JPH067677B2 - Image processing device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an image processing apparatus for extracting an area having saturation and hue within a certain range from an input color image in digital image processing.

<< Prior Art >> In the image processing, when a specific object is extracted, in addition to the shape information, color information is often combined to improve the extraction accuracy. In this case, it is preferable to have a filter for lightness, saturation, and hue that matches the sense of the human eye, but the conventional optical filter is a filter for frequency and cannot sufficiently satisfy the requirements.

By performing digital image processing, a filter for extracting a region having a constant brightness from an RGB image signal can be realized relatively easily.

<< Problems to be Solved by the Invention >> However, realization of a filter for extracting a region having a hue within a certain range or a filter for extracting a region having a saturation or a certain range is generally complicated in calculation and is not easy. Absent.

The present invention has been made to solve the above problems, and in digital image processing, an image processing apparatus for extracting a region having a saturation and hue in a specified range with a small amount of calculation is realized with a simple configuration. The purpose is to do.

<< Means for Solving the Problems >> An image processing apparatus according to the present invention stores constants that define areas of saturation and hue, inputs image signals of two colors out of color image signals, and outputs the above-mentioned constants from the constants. A look-up table for calculating the area of another color image signal of the color image signal; a comparator for comparing the output of the look-up table with the other color image signal of the color image signal; It is provided with a logic circuit for inputting the output of the comparator and a mask circuit for masking the color image signal with the output of the logic circuit, and extracting a region of saturation and hue in a specified range from the color image signal. And

<< Operation >> According to the image processing apparatus having the above configuration, the saturation and the hue are approximated by the look-up table using the image signals of two colors, and the output is compared with the image signal of another one color. After that, a logical operation is performed, and the color image signal is masked by the output of this logical circuit, whereby an area having the saturation and hue in the designated range can be extracted with a small calculation amount.

<Example> The present invention will be described in detail below with reference to the drawings.

FIG. 1 is a configuration block diagram showing an embodiment of an image processing apparatus according to the present invention. 1 is the input color image signal r _i ,
A look-up table (hereinafter referred to as LUT) into which image signals r _i and g _i corresponding to two colors of g _i and b _i are input.
The parts, 11 and 12 are LUs to which the image signals r _i are connected respectively.
TA, LUTB, 13 and 14 are respectively connected to the image signal g _i , and LUTC and LUTD, and 21 to 24 are the LUT.
A comparator in which the outputs S _{1 to} S _{4 of} A to D are connected to one end and the image signal b _i is connected to the other end, 3 is an AND circuit to which the outputs of the comparators 21 to 24 are connected, and 4 is the above A delay circuit to which the input color image signals r _i , g _i , b _i are connected,
Reference numeral 5 is a mask gate circuit to which the output of the delay circuit 4 is connected and which is controlled by the output of the AND circuit 3.

The operation of the image processing apparatus having the above configuration will be described below. In the RGB space of FIG. 2, is a color vector (r, g, b) of the image signal, is a unit (white) vector (1, 1, 1), is a vertical vector from the color vector to the unit vector, is a unit vector It is a reference vector in a plane perpendicular to and including the vector. Here, the lightness of the color vector is proportional to ||, and the saturation is proportional to ||. The hue θ is represented by a rotation angle formed by a vertical vector with respect to a reference vector with a unit vector as the center.

Set the saturation and hue areas to be extracted to θ ₁ ± Δθ ₁
And θ ₂ ± Δθ ₂ , the area of the RGB space in which the saturation and hue are partially in a minute range is approximately r + C ₁ −ΔC ₁ <b <r + C ₁ + ΔC ₁ (1) g + C ₂ It can be expressed as a common region of −ΔC ₂ <b <g + C ₂₊ ΔC ₂ (2). The shaded area in FIG. 3 represents this common area.

Here, C ₁ and C ₂ are constants representing the center value of the RGB space region obtained from θ ₁ and θ ₂ which are the center values of the saturation and hue regions to be extracted, and ΔC ₁ and ΔC ₂ are the above It is a constant representing the range from the center value of the RGB space area, which is obtained from Δθ ₁ and Δθ ₂ which is the range from the center value of the saturation and hue areas to be extracted. That is, when the image signals are r, g, and b, the saturation f (r, g, b) is k
Where k (r ² + g ² + b ² −rg-gb-br) (3), the hue θ (r, g, b) is cot ⁻¹ · {3 ^1/2 · (g− b) / (2r-g-b)} (4). Here, the range of saturation f and hue θ to be extracted θ ₁ −Δθ ₁ <f (r, g, b) <θ ₁ + Δθ ₁ (5) θ ₂ −Δθ ₂ <θ (r, g, b) <Θ ₂ + Δθ ₂ (6) If the image signals r and g are determined, θ ₁ , Δθ ₁ , θ
₂ and Δθ ₂ are known, the image signal b is approximated as r + C ₁ −ΔC ₁ <b <r + C ₁ + ΔC ₁ (7) g + C ₂ −ΔC ₂ <b <g + C ₂ + ΔC ₂ (8), and a constant C ₁ and C ₂ are the constant Δ from θ ₁ and θ _2.
C ₁ and ΔC ₂ can be uniquely obtained from Δθ ₁ and Δθ ₂ , respectively. However, if the constants ΔC ₁ and ΔC ₂ are large values, an error occurs, and therefore the values are set to satisfy ΔC ₁ and ΔC ₂ << (C ₁ ² + C ₂ ² ) ^1/2 (9).

