JP2005150907A - Method and device for enhancing saturation, electronic camera, and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and a device for enhancing saturation in which saturation can be enhanced sufficiently in low saturation regions while suppressing saturation in high saturation regions when saturation of an image signal is enhanced, and to provide an electronic camera and a program for implementing them. <P>SOLUTION: Assuming the larger absolute value of color-difference signals U and V constituting an image signal is a variable β, an amplification factor operating circuit 371 performs such an operation as the operation results when the variable β having some value becomes smaller than the operation results when the variable β having a smaller value thus acquiring an amplification factor α within a predetermined range. Amplifiers 372 and 373 amplify both color-difference signals U and V with that amplification factor α. Since the I/O characteristics of the color-difference signals U and V become nonlinear where the inclination decreases gradually as the variable β increases, saturation can be enhanced sufficiently in low saturation regions while suppressing saturation in high saturation regions. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a saturation enhancement method, a saturation enhancement apparatus, an electronic camera, and a program for realizing them, which are suitable for use in, for example, a digital camera.

  2. Description of the Related Art Conventionally, in a digital camera, various color processes are performed on an image signal output from an image sensor and digitally converted. Common color processing is gamma correction and white balance adjustment, and these are mainly processing relating to adjustment of the color balance (hue) of the entire image. Apart from this, saturation enhancement is performed to enhance the vividness of the subject without losing the color balance. In addition to the digital camera, the saturation enhancement is performed not only in a digital camera but also in various display devices that display a still image or a moving image recorded on a recording medium or a still image or a moving image transmitted by a broadcast signal. Is called.

Further, the above saturation enhancement is the same as Cb and Cr signals in the case where the color space is expressed by YCbCr in this specification, for example, U-signal and V-signal which constitute an image signal together with the luminance signal Y. In the case of an NTSC color video signal, it is possible by amplifying the I signal and the Q signal with a predetermined amplification factor. Further, in the following Patent Document 1, in the configuration in which the color difference signals (R−Y, G−Y, and B−Y) extracted from the R, G, and B signals are amplified with individual amplification factors, the respective amplification factors are set. Color that gives a vivid impression without forcing a faint color by making the gain in a section with a small color difference signal value smaller than that in a section with a large color difference signal value. Only the method of emphasizing is described.
JP 2000-69496 A (see “0136” paragraph, FIG. 1 and FIG. 2)

  However, when the color difference signal is amplified and saturation enhancement is performed as described above, if the value before amplification of the color difference signal (U, V, etc.) is large, the value after amplification exceeds the adjustment range and saturates. It is easy to reduce the reproducibility of a portion where a bright color exists. Further, if the amplification factor is reduced to prevent the saturation, there is a problem that sufficient emphasis cannot be performed when the value before amplification is small, and a dull tone with less color is likely to occur.

  The present invention has been made in view of the above-described conventional problems, and at the time of saturation enhancement for an image signal, saturation that can sufficiently enhance the low saturation region while suppressing saturation in the high saturation region. An object of the present invention is to provide a degree enhancement method, a saturation enhancement apparatus, an electronic camera, and a program for realizing them.

  In order to solve the above-described problem, the invention of claim 1 is a method for performing saturation enhancement on an image signal by amplifying both of the two types of color difference signals constituting the image signal. The amplification factor to be multiplied by the value of the color difference signal is determined based on at least one value of the two color difference signals, and the amplification factor when each value in the two color difference signals is a certain value, A first step of obtaining an amplification factor within a range determined to be smaller than an amplification factor when the value is smaller than the certain value, and a first step of amplifying two color difference signals with the obtained amplification factor, respectively. 2 steps.

  According to such a method, the two color difference signals are amplified with the amplification factor on the maximum value side within the range determined when each value is small, and within the range determined when each value is large. Amplification can be performed with an amplification factor on the minimum value side. Therefore, by setting the minimum value of the amplification factor to “1”, for example, sufficient amplification is performed when the values of the two color difference signals are small, and amplification is performed when each of the two color difference signals is large. It can suppress that a later value exceeds the adjustment range and is saturated.

  In the invention of claim 2, the amplification factor acquired in the first step is obtained by a predetermined calculation using a value based on at least one of the two color difference signals as a variable. The method was value.

  According to a third aspect of the invention, the variable is a value on the larger side of the absolute value of each value in the two color difference signals.

  According to this method, a uniform enhancement degree can be ensured for all colors having the same saturation before enhancement.

