JPH0968764A - Method for image processing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decide exposing conditions of under-exposure, over-exposure, etc., of an image on a film so as to perform excellent tone reproduction and color reproduction based on decision results. SOLUTION: The film image imprinted on a developed photographic film 52 is picked up, and a reference maximum value and a reference minimum value are found from an image signal obtained in the case of a picking up the image. The reference maximum value and the reference minimum value are used in signal processing for adjusting the tone of the image, etc., and the exposing state of the film image is further decided based on at least one of the reference maximum value, the reference minimum value, and the average value of the image signal. When the exposing state is decided as to under-exposure, gamma obtained in the case of the gamma correction is made small than that obtained in the case of standard exposure, so that halftone is prevented from being dark. On the other hand, when the exposing state is decided as the over-exposure, the gamma obtained in the case of gamma correction is made larger than that obtained in the case of the standard exposure, so that the tone is adjusted to prevent the halftone from getting too bright. At least one of the reference maximum value and the reference minimum value is corrected to perform good color reproduction in the case a color image is color failure scene.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing method, and more particularly to an image processing method for determining an exposure state such as underexposure or overexposure of a film image and performing image processing according to the determination result.

[0002]

2. Description of the Related Art FIG. 11 is a graph showing a characteristic curve of a negative film, and A, B and C show exposure areas of standard, underexposure and overexposure, respectively. As shown in the figure, a negative image with underexposed or overexposed light has different gradation characteristics and different gamma characteristics from the standard exposure negative image. Incidentally, as a signal processing circuit using variable gamma so as to be able to deal with image signals having various gradation characteristics, there is a signal processing circuit described in Japanese Patent Application Laid-Open No. 4-107083. This signal processing circuit is an analog processing, and a variable gain amplification circuit is provided in each of a front stage and a rear stage of a gamma correction circuit having a knee characteristic, and gamma is changed by adjusting gains of these variable gain amplification circuits. .

Further, the negative image of underexposure and overexposure has a narrower density range than that of standard exposure, as is apparent from FIG. Japanese Patent Application No. 6-274946 proposes an image processing method for adjusting the tone of a soft image or a hard image. On the other hand, conventionally, as an image processing method for adjusting white balance and black balance of R, G, and B image signals obtained by capturing color images, R, G, and
The reference maximum value and the reference minimum value are obtained from the image signal of B, the offset and the white balance gain are obtained so that the reference maximum value and the reference minimum value have predetermined gradations, respectively, and the offset and the white balance gain are obtained. There is a method of performing offset and gain control of R, G, and B image signals. The reference maximum value and the reference minimum value are obtained by obtaining a histogram for each gradation of the image signal and determining the reference maximum value and the reference minimum value from the histogram.

[0004]

By the way, when gamma correction or the like of an image signal is performed without using logarithmic conversion, an under or over negative image has a different gamma characteristic from the standard exposure negative image. It is necessary to perform gamma correction according to the state. If you perform the same gamma correction as the standard exposure negative image, the underexposed negative image becomes darker,
There is a problem that an over negative image is too bright and the tone is unfavorable.

Further, when adjusting the tone of a soft-tone image or a hard-tone image, if the tone of the image is adjusted to the under- or over-negative image in the same manner as the standard-exposure negative image, the tone changes too much. There is a problem of becoming unnatural. Further, in a color image in which an extremely saturated region exists, the reference maximum value and the reference minimum value for each of R, G, and B tend to vary. For example, as shown in FIG.
The reference minimum value of may be extremely larger than the reference minimum values of other colors.

In such a case, if the reference maximum value and the reference minimum value obtained from the R, G, B image signals are used as they are, the offset and gain control of the R, G, B image signals is performed. However, there is a problem in that the white balance or the black balance is lost and good color reproduction cannot be realized. That is, in the scene as shown in FIG. 12, the white balance gain of the B image signal is applied extremely strongly as compared with the image signals of other colors, so that the image becomes blue as a whole (color ferria). Occurs.

An object of the present invention is to provide an image processing method capable of easily and accurately determining an exposure state such as underexposure or overexposure of a film image.
Another object of the present invention is to provide an image processing method capable of reproducing a good tone even if the exposure state of the film image varies. Still another object of the present invention is an image in which excellent color reproduction can be realized even in a color image in which a region having extremely high saturation exists and the reference maximum value and the reference minimum value for each color greatly vary. It is to provide a processing method.

[0008]

In order to achieve the above-mentioned object, the present invention takes a film image imprinted on a developed photographic film, and sets a reference maximum value and a reference minimum value of an image signal obtained at the time of the image pickup. Value, or a reference maximum value, a reference minimum value and an average value, and determines the exposure state of the film image based on at least one of the obtained reference maximum value, reference minimum value and average value, Image processing is performed based on the maximum value and the reference minimum value and the determination result. For example, the reference maximum value is used to determine the exposure state of the negative film.If this reference maximum value is less than or equal to the reference value for overexposure determination, it is considered as overexposure, and if it is greater than or equal to the reference value for underexposure determination. Is considered as underexposure.