FIG. 4 (A) (B) (C ) (D) are, _C 1, _{C 2} by the control signal Sc, ΔC _1, ΔC ₂ is set LUT11,
It is a characteristic curve figure which shows the function respectively written in 12,13,14.

Input color image signals r _i , g _i , to the above image processing device,
When b _i is input, the image signals r _i and g _i are LU
Enter in T1. The image signal r _i is the LUT 11, 12,
The outputs are converted into outputs S ₁ and S ₂ represented by the following equations, respectively.

S ₁ = r _i + C ₁ + ΔC ₁ (10) S ₂ = r _i + C ₁ −ΔC ₁ (11) Similarly, the image signal g _i is the LUT 13, 14 and the output S ₃ represented by the following equation, respectively. It is converted to _{S 4.}

_{S 3 = g i + C 2} + ΔC 2 ... (12) S 4 = g i + C 2 -ΔC 2 ... (13) comparators 21 to 24 have the following input-output relationship.

3 pin output = 1; 1 pin input> 2 pin input = 0; 1 pin input <2 pin input Therefore, the comparators 21 to 24 input the conversion outputs S _{1 to} S ₄ and the image signal b _i as follows. Produce a different output.

In the comparator 21, _{1 is in} the region of r _i + C ₁ + ΔC ₁ > b _i , the others are 0. In the comparator 22, it is 1 in the region of r _i + C ₁ −ΔC ₁ <b _i , and the other is 0 in the comparator 23 g _i + C ₂ + _{ΔC 2>} 1 with _{b i} region of the others 0 comparator 24 in _{g i + C 2 -ΔC 2 <} 1 in the region of _{b i,} others 0 AND circuit 3 outputs _S 5 ~ comparators 21-24 The logical product of S ₈ is output. That is, the output of the AND gate is r _i + C ₁ −ΔC ₁ <b _i <r _i + C ₁ + ΔC ₁ (14) g _i + C ₂ −ΔC ₂ <b _i <g _i + C ₂ + ΔC ₂ (15) Is 1 in the common area (hatched portion in FIG. 3), and 0 in other areas. The delay circuit 4 inputs the color image signals r _i , g _i , b _i, and outputs the signals r _d , g _d , b _d which are delayed by the LUT 1, the comparators 21 to 24, and the AND circuit 3. . When the mask binary output S _g is 1, the mask gate 5 outputs r _d , g _d , and b _d as they are, respectively, r _o ,
g _o , b _o , output r when the mask binary output S _g is 0
_{o, g o,} a _{b o} is set to 0. That is, by masking the input image with the mask binary output S _{g, the} RGB image signal r _o having the same value as the input image in the area of hue and saturation in the specified range and 0 in the other areas. , G _o , b _o are output.

If the delay due to the LUT1, the comparators 21 to 24, and the AND circuit 3 is sufficiently smaller than the period of the pixel clock, the delay circuit 4 is not necessary.

Further, in the above-mentioned embodiment, the image signals r _i and g _i are added to the LUT1 and b _i are directly added to the comparators 21 to 24, but any combination can be taken depending on the region to be extracted.
Further, the logic circuit is not limited to the AND circuit.

FIG. 5 is a block diagram showing a second embodiment of the present invention. By combining the hue / saturation filter 10 shown in the first embodiment with a lightness filter 20 which is easy to realize,
It is possible to realize a filter that extracts a region whose saturation and brightness are within a certain range. In the figure, r _o1 , g _o1 , and b _o1 are image outputs obtained by extracting regions in which hue and saturation are in a certain range, and r _o2 , g
_o2 and _bo2 are image outputs in which regions having hue, saturation, and lightness within a certain range are extracted.

<< Advantages of the Invention >> As described above, according to the present invention, in digital image processing, an image processing apparatus for extracting a region having a specified range of saturation and hue with a small amount of calculation is realized with a simple configuration. be able to.

[Brief description of drawings]

FIG. 1 is a configuration block diagram showing an embodiment of an image processing apparatus according to the present invention, FIGS. 2 and 3 are principle explanatory diagrams for explaining the operation principle of the apparatus, and FIG. L in Figure 1
FIG. 5 is a characteristic curve diagram showing the contents of the UT section, and FIG.
It is a block diagram showing an example of. 1, 11, 12, 13, 14 ... Look-up table, 3 ... Logic circuit, 5 ... Mask circuit, 21-24 ...
... comparator, r _i , g _i , b _i ... color image signal.

Claims (1)

[Claims] 1. A constant for defining an area of saturation and hue is stored, an image signal of two colors of a color image signal is input, and an area of an image signal of another color of the color image signal is input from the constant. , A comparator for comparing the output of the lookup table with the image signal of the other one color of the color image signals, a logic circuit for inputting the output of the comparator, and the logic circuit An image processing apparatus comprising: a mask circuit for masking the color image signal at an output, and extracting a saturation and hue region in a designated range from the color image signal.