  According to a fourth aspect of the present invention, the variable is a square root of a value obtained by squaring and adding each value in the two types of color difference signals.

  Even in such a method, it is possible to ensure a uniform enhancement degree for all colors having the same saturation before enhancement.

  In the invention of claim 5, the amplification factor acquired in the first step is a method of gradually changing according to the change of each value in the two kinds of color difference signals.

  According to this method, changes in the values of the two types of color difference signals before amplification can be faithfully reflected in the changes in the values of the two types of color difference signals after amplification.

  Further, in the invention of claim 6, the predetermined calculation is determined such that β is the variable, βmax is the maximum value that the variable β can take, and α1 is the maximum value of the determined amplification factor. The minimum value of amplification factor is α2, and the following formula

α = [(βmax−β) × α1 + β × α2] / βmax
From this, the value α was obtained.

  According to the seventh aspect of the present invention, there is provided a saturation enhancement apparatus for performing saturation enhancement on an image signal by amplifying both of the two types of color difference signals constituting the image signal. The gain multiplied by the signal value is determined based on at least one of the two color difference signals, and the acquired value when the values of the two color difference signals are a certain value is the certain value. A magnification acquisition unit that acquires an amplification factor within a predetermined range that is smaller than an acquired value when the frequency is smaller than the amplification value, and an amplification unit that amplifies each of the two color difference signals with the amplification factor acquired by the magnification acquisition unit; Was provided.

  In such a configuration, the amplifying means amplifies the two color difference signals at an amplification factor on the maximum value side within the range determined when the value is small, and within the range determined when the value is large. Can be amplified with an amplification factor on the minimum value side. Therefore, by setting the minimum value of the amplification factor to “1”, for example, sufficient amplification is performed when the values of the two color difference signals are small, and after amplification when the values of the two color difference signals are large. It can suppress that a value exceeds the adjustment range and saturates.

  Further, in the invention of claim 8, a computer having a saturation enhancement apparatus that performs saturation enhancement on an image signal by amplifying both of two kinds of color difference signals constituting the image signal,

  The gain multiplied by the values of the two color difference signals is determined based on the value of at least one of the two color difference signals, and the acquired value when the values of the two color difference signals are a certain value, A first process of acquiring an amplification factor within a predetermined range that is smaller than an acquired value when the value is smaller than the certain value, and a second process of amplifying two types of color difference signals with the acquired amplification factor, respectively. A program for executing processing.

  By using such a program, the above-described method of the present invention can be implemented in a predetermined saturation enhancement apparatus equipped with a computer.

  According to a ninth aspect of the present invention, in an electronic camera that converts a subject image captured by an image sensor into image data, compresses the converted image data, and records it on a recording medium, the output signal of the image sensor When the amplification factor to be multiplied by the values of the two color difference signals constituting the image signal based on is determined based on at least one value of the two color difference signals, and the values of the two color difference signals are a certain value The gain acquisition means for acquiring an amplification factor within a predetermined range that is smaller than the acquisition value when the value is smaller than the certain value, and the amplification factor acquired by the magnification acquisition means is 2 An amplifying means for amplifying each color difference signal was provided.

  In such a configuration, the amplifying means amplifies the two color difference signals at an amplification factor on the maximum value side within the range determined when the value is small, and within the range determined when the value is large. Can be amplified with an amplification factor on the minimum value side. Therefore, by setting the minimum value of the amplification factor to “1”, for example, sufficient amplification is performed when the values of the two color difference signals are small, and after amplification when the values of the two color difference signals are large. It can suppress that a value exceeds the adjustment range and saturates.

  In the present invention, when each value of the two color difference signals is small, sufficient enhancement is performed, and when each value of the two color difference signals is large, the value after amplification exceeds the adjustment range and saturates. Can be suppressed. Therefore, it is possible to place a sufficient color on a portion with less color while maintaining reproducibility of a portion where a bright color exists in an image or the like.

  In the methods of claims 3, 4, 5, and 6, since a uniform enhancement degree can be ensured for all colors having the same saturation before enhancement, saturation of each color can be ensured. Saturation emphasis can be achieved while maintaining a strong and weak balance.

  Further, in the method of claim 5, since the change in each value of the two color difference signals before amplification can be faithfully reflected in the change in each value of the two color difference signals after amplification, Saturation enhancement can be performed while maintaining a balance of saturation of images and the like.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a schematic configuration of an electronic camera 1 according to the present invention.

