JPH0757005B2 - Gradation setting device in image input / output system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention performs gradation conversion from an input image signal to an output image signal in a high precision image input / output system such as a color scanner, a laser camera (for example, Autokon manufactured by ECRM), or an ink jet printer. Regarding the gradation setting device,
More specifically, the present invention relates to a gradation setting device that generates a gradation conversion curve used when performing this gradation conversion.

For example, in a color scanner or the like, an input image light signal incident on the input head is photoelectrically converted by a photomultiplier tube,
If necessary, it is logarithmically converted by a logarithmic conversion circuit, then input to a signal processing device centered on a gradation setting device and converted into a desired output image signal, and converted into an output image light amount signal of a light amount control circuit. After that, the output head exposes the photosensitive material as an output image. The gradation conversion from the input density signal to the output density signal performed by the gradation setting device is
Generally, it is performed based on a gradation conversion curve that generates each set value set by the highlight, middle, and shadow potentiometers on the operation panel as a parameter. The conventional generation process of this curve performed in the floor setting device will be specifically described below.

The respective parameters (H, M, S) are respectively added to the basic functions of h (x), m (x) and s (x) generated by the gradation setting device. An example of these basic functions is shown in FIGS. 1A, 1B, and 1C, respectively. (However, the horizontal axis (x-axis) represents the input density signal and the vertical axis (y-axis) represents the output density signal. The same applies to FIGS. 1D and 1E below. Also, the x-axis and y-axis scales are the same. 1A to 1E.) The amplitudes of these basic functions change according to the set value (parameter) of the potentiometer. That is, each set value (parameter) means a weight given to each basic function.

Next, a linear function y = lx (l is a constant) passing through the origin is generated, and parameters H, M, S corresponding to the basic functions h (x), m (x), s (x) are respectively set. Then, a function (H × h (x) + M × m) obtained by integrating and then adding each of these elements is added.
(X) + S × s (x)) is generated, and then the two generated functions are superimposed on each other to generate the gradation curve function y (see the gradation curve shown in FIG. 1E).

That is, the stepwise curve function y is represented by the following equation.

y = H × h (x) + M × m (x) + S × s (x) + lx ...
1) (However, H, M, and S are parameters) However, the tone curve function generated by such a floor setting device causes some problems as described below.

The first problem is that operators generally highlight
The gradation change in each of the middle and shadow areas is y = lx
Although it is desired to be performed so as to be changed in a direction perpendicular to the straight line, the change does not occur in practice, and thus it may be difficult to handle in operation. That is, for example, when H = S = 0, M is M ₁ and −M
Given ₁ (M ₁ > 0), two functions M ₁ ×
Although m (x) and −M ₁ × m (x) are line-symmetrical with respect to the x-axis, two gradation curve functions M ₁ × m (x) + lx and −M ₁
× m (x) + lx does not have a line symmetry relationship with respect to a straight line of y = 1x.

This will be described with reference to FIG. Y ₁ = shown in (a)
On the straight line of lx, y ₂ = h (x) + m (x) + s shown in (b)
Considering a case where the curve of (x) is superimposed to obtain a gradation curve, the curve y ₃ = y ₁ + y ₂ and the curve y ₄ = y ₁ −y ₂ are straight lines y _{1 as} shown in (c). It is not axisymmetric with respect to. That is, when y ₂ is multiplied by a predetermined coefficient a, y ₁ + ay
₂ does not change in the direction perpendicular to the straight line of y ₁ = lx due to the change in the value of a. As is clear from FIG. 6,
In the conventional gradation curve generation method, each function h (x), m
Even if (x) and s (x) are changed at the same rate, the gradation curve does not change perpendicularly to the straight line of y = lx. Therefore, as described above, the operator feels when generating the gradation curve. There was a problem that it was extremely difficult to handle.

That is, the operator generates a plurality of functions (here, h (x), m (x), s in the reference straight line y ₁ when generating the gradation curve.
(X)) is weighted to a predetermined coefficient (here, H, M, S), and the operation of superimposing a curve y ₂ is performed. At this time, the operator selects the floor displayed on the screen such as CRT. While observing the shape of the tonal curve, it is determined how the above coefficient should be changed in order to generate the desired shape. Then, the coefficient determined by this judgment is inputted by the operator using the potentiometer arranged on the front panel of the apparatus.

