continuous gradation into halftone gradation when producing a print image, and is extremely important.

The significance of the above is important, and it becomes possible to rationally set the halftone dot gradation characteristic curve conventionally used for gradation conversion based on human experience and intuition. .

The present invention is based on the above knowledge, and in a densitometer that is an essential work root in the process of producing a duplicate image, not only the density value but also the gradation intensity value such as the halftone dot area% value described above The display is intended to streamline the production of the duplicate image. For example, a plate-making worker can rationalize gradation conversion by using a densitometer that has an algorithm for calculating a y-value corresponding to the above-described x-value as software, so that gradation reproduction is possible. It becomes possible to obtain a printed image having excellent properties.

In the present invention, the means and method for realizing the calculation of the <relational expression (1)>, and the mode and method of equipping the densitometer with the same are not particularly limited.

Further, any means and method may be used for displaying, utilizing, transmitting, etc., the gradation intensity value converted by the <relational expression (1)>.

Further, the light source of the densitometer is made of glass fiber or the like, and the light source of the image processing device used in the scanner or the like is required, so that the mechanism and function of the densitometer are not particularly limited.

Further, as a matter of course, the output information value (gradation intensity value) obtained by converting the density information value of the continuous tone original image
The embodiment is not limited to the numerical value of the halftone dot area percentage of the halftone dots in the printed image, and may be any one preferable for producing a duplicate image. For example, when a copy image is produced as a duplicate image, when a predetermined pixel is expressed by 256 gradations with a dot coverage, a gradation intensity value (y)
Should be distributed to 256 and output.

The structure of the densitometer of the present invention is such that a density information value is displayed like an ordinary densitometer, and a calculation processing portion having the algorithm of the <relational expression (1)> as software is provided inside the gradation value. The structure is not limited as long as the intensity value is calculated and displayed.

For example, an original image (a density measurement object) is irradiated with light, and transmitted light or reflected light thereof is R (red), G (green),
Spectralize into B (blue), photoelectrically convert it with a photomultiplier or solid-state image sensor (CCD), then A / V convert, convert into concentration information by log amp (logarithmic calculation), C, M, Y, K Separation of (black) component, concentration information of the C, M, Y, K components
Any structure may be used as long as it has a structure in which arithmetic processing is performed using the relational expression (1)> and these can be displayed.

This is shown in FIG.

In FIG. 1, reference numeral 1 is a light source section for measuring density information values, and 2 is a document placing section.

A photoelectric conversion unit 3 is composed of a light receiving element such as a photomultiplier or a CCD. It should be noted that the photoelectric conversion unit 3 performs a logarithmic operation on the A / V conversion unit and the voltage (V) signal to convert it into a density D / lo.
The g (log amp) part is connected, but not shown.
It goes without saying that the photoelectric conversion unit may receive transmitted light or reflected light.

Reference numeral 4 is an A / D conversion unit, and 5 is a gradation intensity value calculation unit for calculating a gradation intensity value from the density information value by <relational expression (1)> which is a feature of the present invention.

6 is an output display unit, 61 is an output of concentration information values, a display unit, 62
Is an output and display unit of gradation intensity values.

In the densitometer of the present invention, the density information value, which is the primitive image information obtained by the measurement with the densitometer, has the above-mentioned relational expression (1).
, For example, when a print image with halftone dots is to be produced, the numerical value (tone intensity value) of halftone dot area percentage, which is important for the tone management of the print image, is scientifically and rational. Will be related to. Therefore, conventional techniques and judgments that depend on human experience and intuition can be changed to scientific and rational ones. Also, because it uses mathematical formulas,
It is natural that the obtained gradation intensity values have a working regularity, and those gradation intensity values are always the most appropriate and natural density gradient obtained from the original image for the human visual sense. It is image information that gives a print image and the like.

The densitometer having such capabilities has a certain and important role to play for the sophistication and rationalization of plate-making technology accompanied by image gradation conversion.

Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to the examples as long as the gist thereof is not exceeded.

(Embodiment) As one embodiment of the present invention, a personal computer NEC PC-980 incorporating the algorithm of <relational expression (1)> and having a gradation conversion processing function of an image in a density region.
A 0 (manufactured by NEC) and a commercially available densitometer were connected.

In the method of connecting the densitometer and the personal computer, the electric signal relating to the density information value obtained by the densitometer can be used as it is as the electric signal for the input information of the personal computer according to the usual method.

In the calculation software of the personal computer, in order to simplify the gradation conversion processing, <Relational expression (2)> is used, and the k value is based on the solid printing density of yellow ink, which is a typical printing ink. We decided to use numerical values.

Color film positive image film provided is 4 "x
The image of a woman wearing a swimsuit having a standard quality of 5 "size was photographed, and the densities of H and S of the original were measured and found to be 0.20 and 2.75, respectively.

At the stage of plate making design, since the quality of this color original is standard, the print image of the eye plate (C plate), which is the basic plate of multicolor printing, is obtained in order to obtain the print image with the desired image quality. 3% of the numerical value (yh) of the dot area percentage of the halftone dot to be put in the highlight part (H), and the numerical value (ys) of the halftone dot area percentage of the dot to be put in the shadow part (S)
Was set to 95%, and the printing ink density value β was set to 0.01 (surface reflection of the ink was 1%). For yellow and magenta plates, in order to improve the color balance,
yh was 2%, ys was 92%, and the difference in halftone dot area percentage with respect to the C plate in the halftone was approximately 12%.

