JPH0824340B2 - Image signal processor - Google Patents

Description

The present invention relates to an image signal for performing gradation correction of an image signal when an image is recorded on a photoconductor by using an optical output modulated by the image signal. The present invention relates to a processing device.

[Prior Art] A conventional general configuration of an apparatus for processing a digitized image signal to obtain a hard copy by optical modulation is shown in FIG. 3, and a frame in which the image signal is recorded is shown. Digital output image signal N output from the memory 1
Is converted into an analog image signal by the D / A converter 2 and input to the optical modulator 3. The light output from a light source 4 such as a laser oscillator is intensity-modulated in an optical modulator 3, and the modulated light output is scanned by a scanning system 5 such as a rotary polygon mirror to form a photoreceptor 6 made of a silver salt film or the like. Record the image on top.

In this image recording apparatus, the input / output characteristic of the optical modulator 3 is not linear, and the characteristic of the photoconductor is the same as that of the silver salt film.
It is difficult to obtain a high-quality recorded image because it depends on the type of photoconductor and the type of film, such as the HD characteristic and the VD characteristic of electrophotography. For example, when image diagnosis is performed using a hard copy such as a medical photograph, if the image density or its gradation is not appropriate, an important diseased part may be overlooked or misdiagnosis may occur. In order to prevent such serious negligence, it is necessary to correct the conversion characteristics of the light modulator 3 and the photoconductor 6, and to perform gradation correction such as brightness adjustment and contrast adjustment.

As such a gradation correction method, the method shown in FIG. 4 has been conventionally adopted. That is, frame memory 1 and D /
Between the A converter 2 and the multiplexer 7, a plurality of ROMs (reads that store the results of calculation of light modulation characteristics, film HD characteristics, several kinds of brightness adjustment values and contrast adjustment values)
A ROM table 8 made up of only memories and a multiplexer 9 are inserted, the multiplexers 7 and 9 are switched by an external operation switch or the like, and a desired gradation correction is performed by a look-up table method.

However, with this method, the film type, brightness adjustment value,
When the number of contrast adjustment value settings increases, the RO
It is necessary to increase the number of M tables 8 or to replace it with another ROM table, and there is a drawback in that it is not easy to use and flexible.

[Object of the Invention] An object of the present invention is to eliminate the drawbacks of the above-mentioned conventional apparatus and provide an image signal processing apparatus capable of performing appropriate gradation correction particularly for the conditions of the photoconductor with a simple configuration and procedure. Especially.

[Summary of the Invention] The gist of the present invention for achieving the above-mentioned object is a D / A converter for converting a digital input image signal into an analog amount,
An image signal for recording an image on a photoconductor by an optical modulator that modulates an optical output from a light source with a signal output from the D / A converter, and the optical output modulated by the optical modulator. The processing device includes a storage unit capable of storing the characteristics of the plurality of photoconductors and the characteristics of the light modulation unit, and a selection unit that selects one photoconductor from the characteristics of the plurality of photoconductors. And a creating means for creating a conversion look-up table for gradation correction based on the characteristics of the photoconductor and the characteristics of the light modulating means, and performing gradation correction of an image using the conversion look-up table. Is an image signal processing device.

Embodiments of the Invention The present invention will be described in detail based on the illustrated embodiments.

FIG. 1 is a block diagram showing a configuration of a main part of an image signal processing device, and a frame memory 11 in which a digitized image signal is stored is a RAM (Random Access Memory).
Is connected to the conversion lookup table 12, and the conversion lookup table 12 and the CPU 13 are connected to each other. Connected in parallel. Furthermore, the conversion lookup table
12 to D / A converter 16, optical modulator 17 including acousto-optic device
Are sequentially connected, and the recording section 18 records on the photoconductor by the modulated light from the optical modulator 17.

Therefore, the parameters such as the film HD characteristic, the optical modulator characteristic, the brightness adjustment value, and the contrast adjustment value, which are input from the input unit 14, are stored in the parameter memory 15 via the CPU 13. The CPU 13 uses these parameters to create table data according to a predetermined procedure, and stores the table data in the conversion lookup table 12.

The digital image signal N from the frame memory 11 is input to the conversion look-up table 12 and further gradation-corrected by the conversion look-up table data, and the D / A converter 16 is supplied.
Input to the optical modulator and converted into an analog image signal V
Enter in 17. The optical output by the laser beam input to the optical modulator 17 is modulated by the optical modulator 17 and recorded in the recording unit.
Reach 18 and draw a recorded image on a photoreceptor such as a silver salt film.

