JPH05183805A - Image pickup device - Google Patents

Abstract

PURPOSE:To obtain an image pickup device capable of supressing the occurrence of a pseudo contour and obtaining an excellent picture quality in a visual sense. CONSTITUTION:When the photometric values of more than two areas of plural photometric areas of a photometric sensor 106 are smaller than a threshold Te, a processing is performed by switching a switch 1 18 to a non-linear conversion circuit B. 117 side and by switching a switch 121 to a table conversion part 119 and a dither processing part 120 side. A non-linear conversion circuit A. 111 is the same as a gamma conversion circuit and a non-linear conversion circuit B. 117 has a characteristic of lifting a lower level than the circuit A. By this constitution, as for an object having large areas whose luminance is low, the part where luminance is low is quantized finer and a dither processing is performed for this low level part and the purpose is attained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image pickup apparatus such as an electronic still camera or a video movie camera for digitizing and processing an image signal, and more particularly to suppressing pseudo contours thereof.

[0002]

2. Description of the Related Art Conventionally, an image pickup apparatus for converting an image signal into a digital signal for recording has a structure as shown in FIG.

In FIG. 4, incident light from a subject is imaged on a light receiving surface of an image pickup device 104 such as a CCD and photoelectrically converted. The image sensor 104 outputs one or more types of signals depending on the type of color filter such as R, G, B, Y, Cr, Cb, and complementary colors.

The CPU 307 drives the shutter 103 and the mirror 102, receives the output signal of the photometric sensor 306, and controls the shutter speed and the opening / closing of a diaphragm (not shown) based on the signal data to adjust the exposure amount. In addition, if necessary, the gain of the image sensor output signal is adjusted to AGC.
Control with 105.

As the photometric sensor 306, multipoint photometry is often used in which a plurality of areas in an image are metered and the exposure amount is determined by weighting each area.

The signal whose gain has been adjusted is the clamp 108,
Sample and hold 109, white balance adjustment 1
10, non-linear conversion of gamma 311 and knee 112,
It is input to the AD converter 113 and converted into a digital signal.

The digital signal processing circuit 114 subjects the digital signal to filter processing, color signal decoding, and the like. Further, the compression processing circuit 115 outputs the output of the digital signal processing circuit 114 to an ADCT (adaptive discrete co).
sine transform) method, DPCM (differential PCM)
Interface circuit 116
Via OMD (magneto-optical disk), memory card,
The data is recorded on a digital recording medium 117 such as a hard disk or a floppy disk.

Depending on the model, an autofocus unit is provided, and the CPU 307 receives the output of the autofocus sensor and outputs a signal for controlling the autofocus motor to focus.

[0009]

However, since the image pickup device using the photoelectric conversion element as in the conventional example has a smaller dynamic range than that of the silver halide camera, an appropriate exposure correction is performed in all photographing situations. Is difficult to do.

If the image is overexposed, it is saturated and the image quality is deteriorated. Further, when the exposure is underexposed, as a result, the gain is often increased to be reproduced, and the S / N is deteriorated.

In particular, in a digital conversion device, noise due to a quantization error appears as a pseudo contour, resulting in a visually unfavorable image quality.

As shown in FIG. 5, the pseudo contour is apt to stand out in a flat portion having a low brightness such as a shaded wall.

The present invention has been made in view of the above circumstances, and provides an image pickup apparatus in which generation of pseudo contours is suppressed and a visually preferable image quality is obtained.

[0014]

According to the present invention, in order to achieve the above-mentioned object, an image pickup device is constructed as in the following (1) to (4).

(1) A plurality of non-linear conversion means for converting image signals having mutually different characteristics, a selection means for selecting one non-linear conversion means from the plurality of non-linear conversion means, and a non-linearity selected by the selection means In the case where the output of the converting means is converted from analog to digital and the predetermined non-linear converting means is selected by the selecting means, the data which is AD converted by the AD converting means is a threshold value. In the above case, the non-linear conversion process is performed so that the same data as that in the case of selecting another non-linear conversion unit is obtained, and when the data is not equal to or more than the threshold value, the image pickup apparatus including a processing unit that performs the dither process. ..

(2) The image pickup device according to (1), wherein the selecting means is manually operated.

(3) A photometric means capable of photometrically measuring a plurality of areas in the image is provided, and the selecting means performs a predetermined non-linear conversion means when the photometric value of the predetermined number of areas of the photometric means is smaller than a threshold value. The imaging device according to (1) above, which is selected.

(4) An autofocus means having a sensor array is provided, and the selecting means selects a predetermined non-linear converting means when the outputs of a predetermined number of sensors of the sensor array are smaller than a threshold value. (1) The image pickup device according to item 1.

[0019]

With the configurations (1) to (4) described above, with respect to a subject having many low luminance regions, the low luminance portion is quantized more finely so that no pseudo contour is generated.

In the configuration (2), the non-linear conversion means is selected manually, in the configuration (3), the non-linear conversion means is selected according to the output of the photometric means, and in the configuration (4). Selection of the non-linear conversion means is performed according to the output of the sensor array of the autofocus means.

[0021]

EXAMPLES The present invention will be described in detail below with reference to examples. (Embodiment 1) FIG. 1 is a block diagram of essential parts of an "electronic still camera" according to Embodiment 1. In FIG. 1, incident light from a subject is imaged by the lens 101 on the light receiving surface of the CCD 104 and photoelectrically converted. In this embodiment, the output signal is Y,
Three types of R and B can be obtained. In the figure, only the Y signal system is shown.

