JPH07199376A - Color image forming method - Google Patents

Abstract

PURPOSE:To provide a color image forming method by which color hard copy images of high image quality having excellent depictability from middle to low densities and compatibility of depictability of a face and skin with the depictability of the highlights of white dresses and shirts are obtainable. CONSTITUTION:This color image forming method comprises photographing a subject and obtaining the color hard copy images consisting of respectively at least one kind of yellow, magenta and cyan dyestuff images. The average gradation degree g1 of a subject luminance region from LE0+0.47 to LE0-0.09, the average gradation degree g2 of the subject luminance region from LE0+0.75 to LE0+0.38 and the average gradation degree of g3 of a density region from a green density of 0.20 to 0.30 are 0.85<=g1<=1.18, 0.70<=g2<=1.05 and 0.40<=g3 when the normal logarithmic value of the subject luminance corresponding to the green density of 0.94 of the hard copy images is defined as LE0 in a gradation reproduction curve expressed by the normal logarithmic value (logE) of the luminance E of the subject and the green density (D) of the hard copy images.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image forming method, and more particularly to a color image forming method for photographing a subject to obtain a color hard copy image, and more particularly, to a high image quality excellent in depiction in medium to low density. The present invention relates to a color image forming method capable of obtaining a color hard copy.

[0002]

2. Description of the Related Art As a color image forming method for obtaining a color hard copy by photographing various subjects, a so-called photographic system using a silver salt sensitive material and a scanner or the like as a medium on which the subject is recorded is used. Then, the recording surface is scanned and converted into an electric signal, or the object is directly converted into an electric signal by using an image pickup device such as a CCD, and then a magnetic recording medium such as a video tape or a floppy disk or a memory of a computer. Etc., and from this information, electrophotographic system, thermal transfer system, ink jet system, exposure to color paper by laser or CRT, and special colors were added to four colors of yellow, magenta, cyan, and black as needed. There are various systems for reproducing a subject image, such as obtaining a hard copy by creating a halftone plate and printing it.

In such a color image forming method,
Especially in the fields of wedding photography and portrait photography,
In terms of achieving both the tone reproducibility of the skin color of the face and the tone reproducibility of a white dress such as a wedding dress,
The image quality level of the current color hard copy is not sufficient, and there is an increasing demand from users for high-quality prints with excellent gradation reproducibility.

As one of the most important factors for determining the gradation reproducibility of a color hard copy image, the input / output characteristics of the system are defined in relation to the brightness of the subject and the density of the color hard copy to be reproduced. There is a tone reproduction curve of a color image forming system.

The tone reproduction curve can be roughly divided into tone reproduction from high density to medium density (shoulder) and tone reproduction from medium density to low density (leg), both of which are important. This is particularly important because it relates to the depiction of the face of a person who is an important subject and the bright highlight portion, and has a great influence on the tone of the entire image.

Tomo Honjo et al., "Comparison of hard copy techniques with emphasis on highlights" (Journal of the Institute of Image Electronics Engineers, pp. 145-150)
Page 15, Vol. 3, No. 3, 1986), the gradation reproducibility of silver salt photographs, offset printing, and highlights of inkjet recording is converted into area fluctuation (in the case of photographs, the density is converted into an amount equivalent to area fluctuation and compared. Are evaluated)
The photographic system shows reproducibility that is one to two orders of magnitude better than other systems. However, due to recent technological advances, the quality of images other than silver halide photography has become considerably high, and it is expected to be widely used in the future due to the ease of processing such as the use of no processing liquid.

As described above, the highest image quality of the final hard copy among the color image forming methods is that of a photographic system using a negative-positive film using a so-called silver salt sensitive material. However, even in a hard copy created using such a system, at present, the tone is hard, and the expression of subtle shades of areas that are considered to be related to the leg gradation particularly in the middle to low densities is present. It's not enough. In particular, when expressing the skin, it is preferable to express even slight changes in shade as continuously as possible, and even a slight jump in shade gives an unfavorable impression. In the silver salt color photographic system, there is a method of softening the gradation of color photographic paper, softening the gradation of a color negative, and a combination thereof in order to express subtle shades. As a result, the reproduction of the face and skin is improved and the image quality is improved, but a simple softening does not clearly show the shadows of highlights such as white dresses and shirts, and the stereoscopic effect is insufficient, resulting in poor descriptiveness and an unfavorable impression. The problem of giving it occurs.

