JP2000278530A - Image processor, image processing method and recording medium recorded with image processing program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily and surely obtain high contrast images even from an exposure excessive or exposure insufficient photo film. SOLUTION: In the luminance image density histogram of images to be outputted, in the case that an output range is less than a desired range, by using a correction gamma calculated by a correction value calculation part 6, the luminance image density histogram is extended so as to make the output range equal to or more than the desired range. Thus, even when the image is recorded in a narrow luminance range on the exposure excessive or exposure insufficient photo film, the image is outputted in a wide luminance range. Also, since the correction gamma is automatically obtained by the correction value calculation part 6 without the intervention of an operator, the time and labor are not required for calculating the correction gamma.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus which performs image processing on image data corresponding to an image recorded on a photographic film such as a negative film and supplies the processed image data to a photographic printing apparatus. The present invention relates to a recording medium on which an image processing program for causing an image processing apparatus to execute image processing is recorded, and particularly to an image processing capable of vividly reproducing an image recorded on an overexposed or underexposed film. The present invention relates to an apparatus, an image processing method, and a recording medium on which an image processing program is recorded.

[0002]

2. Description of the Related Art Conventionally, as a photographic printing apparatus for printing an image recorded on a negative film on photographic paper, an analog printer for directly exposing the photographic paper via a negative film, a scanner for printing an image recorded on the negative film, and the like. Various types of digital printers have been proposed in which a photographic paper is exposed on the basis of image data obtained by temporarily reading the photographic paper. In particular, a digital printer can perform color correction, density correction, and the like that cannot be realized by an analog printer by using the digital printer in combination with an image processing apparatus that performs image processing such as color correction and density correction on image data. At the same time, there is an advantage that an image according to a customer's request can be obtained easily and quickly, and is now widely used.

By the way, when taking a picture on a beach or a ski resort in summer, for example, the exposure is often excessive unless the shutter speed and aperture of the camera are adjusted appropriately.
Also, for example, if a photograph is taken without using a strobe in a dark room, the exposure is naturally insufficient.

An image printed on photographic paper using an overexposed or underexposed color negative film has a low contrast and is smooth. This is because a color negative film generally has characteristics as shown in FIG. 6, and a density of an overexposed film can be expressed only by the width a in the figure, and a film of an underexposed film has the same characteristics. This is because the density can be expressed only by the width b in the figure. That is, the density can be expressed only in a band that is considerably narrower than the width c of the film density in the proper exposure. In addition, the image formed on the film is entirely dark when overexposed, and entirely white when underexposed, which also causes the image printed on photographic paper to be a low contrast image. one of.

Therefore, conventionally, in order to correct a low-contrast image into a sharp and vivid image, an analog printer has responded by changing the exposure time of the entire film. In a digital printer, a film image is temporarily converted into digital image data by a scanner or the like, and the image is converted using an LUT (lookup table) manually created by an operator in the image processing apparatus. I was

[0006]

However, in the above-described method using an analog printer, density correction and color correction cannot be partially performed, and the density of the entire image is increased or decreased, and the entire image is yellowed. You can only make it blue. Therefore, although the image as a whole looks good to a certain extent, an image with high contrast and sharpness cannot be obtained. Therefore, it can be said that an analog printer cannot correct a low-contrast image to a high-contrast image.

[0007] Further, in the above-described method using a digital printer, density correction and color correction can be partially performed.
An operator must create an LUT that can be corrected to a high contrast by trial and error while looking at a monitor or the like, which is troublesome and troublesome.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide an image processing apparatus capable of easily and reliably obtaining a high-contrast image even from an overexposed or underexposed photographic film. It is an object of the present invention to provide an apparatus, an image processing method, and a recording medium that records an image processing program.

[0009]

In order to solve the above-mentioned problems, an image processing apparatus according to the present invention creates a luminance image density histogram of an image to be output based on image data of a digital image. Means for creating a histogram,
Output range detecting means for obtaining an output range of a luminance value in the luminance image density histogram; and expanding the luminance image density histogram so that the output range is equal to or more than a desired range when the output range is less than a desired range. It is characterized by comprising a correction value calculating means for calculating a correction value that can be obtained, and a correcting means for correcting the original image data using the correction value.

According to the above arrangement, in the luminance image density histogram (hereinafter simply referred to as a histogram) created by the histogram creating means, the output range of the brightness value detected by the output range detecting means satisfies a desired range. If not, the correction unit corrects the original image data using the correction value calculated by the correction value calculation unit. Thus, even if an image is recorded in a narrow luminance range on an overexposed or underexposed photographic film, the image can be output in a wide luminance range by the above correction. Also,
Since the correction value is automatically obtained by the correction value calculating means without the intervention of the operator, there is no trouble in calculating the correction value.

