JPS6181075A - Method for processing picture signal - Google Patents

Abstract

PURPOSE:To prevent a change in input/output characteristic even after level processing and tilt processing by making the level processing or tilt processing of picture signal characteristic prior to nonlinear processing when making nonlinear processing of picture signal characteristic and level processing or tilt processing of picture signal characteristic. CONSTITUTION:Digital picture signals N are subjected to tilt processing, level processing and nonlinear processing respectively by conversion tables 1, 2, 3. An output of the conversion table 3 modulates light from a light source 6 through a light modulator 5, and a hard copy of a picture is obtained by a film 7. When changing the tilt of density gradation of a head copy, a changeover switch element S1 is connected to a contact S1b, S2 to S2b, S3 to S3b respectively, and switch elements S4, S5, S6 are turned on. By connecting contacts S1b, S2b, S3b, conversion tables 1, 2, 3 are connected to an address line, and the contents of conversion tables 1, 2, 3 are rewritten according to data signals DT from a data line by on of the switch elements S4, S5, S6.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention performs nonlinear processing of image signal characteristics, and also performs level processing and/or slope processing. / Image signal processing that performs nonlinear processing on image signals to obtain specific density gradation characteristics when obtaining a dark copy, as well as processing to increase/decrease the overall density level and processing to adjust the slope of density gradation. It is about the method.

[Prior Art] For example, when performing image diagnosis using a hard copy of a medical photograph, if the image density and gradation are not appropriate, important diseased areas may be overlooked or misdiagnosed.

The gradation characteristics of a hard copy of an image are HD with silver halide film.
This characteristic is known as the VD characteristic in electrophotography. In general, the relationship between image signals and hard copy density is not a linear relationship due to the influence of nonlinear characteristics. However, a linear relationship can be obtained by using only the portion of the HD or VD characteristics with good linearity. However, the dynamic range of density is narrowed, resulting in a hard copy with poor contrast.

For this reason, conventionally, the image signal is subjected to non-linear processing with the HD characteristic or the inverse characteristic of the VD characteristic, so that a linear relationship (response) can be obtained. Also, 11' from the CRT.
When photographing a hard copy, after nonlinear processing is performed, level processing is performed using brightness adjustment to change the overall density of the hard copy, and slope processing is performed using contrast adjustment to change the slope of the linear relationship. However, if the above-described level processing or slope processing is performed after such nonlinear processing, the linear relationship between the image signal and the hard copy density will collapse again.

FIG. 3 shows an example of a conventional installation, in which the 0 image signal N, which is a device that processes the digitized image signal N and obtains a hard copy by optical modulation, is installed in a ROM (Read Only).
Memory) or RAM (Random Ac
After non-linear processing is performed as an output V by a conversion lookup table 11 consisting of cessMemory), it is converted into an analog signal by a D/A converter 12, and an amplifier consisting of an operational amplifier 13, a resistor R1, variable resistors VRI and VR2 calculates the slope. The processing is done and the configuration is made up of an operational amplifier 14 and variable resistors VR3 and VR4 gi677:r<
, eu v<le's*b<ftgn-c511:'1m
IF device 15 is driven. The light emitted from the light source 16 is modulated by the optical modulator 15 as an exposure start signal according to the output signal of the operational amplifier 14, and the film 17 is exposed. Note that slo and Sll are switch elements that select preset values for variable resistors VRI, VR2, VR3, and VR4 and perform slope processing and level processing, respectively. is unrelated.

Here, the image signal N is not limited to a digital signal.

If the conversion table 11 is configured with an analog circuit, it becomes possible to use an analog signal for the image signal N, and the D/A converter 12 is not required. However, it is not easy to realize specific nonlinear characteristics with an analog circuit. Further, the output of the operational amplifier 14 can be applied to a CRT or the like instead of the optical modulator 15, and the film 17 may be an electrophotographic photoreceptor.

FIG. 4 shows the signal and concentration characteristics in the example of FIG.
The characteristic of the optical modulator 15 is a straight line, where N is the input image signal, ■ is the signal after nonlinear processing, D is the logarithm of the exposure amount, and D is the hard copy density. Conversion table 1
1 to the second quadrant, D/A controller 8 to 12, operational amplifier 13.14. Assuming that the characteristics of the entire optical modulator 15 are in the first quadrant and the HD characteristics of the film 17 are in the second quadrant, the relationship between the input image signal N and the output density is shown in the second quadrant. However, for the sake of simplicity, the HD# property ignores the fog density.