The reference maximum value and the reference minimum value used for these determinations are originally used for image processing.
It is not necessary to separately detect for the determination of the exposure state, and the determination of the exposure state can be easily performed. Further, a value having a high determination accuracy of the exposure state of the film image is appropriately selected from the obtained reference maximum value, reference minimum value and average value according to the exposure state of the film image, and the film is selected based on the selected value. The exposure state of the image is determined. For example, when the obtained reference maximum value is equal to or more than a predetermined threshold value that decreases the accuracy of determining the exposure state of the film image based on the reference maximum value, the film is based on the average value instead of the reference maximum value. The exposure state of the image is determined, which enables highly accurate determination of the exposure state. Further, the exposure state of the film image is determined based on an average value of a plurality of reference maximum values and the like obtained by a plurality of times of image pickup, which enables highly accurate determination of the exposure state. Furthermore, the reference maximum value and the like are normalized based on the average value of the image signal obtained when the unexposed portion of the film is imaged, thereby obtaining a value that is not affected by the film base density, amplifier gain, or the like. ing.

Further, according to the present invention, a reference maximum value and a reference minimum value of an image signal obtained by picking up a film image are obtained, and the image is adjusted so that the reference maximum value and the reference minimum value have predetermined gradations. After the signal is corrected, in the image processing method of gamma correction, the exposure state of the film image is determined, and if underexposure is determined based on the determination result of the exposure state, the gamma at the gamma correction is compared to that at the standard exposure. To prevent the intermediate tone from becoming dark, and when it is determined that overexposure has occurred, the gamma at the time of gamma correction is made larger than that at the standard exposure, thereby adjusting the tone so that the intermediate tone is not too bright. I am trying.

Further, according to the present invention, a reference maximum value and a reference minimum value of an image signal obtained by picking up a film image are obtained, and a ratio or a difference between the reference maximum value and the reference minimum value gives a desired tone. As described above, at least one of the reference maximum value and the reference minimum value is corrected so as to fall within the range between the first threshold value and the second threshold value, and the corrected reference maximum value and the reference minimum value are The image signals are corrected so as to have predetermined gradations, respectively, and thereby, the hard tone image and the hard tone image are adjusted to have a desired tone. At this time, the first threshold value and the second threshold value when correcting at least one of the reference maximum value and the reference minimum value,
It is changed according to the exposure state of the film image. That is, when it is determined that the underexposure or the overexposure is performed, the first threshold value and the second threshold value are changed to the third threshold value and the fourth threshold value, which are lower than those, respectively. The tone of the film image does not change unnaturally, and good tone reproduction is possible.

Further, according to the present invention, a color image is picked up to obtain an image signal for each color, a reference maximum value and a reference minimum value of the image signal for each color obtained at the time of this image pickup are obtained, and the reference maximum value and The image signal is corrected so that the reference minimum value has a predetermined gradation, whereby the reference maximum value for each color,
Even in the case of a color image in which the reference minimum value greatly varies, good color reproduction can be realized. That is, the ratio or difference of the reference maximum value for each color is obtained, and it is determined whether or not this ratio or difference is within a predetermined range in which desired white balance adjustment is possible. , The reference maximum value and / or the reference minimum value for each color are corrected so that the reference maximum value and / or the reference minimum value approach each other.
As a result, variations in the reference maximum value and the reference minimum value are suppressed, and good color reproduction can be realized. It should be noted that instead of the reference maximum value, the reference minimum value may be used to perform the same determination as above.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of an image processing method according to the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 is a block diagram of essential parts showing an embodiment of a film scanner to which the present invention is applied. This film scanner mainly includes a light source 10 for illumination, a photographing lens 12,
CCD line sensor 14, analog amplifier 16, A / D
Converter 18, digital signal processing circuit 20, motor 3
1, a film driving device including a capstan 32 and a pinch roller 33, a central processing unit (CPU) 40, an integrating block 41, and the like.

The light source 10 illuminates the developed negative film 52 drawn out from the film cartridge 50 through an infrared cut filter (not shown), and the film 52 is illuminated.
The transmitted light transmitted through is imaged on the light receiving surface of the CCD line sensor 14 via the taking lens 12. The CCD line sensor 14 is placed in the direction 102 orthogonal to the film transport direction.
The light receiving portion for four pixels is provided, and the image light imaged on the light receiving surface of the CCD line sensor 14 is accumulated in each light receiving portion provided with the R, G, B filters, and the intensity of the light is increased. It is converted into R, G, and B signal charges in an amount corresponding to the level. The R, G, and B charges thus accumulated are transferred to the shift register when a read gate pulse of one line period applied from the CCD drive circuit 15 is applied, and then sequentially converted into voltage signals by register transfer pulses. Is output. Further, the CCD line sensor 14 is provided with a shutter gate and a shutter drain adjacent to each light receiving portion. By driving this shutter gate with a shutter gate pulse, the electric charge accumulated in the light receiving portion is shutter drained. Can be swept up to. That is, the CCD line sensor 14 has a so-called electronic shutter function capable of controlling the electric charge accumulated in the light receiving portion according to the shutter gate pulse applied from the CCD drive circuit 15.

The R, G, B voltage signals read from the CCD line sensor 14 are clamped by a CDS clamp (not shown) and applied to the analog amplifier 16, and the gain is controlled as described later. The R, G, B voltage signals for one frame output from the analog amplifier 16 are dot-sequential R, G, B voltage signals by the A / D converter 18.
After being converted into G and B digital image signals, the digital signal processing circuit 20 performs white balance, black balance, negative / positive inversion, gamma correction, etc., which will be described later, and then stores them in an image memory (not shown).

