JPH0678209A - Photographic characteristic curve generating method - Google Patents

Abstract

PURPOSE:To generate a characteristic curve of photographic film easily and in a short time while considering the measuring error of an observation value. CONSTITUTION:Plural sheets of film obtained by photographing and developing a gray scale with different exposure are prepared, and the images of the film are photographed by a film scanner, and image signals can be obtained (step S1). Thence, the signal level of each gradation of gray scale can be fetched from each of obtained image signals (step S2). Thence, graphic data is computed (step S3), and a graph is displayed at every exposure quantity when photography is performed on the coordinate of a photographic character curve based on such computed data and the data of each signal level (step S4). Correction processing is performed by moving each graph in step 4 while referring to graphic display in the step 4 (steps S5-S8), and a final photographic characteristic curve can be obtained (step S9).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preparing a photographic characteristic curve showing the relationship between exposure amount and color density in a photographic film, and more specifically, a photographic characteristic suitable for signal processing in a film scanner. Regarding the improvement of the method of creating a curve.

[0002]

2. Description of the Related Art The characteristic curve of a photographic film represented by the relationship between exposure amount and density (corresponding to signal level) changes variously depending on the type of film. Further, when signal processing such as negative-to-positive conversion is performed using the image signal of the photographic film obtained by the film scanner, the characteristics of the image sensor and the like are also affected as a result.

When obtaining such a photographic characteristic curve from an actually measured value, the actual situation is that there is no effective method considering the measurement error. For example, there is a method in which a commercially available camera is used to photograph several sheets of the same color chart while changing the exposure amount, and a curve is created using an image of a film obtained by developing them. However, in this case, since there are variations in the characteristics of the color chart and an error in the exposure amount of the camera, an error occurs at each shooting. It is very difficult to absorb such an error and easily obtain a characteristic curve for many kinds of films.

The present invention focuses on these points,
It is an object of the present invention to provide a photographic characteristic curve creating method capable of creating a characteristic curve of a photographic film by a simple method while considering a measurement error of an actually measured value.

[0005]

According to the present invention,
A plurality of films prepared by photographing and developing gray scales with different exposures are prepared, and those images are photographed in the first step to obtain image signals respectively. Next, from the image signal obtained in this step, the signal level of each gray scale gradation is taken in in the second step. Next, the data of each signal level captured in this step is displayed graphically on the coordinate axes of the photographic characteristic curve for each exposure amount at the time of photographing in the third step. Then, with reference to the graph display in this step, in the fourth step, each graph is moved and the correction process is performed to obtain the photographic characteristic curve.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a method for creating a photographic characteristic curve according to the present invention will be described below with reference to the accompanying drawings.
FIG. 1 shows a device configuration according to an embodiment of the present invention. In the figure, the film scanner 10 includes an image sensor 12 and a signal processing unit 14. The image sensor 12 is composed of, for example, a CCD image pickup device, and the signal processing unit 14 amplifies R (red), G (green), and B (blue) image signals input from the image sensor 12, and digital signals. It has the function of converting to and outputting.

Next, the output side of the film scanner 10 is
It is connected to an analysis device 20 composed of a personal computer or the like. More specifically, a scale data acquisition unit 22 is provided on the input side of the analysis device 20.
An input unit 28 is connected to the scale data capturing unit 22 and is configured to capture the data output from the signal processing unit 14 of the film scanner 10 based on an instruction by the input unit 28.

The output side of the scale data acquisition unit 22 is connected to the arithmetic processing unit 24. This arithmetic processing unit 24
Has a function of creating characteristic graph data, which will be described later, and a correction process thereof, and is connected to the graph data storage unit 26 and the input unit 28, respectively. The graph data storage unit 26 has a function of storing the graph data supplied from the arithmetic processing unit 24, and the display unit 30 displays a graph based on this data. The input unit 28 is for instructing data acquisition, display, correction processing, etc., and is composed of a keyboard, a mouse, and the like.