In this way, when the halftone dot area% value at the density of the highlight portion and the shadow portion of the original image is obtained, it is natural that the output of the personal computer is 3% for H of C plate and 95% for S. The numerical value of the halftone dot area percentage of was obtained. Also, the density value on the original image is 0.84, 1.16,
The dot area% values at 2.10 are 48.4%, 62.5%, and 8%, respectively.
The value was 7.0%.

The above numerical values were incorporated into the plate making design to set a halftone dot gradation characteristic curve (color separation work curve), color separation work was performed according to the curve, and proof printing was performed by the chromin proof method.

In the proof print image obtained, as planned at the plate making design stage, the halftone dots of the required control points on the color original, such as the eye plate, the ki plate, and the magenta plate, correspond to the corresponding control points on the proof print image. As expected, the halftone dots came in and the image quality was extremely satisfactory.

Next, the usefulness of the <relational expression (1)> incorporated in the calculation unit of the densitometer of the present invention will be supplementarily described.

This is a supplementary explanation for facilitating the understanding of the present invention, and the usefulness of the <relational expression (1)> applied to the densitometer, particularly the printing of halftone dots from a continuous tone original image, is shown. A case of creating an image will be described.

The usefulness of the <relational expression (1)> will be explained based on the following Tables (1), (2) and (3), Tables 2 and 3 created using the <Relational expression (1)>. To do.

(A) Regarding Table 1, (1), (2) and (3). Table 1 shows the density of printing ink (print image density area) and the range of use of halftone dots (when the black and white (monochrome) print image is created from the original image, according to the ordinary method of black and white halftone printing in the industry, In order to obtain an ideal halftone dot gradation characteristic curve when the use range of halftone dots set in the H part and the S part is changed), each sample [0 / 8 (H), 1/8, 2
8 (M ₂ ), 3/8, 4/8 (M ₁ ), 6/8, 8/8 (S) sample points are shown. The same applies to the table below. ], A method of managing the halftone dot area% value (y value) in [] is calculated according to <relational expression (1)>, and is listed.

In Table 1, the dot% value in the dot% theoretical value column is E =
The values are 1 and (α = 1.0, β = 0), and the others are values at the E value shown in the table. In this case, the E value was determined using α = 1.0, β was a value obtained from the density of the printing ink (print image density area), that is, β = 10 ^{− (print image density area)} .

From Table 1, even if the density of printing ink is the same, H part and S
When the usage range of the halftone dot area% value set for the part is changed,
It is possible to know how the ideal halftone characteristic curve changes or has to be changed.

In addition, mastering the technique and method of creating a black and white print image of halftone dot gradation corresponding to 1: 1 from a continuous tone original image and adjusting the tone of the black and white print image arbitrarily. That is the basis for creating multicolor images.

(B) Regarding Table 2. Similar to Table 1, Table 2 shows that when a black-and-white print image is created from an original image, the print image density range is changed and the use range of the dot area% is set to 0% to 100%. Aside from the contrast of the entire image, the halftone dot area% value (y at each sample point required to create an image having the same image tone and similar image quality to the human visual sense) (y (Value) is a list.

In other words, when the condition is ideal, the numerical value (y value) of the dot area% of each sample point on the ideal halftone dot gradation characteristic curve corresponding to the maximum density value of the printing ink used is It is a list.

(C) About Table 3. Table 3 is the same as Table 2 except that the use range of the dot area% is 5% to 95%, and the dot of each sample point on the ideal dot gradation characteristic curve is It is a list of numerical values (y values) of area%.

The data shown in each of the above tables is extremely useful in the gradation conversion processing of an image, and a print image excellent in gradation reproducibility can be obtained based on these data.

(Effect of the Invention) According to the present invention, it is indispensable for producing a halftone dot duplicate image by converting the density information value obtained from a densitometer, particularly a continuous tone original image. In the densitometer, which is the work root, not only the density information value is displayed, but also the gradation intensity value for converting the density information value to produce a duplicate image with excellent image quality.

Therefore, the densitometer of the present invention is extremely useful in rationally and efficiently producing various duplicate images.

[Brief description of drawings]

 FIG. 1 is a block diagram of the densitometer of the present invention. 1 …… Light source for density information value measurement 2 …… Original document placement section 3 …… Photoelectric conversion section 4 …… A / D conversion section 5 …… Gradation intensity value calculation section 6 …… Output display section

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location G06T 5/00 H04N 1/405

Claims (1)

[Claims] 1. A densitometer useful as a work guide when creating a duplicate image of a halftone dot duplicate image from a continuous tone original image, wherein the densitometer comprises: (i) for measuring the original image density A light source section, (ii) a document image placing section, (iii) a document image density information value measuring section, (iv) a gradation intensity value computing section for converting the density information value into a gradation intensity value, (V) output In addition to the display unit, the gradation intensity value calculation unit displays the density information value at an arbitrary sample point on the original image as follows.
A densitometer, which is processed by a relational expression (1)> to calculate a gradation intensity value (y) on a duplicate image. <Relational expression (1)> However, x: a basic density information value obtained by subtracting the density information value in the brightest portion H on the same image from the density information value at any sample point on the original image. y: Gradation intensity value at a point on the duplicate image corresponding to an arbitrary sample point on the original image. yh: A desired gradation intensity value set in the brightest portion H on the duplicate image. ys: Desired gradation intensity value set in the darkest part S on the duplicated image. α: Surface reflectance of a recording medium for recording a duplicate image. β: Surface reflectance of an expression medium for expressing a duplicate image. k: arbitrary coefficient. Respectively.