As described above, the operation of inputting the determined coefficient while the operator looks at the screen of the CRT or the like is usually performed a plurality of times each time one contour curve is created. That is, the shape of the gradation curve gradually approaches the target shape.

At this time, it is assumed that an operator who is observing a screen such as a CRT determines that the intermediate density of the gradation curve needs to be increased because the intermediate density is insufficient again. At this time, according to the above example, the operator operates to increase the coefficient M of the function m (x).

However, in the above-mentioned conventional technique, when M is increased, the level of the intermediate portion of the gradation curve increases, but the peak of the gradation curve is superposed by y ₂ which is the integration curve of these functions. , The reference straight line y ₁ does not change at the same position and moves in the direction of this straight line y ₁ . That is, the larger the coefficient M, the more the peak moves to the high concentration side.

In this way, for the operator who is trying to generate the desired shape on the reference straight line y ₁ , if the peak moves in the direction of this straight line y ₁ , how much the above coefficient is changed to obtain the predetermined shape? Is extremely difficult to predict.

Although the case where one coefficient M is changed has been described here, for example, there are cases where it is desired to change three coefficients H, M, and S at the same time, and in such a case, the above prediction becomes more difficult.

The second problem is that the basic functions h (x), m (x), s (x)
Since the shape is defined, it may not be possible to obtain all the curves desired by the operator using the gradation curve function generated by the combination of only the parameters H, M, and S.

A third problem is that this gradation curve does not become a monotone increasing curve depending on the combination of the parameters H, M and S. That is, inversion of gradation may occur.

The present invention has been made in order to solve the above problems, and generates a gradation curve that does not cause the problems described above. Furthermore, by using this curve, the output image signal desired by the operator is generated. It is an object of the present invention to provide a gradation setting device capable of outputting the.

The gradation setting device in the image input / output system of the first invention of the present invention is a gradation setting device for outputting an image density signal subjected to gradation processing using a gradation curve. An xy coordinate system in which the output image density signal is taken as the y-axis is formed, and y =
A reference straight line generating means for generating a reference straight line of lx (l is a constant) is provided, and the xy coordinate axis is rotated counterclockwise about the origin to superimpose the x axis on the reference curve. Coordinate axis rotating means (first coordinate axis rotating means) that forms an αβ coordinate system with the axis being the α axis and the y axis being the β axis is provided, and the minimum value coordinate point Pmin is located on the α axis of the αβ coordinate system. And a maximum value coordinate point Pmax are generated, parameter intermediate coordinate points of different numbers of α values are generated between the minimum value coordinate point Pmin and the maximum value coordinate point Pmax, and the β value of these intermediate coordinate points is calculated. I made it possible to change arbitrarily, that is,
A minimum point coordinate point Pmin, a maximum point coordinate point Pmax, and a coordinate point generating means capable of generating several intermediate coordinate points that can be changed in the β-axis direction are provided, and the generated α, A means (second coordinate axis rotating means) for converting the β value into an xy coordinate system is provided, and further, the coordinate points in the converted xy coordinate system are interpolated by a curve interpolation method such as a pure Hermite interpolation method. It is characterized in that a gradation contour curve generating means for generating the gradation curve is provided.