Next, the film sample used in this embodiment will be described with reference to FIG. In this embodiment, the film scanner 10 takes images of eight films as shown in FIG. 2B, and the image signal obtained thereby is used to obtain the characteristic curve of the film.

More specifically, an appropriate camera (not shown) is used to photograph a gray scale 40 as shown in FIG. 1A using a film for which a characteristic curve is desired to be obtained. This gray scale has 11 gradations from A _{1 to} A ₁₁ . Such a gray scale 40 is photographed eight times while continuously changing the exposure amount with one film. That is, eight gray scale 40 photographs with different exposures are obtained. When they are developed, 8 as shown in FIG.
The films F1 to F8 are obtained.

In the following description, the gray scale 4
The reflectance of each gradation of 0 is also shown by A _{1 to} A ₁₁ .
Further, the exposure amount is determined by the relationship between the aperture of the camera and the shutter speed, but in this embodiment, the aperture is kept constant and the shutter speed is changed to change the exposure amount in eight steps.

Next, the procedure for creating the characteristic curve according to this embodiment will be described with reference to the flowchart of FIG. 3 and the graphs of FIGS. 4 and 5. First, 8 shown in FIG.
One of the films F1 to F8 is set on the film scanner 10 (step S1 in FIG. 3) and the image of each film is input to obtain R, G and B image signals. Next, the analysis device 20
The scale data capturing unit 22 of (3) captures the signal levels of R, G, and B for each gray scale gradation from the image signal of each film (step S2). Table 1 summarizes the signals that are captured.

[0013]

[Table 1]

For example, assume that the film F1 is set on the film scanner 10. The grayscale image of the film F1 is picked up by the image sensor 12 and its R,
The G and B image signals are supplied to the signal processing unit 14 and digitized. As a result, digital R, G, B
The signal data is supplied to the scale data acquisition unit 22.

In the scale data fetching section 22, for each of the gray scales A _{1 to} A ₁₁ of the gray scale 40, R,
The signal levels of G and B are captured. That is, as shown in the upper part of the table, for the film F1, the gradation A ₁
The R signal level R ₁ , G signal level G ₁ , and B signal level B ₁ of the image of FIG. Similarly, the gradation A ₂
The R signal level R ₂ , G signal level G ₂ , and B signal level B ₂ of the image of FIG. The signal levels of R, G, and B are similarly taken in for each gradation of A _{3 and} above.

[0016] As a result, from the image signal of the film F1, R signal level R ₁ to R _11, G signal level G ₁ ~G ₁₁ of each tone A ₁ to A ₁₁ of the gray scale 40, B signal levels B ₁ ~ B ₁₁ will be taken in. Similarly, from the image signal of the film F2, R signal level of each tone A ₁ to A ₁₁ of the gray scale 40 R ₁₂ to R _22, G signal level G
_{12 to} G ₂₂ , B signal levels B _{12 to} B ₂₂ are taken in.

Such signal acquisition is achieved by the film F3.
The same applies to ~ F8, and R, as shown in Table 1,
The signal levels of G and B will be captured respectively. These signal levels R _{1 to} R ₈₈ , G _{1 to} G ₈₈ , B ₁ to
B ₈₈ represents the density of each gray scale gradation in each film. For example, the signal levels R ₁₅ , G ₁₅ , and B ₁₅ of the gradation A ₄ of the film F2 are the exposure time T ₂
The density of the gradation A ₄ of the gray scale 40 shown in the film F2 of FIG. Others are the same.

