JPS61186092A - Picture signal processing device - Google Patents

Abstract

PURPOSE:To correct only a hue in an excellent way without giving any affect on the saturation and brightness of a picture by applying hue modulation to a signal only having an intermediate density level based on the level difference between a maximum density level signal and a minimum density level signal. CONSTITUTION:A density level discriminating circuit 20 outputs the maximum density level signal Dmax, intermediate density level signal Dmid and minimum density level signal Dmin among signals DR, DG, DB from outputs A, B, C, and outputs a selection signal SL representing to which of each density signal the signal Dmid corresponds from an output D. The signals Dmax, Dmin are fed to a subtraction circuit 30, and the signal Dmid is fed to an adder circuit 50. A ROM40 uses a modulation control signal MC to designate any of plural tables and reads a value of corresponding modulation DELTAD in the corresponding table every time a saturation signal SA is applied. The value of the modulation DELTAD is fed to the signal Dmid through the adder circuit 50 and the result is fed in common to multiplexers 61, 62, 63 together with the selection signal SL as a modulated intermediate density level signal Dmid'.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image signal processing device that performs hue modulation of an image signal separated into three colors according to each density level of the same image signal.

[Conventional technology]

Conventionally, as a picture signal processing device that performs such hue modulation, there is a method described in the Journal of the Society of Television Engineers, Vol. A, No. 12 (1981) 1.
004 (14) to 1009 (19) pages of "Telecine camera color correction", especially pages 1004 (14) to 1005 (15), which are introduced in the item name "Correction of specific colors" There are some methods that use similar methods.

In other words, in such an image signal processing device, broadly speaking, (1) extracting a specific color based on the image signal separated into the three colors described above, and extracting a corresponding modulation signal (correction signal in the same document);
Take out.

(2) Based on this extracted modulation signal, analog correction calculations are performed on the image signal.

The above-mentioned hue modulation is performed through two steps.

[Problem that the invention seeks to solve]

Although it is certainly possible to correct the hue of a specific color by modulating the image signal in this way, this method only performs hue modulation regardless of the saturation of the image, so in practice This may affect the saturation and brightness of the same image. This does not necessarily result in the desired desired color tone.

[Means and effects for solving the problem] In the present invention, the density level difference between the maximum density level signal and the minimum density level signal of the image signals is regarded as the saturation of the image, and the density level is determined. A required amount of modulation regarding hue is determined based on the difference, and hue modulation is performed in accordance with the determined amount of modulation only for signals at an intermediate density level among the image signals. As a result, only the hue can be favorably corrected without significantly affecting the saturation and brightness of the image.

〔Effect of the invention〕

As described above, according to the present invention, the hue can be modulated while minimizing the influence on the saturation and brightness of the image.

Further, according to the present invention, since the above-mentioned modulation is applied only to the intermediate density level signal among the three image signals, it is easy to simplify the device and further increase the processing speed. It is.

The image signal processing device according to the present invention is particularly applicable to equipment such as color digital copying machines that require high-speed processing of image signals in real time and also require the ability to arbitrarily change the color tone of an original image. The significance of applying this is significant.

〔Example〕

First, the present invention will be explained in detail with reference to FIGS. 2 and 3.

Figure 2 is a well-known color wheel diagram, where R is red, G is green, B is blue, and their complementary colors C is cyan, M is magenta,
Y represents yellow (R=G=B is an achromatic color).

Now, if we assume that the light intensity signals R, G, and B of the image signal obtained by color-separating an image into three colors are each, on the color wheel shown in Figure 2, the vector sum of these signals is A certain point A indicates the chromaticity of the image. At this time, the saturation of the image is expressed as the length of the line segment τT, and the hue of the image is expressed as the direction of the line molecule τ. That is, if you want to modulate only the hue without changing the saturation of the same image, the signal R is changed so that only the direction of the line molecule τ is changed to the desired direction without changing the length of the line molecule τ.
,G.

What is necessary is to change the value of B.

In this invention, each of the density signals of the above-mentioned image signals is
As r DG r DB, the difference in density level between the signal with the maximum density level and the signal with the minimum density level is the saturation of the image, and the same saturation is applied only to the signal at the intermediate density level, which has the least influence on this saturation. The hue is corrected by performing the required amount of modulation determined based on the . Incidentally, in the example shown in Figure 2, the magnitude relationship of the density levels in this case is (DR
Since <DG<DB), the saturation of the same image is (DRDB
), and the signal is at an intermediate concentration level.

The required amount of modulation determined based on the obtained saturation is applied to the color saturation. As a result, only the direction of the line segment OA can be changed as required without significantly affecting the length of the line segment OA. Of course, this means that the saturation and brightness of the image are maintained and only the hue is corrected.

Note that the required modulation amount determined based on the saturation is a value that can be preset arbitrarily or empirically as a value proportional to the saturation i, for example, as shown in FIG. It can be set in various ways.

That is, in the diagram shown in Fig. 3, the horizontal axis is the saturation SA,
The vertical axis is the above-mentioned modulation amount ΔD, and if the characteristic is set as shown by line L1, the modulation amount ΔD that is always in a proportional relationship with respect to the saturation SA obtained above can be obtained, and the characteristic as shown by line L2 is obtained. If set, a similarly proportional modulation amount ΔD will be obtained for colors with high saturation, but the modulation amount ΔD will be 0 for colors with low saturation, and the above-mentioned hue modulation will be prohibited. It becomes like this. The selection of these characteristics and the setting of the slope of the characteristic line are arbitrary, and can be freely selected and set according to the purpose and actual situation.