Next, the procedure for creating table data stored in the conversion lookup table 12 will be described with reference to FIG. Second
The quadrant I of the figure is a graph showing the relationship between the digital input image signal N and the density D of the image drawn on the photoconductor, where the horizontal axis represents the digital input image signal N and the vertical axis represents the image density. D is displayed. The digital input image signal N uses 10 bits in this embodiment and has a gradation range of 0 to 1023. In this embodiment, the digital input image signal N
Since the gradation correction is performed so that the characteristics of the density and the density D are linear, the characteristics in the I quadrant are D = Dm when N = 0.
If in = N = 1023 and D = Dmax, a straight line with a slope (Dmax-Dmin) / 1023 with Dmin as the D-axis intercept is obtained.

Quadrant II shows the HD characteristic curve of the film,
It is represented by a logarithm logE where the vertical axis is the density D and the horizontal axis is the exposure amount E, and the characteristic curve is usually an inverted oblique S-shape.

The third quadrant shows the characteristic curve of the optical modulator 17, and the horizontal axis is an optical modulator composed of an acousto-optic device having a proportional relationship with the exposure amount E.
The diffraction efficiency η of 17 is on the same axis as the horizontal axis logE of the second quadrant, and the vertical axis is the analog input image signal V of the optical modulator 17. The input / output characteristics of the optical modulator 17 in the third quadrant are not usually linear.

Quadrant IV shows the output characteristics of the D / A converter 16 with respect to the digital input image signal N, the horizontal axis is the digital input image signal N, and the vertical axis is the analog output image signal V of the D / A converter 16. Normally, the input / output characteristics of the D / A converter 16 can be regarded as linear, so that it is the data in the conversion look-up table 12 that determines the characteristic curve of the IV quadrant. The analog output image signal V of the D / A converter 16 is associated. Then, since the analog input image signal V to the optical modulator 17 and the diffraction efficiency η are related by the characteristic curve of the optical modulator 17 in the third quadrant, the digital input image signal N in the fourth and third quadrants is related. And the diffraction efficiency η are related to each other, and the HD characteristic curve of the film in the second quadrant is related to the logarithm logE of the exposure amount E proportional to the diffraction efficiency η and the film density D,
Further, the digital input image signal N and the film density D are related in the quadrant I.

Therefore, the data in the conversion look-up table 12 is converted into the film characteristic / light modulator characteristic or the desired brightness adjustment value
If the contrast adjustment value is obtained, the final gradation correction will be performed. As a specific procedure for performing the gradation correction, the data to be stored in the conversion look-up table 12 may be determined by performing back calculation from the formula to be finally obtained. First, from the input section 14 such as the terminal, the maximum film density Dm
When ax and the minimum density Dmin are input, these input data are stored in the parameter memory 15.

The relationship between the desired digital input image signal N and the density D is
Since it is linear as shown in the I quadrant, the density D for each digital input image signal N is respectively calculated by the following straight line formula: D = {(Dmax−Dmin) / 1023} · N + Dmin (1) Desired.

Next, the film HD characteristics shown in the second quadrant, which are the multiple points of the film characteristic data, namely Di, (log
E) The relationship with i is input from the input unit 14 and stored in the parameter memory 15. Normally, the HD characteristic curve of the film can be regarded as a straight line, except for the indefinite exposed part of the foot part and the overexposed part of the shoulder part in the second quadrant, so it can be regarded as a straight line.
For the density D with respect to the digital input image signal N obtained by the equation (1), a range of Di ≦ D <Di _{+ 1} is obtained, and a linear approximation equation, logE = [{(logE) _{i + 1−} (logE) i} / (D _{i + 1} −D
i)]-(D-Di) + (logE) i (2) The logE value for each concentration D is obtained.

Next, regarding the characteristics of the optical modulator 17 shown in the third quadrant, the data of multiple points, that is, V
The relationship between i and ηi is input from the input unit 14 and stored in the parameter memory 15. First, with respect to logE obtained by the equation (2), Then, the exposure amount E for each density D is obtained.

If the light output from the laser oscillator reaches each pixel with 100% efficiency, and the exposure amount is E0, the optical modulator
When the diffraction efficiency of 17 is η, the exposure amount E reaching each pixel
Since E = E0 · η ... (4), conversely, η = E / E0 ... (5), and the exposure amount E for each density D can be obtained from the equations (2) and (3). For example, the diffraction efficiency η for each density D of the optical modulator 17 can be obtained using the equation (5). That is, using the exposure amount E for each density D, η is obtained by the equation (5), and the optical modulator 17 is obtained as in the case of the film HD characteristic.
The input / output characteristic of is also linearly approximated as V = {(V _{i + 1} −Vi) / (η _{i + 1} −ηi)} · (η−ηi) + Vi (6), and η depends on E, Since E depends on D and D depends on N, V depends on N, and the analog image signal V with respect to the digital input image signal N can be obtained.