Therefore, according to the above configuration, a high-contrast image can be easily and reliably obtained even from an overexposed or underexposed photographic film, and an image recorded on an overexposed or underexposed film can be obtained. It can be reproduced vividly.

According to a second aspect of the present invention, there is provided an image processing apparatus according to the first aspect, wherein:
The output range detecting means obtains an output range of the luminance value based on the minimum value and the maximum value of the luminance value in the luminance image density histogram, and the correction value calculating means determines that the minimum value of the detected luminance value is It is characterized in that a correction value is calculated so that the luminance image density histogram can be expanded so as to be the minimum value in the desired range.

For example, when the histogram created based on the original image data is biased toward the high luminance side, the difference between the maximum value and the minimum value of the luminance value corresponds to a desired range by the above correction. Although it is the length, the minimum value of the luminance value of the histogram may not be the minimum value of the desired range. Then, the portion that must be represented blackest is represented, for example, by black, which is close to gray, and as a result, an image with insufficient black tightness and insufficient rim may be obtained.

However, according to the above configuration, the histogram is expanded so that the minimum value of the luminance value becomes the minimum value of the desired range. (Black), and it is possible to ensure that the image has black tightness. Therefore,
A sharp image can be reliably obtained, and a high-contrast image can be more reliably realized.

According to a third aspect of the present invention, in the image processing apparatus according to the first or second aspect of the present invention, the correction value calculating means is configured to calculate a luminance image density histogram according to a luminance value. It is characterized in that correction values having different degrees of expansion are calculated.

According to the above configuration, for example, when the high-luminance side of the histogram is left as it is, only the low-luminance side is expanded, or even when both the high-luminance side and the low-luminance side are expanded, the low-luminance side is used. Or only the sides can be stretched more. In addition, the histogram may be divided into multiple regions instead of only the two regions on the low luminance side and the high luminance side of the histogram, and the degree of expansion may be different for each region. Therefore, various corrections in contrast correction, such as contrast correction according to the degree of deviation of the histogram toward the low luminance side or high luminance side, and contrast correction according to the shape of the histogram, can be performed. Images can be expressed with optimal contrast.

According to a fourth aspect of the present invention, there is provided an image processing apparatus according to any one of the first to third aspects, wherein the degree of expansion of the luminance image density histogram can be changed. Features.

According to the above arrangement, the degree of expansion of the histogram can be changed as appropriate by, for example, an input instruction from an operator. Therefore, the intensity of correction for obtaining a high-contrast image can be set each time. Accordingly, various high-contrast images can be realized.

According to a fifth aspect of the present invention, there is provided an image processing method comprising: a first step of creating a luminance image density histogram of an image to be output based on image data of a digital image; A second step of obtaining a luminance value output range in the luminance image density histogram;
A third step of calculating a correction value that can expand the luminance image density histogram so that the output range is equal to or larger than the desired range when the output range is less than the desired range; And a fourth step of correcting the original image data.

According to the above-described method, when the output range of the luminance value in the created histogram is less than the desired range, a correction value which can expand the histogram so that the output range is equal to or larger than the desired range is obtained. To correct the original image data. Thus, even if an image is recorded in a narrow luminance range on an overexposed or underexposed photographic film, the image can be output in a wide luminance range by the above correction.

Therefore, according to the above method, a high-contrast image can be easily and reliably obtained even from an overexposed or underexposed photographic film, and an image recorded on an overexposed or underexposed film can be obtained. It can be reproduced vividly.

According to a sixth aspect of the present invention, there is provided an image processing method according to the fifth aspect, wherein:
The second step is a step of obtaining an output range of the luminance value based on the minimum value and the maximum value of the luminance value in the luminance image density histogram. The third step is that the minimum value of the detected luminance value is It is characterized in that it is a step of calculating a correction value such that the luminance image density histogram can be expanded so as to be the minimum value in the desired range.

For example, when the histogram created based on the original image data is biased toward the high luminance side, the difference between the maximum value and the minimum value of the luminance value corresponds to a desired range by the above correction. Although it is the length, the minimum value of the luminance value of the histogram may not be the minimum value of the desired range. Then, the portion that must be represented blackest is represented, for example, by black, which is close to gray, and as a result, an image with insufficient black tightness and insufficient rim may be obtained.

However, according to the above method, the histogram is expanded so that the minimum value of the luminance value becomes the minimum value of the desired range. (Black), and it is possible to ensure that the image has black tightness. Therefore,
A sharp image can be reliably obtained, and a high-contrast image can be more reliably realized.