If this HD characteristic is approximated as an arbitrary nonlinear function f (I), it can be expressed as D=f (I) (1). Here, if N=f(V)...(2), the V/I characteristic in the Ⅰ quadrant is a straight line, so I=V...(3
), and equation (1) is.

D=f(V)...(4), and from equations (1) and (4), D=N...(5),
Therefore, the conversion table 11 has the characteristics as shown in equation (2),
That is, it is sufficient to store conversion data having characteristics opposite to the HD characteristics of the film 17.

The explanation so far corresponds to FIG. 4(a), where the input value Nl of the image signal N is converted to Vl by the conversion table 11,
It becomes an exposure layer Il in the D/A converter 12, operational amplifiers 13 and 14, and optical modulator 15, and becomes a density D1 on the film 17. This can be intuitively understood because if the first and second quadrants are symmetrical in FIG. 4(a), then the first quadrant will be symmetrical with the second quadrant.

Here, if the variable resistor VR3 is adjusted in an attempt to raise the overall density level of the film 17, the equation (3) becomes r=v+Ar (6), where Δ is the adjustment amount.
(1) Equation is.

D=f(V+ΔI)...(7),
Since f (V) is non-linear, there is no longer a linear relationship between the image signal N and the resulting hard copy density.

FIG. 4(b) shows this, and variable resistor VR3
By adjusting the V/r characteristic, the output 2 with respect to the input V2 increases as shown by the broken line, and the N/D characteristic also increases nonlinearly as shown by the broken line and is no longer a straight line. This means that the V/I characteristic becomes like the broken line.
This is equivalent to moving the D-V axis by AI like the D'-V' axis, and since the symmetry of the H quadrant and the This can also be understood from the fact that the 1st and 2nd quadrants are no longer symmetrical.

Similarly, when variable resistor VRI is adjusted in an attempt to increase the slope of the gradation characteristics of the film 17, equation (3) becomes I=C・V (8), where the slope adjustment value is C.
Equation 1) is D=f(CΦV) (9). f
Since (V) is nonlinear, a linear relationship in N/D characteristics cannot be obtained. FIG. 4(C) shows this, and the V/I characteristic when the variable resistor VRI is adjusted becomes as shown by the broken line. In this case, D-
This is equivalent to the V axis and I-N axis being tilted, and the tilted D''
−■” axis.

This can be similarly understood from the fact that for r"-N" Tsukuda 1111, the symmetry between the H-th quadrant and the male quadrant breaks down, so the 1st &nd and 2nd quadrants are also no longer symmetrical, and the input image signal value N3 A nonlinear density D3 corresponding to is obtained.

In addition, FIG. 4(d) shows the characteristics of all the conversion table 11, D/A converter 12, operational amplifier 13, 14, and optical modulator 15 in the fourth nail quadrant, and adjusts the variable resistor VR3 to
This is a case of level processing of the I characteristic, and from this (d), the symmetry of the 2nd quadrant and the 2nd quadrant breaks down, and the input image signal value N
It can be understood that the concentration for 4 becomes D4 from Dl, and the N/D characteristic is no longer a straight line.

As described above, the conventional apparatus has a major drawback in that when level processing and slope processing are performed, the characteristics of the density of the input image signal and the output bird copy change.

[Object of the Invention] An object of the present invention is to provide an image signal processing method that eliminates the drawbacks of the above-mentioned conventional apparatus and in which the input/output characteristics do not change even when level processing and slope processing are performed.

[Summary of the Invention] The gist of the present invention for achieving the above-mentioned object is that, when performing nonlinear processing of image signal characteristics and level processing or slope processing of image signal characteristics, prior to performing the nonlinear processing, the This is an image signal processing method characterized by performing level processing and/or slope processing of signal characteristics.

[Embodiments of the Invention] The method according to the present invention will be explained in detail based on the embodiments illustrated in FIGS. 1 and 2.