  The electronic camera 1 captures a subject with a CCD 2 that is an image sensor, displays the captured subject image on an LCD (liquid crystal display device) 4, and compresses the captured subject image data in accordance with a shooting operation. This is a configuration for recording in the image memory 5. The image memory 5 is a non-volatile memory (recording medium) such as a flash memory that is built in or detachable from the camera body.

  The CCD 2 is provided with a Bayer array color filter array in the photosensitive portion. The analog image pickup signal output from the CCD 2 is subjected to various signal processing in the signal processing portion 3 and finally a luminance signal ( YUV data comprising a Y signal) and color difference signals (U signal, V signal), that is, output as a digital image signal. Details of the signal processing unit 3 will be described later. The image signal output from the signal processing unit 3 is sequentially stored in a working memory of the CPU 6 and a RAM (for example, DRAM) 7 used as a memory for temporarily storing image data. Sent to and displayed as a through image.

  At the time of shooting operation, the luminance (Y) and color difference signals (U, V) for one frame stored in the RAM 7 are read out in units called basic blocks of 8 pixels vertical by 8 horizontal pixels for each component. At the same time, the data is sent to the JPEG conversion unit 8 where data compression is performed by processing such as DCT conversion and Huffman coding, and the data is recorded in the image memory 5 as an image file in a format compliant with JPEG. The compressed image data (image file) recorded in the image memory 5 is read by the CPU 6 as necessary, once decompressed by the JPEG conversion unit 8, and then reproduced and displayed on the LCD 4 as a still image or a moving image. The

  The electronic camera 1 also includes a ROM 9 in which a control program necessary for the CPU 6 to control each unit is recorded, a key input unit 10, and a lens driving unit 11. The key input unit 10 includes a shutter key, a mode switching key used for switching operation modes, and the like, and outputs an operation signal corresponding to the key operation to the CPU 6. The lens driving unit 11 includes a motor that drives a lens group including a focus lens disposed in front of the CCD 2 in the optical axis direction, a driver for controlling the motor, and the like. The lens position is changed based on the command.

  FIG. 2 is a block diagram showing details of the signal processing unit 3 described above. The signal processing unit 3 includes an analog processing unit 31 to which an analog imaging signal input from the CCD 2 is input, a black level adjustment unit 32, a white balance adjustment unit 33, a gamma correction unit 34, a pixel interpolation processing unit 35, and a YUV conversion processing unit. 36, the saturation enhancement processing unit 37.

  The analog processing unit 31 includes a correlated double sampling circuit (CDS circuit) that reduces drive noise of the CCD 2 included in the imaging signal output from the CCD 2, and an automatic gain control circuit (AGC) that adjusts the gain of the signal after noise reduction. Circuit), an A / D converter that samples the signal after gain adjustment and converts it into a digital signal having a predetermined number of bits, and the analog imaging signal input from the CCD 2 corresponds to a digital image signal, that is, a color filter array It is converted into R, G, B pixel data (Bayer data) in the array.

  The black level adjustment unit 32 clamps the digitized image signal to a predetermined black level, and the white balance adjustment unit 33 adjusts the white balance by performing gain adjustment for each of R, G, and B with respect to the clamped image signal. To do. The gamma correction unit 34 corrects gamma characteristics (gradation characteristics) of the image signal after white balance adjustment, and the pixel interpolation processing unit 35 converts RGB data for each pixel based on the image signal (Bayer data) after gamma correction. Generate pixel interpolation. The YUV conversion processing unit 36 generates YUV data composed of a luminance signal (Y) and color difference signals (U, V) for each pixel from the R, G, B color component data.

  The saturation enhancement processing unit 37 performs saturation enhancement on the YUV data generated by the YUV conversion processing unit 36 to amplify the color difference signal (U, V) in units of pixels. The adjusted YUV data is temporarily stored in the RAM 7 as described above, and an image based on the stored YUV data for one frame is displayed on the LCD 4 or sent to the JPEG conversion unit 8 and compressed.

  FIG. 3 is a diagram showing a circuit configuration of the saturation enhancement processing unit 37. The saturation enhancement processing unit 37 has amplification factors (multiplication coefficients) corresponding to the values of the color difference signals U and V of the input YUV signal. An amplification factor calculation circuit 371 which is a magnification acquisition unit of the present invention that calculates and outputs α, and amplifies the color difference signals Uin and Vin by the amplification factor α and outputs amplified color difference signals Uout and Vout, respectively. The amplifiers 372 and 373 are amplification means. The amplification factor calculation circuit 371 includes a register (not shown) in which calculation coefficients α1 and α2 indicating the maximum value and minimum value of the amplification factor used for the calculation are set.