According to a seventh aspect of the present invention, there is provided an image processing method according to the fifth or sixth aspect, wherein the third step comprises the steps of: It is characterized in that it is a step of calculating a correction value having a different degree of expansion.

According to the above-described method, for example, when the high luminance side of the histogram is left as it is, only the low luminance side is expanded, or even if both the high luminance side and the low luminance side are expanded, the low luminance side Or only the sides can be stretched more. In addition, the histogram may be divided into multiple regions instead of only the two regions on the low luminance side and the high luminance side of the histogram, and the degree of expansion may be different for each region. Therefore, various corrections in contrast correction, such as contrast correction according to the degree of deviation of the histogram toward the low luminance side or high luminance side, and contrast correction according to the shape of the histogram, can be performed. Images can be expressed with optimal contrast.

According to another aspect of the present invention, there is provided a recording medium on which an image processing program is recorded.
A first process of creating a luminance image density histogram of an image to be output based on image data of a digital image, a second process of obtaining an output range of a luminance value in the luminance image density histogram, And a third process of calculating a correction value that can expand the luminance image density histogram so that the output range is equal to or greater than the desired range when the output image range is smaller than the desired range. And an image processing program for causing a computer to execute the fourth process for correcting the error.

According to the above configuration, when the output range of the luminance value in the created histogram is less than the desired range, the correction value that can expand the histogram so that the output range is equal to or larger than the desired range is set. To correct the original image data. Thus, even if an image is recorded in a narrow luminance range on an overexposed or underexposed photographic film, the image can be output in a wide luminance range by the above correction.

Therefore, according to the above configuration, a high-contrast image can be easily and reliably obtained even from an overexposed or underexposed photographic film, and an image recorded on an overexposed or underexposed film can be obtained. It can be reproduced vividly.

According to a ninth aspect of the present invention, there is provided a recording medium on which an image processing program is recorded.
In the configuration according to claim 8, the second process is a process for obtaining an output range of the luminance value based on a minimum value and a maximum value of the luminance value in the luminance image density histogram. It is characterized in that it is a process of calculating a correction value such that the luminance image density histogram can be expanded so that the minimum value of the obtained luminance value becomes the minimum value of the desired range.

For example, when the histogram created based on the original image data is biased toward the high luminance side, the difference between the maximum value and the minimum value of the luminance value corresponds to a desired range by the above correction. Although it is the length, the minimum value of the luminance value of the histogram may not be the minimum value of the desired range. Then, the portion that must be represented blackest is represented, for example, by black, which is close to gray, and as a result, an image with insufficient black tightness and insufficient rim may be obtained.

However, according to the above configuration, the histogram is expanded so that the minimum value of the luminance value becomes the minimum value of the desired range. (Black), and it is possible to ensure that the image has black tightness. Therefore,
A sharp image can be reliably obtained, and a high-contrast image can be more reliably realized.

According to a tenth aspect of the present invention, in a recording medium recording an image processing program according to the eighth aspect of the present invention, the third processing is performed according to a luminance value. It is characterized in that it is a process of calculating a correction value such that the degree of expansion of the luminance image density histogram is different.

According to the above configuration, for example, when the high-luminance side of the histogram is left as it is, only the low-luminance side is expanded, or even when both the high-luminance side and the low-luminance side are expanded, the low-luminance side is used. Or only the sides can be stretched more. In addition, the histogram may be divided into multiple regions instead of only the two regions on the low luminance side and the high luminance side of the histogram, and the degree of expansion may be different for each region. Therefore, various corrections in contrast correction, such as contrast correction according to the degree of deviation of the histogram toward the low luminance side or high luminance side, and contrast correction according to the shape of the histogram, can be performed. Images can be expressed with optimal contrast.

[0035]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described.
The following is a description based on FIGS. 1 to 5.

As shown in FIG. 1, the digital exposure system according to the present embodiment includes a film scanner 1, an image processing device 2, and a photographic printing device 3. The film scanner 1 converts light obtained through a negative film, which is a photographic film, into a CCD (Charge Coupled D), for example.
evice), the image recorded on the negative film is read, and image data corresponding to the image is output to the image processing device 2 for each of R, G, and B.

The photographic printing device 3 is a digital printer that prints an image on a photographic paper by exposing a photographic paper, which is a photosensitive material, based on image data from the image processing device 2. The exposure unit that exposes the photographic paper may be any unit that can modulate the irradiation light on the photographic paper according to the digital image data. For example, a PLZT exposure head, a DMD
(Digital micromirror device), LCD (liquid crystal display), LED panel, laser, FOCRT (Fibe
r Optic Cathode Ray Tube), CRT, etc.