The image signal for one frame stored in the image memory is repeatedly read out, converted into an analog signal by the D / A converter, and then NT by the encoder.
It is converted into an SC composite video signal and output to the monitor TV. As a result, the film image can be viewed on the monitor TV. The film drive device engages with the spool 50A of the film cartridge 50 and drives the spool 50A in forward / reverse rotation, and a film take-up unit that takes up the film 52 sent from the film supply unit. The film 52 is arranged in the film transport path, and is constituted by means for sandwiching the film 52 between a capstan 32 driven by a motor 31 and a pinch roller 33 and transporting the film 52 at a desired speed. The film supply unit drives the spool 50A of the film cartridge 50 in the clockwise direction in FIG. 1 to feed the film 52 from the film cartridge 50 until the leading end of the film is wound by the film winding unit. . Further, the CPU 40 can control forward / reverse rotation of the motor 31, start / stop, and control of the film transport speed by pulse width modulation through the motor rotation speed / direction control circuit 34.

Next, the procedure of image processing will be described with reference to the flowchart shown in FIG. First, the film cartridge 50 is set in a cartridge storage unit (not shown), the film 52 is sent out from the film cartridge 50, and the leading end of the film is wound around the winding shaft of the film winding unit (when the film loading is completed). The following calibration is executed (step S10).

That is, the electronic shutter value T ₁ of the CCD line sensor 14 is set to a prescribed value (for example, 40%), and an unexposed portion of the film 52 (for example, a negative base at the tip of the film) is imaged. Then, the gain of the analog amplifier 16 is determined so that each of the R, G, and B signals has a predetermined maximum value (that is, the input range of the A / D converter 18 is maximum).

After adjusting the gain of the analog amplifier 16 in this way, the film 52 is conveyed at a constant speed,
A scan (prescan) of the film image is executed (step S20). During this pre-scan, a dot-sequential R, G, and
The B digital image signal is captured.

The integrating block 41 integrates the gradation (8 bits (0 to 255) gradation in this embodiment) of the digital image signal in a predetermined integrating area for each R, G, B digital image signal. Then, the average gradation of the integrated area is obtained, and each gradation data of the integrated area of 5000 to 10000 points is created per screen. Furthermore, the integration block 41 counts the frequency for each gradation based on the gradation data that is sequentially created, and this frequency is a threshold value TH (in this embodiment, the total value) set for the total score of the gradation data. If it exceeds 1% of the score), stop counting.

That is, the integration block 41, as shown in FIG. 3, has a maximum threshold value TH for all gradations from 0 to 255.
A simple histogram (a histogram shown by diagonal lines in FIG. 3) counted up to is created (step S21). still,
By not counting the frequency that exceeds the threshold TH, the number of bits of the counter can be significantly reduced. Further, the chain double-dashed line in FIG. 3 is the original histogram when the total number of points is counted.

The CPU 40 sequentially accumulates the frequencies from the one with the smallest gradation in the simple histogram shown in FIG. 3, and the gradation when the accumulated frequency coincides with the threshold value TH or first exceeds the reference value is the reference minimum value. As the R, G, and B values, the frequencies are sequentially accumulated from the one with the highest gradation in the simple histogram, and the gradation when the accumulated frequency matches or first exceeds the threshold TH is the reference maximum value. As R, G, B. Further, the maximum value Dmax among R, G and B is obtained from the simple histogram (step S22).

Next, based on the reference maximum value and the reference minimum value obtained as described above, the exposure state such as underexposure or overexposure of the film image is determined, and the tone determination such as soft tone or hard tone is performed. The electronic shutter value T ₂ is determined by the maximum value Dmax (step S23). That is, the reference maximum value is used for the determination of the exposure state, and if this reference maximum value is less than or equal to the reference value for overexposure determination, it is considered as overexposure, and if it is greater than or equal to the reference value for underexposure determination. , Underexposure.

The determination of the exposure state of the film image is not limited to the determination of underexposure, standard exposure, and overexposure, and the exposure state may be determined more finely.
Further, the determination of the exposure state is not limited to the case where the reference maximum value is used, and the reference minimum value or the average value of all the gradation data described above may be used, and further, the reference maximum value, the reference minimum value and the average value. The exposure state may be determined using any two or three of the values.

FIG. 4 is a line graph showing the reference maximum value and the average value corresponding to the exposure state of the film image. Here, the reference maximum value and the average value shown in FIG. 4 are values normalized by the average value of the image signals obtained by imaging the negative base after the calibration in step S10 as shown in the following equation. is there.

[0026]

[Equation 1]

[0027]

[Equation 2] By using the normalized value as above,
Even if the maximum value at the time of calibration has a slight fluctuation range (the range for determining the analog gain), the reference maximum value and average value that are not affected by the fluctuation range can be obtained.

The three line graphs of the reference maximum value shown in FIG. 4 are the standard exposure film image and -1EV to -3EV.
Underexposed film image, negative base and 1E
3 over-exposed film images of V to 6 EV each
From a line graph created from the average value of 30 reference maximum values (◆ in FIG. 4) obtained by imaging 0 times and the maximum value of 30 reference maximum values (■ in FIG. 4) It is the line graph created and the line graph created from the minimum value of the 30 reference maximum values (A in FIG. 4). Similarly, the line graph of the average values shown in FIG. 4 is a line graph created from the average values of the film images obtained by a certain image pickup.