In this embodiment, the amplification factor calculation circuit 371 is configured to calculate the amplification factor α based on the following equation. In the following equation, the number of quantization bits of each pixel is 24 bits, and the values of the color difference signals Uin and Vin change to signed 8 bits, that is, from -128 to 127. It is assumed that the degree can be expressed in 128 levels.
[formula]
β = max (abs (Uin), abs (Vin))
(Max: function for obtaining the larger value, abs: function for obtaining the absolute value)
α = [(128−β) × α1 + β × α2] / 128
However, α1> α2 and “128” are the maximum values (βmax) that β can take.

  In this configuration, the amplification factor α output from the amplification factor calculation circuit 371 to the amplifiers 372 and 373 has a variable β (an absolute value of U or an absolute value of V) based on U and V signals of 0 to 128. To change gradually from α1 to α2. Therefore, the input / output characteristics of the color difference signals U and V in the saturation enhancement processing unit 37 are nonlinear characteristics in which the slopes gradually decrease as the input values Uin and Vin increase as shown by the solid lines in FIG. .

  This figure is an example where U = V and α1 is 1.5 and α2 is 1.0. If α2 is set to 1.0, that is, the minimum value of the amplification factor is 1.0. The output values Uout and Vout when the input values Uin and Vin are the maximum values can be kept as the input values Uin and Vin. That is, when the amplification factor is fixed to 1.5 as shown by the broken line in the figure, saturation occurs in the high saturation region (input values Uin and Vin are 85 or more) and clipping occurs. Can be eliminated.

  Therefore, in the present embodiment, a sufficient color can be placed on a portion with less color while maintaining the reproducibility of the portion where a bright color exists in the subject image captured by the CCD 2. . As a result, the quality of the through image displayed on the LCD in the shooting standby state and the image recorded in the image memory 5 can be improved.

  Here, the case where α1 is 1.5 and α2 is 1.0 has been described as an example, but the values of α1 and α2 can be appropriately changed as necessary. In addition, the calculation coefficient α2 indicating the minimum value of the amplification factor may be 1.0 or more. In this case, setting a value closer to 1.0 improves the reproducibility of a portion where a bright color exists. It can be maintained more reliably.

  Further, in the present embodiment, the variable β used for calculating the amplification factor α of the color difference signals U and V is set to the larger value of the absolute values of the respective values in the color difference signals U and V. Thus, by reflecting both the values of the color difference signals U and V in the amplification factor, a uniform enhancement degree can be ensured for all colors having the same saturation before enhancement. Therefore, it is possible to enhance saturation while maintaining a balance of saturation between colors.

Such an effect can also be obtained when the variable β is, for example, the square root (β = √ (U ² + V ² )) of values obtained by squaring the values of the color difference signals U and V. .

  Further, in the present embodiment, the amplification factor α obtained by the saturation enhancement processing unit 37 is such that the input / output characteristics of the color difference signals U and V gradually decrease as the input values Uin and Vin increase. Since it has nonlinear characteristics, changes in the input values Uin and Vin can be accurately reflected in the output values Uout and Vout. Therefore, it is possible to perform saturation enhancement while maintaining a saturation balance in the subject image before saturation enhancement.

  However, the present invention is not limited to this, and the input / output characteristics of the color difference signals U and V are input to the amplification factor calculation circuit 371 as shown in FIGS. 5 (a) and 5 (b), for example. It is also possible to obtain the amplification factor α, which has a nonlinear characteristic in which the slope decreases stepwise as the value increases. Even in such a case, a sufficient color can be put on a portion with less color while maintaining the reproducibility of the portion where the bright color exists in the subject image captured by the CCD 2. In short, it is only necessary to perform an operation in which the amplification factor α when the variable β is a certain value is smaller than the amplification factor α when the variable β is smaller than the certain value. Further, the saturation enhancement processing unit 37 may be made to obtain the amplification factor α at which the nonlinear characteristic shown in FIG. 4 is obtained by a calculation different from the calculation described above.

  In this embodiment, the signal processing unit 3 is provided with the dedicated saturation enhancement processing unit 37 to amplify the color difference signals U and V. However, a predetermined program for saturation enhancement processing is stored in the ROM 9. It is also possible to store them and cause the CPU 6 to perform part or all of the signal processing described above by the saturation enhancement processing unit 37. In this case, however, it is necessary to use a CPU 6 having a high data processing capability. In addition, including the above case, the amplification factor α of the color difference signals U and V does not necessarily have to be obtained by the above-described calculation. For example, a predetermined value indicating the amplification factor α corresponding to the value of the color difference signals U and V is used. You may make it acquire directly using the look table of.