The photographic printing apparatus 3 may be configured to perform both scanning of a negative film and exposure of photographic paper. In this case, by configuring the digital exposure system with the image processing device 2 and the photographic printing device 3, the system can be simplified.

The image processing apparatus 2 performs image processing such as color correction, density correction and gradation conversion on image data from the film scanner 1 and supplies the image data to the photographic printing apparatus 3 as shown in FIG. As described above, the histogram creation unit 4 (histogram creation unit), the output range detection unit 5 (output range detection unit), the correction value calculation unit 6 (correction value calculation unit)
And a correction unit 7 (correction means).

The histogram creating section 4 creates a luminance image density histogram (hereinafter simply referred to as a histogram) as shown in FIG. 2A based on the image data of the digital image obtained by the film scanner 1. Things. This histogram shows the relationship between the luminance value of each pixel of the image data and its frequency. If the image data from the film scanner 1 is in the R, G, B format, the histogram creation unit 4 After being converted into luminance image data, a histogram is created. The luminance image data is, for example, (R + G + B) / 3 or 0.30R +
It is obtained by calculating 0.59G + 0.11B.

The histogram creating unit 4 also calculates a histogram of an image obtained by multiplying the original image data by a normal input gamma or a correction gamma (described later) calculated by the correction value calculating unit 6. A histogram of the image obtained by multiplying the data is also created. As a result, the histogram of the image to be output is obtained in the histogram creating unit 4.

The input gamma is defined as film characteristics, light receiving sensitivity of the CCD of the film scanner 1, CCD
Is supplied to the photographic printing apparatus 3 by multiplying the image data by the above-mentioned input gamma, so that a clear and standard image can be obtained.

The output range detecting section 5 detects the minimum value and the maximum value of the luminance values in the histogram and the histogram obtained when it is assumed that the input histogram is multiplied by the normal input gamma. An output range (length of the histogram) of the luminance value in the histogram is obtained based on the maximum value and the minimum value of the values.

Here, both extreme ends of each of the above-mentioned histograms have extremely low frequencies as compared with the other histograms, and are considered to be essentially error ranges. Therefore, the output range detection unit 5 cuts both ends of the histogram by an amount corresponding to, for example, 0.5% of the total frequency, removes the error range, and then obtains the minimum value and the maximum value of the luminance value. I have. As described above, by performing the contrast correction of the present invention based only on the effective portion of the histogram, it is possible to enhance the reliability when obtaining a high-contrast image.

Note that the amount of cutting both ends of the histogram is not limited to the above amount, but may be any amount according to the range of the error. In the following description,
When obtaining the minimum value and the maximum value of the histogram, it is assumed that both ends of the histogram are cut by a predetermined amount in this way.

When the output range obtained by the output range detector 5 is less than a desired range (for example, from 0 (black) to 255 (white) for 8 bits), the correction value calculator 6 A correction gamma (correction value) that can expand the histogram so that the range is equal to or larger than a desired range is calculated. The correction unit 7 corrects the original image data by multiplying the original image data (pixel value or luminance value) by the correction gamma obtained by the correction value calculation unit 6.

Here, the reason why the above-mentioned correction gamma is calculated separately from the above-mentioned input gamma is as follows. That is, if a histogram of an image recorded on an overexposed or underexposed film is as shown in FIG. 2A, for example, multiplying the image data corresponding to the image by the input gamma only results in FIG. ), The minimum value c and the maximum value d of the histogram do not reach the minimum value 0 and the maximum value 255 of the desired range, respectively. As a result that the output range of the histogram does not completely use the desired range, the above image becomes a low-contrast image.

Therefore, in the present invention, the above-mentioned correction gamma is multiplied by the original image data first, and when this is then multiplied by the normal input gamma, the output range of the histogram becomes the desired range. Is used up, and as a result, a high-contrast image can be obtained. That is, in the present invention, an amount that cannot be corrected by multiplying the original image data by the normal input gamma is corrected by the correction gamma.

Next, the operation of the image processing apparatus 2 will be described mainly with reference to the flowchart of FIG. In the present invention, after performing a predetermined process by multiplying the image data first by the correction gamma, a process of multiplying the input data by a normal input gamma is performed. Yes, it is. Actually, the output image is finally obtained by multiplying the image data by the input gamma in S12.
It is refused earlier that this is a subsequent step.

First, the histogram creating section 4 creates a histogram indicating the relationship between the luminance value and the frequency based on the image data sent from the film scanner 1 (step 1; hereinafter, the steps are simply abbreviated as S). Then
As shown in FIG. 2A, the output range detection unit 5 cuts an amount corresponding to 0.5% of the total frequency from both ends of the histogram, and outputs the minimum value a and the maximum luminance value a in the remaining histogram. The value b is detected (S2).