In "Theory of Photographic Process, 4th Edition" (edited by James, pp. 537-540, published by Macmillan, 1977),
When reproducing tones of reflective objects, it is said that the reproduction of the skin will be favorable by reproducing the density lower than the subject in the color photography system as in the case of monochrome photography, but the highlight legs of white dresses and shirts. There is no description showing the preferred direction of reproduction, and it is said that the highlight part is compressed to reproduce the density as a whole and rather sacrifices the reproduction, and the reproduction of the skin and the white dress or shirt There is no suggestion of concrete measures for achieving both descriptiveness.

"Basics of photographic engineering (silver salt photography)"
(Edited by The Photographic Society of Japan, pp. 398-400, Corona Publishing, 1978)
Then, as a subjectively preferable tone reproduction, from the straight line showing the accurate tone reproduction, it is said that the density is lowered by 0.2 to 0.3 and the inclination other than the highlight part is set to 1.1 to 1.2, and the contrast is lowered for the highlight part. Although it is acceptable from an objective judgment even if it is done, it is said that compression in the high brightness range is possible, but there is no specific guideline regarding the highlight part, and this method has a problem of reproduction of the depiction of a white dress or shirt. No answer to.

Also, "Imaging Part 1" (Electronic Society of Japan, pp. 77-139, published by Photo Industry Co., Ltd., 198
In 8), there are descriptions about silver salt photography, electrophotography, thermal transfer, ink jet, and gradation reproduction of printed images. Regarding silver halide photography, unlike "Theory of Photographic Process 4th Edition" and "Basics of Photographic Engineering (Silver Salt Photography)", the base density of color photographs is about 0.1 higher than that of monochrome photographs. The ideal skin color reproduction density range also increases by about 0.1,
Only highlights are described as being more and more compressed, and there is no description for highlight gradations that balance the reproduction of skin and white dress. Regarding the print image, in order to obtain a faithful reproduction with respect to the input original, compression is performed in the high density region from the limit of the maximum reproducible density based on γ = 1. Similarly, in inkjet recording, thermal transfer recording, electrostatic recording, etc., there is a description that the purpose of the apparatus alone is to set γ of output to input to 1,
It is not for reproduction of the subject but for the input document, and there is no guideline of tone reproduction characteristics for the highlight of the subject.

Further, JP-A-4-134339 and JP-A-63-28684
7, JP-A-2-289848, JP-A-62-169159, JP-A-62
-169160, JP-A-62-172358, JP-A-61-50135, JP-A-63-128337, JP-A-52-11029, JP-A-52-18310
No. 62-198860, British Patent 1,535,016, U.S. Pat. No. 3,448,709, etc., show gradation conversion methods for silver salt sensitive materials, but the density of highlights including skin and white dress There is no description showing the target value of the preferable gradation characteristic for the range.

Further, in JP-A-58-117540, the average photographic gradation of a silver halide color negative photographic light-sensitive material for photographing is 0.9 or more, and the average photographic gradation of a silver halide color photographic light-sensitive material for printing is 1.80. In the following, a technology is disclosed in which the overall photographic gradation is 1.1 to 1.7, but this is a technology for improving sharpness and graininess that deteriorate with respect to the small format of a negative photosensitive material, There is no suggestion for improving the descriptiveness of leg gradation.

Further, in Japanese Patent Laid-Open No. 4-284442, in a photographic printer, photographing information is read from a magnetic recording layer of a film, and a plurality of photographic papers having different gradations are prepared and selectively used according to the information. Methods such as devising printer exposure control, changing development conditions, or using electronic image technology to perform gradation correction on an image read by a scanner and then output using a laser diode, CRT, liquid crystal panel, etc. It is disclosed to correct the gradation used. However, there is no detailed description about the target gradation to be corrected, and there is no suggestion for the tone reproduction of the highlight part that makes it possible to reproduce the white dress or shirt and the face at the same time.