Although the same gray scale 40 is photographed, the exposure amount is different for each film. Therefore, when the signal levels of a certain gradation are compared between the films, they do not match. Also, at the time of this data acquisition,
The values of the exposure times T _{1 to} T _{8 of the} films F _{1 to} F ₈ and the reflectances A _{1 to} A ₁₁ of the gray scales of the gray scale 40 are input to the input unit 28.
Entered by

The eight sets of scale data for each of the eight films thus fetched are supplied to the arithmetic processing section 24, where the exposure amount of each signal level is calculated (step S3). More specifically, as shown in Table 1, the reflectance of each gradation of the gray scale 40 is A ₁ , A ₂ , A ₃ , ...
…, A ₁₁ . On the other hand, eight films F1, F2, F
The exposure time of 3, ..., F8 is as shown in Table 1.
T ₁ , T ₂ , T ₃ , ..., T ₈ . Therefore, first, the gradation A
_{For 1} , the exposure amount is obtained from the logarithm of the product of the reflectance A ₁ and the exposure time T ₁ . For example, the exposure amount H _1-1 of the gradation A ₁ of the film F1 is H 1 as shown in the top row of Table 1.
It is obtained by _1-1 = log (A ₁ · T ₁ ). Similarly, the exposure amount H _2-1 of the gradation A ₂ is obtained by H _2-1 = log (A ₂ · T ₁ ). The same applies to gradations A _{3 and} below.

Further, the gradation A of the film F2₁Exposure amount H
_1-2Is H_1-2= Log (A₁・ T₂) Is required. As well
To gradation A₂Exposure amount H_2-2Is H_2-2= Log (A₂・ T
₂) Is required. Gradation A₃The same applies to the following.
The same applies to films F3 and below, as shown in Table 1.
Growls The exposure dose is generally expressed as H_ij= Log (A_i・ T_j) ………… It becomes (1). However, i = 1 to 11 and j = 1 to 8. This
In this way, in the arithmetic processing unit 24,
Exposure H_ijAre calculated respectively. The calculation data is
Applicable signal level R_k, G_k, B_k(K = 1 to 88) and
It is stored in the graph data storage unit 26.

The graph data stored in the graph data storage unit 26 is supplied to the display unit 30. The display unit 30 plots the graph data with the exposure amount on the horizontal axis and the signal level on the vertical axis to obtain characteristic curves for R, G, and B and display them (step S4). FIG. 4 shows a part of the characteristic curve of R. As shown in the figure, the horizontal axis represents the exposure amount expressed in logarithm and the vertical axis represents the signal level of R. First, when the signal levels R _{1 to} R ₁₁ obtained from the film F1 are plotted, the graph GR1 shown in the same figure is obtained. As shown in Table 1, the display unit 30 color-displays this graph GR1 in red. Similarly, the signal level R ₁₂ obtained from the film F2
When R ₂₂ is plotted, a graph GR2 shown in the same figure is obtained. The display unit 30 displays the graph G as shown in Table 1.
R2 is displayed in pink.

Similarly, the signal levels below the film F3 are also displayed, and each of them is displayed in color in the colors shown in Table 1. That is, the graphs GR1 to GR1
GR8 will be displayed in a different color. Further, these display processes are similarly performed for G and B, and the graphs GG1 to GG8 and GB1 to GB8 are displayed respectively. These graphs are shown in FIGS. 5 (A) to 5 (C).

The graph thus created and displayed is
The error of the exposure amount for each film can be clearly confirmed. That is, ideally, those graphs should be placed on one smooth characteristic curve, but discontinuity may occur due to an error in the reflectance of each gradation of the gray scale 40 or an error in the shutter speed of the camera. It will be

Therefore, in this embodiment, error correction is performed as follows. Since this error correction is similarly performed for R, G, and B, R will be described below as a representative. First, the graph to be corrected and the correction amount are input by the input unit 2
Input from 8 (step S5). For example, to specify the graph GR1 shown in FIG. 4, and the correction amount set to -P _1.
In the arithmetic processing unit 24, the exposure amount H of the signal levels R _{1 to} R ₁₁ forming the graph GR1 is based on the input data.
_The correction amount −P ₁ is added to _i−1 (i = 1 to 11) (P ₁ is subtracted). That is, the calculation of H _i-1 = log (A _i · T ₁ ) −P ₁ (2) is performed, and these are output to the graph data storage unit 26 as the corrected exposure amount (step S6). . Then,
In the display section 30, the signal level R ₁ to R ₁₁ are plotted based on the exposure amount after the correction (step S7). Therefore, the graph GR1 as a whole is shifted to the left by the exposure amount P ₁ as indicated by the arrow fa.