Subsequently, the histogram creating section 4 creates a histogram of the image assuming that the original image data is multiplied by the normal input gamma, and the output range detecting section 5
Based on the histogram, as shown in FIG. 2B, the minimum value c and the maximum value d of the luminance value are calculated by the same method as in S2, and the difference between the maximum value d and the minimum value c is calculated from the difference between the maximum value d and the minimum value c. Histogram length (histogram output range)
Is calculated (S3).

Next, the correction value calculator 6 determines the length of the histogram obtained in S3 and the desired range (for example, 0 to 25).
5) is compared with a length (for example, 256), and if the length of the histogram matches the length corresponding to the desired range, the histogram is used as the correction gamma even if the image data is multiplied by the correction gamma. A value that does not change (for example, “1”) is set. Further, the correction value calculating unit 6 determines a value that can reduce the histogram so that the length of the histogram matches the length corresponding to the desired range if the length of the histogram is larger than the length corresponding to the desired range. (For example, a value smaller than “1”) is set as the correction gamma. Further, the correction value calculation unit 6 determines a value that can expand the histogram so that the length of the histogram matches the length corresponding to the desired range if the length of the histogram is smaller than the length corresponding to the desired range. (For example, a value larger than "1") is set as the correction gamma (S4).

That is, in S4, the correction value calculation unit 6
By multiplying the image data of the histogram No. 3 by the correction gamma, a correction gamma is obtained such that the histogram shown in FIG. 2C whose histogram length corresponds to the desired range is obtained.

Next, the correction value calculation section 6 compares the correction gamma obtained in S4 with a threshold value (for example, "1") (S4).
5) If the correction gamma is larger than the threshold value, the correction gamma is sent to the histogram creation unit 4 so that the histogram creation unit 4 creates a histogram of an image obtained by multiplying the original image data by the correction gamma. And
The output range detection unit 5 calculates the minimum value and the maximum value of the luminance value of the histogram (S6).

On the other hand, if the correction gamma is smaller than the threshold value in S5, the correction value calculator 6 simply multiplies the image data by the normal input gamma to determine the length of the histogram corresponding to the desired range. Therefore, it is determined that the correction for expanding the histogram is not necessary, and the values obtained in S3 are used as the minimum and maximum values of the histogram as they are (S3).
7).

By the way, for example, as shown in FIG. 4A, when the original histogram is entirely biased toward the low luminance side from the beginning, the correction gamma and / or the input gamma are added to the original image data. When multiplied, as shown in FIG. 4B, the length of the histogram is the length corresponding to the desired range, but the histogram may not reach the maximum value of the desired range on the high luminance side. . However, since the histogram has reached the minimum value of the desired range on the low luminance side, an image with black tightness and sharpness is obtained in this case.

However, as shown in FIG. 5A, when the original histogram is entirely biased toward the high luminance side from the beginning, the original image data is multiplied by the correction gamma and / or the input gamma. As shown in FIG. 5B, there are cases where the histogram does not reach the minimum value in the desired range on the low-luminance side, in which case the black is not tight and the whole image is blurred, which is a so-called sleepy image. Become.

Therefore, according to the present invention, in order to reliably obtain an image with black tightness irrespective of the bias of the original histogram toward the low luminance side or the high luminance side, the histogram is set to the low side and the H side.
and the Lo side as necessary, as shown below.
The correction gamma on the w side is corrected. The low side is a histogram smaller than a certain point (for example, 128 in the case of 8 bits) in a desired range, and the high side is a histogram which is larger than the point. It is a histogram.

Here, with respect to the High-side correction gamma for correcting the High side of the histogram, the correction value calculation unit 6
Sets the correction gamma obtained in S4 as it is as the High-side correction gamma (S8). On the other hand, with respect to the low-side correction gamma for correcting the low side of the histogram, the correction value calculation unit 6 performs the setting as follows.

First, the correction value calculation unit 6 determines whether S6 or S7
The minimum value of the histogram is compared with a threshold value (for example, 0 which is the minimum value of a desired range) (S9). If the minimum value of the histogram is larger than the threshold value, as shown in FIG. Low so that the minimum value of the histogram becomes the threshold
A correction value that can expand the histogram on the side is recalculated (S10), and this is set as a low-side correction gamma (S11). On the other hand, if the minimum value of the histogram is equal to or smaller than the threshold in S9, the process directly proceeds to S11, and the correction value calculation unit 6 sets the correction gamma obtained in S4 as the low-side correction gamma.