Next, the gradation setting device in the image input / output system of the second invention of the present invention is the gradation setting device for outputting the image density signal subjected to the gradation processing using the gradation curve, wherein x
A reference straight line generating means for forming an xy coordinate system in which an input image density signal is taken as an axis and an output image density signal is taken as ay axis, and a reference straight line of y = lx (l is a constant) is created on the xy coordinate system. Also, the xy coordinate axis is rotated counterclockwise about the origin and the x axis is superimposed on the reference curve. At this time, the x axis is the α axis and the y axis is the β axis, and the αβ coordinate system is set. The coordinate axis rotating means (first coordinate axis rotating means) for forming the above is provided, and the minimum value coordinate point Pmin is set on the α axis of this αβ coordinate system.
And the maximum value coordinate point Pmax are generated, and the minimum value coordinate point Pm is generated.
Between in and the maximum value coordinate point Pmax, a number of parameter intermediate coordinate points having different α values are generated, and β values of these intermediate coordinate points can be arbitrarily changed.
That is, the minimum point coordinate point Pmin, the maximum point coordinate point Pmax, and several coordinate point generating means capable of generating several intermediate coordinate points that can be changed in the β-axis direction are provided.
A gradation curve generating means for generating the gradation curve by interpolating between the coordinate points in the coordinate system by a curve interpolation method such as a forward Hermite interpolation method, and converting the generated α and β values into an xy coordinate system. Means (second coordinate axis rotating means) is provided.

FIG. 2A shows x formed by the reference straight line generating means.
A graph showing an example of the axis, y-axis and y = lx, FIG. 2B is
A graph showing an example of the αβ coordinate system formed by the first coordinate axis rotating means together with the x axis and the y axis, and FIG. 2C is a minimum value coordinate generated by the coordinate point generating means on the αβ coordinate system. A graph showing an example of the point Pmin, the maximum value coordinate point Pmax, and several intermediate coordinate points together with the x-axis and the y-axis,
The 2D diagram shows that each coordinate point is
FIG. 2E is a graph showing the conversion to the xy coordinate system, and FIG. 2E is a graph showing an example of the gradation curve generated on the xy coordinate system by the gradation curve generating means.

The α coordinates of the maximum value coordinate point and the minimum value coordinate point are values corresponding to the maximum value and the minimum value of the input image density signal.

It should be noted that the number of the intermediate coordinate points may be set to a desired number of 2 or more, and in addition to this, coordinate points such that the α value is the minimum value coordinate point Pmin or less or the maximum value coordinate point Pmax or more are provided. The stability for curve generation may be improved.

Further, the curve interpolation method is an interpolation method in which the differential coefficients of the first derivative and the second derivative of the curve generated by the interpolation are continuous. The interpolation method used.

According to the gradation setting device in the image input / output system of the present invention, it is possible to select a desired number of coordinate points to be the parameters used when determining the gradation curve, and the α coordinate of each coordinate point can be selected. Can be set to desired values respectively, so that the gradation curve has a high degree of freedom and a smooth curve can be generated. Therefore, highly accurate gradation processing can be performed.

Furthermore, the device of the present invention is provided with coordinate rotation means, y
Since each intermediate coordinate point can be changed with respect to the reference line of = lx, the gradation curve also changes with respect to the reference line of y = lx according to the value of the parameter set by the operator.

This will be described with reference to FIG. 7 corresponding to FIG. 6 showing the prior art. That is, in the device of the present invention, the x, y coordinate system is rotated and the coordinates are converted to the α, β coordinate system, and y = 1x is represented as β ₁ = 0 as shown in (a). . Therefore, as shown in (b), αβ
Curved line β ₁ = 0 in the coordinate system The gradation curve generated by superimposing is β ₁ =
It becomes easy to change it to 0, that is, y = lx vertically. That is, as shown in (c), the curve β ₃ = β ₁
+ Β ₂ and the curve β ₄ = β ₁ −β ₂ are line symmetric with respect to the straight line y = 1x. The above p is And H, M and S represent coefficients operated by the operator. This makes it possible to obtain a gradation curve that changes with respect to the straight line of y = 1x desired by the operator. Therefore, the work efficiency can be extremely improved.

Hereinafter, examples of the present invention will be described in detail.

FIG. 3 is a block diagram showing one embodiment of the device of the first invention of the present invention.