As shown in the figure, underexposure (-1E
The film images of (V to -3EV) have a small change in the reference maximum value with respect to the change of the exposure state (that is, the gradient of the line graph is small), and the film is based on the normalized reference maximum value obtained by the equation (1). The exposure state of the image cannot be accurately determined. For example, the maximum value of the 30 reference maximum values of the -2EV film image (■ in FIG. 4)
Is larger than the minimum value (▲ in FIG. 4) of the 30 reference maximum values of the -3EV film image, and the relationship between the size of the reference maximum value and the exposure state of the film image is reversed. There is.

Therefore, in another embodiment of the present invention, the average value of the film image is used in addition to the reference maximum value, and the exposure state of the underexposed film image is determined based on the average value. That is, when the normalized reference maximum value becomes equal to or greater than a predetermined value (a value that guarantees the determination accuracy of the exposure state of the film image based on the reference maximum value, 110 in the embodiment shown in FIG. 4), the normalization is performed. Instead of the reference maximum value, the exposure state of the film image is determined based on the normalized average value obtained by the equation (2).

When the film image is underexposed, the normalized average value has a larger slope than the normalized reference maximum value as shown in FIG. Therefore, when the film image is underexposed, the exposure state of the film image is determined based on the normalized average value, so that accurate determination can be performed. In the case of a film image obtained by shooting a person with flash at night, the maximum reference value of the film image is
The value depends on the background that the flash does not reach, but the average value takes into account the brightness of the person illuminated by the flash. Therefore, by determining the exposure state of the film image using the normalized average value, there is an advantage that the exposure state can be determined with an emphasis on the person (main subject).

In the above embodiment, the reference maximum value and the average value are switched and used, but the present invention is not limited to this, and the exposure of the film image is selected from the reference maximum value, the reference minimum value and the average value. It is also possible to appropriately select a value that increases the accuracy of determining the exposure state of the film image according to the state and determine the exposure state of the film image based on the selected value.

As information obtained from the film image for determining the exposure state of the film image, a value obtained by averaging a plurality of reference maximum values obtained by photographing the same film image a plurality of times (in FIG. 4). (Refer to the line graph shown by ◆)
May be used. In this case, the reference maximum value can be obtained with high accuracy even for an underexposed film image, so that the exposure state of the film image can be accurately determined. The exposure state of the film image may be determined by using not only the averaged reference maximum value but also the averaged reference minimum value, the averaged average value of the film image, and the like.

On the other hand, the soft and hard tones of the film image
The judgment is made by the ratio of the reference maximum value and the reference minimum value (hereinafter, the brightness ratio
Based on). That is, the brightness ratio G of G_max/ G
_minAnd a predetermined threshold Th that indicates a high contrast₁And places that exhibit a soft tone
Constant threshold Th₂Compare with. And the brightness ratio G_max/
G_minIs the threshold Th₁In the following cases, it is regarded as a high contrast and the brightness
Ratio G_max/ G_minIs the threshold Th₂If it is above, it is considered to be soft
Eggplant Here, the threshold Th₁And threshold Th₂Is the standard
This is set for the negative image that was judged to be exposed.
Is judged to be overexposure or underexposure described above.
For the negative image, the threshold Th₁And threshold Th₂
Threshold values Th that are set lower than _ThreeAnd threshold Th
_FourThe condition is determined based on.

Further, the electronic shutter value T ₂ is determined by using the maximum value Dmax obtained from the simple histogram, and the maximum value at the time of fine scanning described later is a predetermined value (for example, 8).
In the case of a bit system, the electronic shutter value T ₂ is determined so as to be 255). That is, the electronic shutter value T ₂ is given by

[0036]

## EQU3 ## Determined by T ₂ = 255 * T ₁ / Dmax (3). Here, T ₁ is an electronic shutter value at the time of prescan. Next, the reference maximum values R _max, G _max , B _max and the reference minimum value R _min, obtained for each of R, G, and B.
G _min and B _min are corrected based on the exposure state, the tone determination result, and the electronic shutter value T ₂ (step S2).
4).

First, when it is determined that the tone is hard or soft by the tone determination, in a negative image of standard exposure, overexposure is performed so that the brightness ratio G _max / G _min falls within the range of the threshold Th ₁ to the threshold Th _1. Alternatively, in a negative image of underexposure, the luminance ratio G _max / G _min is the threshold value Th ₃ to the threshold value T.
At least one of the reference maximum value G _max and the reference minimum value G _min is corrected so as to fall within the range of h ₄ . The reference maximum value R _max, B _{ma x} and the reference minimum value R _min, B _min
Is corrected corresponding to the correction of the reference maximum value G _max and the reference minimum value G _min . When the brightness ratio is within the range of the threshold value, the reference maximum value and the reference minimum value are not corrected. Further, in this embodiment, the tone determination of soft tone, hard tone, etc. is performed based on the ratio between the reference maximum value and the reference minimum value, but the present invention is not limited to this, and the difference between the reference maximum value and the reference minimum value. The condition may be determined based on the.