Finally, the correcting section 7 multiplies the original image data (pixel value or luminance value) by the two correction gammas set in S8 and S11, and outputs the Low side and High level.
Side contrast correction is performed (S12). Thereafter, an image obtained by multiplying this image data by a normal input gamma is output.

As described above, according to the present invention, when an output range of a histogram of image data does not use up a desired range, for example, an image recorded on an overexposed or underexposed film, By performing correction to expand the histogram so as to use up the desired range, an image can be expressed in a wide luminance range as in the case of proper exposure. Therefore, even when printing an image on photographic paper based on an overexposed or underexposed film, an image that would normally be printed with low contrast can be printed with high contrast, and overexposed or underexposed film can be printed. The recorded image can be rescued.

Further, since the histogram is expanded so that the histogram always reaches the minimum value in the desired range on the low luminance side, a high-contrast image with good black tightness can be reliably obtained.

In the present embodiment, the correction value calculation unit 6 sets the correction gamma for each area by dividing the histogram into two parts, a low side and a high side.
The histogram may be divided into three or more regions according to the luminance value, and a correction gamma may be calculated such that the degree of expansion of the histogram differs for each region.
In this case, various corrections can be made in contrast correction, such as contrast correction according to the degree of deviation of the histogram toward the low luminance side or high luminance side, and contrast correction according to the shape of the histogram. It is possible to express with an optimum contrast.

The parameters such as the amount of cutting both ends of the histogram in S2 and S3 and the thresholds shown in S5 and S9 can be freely changed by the operator, or can be fixed at all times. . Since the parameters can be changed in this manner, the intensity of correction (the degree of expansion of the histogram) can be changed each time, so that various high-contrast images having different correction intensities can be realized.

In this embodiment, the histogram L
An example in which the correction value is reviewed only on the ow side has been described. In addition, on the High side, a correction value in which the maximum value of the luminance value is equal to or larger than the maximum value of the output range is reviewed. You may. By correcting the original image data based on such both correction values, not only is it possible to obtain an image with good black tightness irrespective of the degree of deviation of the histogram to the low side or high side, but also to obtain a high chroma portion. Images that express vividly even colors can be obtained.

In this embodiment, the luminance value is represented by 8 bits (256 tones from 0 to 255), but this is only an example, and for example, 12 bits (4096 tones from 0 to 4095). Of course, it is also possible to indicate with other bit numbers.

A program for causing the image processing apparatus 2 as a computer to execute the image processing described in the present embodiment is recorded on a recording medium such as an optical disk, a magneto-optical disk, and the like. The image processing device 2 may be configured to operate automatically.

[0069]

According to the first aspect of the present invention, there is provided an image processing apparatus comprising:
As described above, a histogram creating unit that creates a luminance image density histogram of an image to be output based on image data of a digital image, an output range detecting unit that calculates an output range of a luminance value in the luminance image density histogram, If the output range is less than the desired range,
A correction value calculation unit that calculates a correction value that can expand the luminance image density histogram so that the output range is equal to or greater than a desired range; and a correction unit that corrects original image data using the correction value. Configuration.

Therefore, even if an image is recorded in a narrow luminance range on an overexposed or underexposed photographic film,
This image can be output in a wide luminance range by the above correction. Further, since the correction value is automatically obtained by the correction value calculating means without intervention of the operator, there is no trouble in calculating the correction value.

Therefore, according to the above configuration, a high-contrast image can be easily and reliably obtained even from an overexposed or underexposed photographic film, and an image recorded on an overexposed or underexposed film can be obtained. This has the effect that it can be reproduced vividly.

As described above, in the image processing apparatus according to the second aspect of the present invention, in the configuration of the first aspect, the output range detecting means is configured to detect the output range based on the minimum value and the maximum value of the luminance value in the luminance image density histogram. The correction value calculating means calculates a correction value that can expand the luminance image density histogram so that the minimum value of the detected luminance value becomes the minimum value of the desired range. It is a configuration for calculating.

Therefore, since the histogram is expanded so that the minimum value of the luminance value becomes the minimum value of the desired range, the darkest part in the image is represented by the original black, and the black It is possible to ensure tightness. Therefore, in addition to the effect of the structure of claim 1,
This has the effect that a sharp image can be reliably obtained, and a high-contrast image can be realized more reliably.

As described above, in the image processing apparatus according to the third aspect of the present invention, in the configuration of the first or second aspect, the correction value calculating means varies the degree of expansion of the luminance image density histogram according to the luminance value. Such a correction value is calculated.

Therefore, various countermeasures can be taken in contrast correction, such as contrast correction according to the degree of deviation of the histogram toward the low luminance side or high luminance side, and contrast correction according to the shape of the histogram. In addition to the effect of the second configuration, there is an effect that an image recorded on a film can be expressed with optimum contrast.