FIG. 1 shows a configuration example for implementing the method according to the present invention, in which 1, 2, and 3 are conversion lookup tables each consisting of a RAM, conversion table 1 is for slope processing, and conversion table 2 is for level processing. The second conversion table 3 is for nonlinear processing. Changeover switch elements S1, S2, and S3 are provided on the input side of each conversion table 1.2.3, respectively, and changeover switch element S1 receives the image signal N and the address ID number d from the address line of the microcomputer. The changeover switch element S2 switches between the output of the conversion table 1 and the address signal An, and the changeover switch element S3 switches between the output of the conversion table 2 and the 7 address signal AD. There is. Further, the contents of each conversion table 1, 2, and 3 can be rewritten into a data signal DT from a data line of the computer, and each data line is provided with switch elements S4, S5, and S6, respectively. The output from the conversion table 3 is connected to a light modulator 5 via a D/A converter 4, and is configured to modulate the light emitted from the light source 6 and expose the film 7.

When taking a hard copy of the image, the changeover switch element Sl is connected to the contact Sla, S2 is connected to the contact S2a, and S3 is connected to the S3a side, and the switch elements S4, S5, and S6 are turned off. The digital image signal N is subjected to slope processing, level processing, and nonlinear processing using conversion tables 1.2° and 3! is done, and the output of conversion table 3 is D/
The light from the light source 6 is modulated through the A converter 4 and the light modulator 5, and a hard copy of the image is made 911 on the film 7.

When changing the slope of the density gradation of the hard copy, when changing the density level, and when changing the characteristics of nonlinear processing, changeover switch element S1 is connected to contacts Slb and Slb, respectively.
2 to S2b and S3 to S3b, and turn on switch elements S4, S5, and S6, respectively. Contact Slb
, S2b, S3b, the translation table 1.2.3 is connected to the address line.

By turning on the switch elements S4, S5, S6, the conversion tables 1, 2, .
The contents of 3 will be rewritten. In the embodiment shown in FIG. 1, it is also possible to drive a CRT by the output of the D/A converter 4, as in the case shown in FIG. 3, and the film 7 may be an electrophotographic film.

Figure 2 shows the relationship between the signal and IIa degree in this case, and (a), (b), and (c) are the 4th degree, respectively.
This corresponds to FIGS. 11(a), (b), and (c). N, engineering, and D are the same as in the case of FIG. 4, and in the embodiment of FIG. - to 4° If it is assumed that the optical modulator 5 has linear characteristics, it is equivalent to M and can be omitted.

In the conventional apparatus explained in FIGS. 3 and 4, the level processing and slope processing are performed after the nonlinear processing, so the characteristics of the nonlinear processing are in the Since this is done after processing and slope processing, the characteristics of level processing and slope processing can be written in quadrant (2) of FIG. 2, and the characteristics of nonlinear processing can be written in quadrant (2).

In this case, equation (1) is the same as before, and equation (2) is the characteristic of conversion table 1.2, where M=f (1) ... (lO), that is, N7M in the second quadrant.
Since the characteristic is a straight line, M=N...(11), and from equations (1), (10), and (11), equation (5) holds, that is, D=N...(12). do.

In FIG. 4, which shows a conventional example, the r-th quadrant and the
In the diagram, the ■quadrant and the ■quadrant, and the ■quadrant and the ■quadrant are symmetrical, respectively. Therefore, no matter how you change the 2nd quadrant, the linear symmetry of the 2nd quadrant and the 2nd quadrant with respect to the I-N axis does not change, so the r-th quadrant is
It can be intuitively understood from FIG. 2(a) that there is line symmetry with respect to the N-axis.

Here, rewrite the contents of conversion table 2 to create film 7.
When trying to increase the concentration level of
・(13), and from equations (1), (1o), and (13), D=N+ΔM...(14) However, the unit system as a physical quantity is not considered here.

That is, as shown in FIG. 2(b), N7 in the
The M characteristic changes as shown by the broken line, and the output signal M2 is increased by ΔM compared to the image signal Nl, resulting in a nonlinear M characteristic in the second quadrant.
Due to the /I characteristic, the exposure amount becomes ■2, and furthermore, due to the HD characteristic of the quadrant ■, which is line-symmetrical to the M/I characteristic, it is more than Dl! lI
An increased moisture level D2 is obtained, and a linear relationship is maintained in the N/D characteristics.