Next, during fine scanning, the exposure amount becomes T ₂ / T ₁ times larger than during prescanning, so the amount of change in the electronic shutter value during prescanning and fine scanning is the reference maximum value and reference value. Correct the minimum value. In this way, the offset and white balance gain (WB gain) used for adjusting the white balance and the black balance are determined based on the reference maximum value and the reference minimum value finally obtained (step S25).

That is, the CPU 40 calculates the offset for each R, G, B based on the finally obtained reference maximum value by the following equation:

[0040]

[Equation 4] Offset = 255−G _max (4) The gain for each of R, G and B is calculated based on the reference maximum value and the reference minimum value by the following equation,

[0041]

WB gain = 255 / (G _max −G _min ) ... (5) The expressions (4) and (5) relate to G, but other color channels are calculated in the same manner. In step S25, the R, G, and B gamma gains are determined based on the exposure state of the negative image, the details of which will be described later.

Next, a fine scan of the negative image is executed based on the electronic shutter value T ₂ , offset, WB gain and gamma gain determined above (step S30). That is, at the time of fine scanning, the electronic shutter value of the CCD line sensor 14 is set to T ₂ , the film 52 is conveyed at a constant speed, and the film image is scanned (fine scanning). During this fine scan, the CCD line sensor 14 and the analog amplifier 16
Also, dot-sequential R, G, B digital image signals are output to the digital signal processing circuit 20 via the A / D converter 18.

Next, the signal processing in the digital signal processing circuit 20 will be described. A / during fine scan
For the original G _org output from the D converter 18, the following equation,

[0044]

[ _Equation 6] G1 = G _org + offset (6) By adding the G offset, the digital image signal G1 with the black point offset can be obtained. By performing the same processing on the R and B originals, the peak values of the R, G, and B digital image signals (black of the positive image) are matched (see FIG. 5A).

Then, for the offset digital image signal G1, the following equation:

[0046]

## EQU00007 ## Negative-positive inversion is performed by executing the calculation of G2 = 255-G1 (7) (see FIG. 5B). Next, by multiplying the negative-positive inverted digital image signal G2 by the WB gain obtained by the equation (5) as shown in the following equation,

[0047]

## EQU00008 ## G3 = G2.times.WB gain (8) The other peak values (white of the positive image) of the R, G, B digital image signals are matched (see FIG. 5C). Finally, different gamma corrections are performed on the R, G, and B digital image signals multiplied by the 5B gain, so that grays are matched (see FIG. 5D).

Next, the gamma correction will be described in more detail. First, a lookup table (hereinafter referred to as a base LUT) that serves as a reference when performing gamma correction is prepared. This base LUT stores a gamma correction value for each gradation, which indicates the difference between the gamma curve of a negative film and the gamma curve of a video signal output to a cathode-ray tube (generally γ = 0.45). Has been done. An actual look-up table (hereinafter, referred to as an actual LUT) showing the input / output characteristics is a function y as shown in FIG.
= X minus the base LUT (gamma correction value).

The base LUT can be changed by multiplying the base LUT by the gamma gain (see FIG. 6B). Thus, by multiplying an appropriate gamma gain from one base LUT, it is possible to obtain an LUT in which the gamma correction value is expanded or compressed for each of R, G, and B. Note that FIG. 6C shows the function y
= X obtained by subtracting the LUT in which the gamma correction values are expanded or compressed for R, G, and B, respectively,
It is an actual LUT for each of G and B.

Therefore, when the white balance and the black balance are adjusted by the above-mentioned equations (6) to (8) and the gamma correction is performed on the negative-positive inverted dot-sequential R, G, B digital image signals, Gamma correction values are sequentially read out from the base LUT based on dot-sequential R, G, B digital image signals, and the gamma correction values are multiplied by R, G, B gamma gains and expanded or compressed as appropriate. Is obtained, and the gamma correction value expanded or compressed for each color is subtracted from the dot-sequential R, G, B digital image signal to perform the gamma correction for each color in the dot sequence.

The gamma gain for each of R, G, and B is set in advance according to the gradation characteristic of the negative film of standard exposure, but as shown in FIG. The gradation characteristics of different negatives are different, and the difference is shown in FIG.
The gamma characteristics are also different as shown in. Therefore, FIG.
As shown in, it is necessary to change the base LUT according to the negative exposure amount.

Therefore, the gamma gain (R _{ga mgain,} G _gamgain, B) for _each color is utilized by utilizing the determination result of the exposure state of the negative image.
_gamgain ) is changed according to the exposure state, and gamma correction is performed according to the exposure state of the negative image. That is, when the negative image is determined to be underexposed, the gamma gain is made smaller than the gamma gain of standard exposure, while when it is determined to be overexposed,
The gamma gain is set to be larger than the gamma gain of standard exposure, and the tone is adjusted accordingly.

FIG. 8 is a block diagram including the internal configuration of the digital signal processing circuit 20 shown in FIG. The digital signal processing circuit 20 performs the digital signal processing described above, and mainly includes adders 21, 22, 24, a multiplier 23,
26 and a base LUT 25. The adder 21 includes a dot-sequential R,
G, B digital image signal CMPAD is input. The digital image signal CMPAD flows in time series R, G, B, G according to a predetermined clock.