According to a fourth aspect of the present invention, as described above, in any one of the first to third aspects, the degree of expansion of the luminance image density histogram can be changed.

Therefore, the intensity of correction for obtaining a high-contrast image can be set each time by an operator or the like, whereby various effects can be obtained in addition to the effects of any one of the first to third aspects. There is an effect that a high-contrast image can be realized.

In the image processing method according to the fifth aspect of the present invention, as described above, the first method of creating a luminance image density histogram of an image to be output based on image data of a digital image is provided.
And a second step of obtaining an output range of a luminance value in the luminance image density histogram; and, when the output range is less than a desired range, the luminance image is adjusted so that the output range is equal to or more than a desired range. The configuration includes a third step of calculating a correction value that can expand the density histogram, and a fourth step of correcting the original image data using the correction value.

Therefore, even if an image is recorded in a narrow luminance range on an overexposed or underexposed photographic film,
This image can be output in a wide luminance range by the above correction. Therefore, high-contrast images can be easily and reliably obtained even from overexposed and underexposed photographic films, and the effect of vivid reproduction of images recorded on overexposed and underexposed films can be obtained. To play.

According to a sixth aspect of the present invention, in the image processing method according to the fifth aspect, the second step is based on the minimum value and the maximum value of the luminance value in the luminance image density histogram. The third step is a step of calculating a correction value that can expand the luminance image density histogram so that the minimum value of the detected luminance value becomes the minimum value of the desired range. This is a configuration that is a step of calculating.

Therefore, since the histogram is expanded so that the minimum value of the luminance value becomes the minimum value of the desired range, the darkest part in the image is represented by the original black, and the black It is possible to ensure tightness. Therefore, in addition to the effect of the method of claim 5,
This has the effect that a sharp image can be reliably obtained, and a high-contrast image can be realized more reliably.

As described above, in the image processing method according to the seventh aspect of the present invention, in the method of the fifth or sixth aspect, in the third step, the degree of expansion of the luminance image density histogram varies depending on the luminance value. The configuration is a process of calculating such a correction value.

Therefore, various countermeasures in contrast correction, such as contrast correction according to the degree of deviation of the histogram toward the low luminance side and high luminance side, and contrast correction according to the shape of the histogram, can be made. In addition to the effect of the configuration of the sixth aspect, there is an effect that an image recorded on a film can be expressed with an optimum contrast.

The recording medium storing the image processing program according to the eighth aspect of the present invention provides a first processing for creating a luminance image density histogram of an image to be output based on image data of a digital image, as described above. A second step of obtaining an output range of a luminance value in the luminance image density histogram;
And a third process of calculating a correction value that can expand the luminance image density histogram so that the output range is equal to or greater than the desired range when the output range is less than the desired range. An image processing program for causing a computer to execute a fourth process of correcting the original image data using the correction value is recorded.

Therefore, even if an image is recorded in a narrow luminance range on an overexposed or underexposed photographic film,
This image can be output in a wide luminance range by the above correction. Therefore, high-contrast images can be easily and reliably obtained even from overexposed and underexposed photographic films, and the effect of vivid reproduction of images recorded on overexposed and underexposed films can be obtained. To play.

According to a ninth aspect of the present invention, in the recording medium storing the image processing program according to the eighth aspect of the present invention, the second processing comprises the steps of: The third process is a process for obtaining an output range of a luminance value based on the maximum value.
The configuration is a process of calculating a correction value that can expand the luminance image density histogram so that the detected minimum value of the luminance value becomes the minimum value of the desired range.

Therefore, since the histogram is expanded so that the minimum value of the luminance value becomes the minimum value of the desired range, the darkest part in the image is represented by the original black, and the black It is possible to ensure tightness. Therefore, in addition to the effect of the structure of claim 8,
This has the effect that a sharp image can be reliably obtained, and a high-contrast image can be realized more reliably.

According to a tenth aspect of the present invention, as described above, in the recording medium according to the eighth or ninth aspect, the third processing is performed by a luminance image density histogram according to a luminance value. This is a configuration for calculating a correction value such that the degree of expansion is different.

Therefore, various countermeasures in contrast correction, such as contrast correction according to the degree of bias of the histogram toward the low luminance side and high luminance side, and contrast correction according to the shape of the histogram, can be made. In addition to the effect of the configuration of 9, the image recorded on the film can be expressed with optimal contrast.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a schematic configuration of an image processing apparatus according to the present invention and a digital exposure system including the image processing apparatus.