The reference straight line generating means 1 generates the x-axis, the y-axis, and y = lx, and the first coordinate rotating means 2 rotates the xy coordinate axis counterclockwise about the origin until the x-axis overlaps the straight line of y = lx. The rotated X-axis is converted into the α-axis and the y-axis is converted into the β-axis to form the αβ coordinate axis. Thereafter, αβ is set according to each parameter value input by the coordinate point generation means 3.
Each coordinate point is generated on the coordinate system. After that, the second coordinate axis rotating means 4 rotates only the αβ coordinate axis clockwise around the origin until the α axis overlaps the x axis formed by the reference straight line generating means 1, and the α axis becomes the x axis. , Β
The axes are transformed into the y-axis to generate the xy coordinate system. After this,
The gradation curve generation means 5 interpolates between coordinate points on the xy coordinate system by the quasi-Hermitian interpolation method to generate a gradation curve. Based on the gradation curve thus generated, the input image density signal input to the gradation setting device is converted into an output image density signal. FIG. 4 is formed by rotating the x and y axes formed by the reference straight line generating means 1 and the first coordinate axis rotating means 2 about the xy coordinate axis counterclockwise about the origin by a rotation angle of θ. Α axis (overlapping with the reference straight line of y = 1x) and β axis, eight points generated on the α axis by the coordinate point generating means 3 and coordinate points P _{1 to} P ₈ (P ₂ and P ₇ are fixed points) It is a graph which shows.

As a concrete coordinate point generation method, first, the operator sets each parameter value of highlight, middle, and shadow
H, M, S are set, these H, M, S values are input to the coordinate point generation means 3, and the β coordinate of each coordinate point of P _{1 to} P ₈ is set.
For example, P ₂ is O, P ₃ is H, P ₄ and P ₅ are M, P ₆ is S, P ₇ is O, Will have β coordinates of. Then, these coordinate points P ₁
P ₂ (minimum coordinate point) of α coordinates to P ₈ are O, P ₇ (maximum coordinate point) is set to a value of 100, which is standardized. It should be noted that 0 and 100 on the α coordinate correspond to the input image density signal and the minimum and maximum density values. In general, the range of highlight, middle, and shadow areas is highlight 5
~ 35, middle is 30-70, and sheado is 65-95. Therefore, in this embodiment, the coordinate point P ₃ corresponding to the highlight is 15, and the coordinate points P ₄ and P ₅ corresponding to the middle (two points are taken in order to smoothly generate the gradation curve). 49,5
1, the coordinate point P ₆ corresponding to shadow is set to have an α coordinate of 85. The coordinates of coordinate points P ₁ and P ₈ are Is set to. These two coordinate points are for improving the stability when generating the gradation curve.

Next, the second coordinate axis rotating means 4 converts the coordinate points P _{1 to} P ₈ on the αβ coordinate system into the coordinate points on the xy coordinate system. Specifically, the coordinates (α, β) of each coordinate point are converted into the coordinates (x, y) by the following expression 2).

That is, (Note that θ is the angle formed by the x-axis and the α-axis.) Next, the gradation curve generating means 5 determines the coordinate points P _{1 to} P ₈ of the xy coordinate system obtained as described above. Coordinates (x _i , y _i ) (i =
1, ..., quasi-Hermitian interpolation to each data of 8) (e.g., coefficient sequence by applying the Fujitsu reference made FACOM FORTRAN SSL II used handbook 99SP-0050-4 P235~237 Ltd.) c _i, d _i , e _i (i = 1, ..., 7) is obtained. After that, a gradation curve is generated from these coefficient sequences c _i , d _i , e _i . That is, in the section of x _i ≦ x ≦ x _i +1 y = y _i + (c _i + (d _i + e _i · x) x) x = y _i + c _i · x + d _i · x ² + e _i · x ³ ... By 3), the gradation curve 7 is generated. FIG. 5 is a graph showing an example of the gradation curve thus generated. In this figure, 17 gradation curves generated by changing the parameters are shown. From this figure, it can be seen that the gradation curve is changing with respect to the reference line of y = 1x as the parameters are changed. That is, according to this embodiment, it is possible to obtain a gradation curve that partially changes in the direction perpendicular to the reference straight line of y = 1x desired by the operator. Further, in this embodiment, since the parameters of c _i , d _i , and e _i can be determined by the combination of the parameters H, M, S, it is possible to generate a smooth curve with a large degree of freedom in generating the curve. You can In addition, we selected 15,49,51,85 as the α coordinate of highlight, middle, and shadow, but these coordinates can be changed to any value, and this change gives more freedom in generating a curve. growing.
Further, according to this embodiment, when a combination of c _i , d _i , and e _i such that the gradation curve does not become a monotone increasing curve is input, it is preset so that the combination can be blocked. Since it is possible to set it, it is easy to generate only the monotonically increasing curve.