On the other hand, the CPU 40 uses the equations (4) and (5).
As shown in, the offset (R _offset,
G _offset , B _offset ) and WB gain (R _wbgain, G
_wbgain , B _wbgain ) is calculated and stored, and R,
_Gamma gain (R _{ga mgain,} G _gamgain, B
_gamgain ) is remembered. Further, these offsets and the like are stored for each frame. Then, an offset or the like corresponding to the frame to be scanned is selected by the address decoder 42, and the R, G, B offsets are registered by the registers 43R, 43G, 4 by INTDATA in FIG.
3B, the gains of R, G and B are stored in the register 44.
It is stored in R, 44G, 44B, and the gamma gains of R, G, B are stored in the registers 45R, 45G, 45B.
Incidentally, these registers hold the R, G, B digital image signals for one frame until they are processed.

The offsets (R _offset, G _{offs et} , B _offset ) stored in the registers 43R, 43G, 43B are added to the multiplexer 46, and the multiplexer 4
Timing signals INTCOLSL0, 1 generated by dividing the frequency of the predetermined clock are applied to the other inputs of the reference numeral 6. The multiplexer 46 uses the timing signal INTCOLSL
One of the three offsets is selected by 0 and 1, and the selected offset is output to the other input of the adder 21 of the digital signal processing circuit 20.

Similarly, the multiplexer 47 _selects one of the three WB gains (R _wbgain, G _wbgain , B _wbgain ) input from the registers 44R, 44G, 44B and selects the selected WB gain. Multiplier 23
To the register 45.
Any one gamma gain is selected from the three gamma _gains (R _gamgain, G _gamgain, B _gamgain ) input from R, 45G, and 45B, and the selected gamma gain is output to the multiplier 26.

On the other hand, as described above, the digital image signal CMPAD is input to the adder 21, and the adder 21 adds the digital image signal CMPAD and the offset. As a result, a digital image signal with a black point offset is obtained (equation (6), see FIG. 5A). The black-dot-offset digital image signal output from the adder 21 is added to the negative input of the adder 22, and the positive input of the adder 22 is added with a value (255) indicating the white peak level. The device 22 subtracts the black-point-offset digital image signal from 255. As a result, a negative-positive inverted digital image signal is obtained (see formula (7) and FIG. 5B).

Subsequently, the negative-positive inverted digital image signal is added to the multiplier 23. The WB gain is applied to the other input of the multiplier 23 from the multiplexer 47, and the multiplier 23 multiplies the two inputs to obtain R,
The whites of the positive images of the G and B digital image signals are matched (see equation (8) and FIG. 5 (C)). Next, the digital image signal output from the multiplier 23 is added to the adder 24 and the base LU.
Added to T25. The base LUT 25 is shown in FIG.
As shown in FIG. 3, it has a gamma correction value corresponding to the gradation of the input signal, reads the gamma correction value corresponding to the gradation of the input digital image signal, and uses this gamma correction value in the multiplier 2
6 is output. To the other input of the multiplier 26, a gamma gain according to the exposure state of the negative image (smaller as the exposure state of the negative image becomes smaller, and larger as the exposure state of the negative image becomes larger) is applied from the multiplexer 48 to the multiplication. The device 23 multiplies the two inputs to generate a gamma correction value for each color of the R, G, B digital image signals, and outputs this to the negative input of the adder 24.

The adder 24 subtracts the expanded or compressed gamma correction value for each color from the input R, G, B digital image signals. With this, gamma-corrected regular R,
G, B digital image signals RGBG _gam are obtained. still,
The gamma correction method is based on the base LUT shown in this embodiment.
The method is not limited to the above method, and any method may be used as long as it is a gamma correction method that allows variable gamma. For example, a plurality of gamma correction LUTs corresponding to the exposure state of the negative image are provided, and an optimum LUT is selected from the plurality of gamma correction LUTs based on the determination result of the exposure state of the negative image.
Gamma correction may be performed using the selected LUT.

Next, image processing that enables good color reproduction
For the method, refer to the flowchart shown in FIG.
Will be described. First, prescan is executed (step S
110), a simple histogram (see Fig. 3) is created and
Semi-minimum value R_min,G_min, B_minAnd reference maximum value R
_max,G _max, B_maxIs calculated (step S112).
The processing up to this point is shown in the flowchart of FIG.
Since it is similar to the processing, detailed description thereof will be omitted.

Next, from the reference maximum values R _max, G _max , and B _max obtained as described above, the ratio X and Y of each reference maximum value is calculated by the following equation: X = R _max / G _max Y = B _{It is} determined by _max / G _max (step S114). Then, based on these ratios X and Y, the variation of the reference maximum value for each color is
It is determined whether or not it is within a predetermined range in which desired white balance adjustment is possible (step S116).

That is, when the color ferria detection frame is set as shown in FIG. 10 and the coordinates in FIG. 10 determined by the ratios X and Y deviate from this color ferria detection frame, it is determined that it is a color ferria scene. To do. Then, when it is judged that the scene is a color ferria scene, the reference maximum value R of R and B
_{The max and} B _max are corrected so as to be close to the G reference maximum value G _max , and the R and B reference minimum values R _min and B _min are corrected.
Is corrected so as to approach the G reference minimum value G _min (step S118).