As described above, in the prior art, no means has yet been found for achieving both the depiction of face and skin and the depiction of highlights such as white dresses and shirts.
Further, since the relationship between the shape of the tone reproduction curve and the descriptiveness has not been clarified, it is not easy to quantitatively show the target value of the preferable shape, which is a big problem.

[0015]

In contrast to the problems described above, the object of the present invention is to provide excellent depiction in medium to low densities, depiction of face and skin, and high depiction of white dresses and shirts. An object of the present invention is to provide a color image forming method capable of obtaining a high-quality color hard copy image having both light descriptiveness.

[0016]

DISCLOSURE OF THE INVENTION As a result of intensive studies on the relationship between the shape of a tone reproduction curve and the descriptiveness of a color hard copy image, the present inventors have found that In a color image forming method for obtaining a color hard copy image composed of at least one kind of yellow, magenta, and cyan dye images, respectively, it is represented by a common logarithmic value (logE) of the brightness E of the subject and a green density (D) of the hard copy image. In the tone reproduction curve, when the common logarithmic value of the subject brightness corresponding to the green density 0.94 of the hard copy image is LE ₀ , the average gradation degree g1, LE _{0 in} the subject brightness range of LE ₀ +0.47 to LE ₀ -0.09. From +0.75 to LE ₀ +0.3
Average brightness g2 in the subject brightness range of 8, green density 0.20 to 0.
0.85 ≦ g1 ≦ 1.18 for average gradation g3 in 30 density ranges
And 0.70 ≦ g2 ≦ 1.05 and 0.40 ≦ g3, the present invention has been completed and the present invention has been completed.

The tone reproduction curve in the present invention is a curve in which the horizontal axis is the common logarithmic value (logE) of the brightness E of the subject image and the vertical axis is the density D of the hard copy. Specifically, for example, several types of neutral gray charts with different densities from white to black, whose spectral reflectances are almost constant in the visible light region, were photographed, and the final charts were obtained by making these charts gray. In the color hard copy image, the green density of the chart used for shooting
It is obtained by plotting the value multiplied by 1 on the horizontal axis and the green density of the corresponding chart on the color hard copy image on the vertical axis.

Here, the measurement of the concentration in the present invention is carried out by JI
SK 7651-1988, JIS K 7653-1988, JIS K 7654-1
According to the method specified in 990, the spectroscopic conditions are IS
The ISO standard reflection density is used as the O-status A density and the geometric condition. The green density in the present invention refers to the reflection density of green separation measured as described above.

Average gradation degrees g1, g2, g3 in the present invention
Is defined as follows. In the tone reproduction curve obtained by the above method, the value of the common logarithmic value logE of the exposure amount corresponding to the green density 0.94 is LE _0, and the green densities corresponding to the log E of LE ₀ +0.47 are D ₁ and LE _0. When the green density D ₂ corresponding to logE of −0.09 is set, the average gradation g1 is calculated by the following equation (1).
Is defined.

[0020] _{g1 = (D 2 -D 1)} /0.56 (1) Similarly green density D ₄ corresponding to the logE the green density D _3, LE ₀ +0.38 corresponding to the value of logE of LE ₀ +0.75 Then, the average gradation g2 is defined by the following equation (2).

G2 = (D ₄ −D ₃ ) /0.37 (2) When the value of logE corresponding to the green density of 0.20 is LE ₁ and the value of logE corresponding to the green density of 0.30 is LE ₂ , the following equation is obtained: The average gradient g3 is defined in (3).

G3 = 0.10 / (LE ₁ −LE ₂ ) (3) As is clear from the above, in the tone reproduction of the leg, g1
Is a parameter that defines the shape of a relatively high density portion, and g2 and g3 are parameters that define the shape of a low density portion.