By the way, since the input characteristic of the D / A converter 16 can be regarded as usually linear as described above, the output of the D / A converter 16 is the D / A converter 16 when the analog image signal V previously obtained is obtained. When the digital input image signal Sd to be input to
When N = 0, N = 1023, V = V0, and V = (V0 / 1023) · Sd (7) and Sd = (1023 · V) / V0 (8). Therefore, the digital image signal Sd corresponding to the analog image signal V for each diffraction efficiency η can be obtained from the equations (6) and (8).

In this way, in order to realize the formula of the I quadrant, the relationship between the digital input image signal N and the input image signal Sd to the digital D / A converter 16, that is, the conversion lookup table
The table data to be stored in 12 can be determined.

In the above description, the gradation correction for the HD characteristics of the film and the input / output characteristics of the optical modulator has been described, but the brightness / contrast can be adjusted by almost the same procedure.

That is, in the quadrant I, when considering the brightness adjustment / contrast adjustment, since the brightness adjustment is above and below the overall brightness, nothing but movement of the straight D-axis intercept and contrast adjustment is a gradual change in density. Therefore, the equation (1) can be transformed into the following equation, not to mention the change in the gradient. Here, assuming that the brightness adjustment parameter is B and the contrast adjustment parameter is C, D = {(Dmax-Dmin) / 1023} · C · N + (Dmin + B) (9) If the parameters B and C are input from the input unit 14 instead of the formula), the subsequent procedure is exactly the same as the previous correction, and the brightness adjustment is performed at the same time as the gradation correction for the HD characteristics / optical modulator characteristics.・ Contrast adjustment can be easily achieved.

In this way, the conversion lookup table can be rewritten in a simple procedure for conversion correction, fine adjustment of brightness, and contrast, even if the type of film changes.

In the examples, the HD characteristics of the film and the input / output characteristics of the optical modulator were obtained by linear approximation for the sake of simplification, by inputting a plurality of sampling data. It is also possible to use various approximation functions such as

Further, in the above description, the film HD characteristic is assumed to be a single for ease of explanation, but in reality, the HD characteristics of a plurality of films are stored in a non-volatile memory such as a magnetic storage device and the film is operated by an operation switch. The type can be selected, and when the switch is changed, the calculation is performed as in the embodiment. Similarly, although the brightness adjustment value / contrast adjustment value has been treated as a single value, a plurality of brightness adjustment values / contrast adjustment values are stored in a non-volatile memory such as a magnetic storage device, and the operation switch switches the level of the captured image. It is also possible to obtain an image signal processing device with better operability by making the key selectable and performing the calculation as in the embodiment when the switch is changed. By doing so, since the storage capacity of only the parameters is sufficient, various characteristics can be realized with a small storage capacity.

Further, in the embodiment, the gradation of the final image is linear as shown in the quadrant I of FIG. 2, but an approximation function or a plurality of samplings may be used so that more complicated characteristics can be obtained if desired. It is also possible to use data approximation.

In this embodiment, the laser beam is used as an optical modulator.
Although the modulation is performed by 17, the output of the semiconductor laser oscillator can be directly modulated without using the optical modulator 17 in the case of the semiconductor laser, and the present invention can be applied to this case as well.

[Effects of the Invention] As described above, the image signal processing apparatus according to the present invention creates various conversion look-up tables based on at least one of the stored photoreceptor characteristics and the light modulation means characteristics. It is possible to easily adapt to film, realize high-quality images by performing gradation adjustments that allow fine adjustments, and easily adopt a configuration that stores and saves a large number of parameters, thus increasing hardware. It enables a wide range of gradation correction.

[Brief description of drawings]

1 and 2 show an embodiment of an image signal processing apparatus according to the present invention, and FIG. 1 is a block circuit configuration diagram,
FIG. 2 is a characteristic diagram, and FIGS. 3 and 4 are block circuit configuration diagrams of a conventional image signal processing device. Reference numeral 11 is a frame memory, 12 is a conversion lookup table, 13 is a CPU, 14 is an input unit, 15 is a memory for parameters, 1
6 is a D / A converter, 17 is an optical modulator, and 18 is a recording unit.

Claims (2)

[Claims] 1. A D / A converter for converting a digital input image signal into an analog amount, and an optical modulator for modulating an optical output from a light source by a signal output from the D / A converter, An image signal processing device for recording an image on a photoconductor by the light output modulated by the light modulation device, the storage device being capable of storing the characteristics of a plurality of photoconductors and the characteristics of the light modulation means. Selection means for selecting one photoconductor from among the characteristics of a plurality of photoconductors, and creating a conversion look-up table for gradation correction based on the selected photoconductor characteristics and the characteristics of the light modulation means An image signal processing apparatus, comprising: means for performing gradation correction of an image using the conversion lookup table. 2. A means for storing a brightness adjustment value and a contrast adjustment value, wherein the creating means creates the conversion lookup table based on the brightness adjustment value and the contrast adjustment value stored in the storage means. Claims No. 1
The image signal processing device according to item.