Similarly, when trying to increase the slope of the density gradation of film 7 by rewriting the contents of conversion table 1, equation (11) becomes M=C・N (15), where the adjustment amount is C.
From equations (1), (10), and (15), D=C@
N...(16) is obtained. This case is shown in Figure 2(c), where N7M
Even if the slope of the characteristic changes as shown by the broken line, the image signal Nl is converted from old → signal H3 → exposure amount adjustment 3 → density D3, and N/
It can be seen that the Da properties are similarly maintained in a linear relationship.

Also, if both the level and slope are changed, formula (11) % formula %
(17), and from (1), (IQ), and equation (17), D=
C@N+AM...(18)
becomes. This case is shown in Fig. 2(d), and even if the N7M characteristic changes both in level and slope in quadrant ①,
The image signal N4 is converted as follows: old→signal M4→exposure 114+density D4, and the N/D characteristics have a linear relationship.

Therefore, if the processing shown in equation (17) is performed using one conversion lookup table, the level processing and slope processing can be performed using the same conversion lookup table, and the conversion tables 1 and 2 can be combined into one.

In the above embodiment, the optical modulator 5 has a linear characteristic, but an acousto-optic element etc. does not have a linear characteristic. In this case, the conversion lookup table 3 for nonlinear processing
It is sufficient to combine the D characteristic and the characteristic of the acousto-optic element, and input the inverse characteristic.

Furthermore, it is also possible to separately provide a conversion table for the inverse characteristics of the HD characteristics and a conversion table for the inverse characteristics of the acousto-optic element characteristics.

In addition, although the above embodiment describes an example in which nonlinear processing is corrected to linear characteristics, the output can have any characteristics.
Due to the symmetry in FIG. 2, the output of the 1st quadrant becomes symmetrical with the characteristics of the 2nd quadrant. Therefore, the present invention is not only applicable to making hard copies of images, but has a wide range of applications.

[Effects of the Invention] As explained above, according to the image signal processing method according to the present invention, it is possible to arbitrarily adjust the level and slope of image signal characteristics without changing the characteristics obtained by nonlinear processing. can. Furthermore, if the level processing and slope processing are performed using a rewritable conversion lookup table, it is possible to perform the processing without increasing the hardware.

[Brief Description of the Drawings] FIGS. 1 and 2 show an embodiment of the image signal processing method according to the present invention, and FIG. 1 is a block circuit diagram for realizing the method, and FIG. Figures 2 (a) to (d) are relationship diagrams between the signals and density, Figure 3 is a block circuit diagram of a conventional image signal processing device, and Figures 4 (a) to (d) are diagrams showing the relationship between the signals and density. FIG. 3 is a relationship diagram between signals and concentrations. 1.2.3 is a conversion lookup table, 4 is D/
A converter, 5 is a light modulator, 6 is a light source, and 7 is a film. Patent Applicant Canon Co., Ltd. Agent Patent Attorney Masaru Hibiya. (Knee 2-1 Figure 1 Figure 2 (G) Figure 4 Figure 4

Claims (1)

[Claims] 1. In the case of performing nonlinear processing of image signal characteristics and level processing or slope processing of image signal characteristics, prior to performing the nonlinear processing, level processing of the image signal characteristics or (
and) an image signal processing method characterized by performing tilt processing. 2. The image signal processing method according to claim 1, wherein the nonlinear processing corrects the HD characteristics of a silver halide film or the VD characteristics of an electrophotograph. 3. The image signal processing method according to claim 1 or 2, wherein the nonlinear processing corrects characteristics of an acousto-optic element. 4. The image signal processing method according to claim 1, wherein the nonlinear processing, level processing, and slope processing are performed using separate conversion lookup tables. 5. The image signal processing method according to claim 1, wherein the level processing and the slope processing are performed using the same conversion lookup table. 5. The image signal processing method according to claim 3, wherein the HD characteristics and the characteristics of the acousto-optic element are corrected using separate conversion lookup tables. 7. The image signal processing method according to claim 4, 5, or 6, wherein the conversion lookup table is rewritable.