In the present invention, both the depiction characteristics of the face and the skin and the depiction characteristics of the highlight are made compatible in the regions of 0.85 ≦ g1 ≦ 1.18, 0.70 ≦ g2 ≦ 1.05 and 0.40 ≦ g3. You can Further, when g3 ≦ 2.00, the highlight texture is higher and it is preferable. Also, g
When the ratio of 1 to g2 is A = g2 / g1, if A ≦ 1.1, the depiction of the entire image is high, which is preferable. A more preferable range of A is 0.7 ≦ A ≦ 1.1. Also, 0.
The area of 92 ≦ g1 ≦ 1.07, 0.75 ≦ g2 ≦ 0.98, and 0.40 ≦ g3 ≦ 2.00 is not only good for depiction of the face and highlight, but also well-balanced and natural. It is a preferable region, and more preferably 0.8
It is a region that satisfies ≦ A ≦ 1.0.

The color image forming method in the present invention is divided into a so-called photographic system using a silver salt sensitive material and a system for obtaining a hard copy after once converting an electric signal in the middle of photographing a subject image. As a photographic system, you can shoot with negative film and print it on negative paper to get a color print, and with a negative-positive system, you can shoot with positive film and print it on positive paper, or drop it once on the inter negative and print it on negative film Systems for obtaining color prints are known. In these systems, the shape of the characteristic curve of the negative film, negative paper, positive film, positive paper, etc. used greatly affects the tone reproduction curve. For example, in a negative-positive system, the shape of the leg of the tone reproduction curve is related to the shape of the shoulder of the characteristic curve of the negative film and the shape of the leg of the characteristic curve of the negative paper. Since the flare at the time of shooting or exposure and the relationship between the spectral density of the negative film and the spectral sensitivity of the negative paper influence, it is not possible to obtain an accurate tone reproduction curve shape only from the shape of each characteristic curve. In these systems, the present invention can be achieved by optimizing the shape of the characteristic curve of the photosensitive material used.

As a system for obtaining a hard copy after once changing an electric signal in the middle of photographing a subject image, a photographed negative film, positive film, or print image is read by an image input device such as a scanner and image data is read. As a signal, various processing is performed as necessary, laser scanning, exposure to silver salt paper with flying spots, etc., making color hard copy with various color image output devices such as sublimation thermal, yellow, magenta, A method is known in which a halftone plate in which a special color is added as necessary to the four colors of cyan and black is used to obtain a printed image. There is also a method in which a subject image is directly photographed by a CCD or a TV camera and the electrical signal is captured. In these systems, the present invention can be achieved by adjusting the shape of the tone reproduction curve by processing image data signals, for example, so-called image processing such as conversion using a look-up table.

As the color image forming method of the present invention, an example in which a negative image is read, gradation conversion is performed, and then a color print is reproduced using a laser printer will be given, but the present invention is not limited to this. .

A laser printer device that is considered to be applicable to such a system is, for example, Japanese Patent Laid-Open No. 55-407.
1, JP-A-59-11062, JP-A-63-197947, JP-A-2-
74942, Japanese Patent Laid-Open No. 2-236538, Japanese Patent Publication No. 56-14963, Japanese Patent Publication No. 56-40822, European Wide Area Patent 77410, Electronic Communication Department Technical Report 80, No. 244, and Movie Television Technical Journal 1984/6
(382), pages 34-36, etc.

The configuration of the system used in the present invention is described in Konica Technical Report Vol. 5 (pages 53 to 57, 1992), and therefore only a brief outline will be given here. The system consists of an image data input system, a gradation conversion system, and an image data output system. The negative image of the subject is recorded using a drum scanner,
The density data is converted into red density, green density, and blue density, and in the gradation conversion system, the density data that has been read is converted to match the characteristic values of the gradation reproduction of the color printing paper output by the laser printer, and the target tone is reproduced. The gradation conversion is performed using a look-up table so that the output signal to the laser printer is generated. Based on this signal, the laser light intensity is modulated and scanning exposure is performed on a color photographic paper to create an image having a target tone reproduction curve.