Similarly, when the exposure amount + P ₂ is corrected for the graph GR2, the graph GR2 as a whole is shifted to the right by the exposure amount P ₂ as indicated by the arrow fb. The same applies to other graphs GR3 and below.
By repeating such an operation for each graph (steps S8, S5, S6, S7), a whole smooth curve is drawn (see graph SR in FIG. 4 and graphs SR, SG, SB in FIG. 5). ). The exposure amount P for error correction is commonly applied to R, G, and B. Next, after completion of such correction processing, for smoothing processing and data interpolation, the corrected R, G, and B graphs are curve-approximated by an appropriate mathematical expression to finally obtain characteristic curve data. (Step S
9).

As described above, according to the present embodiment, the error of the exposure amount is treated as being caused by the change of the exposure time, and the curve approximation is performed by correcting the exposure amount. Overall, the process of averaging a large number of data having different exposure amounts is realized by a simple method of moving a graph. Therefore, the error can be corrected and a good characteristic curve can be easily obtained without special knowledge of the photographic characteristic curve. Further, even if some data is missing due to a measurement error, it is possible to easily find them by referring to the display screen.

The present invention is not limited to the above embodiments, and includes the following, for example. (1) In the above embodiment, the finally obtained characteristic curve is approximated by a mathematical expression, but of course it may be stored as a data table or the like. This data is used when a negative-positive conversion process is performed by a film scanner or the like, but may be stored in the device by a convenient method. (2) Although the gray scale having 11 gradations is used in the above embodiment, an appropriate number of gradations may be used. Also, the exposure amount of the film was changed in 8 steps, but this may be an appropriate number. However, better results are obtained with more measurement sample points.

[0028]

As described above, according to the method for creating a photographic characteristic curve according to the present invention, the signal level of each gradation is taken in from the images of a plurality of films developed by photographing gray scales with different exposure amounts, and further, Data of each signal level is displayed as a graph on the coordinate axis of the photographic characteristic curve, and the graph is moved while referring to this to perform correction processing, so expertise is required while considering the measurement error of the actual measurement value. There is an effect that a characteristic curve of a photographic film can be simply created in a short time without the need.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a configuration example of a creation assisting device used in an embodiment of a photographic characteristic curve creating method according to the present invention.

FIG. 2 is an explanatory view showing a sample of a film used in an example of the present invention.

FIG. 3 is a flowchart showing a procedure for creating a characteristic curve in the example.

FIG. 4 is a partially enlarged graph showing the operation of the embodiment.

FIG. 5 is a graph showing the operation of the above embodiment.

[Explanation of symbols]

10 ... Film scanner, 12 ... Image sensor, 14
... Signal processing unit, 20 ... Analysis device, 22 ... Scale data acquisition unit, 24 ... Arithmetic processing unit, 26 ... Graph data storage unit, 28 ... Input unit, 30 ... Display unit, 40 ... Gray scale, F1 to F8 ... Film, GR1-GR8, GG1-
GG8, GB1 to GB8 ... Graph for each exposure amount at the time of shooting,
SR, SG, SB ... Characteristic curve after correction.

Claims (1)

[Claims] 1. A first step of obtaining an image signal by picking up images of a plurality of films developed by taking gray scales with different exposure amounts, and grayscale gradations from the image signal obtained in this step. The second step of capturing the signal level of, and the third step of displaying the data of each signal level captured in this step on the coordinate axis of the photographic characteristic curve for each exposure amount at the time of shooting, and this step And a fourth step of performing a correction process by moving each graph while referring to the graph display according to FIG.