In this step S118, for example, the reference ratios for the ratios X and Y are set to X _ref = K1 and Y, respectively.
_{If ref} = K2, the reference maximum values R _max, B of R _and B
_max is corrected to R _max ′ _and B _max ′ shown in the following equations, respectively. R _max ′ = K1 * G _max B _max ′ = K2 * G _max The reference minimums 1 R _min and B _min are similarly corrected. That is, the reference minimum values R _min and B _min of R and B are respectively
Based on the predetermined reference ratios K3, K4 and the reference minimum value G _min of G, R _min ′ and B _min ′ shown in the following equations are corrected.

R _min ′ = K3 * G _min B _min ′ = K4 * G _min Next, when it is determined that a color ferria scene is used, it is determined that the corrected reference minimum value and reference maximum value are used, and it is not a color ferria scene. , The offset and the white balance gain (WB gain) used to adjust the white balance and the black balance by the above equations (4) and (5) using the reference minimum value and the reference maximum value obtained in step S112 as they are. Is determined (step S120).

Next, the determined offset and WB
Fine scan of the negative image is executed based on the gain (step S122). That is, at the time of fine scanning, the film 52 is conveyed at a constant speed to scan the film image (fine scanning) (step S).
122). During this fine scan, the CCD line sensor 14, the analog amplifier 16 and the A / D converter 1
To the digital signal processing circuit 20 via 8
G and B digital image signals are output.

In this embodiment, whether or not to correct the reference maximum value and the reference minimum value is determined based on the ratio of the reference maximum value for each color. However, the present invention is not limited to this, and it is not limited to this. It is also possible to determine the difference between the reference maximum values of and determine whether or not to correct the reference maximum value and the reference minimum value from this difference. Further, instead of the reference maximum value, the reference minimum value may be used to perform the same determination as above. Further, in this embodiment, both the reference maximum value and the reference minimum value are corrected, but either the reference maximum value or the reference minimum value may be corrected. Further, the reference maximum value and the reference minimum value of R and B are corrected so as to approach the reference maximum value and the reference minimum value of G. However, the present invention is not limited to this, and the reference maximum value and / or each color of each color is corrected. Any method may be used as long as it is a method of correcting another reference minimum value so that each value approaches each other.

[0067]

As described above, according to the image processing method of the present invention, when the image processing is performed based on the reference maximum value and the reference minimum value of the image signal obtained when the film image is captured, Since image processing is performed according to the exposure state, good tone reproduction is possible. In particular, if the reference maximum value or the reference minimum value is used for the determination of the exposure state of the film image, the load of the circuit and software required for the determination of the exposure state can be minimized, and the determination of the exposure state can be simplified. It can be carried out. In addition, the exposure state of the film image is determined based on an average value of a plurality of reference maximum values obtained by imaging a plurality of times, or the film image is exposed from the reference maximum value, the reference minimum value, and the average value of the film image. A value with high accuracy in determining the state is appropriately selected according to the exposure state of the film image, and the exposure state of the film image is determined based on the selected value. Can determine the exposure state with high accuracy. Furthermore, since the reference maximum value and the like are normalized based on the average value of the image signal obtained when the unexposed portion of the film is imaged, the film is not affected by the density of the film base or the amplifier gain. The exposure state of the image can be determined.

Further, according to the present invention, when the exposure state of the film image is underexposure, the gamma at the time of gamma correction is made small, and at the time of overexposure, the gamma is made large, so that at the time of underexposure and overexposure. The halftone brightness of can be adjusted appropriately. Also, the ratio or difference between the reference maximum value and the reference minimum value of the film image is
At least one of the reference maximum value and the reference minimum value is corrected so as to fall within the range of the first and second threshold values set in advance, thereby adjusting the tone of the hard-tone image and the hard-tone image. When the exposure state of the film image is underexposed or overexposed, the first and second threshold values are changed to the third and fourth threshold values respectively lower than them, so that the tone of the film image changes unnaturally. No, you can reproduce good tone.

Further, according to the present invention, even in a color feria scene in which there is an extremely high saturation area and the reference maximum value and the reference minimum value for each color vary greatly, In this case, since the variation of the reference maximum value and / or the reference minimum value for each color is corrected, desired white balance adjustment becomes possible, and good color reproduction can be realized.

[Brief description of drawings]

FIG. 1 is a principal block diagram showing an embodiment of a film scanner to which the present invention is applied.

FIG. 2 is a flowchart used to explain an image processing procedure in the film scanner shown in FIG.

FIG. 3 is a histogram used for explaining how to obtain a reference maximum value and a reference minimum value.

FIG. 4 is a line graph showing a reference maximum value and an average value corresponding to an exposure state of a film image.

5A to 5D are graphs showing processing contents in respective units of the digital signal processing circuit of FIG. 1, respectively.

6A to 6C are graphs used to describe an example of a gamma correction method.

FIGS. 7A to 7C are graphs showing negative tone characteristics, gamma characteristics, and base LUT of different exposure states.

FIG. 8 is a block diagram showing a detailed configuration of the digital signal processing circuit of FIG.

9 is a flowchart used for explaining another image processing procedure in the film scanner shown in FIG.

FIG. 10 is a graph used for explaining discrimination of a color ferria scene and the like.

FIG. 11 is a graph showing a characteristic curve of a negative film.

FIG. 12 is a histogram of R, G, and B when the reference minimum value of B is extremely larger than the reference minimum values of other colors.