[0029]

EXAMPLES The present invention will be described below with reference to examples, but the embodiments of the present invention are not limited thereto.

Example 1 Using a color negative film sold as Konica Color Professional Type S, a neutral gray chart was inserted under the same photographing conditions, and the following wedding scene was photographed.

(Scene 1) Long cut of a woman in a wedding dress (Scene 2) Up of a woman in a wedding dress (Scene 3) Long cut of a pure white woman (Scene 4) Group photo Appropriate color development of these negative films After the processing, the system described in Konica Technical Report Vol. 5 (pages 53 to 57, 1992) reads the image and performs gradation conversion, outputs to Konica Color QA Paper A5 Type G, and samples 101- Created 116. The tone reproduction curve is obtained from the density of the gray chart used for shooting the subject and the density of the gray chart imprinted during printing, and the average gradation degree g1,
g2 and g3 were determined. In addition, these color prints were presented to 10 subjects who were accustomed to image evaluation to show the good depiction of the face, the depiction of highlights such as white dresses, and the overall image quality from the entire print. Evaluated, very good (5 points), excellent (4 points), normal (3
5) as slightly inferior (2 points) or inferior (1 point)
A graded evaluation was performed and an average value was calculated. The results are shown in Table 1 below.

[0032]

[Table 1]

Samples 101, 102, 105, and 106 having a small g2 have good facial depiction, but have poor stereoscopic effect of highlight and poor descriptiveness. Samples 109 to 116 having larger g2 than these samples all have good facial depiction,
Moreover, the depiction of highlights has been improved, and the overall image quality has been highly evaluated. In particular, Samples 110 and 111 continuously reproduce the subtle shades of the skin and have a high texture. Furthermore, there is a clear three-dimensional effect such as white dresses and folds of kimono, embroidery, etc., and the overall tone of the image is rich and the overall evaluation value is higher. However, even in the samples with large g2 such as the samples 103 and 104, if g1 is too large, the highlight is good, but the face is hard and the skin connection is poor, and the overall evaluation value is lowered. On the other hand, even if both g1 and g2 satisfy the conditions, the samples 107 and 108 having a small g3 lack the depiction of the highlight portion, and the overall evaluation value is lowered.

Example 2 The photographic negative of the above scene of the color negative film prepared in Example 1 was read by the color scanner of Example 1,
The image was captured as digital image data, the same image processing as in Example 1 was performed, and color prints of Samples 201 to 214 were created using a sublimation type color printer SP5500 manufactured by Victor Company of Japan. As the image input / output system, Table 2 below shows the results of evaluation of these samples 201 to 214 in the same manner as in Example 1.

[0035]

[Table 2]

Similar to Example 1, sample 207 according to the present invention
It can be seen that each of ~ 214 has a good facial depiction and also has a good highlight depiction, and thus has a high evaluation score as the overall image quality. Further, it can be seen that especially the samples 208 and 209 have good depiction characteristics and high image quality.

[0037]

As is clear from the results of the examples, according to the present invention, excellent depictability in medium to low concentrations,
It is possible to provide a color image forming method capable of obtaining a high-quality color hard copy image in which the depiction of a face or skin and the depiction of a highlight such as a white dress or a shirt are compatible.

Claims (1)

[Claims] 1. A color image forming method for obtaining a color hard copy image comprising at least one kind of yellow, magenta, and cyan dye images by photographing a subject, and a common logarithm (logE) of the brightness E of the subject and a hard copy. In the tone reproduction curve represented by the green density (D) of the image, when the common logarithmic value of the subject brightness corresponding to the green density of 0.94 of the hard copy image is LE ₀ , LE ₀ +0.47 to LE ₀ -0.09 Average gradation g1 in subject brightness range, LE ₀ +
Average gradation g2 in the subject brightness range from 0.75 to LE ₀ +0.38,
A color image forming method characterized in that 0.85 ≦ g1 ≦ 1.18, 0.70 ≦ g2 ≦ 1.05, and 0.40 ≦ g3 with respect to an average gradation degree g3 in a density range of green density 0.20 to 0.30.