  Although the saturation enhancement processing in the electronic camera 1 has been described here, the present invention is recorded on a recording medium, for example, as long as it has a configuration for enhancing the saturation of an image in addition to the electronic camera. The present invention can also be applied to various display devices that display still images and moving images, or still images and moving images transmitted by broadcast signals, other video devices, and image processing devices. Even in such a case, the effects described above can be obtained. In this case, the color difference signals to be amplified for saturation enhancement are not limited to the U and V signals, and may be other color difference signals such as an I signal and a Q signal.

1 is a block diagram of an electronic camera according to the present invention. It is a block diagram which shows the detail of a signal processing part. It is a circuit block diagram of a saturation emphasis processing unit. It is a figure which shows the input-output characteristic of the color difference signals U and V in a saturation emphasis processing part. It is a figure which shows the input-output characteristic of the color difference signals U and V in other embodiment.

Explanation of symbols

1 Electronic camera 2 CCD
3 Signal Processing Unit 5 Image Memory 6 CPU
8 JPEG Conversion Unit 35 Pixel Interpolation Processing Unit 36 YUV Conversion Processing Unit 37 Saturation Enhancement Processing Unit 371 Amplification Factor Calculation Circuit 372 Amplifier 373 Amplifier

Claims (9)

A method of performing saturation enhancement on an image signal by amplifying both of two kinds of color difference signals constituting the image signal,
The amplification factor to be multiplied by the values of the two color difference signals is determined based on at least one value of the two color difference signals, and the amplification factor when each value of the two color difference signals is a certain value. A first step of obtaining an amplification factor within a range determined to be smaller than an amplification factor when each of the values is smaller than the certain value;
And a second step of amplifying each of the two color difference signals with the obtained amplification factor.   The gain obtained in the first step is a value obtained by a predetermined calculation using a value based on at least one of two color difference signals as a variable. Saturation enhancement method.   The saturation enhancement method according to claim 2, wherein the variable is a larger value of absolute values of respective values in the two kinds of color difference signals.   The saturation enhancement method according to claim 2, wherein the variable is a square root of a value obtained by squaring and adding each value in the two kinds of color difference signals.   The saturation enhancement method according to claim 1, 2 or 3, wherein the amplification factor acquired in the first step gradually changes in accordance with a change in each value of the two types of color difference signals. In the predetermined calculation, β is the variable, βmax is the maximum value that the variable β can take, α1 is the maximum value of the determined gain, and α2 is the minimum value of the determined gain. α = [(βmax−β) × α1 + β × α2] / βmax
The saturation enhancement method according to claim 5, wherein the value α is obtained from the value. A saturation enhancement apparatus that performs saturation enhancement on an image signal by amplifying both of two types of color difference signals constituting the image signal,
The amplification factor by which the values of the two color difference signals are multiplied is determined based on the value of at least one of the two color difference signals, and the acquired value when the values of the two color difference signals are a certain value, Magnification acquisition means for acquiring an amplification factor within a determined range that is smaller than an acquired value when the value is smaller than the certain value;
A saturation enhancement apparatus comprising: amplification means for amplifying two kinds of color difference signals at the amplification factor acquired by the magnification acquisition means. A computer having a saturation enhancement device that amplifies both of the two color difference signals constituting the image signal to enhance the saturation of the image signal;
The amplification factor by which the values of the two color difference signals are multiplied is determined based on the value of at least one of the two color difference signals, and the acquired value when the values of the two color difference signals are a certain value, A first process of acquiring an amplification factor within a determined range that is smaller than an acquired value when the value is smaller than the certain value;
A program for executing a second process of amplifying two types of color difference signals with the obtained amplification factor. In an electronic camera that converts a subject image captured by an image sensor into image data, compresses the converted image data, and records it on a recording medium.
The amplification factor to be multiplied by the values of the two color difference signals constituting the image signal based on the output signal of the image sensor is determined based on the value of at least one of the two color difference signals and the values of the two color difference signals. A magnification acquisition means for acquiring an amplification factor within a determined range in which an acquired value when a certain value is smaller than an acquired value when the value is smaller than the certain value;
An electronic camera comprising: amplification means for amplifying each of the two types of color difference signals at the amplification factor acquired by the magnification acquisition means.

Images