[Explanation of symbols]

 10 ... Light source 12 ... Photographing lens 14 ... CCD line sensor 15 ... CCD drive circuit 18 ... A / D converter 20 ... Digital signal processing circuit 21, 22, 24 ... Adder 23, 26 ... Multiplier 25 ... Base LUT 40 ... Center Processor (CPU) 41 ... Accumulation block 50 ... Film cartridge 52 ... Negative film

Claims (13)

[Claims] 1. A film image imprinted on a developed photographic film is taken, and a reference maximum value and a reference minimum value, or a reference maximum value, a reference minimum value and an average value of the image signal obtained at the time of the image pickup are obtained. An exposure state of the film image is determined based on at least one of the obtained reference maximum value, reference minimum value and average value, and image processing is performed based on the reference maximum value and reference minimum value and the determination result. An image processing method comprising: 2. As the reference maximum value, reference minimum value or average value for determining the exposure state of the film image,
2. The image processing method according to claim 1, wherein a value obtained by averaging a plurality of reference maximum values, a plurality of reference minimum values, or a plurality of average values obtained by capturing the same film image a plurality of times is used. 3. A value having a high determination accuracy of the exposure state of the film image is appropriately selected from the obtained reference maximum value, reference minimum value and average value according to the exposure state of the film image, and based on the selected value. 2. The image processing method according to claim 1, wherein the exposure state of the film image is determined. 4. When the obtained reference maximum value is equal to or higher than a value that guarantees the determination accuracy of the exposure state of the film image based on the reference maximum value, the average value is used instead of the reference maximum value. The image processing method according to claim 1, wherein an exposure state of the film image is determined. 5. When all gradation data for one frame is obtained from the image signal obtained at the time of image pickup, and all gradation data for one frame is counted for each gradation to create a histogram. , A simple histogram with a predetermined frequency as an upper limit is created, and the reference maximum value is a point at which the cumulative frequency counted from the larger gradation of the simple histogram exceeds a predetermined ratio with respect to the total score of the gradation data. The reference minimum value is obtained based on a point where the cumulative frequency counted from the smaller gradation of the simple histogram exceeds a predetermined ratio with respect to the total score of the gradation data. The image processing method according to claim 1, which is characterized in that. 6. The grayscale data is average grayscale data in an area divided in units of a plurality of pixels.
Image processing method. 7. Before capturing the film image, an unexposed portion of the developed photographic film is captured in a predetermined exposure state, and an image signal obtained when capturing the unexposed portion has a predetermined signal level. 2. The image processing method according to claim 1, wherein the predetermined exposure state is corrected so that the film image is captured in the corrected exposure state. 8. The reference maximum value, reference minimum value, or average value for determining the exposure state of the film image is normalized based on the average value of image signals obtained at the time of capturing the unexposed portion. The image processing method according to claim 1, wherein 9. A reference maximum value and a reference minimum value of an image signal obtained by picking up a film image are obtained, and the image signal is corrected so that the reference maximum value and the reference minimum value have predetermined gradations, respectively. Along with, in an image processing method for gamma correction, the exposure state of the film image is determined, and if underexposure is determined based on the determination result of the exposure state, the gamma at the time of gamma correction is made smaller than that at the time of standard exposure, An image processing method characterized in that, when it is determined that overexposure, gamma at the time of gamma correction is made larger than that at standard exposure. 10. A reference maximum value and a reference minimum value of an image signal obtained by capturing a film image are obtained, and a ratio or a difference between the reference maximum value and the reference minimum value is set in advance so that a desired tone is obtained. At least one of the reference maximum value and the reference minimum value is corrected so as to fall within the range between the set first threshold value and the set second threshold value, and the corrected reference maximum value and reference minimum value are respectively predetermined floors. In the image processing method for correcting the image signal so as to obtain a gradation, the exposure state of the film image is determined, and when it is determined as underexposure or overexposure based on the determination result of the exposure state, the first threshold value and An image processing method, wherein the second threshold value is changed to a third threshold value and a fourth threshold value which are lower than the first threshold value and the second threshold value, respectively. 11. The exposure state of the film image is determined based on at least one of the reference maximum value, the reference minimum value, and the average value of the image signal. Image processing method. 12. A color image is picked up to obtain an image signal for each color, a reference maximum value and a reference minimum value of the image signal for each color obtained at the time of picking up are obtained, and a ratio of the reference maximum value for each color or The difference or the ratio or difference of at least one of the reference minimum values of the respective colors or the difference is obtained, and it is determined whether or not the obtained ratio or difference is within a predetermined range in which desired white balance adjustment is possible. However, when the obtained ratio or difference exceeds the above range,
The reference maximum value for each color and / or the reference minimum value for each color are corrected so that the values are close to each other, and when the obtained ratio or difference does not exceed the range, the reference maximum value before correction is set. When the image signal is corrected so that the value and the reference minimum value are each a predetermined gradation, and the obtained ratio or difference exceeds the range,
An image processing method, characterized in that the image signal is corrected so that the corrected reference maximum value and reference minimum value have predetermined gradations. 13. The image signal for each color is an R, G, B image signal, and when the obtained ratio or difference exceeds the range, the reference maximum value and / or the reference minimum value of G are set. 13. The image processing method according to claim 12, wherein the reference maximum value and / or the reference minimum value of another color is corrected so as to approach the value.