FIG. 1 shows an embodiment of an image signal processing apparatus according to the present invention constructed based on this principle.

In this embodiment device, Log circuits 11, 12, and 13 are circuits that logarithmically compress image signals R, G, and B separated into three colors and convert them into corresponding density signals DR, DC, and DB. The density signals DR2DG and DB thus converted are sent to multiplexers 61 and 6.
The signals are applied to the A inputs 2 and 63, respectively, and are also applied to the density level determination circuit 20 to compare and determine the magnitude of each density level.

Based on the comparison and determination of the density levels of the density signals DRIDG and DB, the density level determination circuit 20 selects one of these signals DR2DG and DB that is at the maximum density level as a signal Dmax, and one that is at an intermediate density level as a signal Dmid. , the one at the minimum concentration level is the signal D m
In is output from the human output, B output, and C output, respectively, and a selection indicating which of the density signals DR, DC, and DB the intermediate density level signal Dmid corresponds to is output from the D output. This circuit outputs a signal SL, and among these signals, the maximum density level signal Dmax and the minimum density level signal Dmin are sent to the subtraction circuit 30, the intermediate density level signal Dm i d is sent to the addition circuit 50, and the selection signal SL is sent to the subtraction circuit 30. is each multiplexer 6
1.62 and 63, respectively. Note that this selection signal SL is, for example, a 2-bit signal strength)
As an example, the contents are as shown in the table below.

In other words, if the signal at the intermediate density level in the image is the signal DR, the signal content will be "0,0", and if the signal is also the signal DR, the signal content will be "0,0".
o, i'', and if it is the signal DB, the signal content will be '1.0'.

The subtraction circuit 30 calculates the minimum density level signal D from the density level of the maximum density level signal Dmax based on the principle described above.
This circuit calculates the saturation of the image by subtracting the density level of min, and the calculated saturation signal SA is added to the ROM 40 as an address signal.

In the ROM4Q, the values of the modulation amount ΔD relative to the saturation SAJ corresponding to the characteristic line shown in FIG. ing. It is assumed that the degree of inclination of this characteristic line is selected and designated in advance by the operator through a modulation degree control signal MC applied from an operation panel (not shown) or the like. In other words, this modulation degree control signal MC is a parameter that determines the degree of hue modulation described above, and is a parameter that determines the degree of hue modulation described above.
It has the function of switching between the above plurality of tables corresponding to "normal", "weak", etc. Therefore, in this ROM 40, one of the plurality of tables is designated by the modulation degree control signal MC, which is a so-called first address signal, and the obtained saturation signal SA is used as a second address signal.
Each time ΔD is added, the corresponding value of the modulation amount ΔD is read out in the table. The value of the read modulation amount ΔD is added to the previous intermediate density level signal D m i d through the adding circuit 50, and is sent to each of the multiplexers 61, 62, and 63 as the modulated intermediate density level signal D m i d'. Commonly added to B input.

The multiplexers 61, 62, and 63 are circuits that selectively output either the signal applied to the A input or the signal applied to the B input according to the content of the selection signal SL applied to the selection control terminal S, respectively, Here, based on the above table, it is assumed that the multiplexer 61 selects the B input when the content of the signal SL is "0°0", and selects the A input otherwise.
2 selects the B input when the content of the signal SL is ``0, 1'', and selects the A input otherwise,
Then, the multiplexer 63 selects the content of the signal SL as '1'.
．． 0", select B input, otherwise select A.
Suppose we select an input. That is, as a result, only the signal at the intermediate density level of the density signals DRtDC1 and DB undergoes hue modulation and is output from the device, while the other signals at the maximum density level and the signal at the minimum density level are output as they are. Become so.

In this way, according to the apparatus of this embodiment, as explained in the previous principle, it is possible to apply the required modulation based on the saturation of the image to only the signal at the intermediate density level. Hue modulation can be performed satisfactorily without significantly affecting brightness and brightness.

Although the explanations in the above principles and embodiments have been omitted, the density level of the modulated intermediate density level signal, that is, the modulated intermediate density level signal Dmid', and the maximum density level signal Dm
The density level right of ax and the density level of the minimum density level signal Dmin are compared, and if this is Dmax (Dm i d' or Dmin)Dm
id', the modulated intermediate density level signal Dmid
' clip the density level appropriately and always set Dmax.
)Dmid')Dmin may be further added, or the value of the modulation amount ΔD stored in the ROM 40 may be clipped in advance so that the same relationship is maintained. . Thereby, it is possible to perform hue modulation limited to the specified color region.

Further, in the above embodiment, the subtraction circuit 30 calculates the saturation of the image and then uses this as an address signal to read out the required modulation amount ΔD from the ROM 40. However, in addition, for example,
Maximum density level signal Dmax and minimum density level signal Dm
An arithmetic circuit may be provided that directly calculates and outputs a value corresponding to the modulation amount ΔD based on in.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an embodiment of an image signal processing device according to the present invention, FIG. 2 is a color wheel diagram for explaining the present invention in detail, and FIG. 3 is a modulation amount extraction method according to the present invention. FIG.

Claims (1)

[Claims] It is determined which of a plurality of preset color areas the image belongs to based on the magnitude relationship of each density level of the image signal separated into three colors, and the image signal is exclusively assigned to this color area. In an image signal processing device that performs hue modulation according to a specified degree of modulation, a required amount of modulation is determined based on a density level difference between a signal with a maximum density level and a signal with a minimum density level among the image signals. An image signal processing device characterized in that hue modulation is applied to only signals at an intermediate density level among the image signals in accordance with the determined modulation amount.