The block diagram of the second embodiment of the present invention can be obtained by replacing the second coordinate axis rotating means 4 and the gradation curve generating means 5 of the block diagram of FIG. According to this embodiment, the same effect as the above embodiment can be obtained.

Each means in the above two embodiments may be formed by using a digital circuit in which a microprocessor (for example, Z-80), ROM, RAM and the like are combined, or a plurality of nonlinear amplifiers may be combined. It may be formed by using an analog circuit.

[Brief description of drawings]

1A to 1E are graphs for explaining the prior art, and FIGS. 2A to 2E are graphs showing coordinate axes, coordinate points and gradation curves generated by each means of the apparatus of the present invention, and FIG. Is a block diagram showing one embodiment of the present invention, FIG. 4 is a graph showing a method of generating coordinate points in the embodiment of FIG. 3, and FIG. 5 is a gradation curve generated by the embodiment of FIG. 6 is a graph for explaining the gradation curve generated by the conventional technique, and FIG. 7 is a graph for explaining the gradation curve generated by the device of the present invention. 1 ... Reference straight line generating means, 2 ... First coordinate axis rotating means 3 ... Coordinate point generating means, 4 ... Second coordinate axis rotating means 5 ... Tone curve generating means

Claims (2)

[Claims] 1. A gradation setting for performing gradation processing based on a gradation curve on an input image density signal from an image signal input device and sending the output image density signal after the gradation processing to the image signal output device. In the apparatus, an xy coordinate system is formed in which the input image density signal is taken as the x-axis and the output image density signal is taken as the y-axis, and a reference straight line of y = lx (where l is a constant) is further formed on this xy coordinate system. A reference straight line generating means for generating, the xy coordinate axis is rotated counterclockwise about the origin until the x axis overlaps with the reference straight line, and the x axis after rotation is set as the α axis and the y axis is set as the β axis. Coordinate axis rotating means forming an αβ coordinate system, generating a minimum value coordinate point Pmin and a maximum value coordinate point Pmax on the α axis of this αβ coordinate system, and between the minimum value coordinate point Pmin and the maximum value coordinate point Pmax. Generate intermediate coordinate points for several parameters with different α values in Coordinate point generation means capable of arbitrarily changing the β value of these intermediate coordinate points, means for converting the generated αβ value into an xy coordinate system, and the above-mentioned each in the converted xy coordinate system. A gradation setting device in an image input / output system, comprising gradation equal curve generating means for generating a gradation curve by performing curve interpolation between coordinate points. 2. A gradation setting for performing gradation processing on an input image density signal from an image signal input device based on a gradation curve and sending the output image density signal after the gradation processing to the image signal output device. In the apparatus, an xy coordinate system is formed in which the input image density signal is taken as the x-axis and the output image density signal is taken as the y-axis, and a reference straight line of y = lx (where l is a constant) is further formed on this xy coordinate system. A reference straight line generating means for generating, the xy coordinate axis is rotated counterclockwise about the origin until the x axis overlaps with the reference straight line, and the x axis after rotation is set as the α axis and the y axis is set as the β axis. Coordinate axis rotating means forming an αβ coordinate system, generating a minimum value coordinate point Pmin and a maximum value coordinate point Pmax on the α axis of the αβ coordinate system, and between the minimum value coordinate point Pmin and the maximum value coordinate point Pmax. Generate intermediate coordinate points for several parameters with different α values in Coordinate point generation means capable of arbitrarily changing the β value of the intermediate coordinate points, and gradation curve generation for generating the gradation curve by performing curve interpolation between the coordinate points in the αβ coordinate system. A gradation setting device in an image input / output system, which is provided with means and means for converting the generated αβ value into an xy coordinate system.