FIG. 2A is an explanatory diagram showing a histogram created based on image data read by a film scanner. (B) is an explanatory diagram showing a histogram when it is assumed that the image data is multiplied by an input gamma.
FIG. 4C is an explanatory diagram showing the histogram in which the length of the histogram becomes a length corresponding to a desired range when the histogram is expanded.

FIG. 3 is a flowchart illustrating a flow of an operation in the image processing apparatus.

FIG. 4A is an explanatory diagram showing a histogram created based on image data read by a film scanner when the histogram is biased toward a low luminance side. (B) is an explanatory view showing the histogram in which the length of the histogram becomes a length corresponding to a desired range when the histogram is expanded.

FIG. 5A is an explanatory diagram showing a histogram created based on image data read by a film scanner when the histogram is biased toward a high luminance side. (B) is an explanatory view showing the histogram in which the length of the histogram becomes a length corresponding to a desired range when the histogram is expanded. FIG. 3C is an explanatory diagram showing a histogram of an image when the histogram is divided into a low side and a high side, and the corresponding image data is corrected by different correction gammas.

FIG. 6 is a graph showing the relationship between film exposure and film density.

[Explanation of symbols]

 2 Image processing device 4 Histogram creation unit (histogram creation unit) 5 Output range detection unit (output range detection unit) 6 Correction value calculation unit (correction value calculation unit) 7 Correction unit (correction unit)

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Minoru Uchida 11-30 Enomachi, Suita-shi, Osaka F-term in Toyo Information System Co., Ltd. (Reference) 5B057 AA20 BA02 CA01 CA08 CA12 CA16 CB08 CB12 CB16 CE11 CH18 DC23 5C022 AB17 AB33 AC42 5C072 AA01 BA19 RA20 UA17 UA20 VA03 XA01 XA10 5C077 MP08 NN03 NP01 PP15 PP32 PP43 PQ08 PQ19 PQ22 TT06 TT10

Claims (10)

[Claims] 1. A histogram creating means for creating a brightness image density histogram of an image to be output based on image data of a digital image; an output range detecting means for obtaining an output range of a brightness value in the brightness image density histogram; When the output range is less than the desired range, a correction value calculating unit that calculates a correction value that can expand the luminance image density histogram so that the output range is equal to or more than the desired range; and An image processing apparatus comprising: a correction unit configured to correct original image data. 2. An output range detecting means for obtaining an output range of a luminance value based on a minimum value and a maximum value of a luminance value in a luminance image density histogram. 2. The image processing apparatus according to claim 1, wherein a correction value is calculated such that the luminance image density histogram can be expanded so that the minimum value is the minimum value in the desired range. 3. The image processing apparatus according to claim 1, wherein said correction value calculating means calculates a correction value such that the degree of expansion of the luminance image density histogram varies according to the luminance value. 4. The image processing apparatus according to claim 1, wherein the degree of expansion of the luminance image density histogram can be changed. 5. A first method for creating a luminance image density histogram of an image to be output based on image data of a digital image.
And a second step of obtaining an output range of a luminance value in the luminance image density histogram. If the output range is less than a desired range, the luminance image is adjusted so that the output range is equal to or more than a desired range. An image processing method, comprising: a third step of calculating a correction value capable of expanding a density histogram; and a fourth step of correcting original image data using the correction value. 6. The second step is a step of obtaining an output range of the luminance value based on the minimum value and the maximum value of the luminance value in the luminance image density histogram. 6. The image processing method according to claim 5, further comprising the step of calculating a correction value capable of expanding the luminance image density histogram so that the minimum value is the minimum value in the desired range. 7. The image according to claim 5, wherein the third step is a step of calculating a correction value such that the degree of expansion of the luminance image density histogram is different according to the luminance value. Processing method. 8. A first method for creating a luminance image density histogram of an image to be output based on image data of a digital image.
And a second process for obtaining an output range of the brightness value in the brightness image density histogram; and a process for setting the brightness image so that the output range is equal to or more than a desired range when the output range is less than a desired range. A recording in which an image processing program for causing a computer to execute a third process of calculating a correction value capable of expanding a density histogram and a fourth process of correcting original image data using the correction value is recorded. Medium. 9. The second process is a process for obtaining an output range of a luminance value based on a minimum value and a maximum value of a luminance value in a luminance image density histogram. 9. The image processing program according to claim 8, wherein the correction value is a process of calculating a correction value that can expand the luminance image density histogram so that the minimum value is the minimum value in the desired range. recoding media. 10. The image according to claim 8, wherein the third processing is processing for calculating a correction value such that the degree of expansion of the luminance image density histogram is different according to the luminance value. A recording medium on which a processing program is recorded.