The CPU 107 drives the shutter 103 and the mirror 102, receives the output signal of the photometric sensor 106, and controls the shutter speed and the opening / closing of a diaphragm (not shown) based on the signal data to adjust the exposure amount. ..
Also, if necessary, the gain of the image sensor output signal
Control with C105.

The photometric sensor 106 uses multipoint photometry in which a plurality of areas in the image are metered and the exposure amount is determined by weighting each area.

The signal after the gain adjustment is the clamp 108,
Sample and hold 109, white balance 110
Processed by.

In this embodiment, the photometric values at two or more locations among the plurality of photometric areas of the photometric sensor 106 are threshold values Te.
If it is smaller, the switch 118 is changed over to be processed by the non-linear conversion circuit B 117, and otherwise the non-linear conversion circuit A 111 is processed.

The characteristic of the non-linear conversion circuit A 111 is shown by the solid line A in FIG. 2, and the characteristic of the non-linear conversion circuit B 117 is shown by the solid line B. The non-linear conversion circuit A · 111 is the same as the gamma conversion circuit (gamma = 0.45). Further, in this embodiment, the threshold value Te is set to a brightness of 15%.

The output of the non-linear conversion circuit A or B is processed by the knee conversion 112 and converted into digital data by the AD converter 113.

When the switch 121 and the switch 118 are interlocked and processed by the non-linear conversion circuit B · 117,
A correction process that is equivalent to the nonlinear conversion circuit A · 111 is performed.

In the correction process, the table conversion unit 119
Outputs table values for digital data values larger than the threshold value Td, and outputs 0 values for others. The dither processing unit 120 carries out dither processing for values smaller than the threshold value Td, and otherwise outputs 0 value. In this embodiment, the error diffusion method is used for the dither processing.

The table conversion unit 119 and the dither processing unit 12
The output of 0 is added by the adder 122.

The digital signal processing circuit 114 subjects the digital signal to filter processing, color signal decoding, and the like. Further, the compression circuit 115 compresses the output of the digital signal processing circuit 114 by the ADCT method and outputs it, and records it in the memory card 117 via the interface circuit 116.

In this way, for a subject with many low-luminance regions, the low-luminance portion is quantized more finely, and the small value after quantization is dithered, so that fine gradations can be expressed and pseudo The generation of contours is suppressed, and a visually pleasing image quality is obtained.

Although table conversion is used in this embodiment, it may be calculated for each value.

In this embodiment, the dither processing is carried out by the error diffusion method. However, a method of adding a pseudo random number such as Bayer pattern may be used, or another method may be used.

Further, in the present embodiment, the present invention is applied only to the Y signal, but it may be applied to other R and B signals, and it is also applicable to other color combinations such as complementary color type. it can.

In this embodiment, the non-linear conversion curve is automatically selected, but it may be selected manually.

The automatic selection method may or may not be weighted for each photometric area. Further, three or more types of non-linear conversion may be prepared and finely selected.

(Embodiment 2) FIG. 3 is a block diagram of the essential parts of an "electronic still camera" according to a second embodiment. As shown in the figure, the present embodiment is provided with an autofocus unit and uses the sensor output of the autofocus unit for switching the switches 118 and 121.

In FIG. 3, reference numeral 124 is an autofocus sensor array, and 123 is an autofocus motor, which together with the CPU 107 constitute a phase difference type autofocus section.

When the number of sensors whose output is smaller than the threshold value Ty among the sensors of the sensor array 124 is 50% or more of the total number of sensors, the switch 118 is set to the non-linear conversion circuit B.
Switch to the 117 side, and if not more than 50%, switch 118 to the non-linear conversion circuit A • 111 side for processing.

The operation, effect, and modification of this embodiment are the same as those of the first embodiment.
The description is omitted because it is similar to the above.

In the present embodiment, the selection criterion for nonlinear conversion is determined by the autofocus area, but a different area may be used as the reference by using an autofocus sensor array.

Although each embodiment is an electronic still camera, the present invention is not limited to this and can be applied to various video cameras.

[0044]

As described above, according to the present invention,
For a subject with many low-luminance regions, it is possible to suppress the occurrence of false contours and obtain a visually preferable image quality.

[Brief description of drawings]

FIG. 1 is a block diagram of a main part of a first embodiment.

FIG. 2 is an explanatory diagram of the first embodiment.

FIG. 3 is a block diagram of a main part of the second embodiment.

FIG. 4 is a block diagram of a conventional example.

FIG. 5 is an explanatory diagram of a pseudo contour.

[Explanation of symbols]

 107 CPU 111 Non-Linear Conversion Circuit A 117 Non-Linear Conversion Circuit B 113 AD Converter 118, 121 Switch 119 Table Conversion Unit 120 Dither Processing Unit

Claims (4)

[Claims] 1. A plurality of non-linear conversion means having different characteristics for converting an image signal, a selection means for selecting one non-linear conversion means from the plurality of non-linear conversion means, and a non-linear conversion selected by the selection means. In the case where the A / D conversion means for analog-digital converting the output of the means and the predetermined non-linear conversion means are selected by the selection means, the data AD-converted by the AD conversion means is equal to or more than the threshold value. In the case of, non-linear conversion processing is performed so that the same data as when other non-linear conversion means is selected, and when the data is not greater than or equal to the threshold value, processing means for performing dither processing are provided. Image pickup device. 2. The image pickup apparatus according to claim 1, wherein the selecting means is manually operated. 3. A photometric means capable of photometrically measuring a plurality of areas in an image, wherein the selecting means selects a predetermined non-linear conversion means when a photometric value of a predetermined number of areas of the photometric means is smaller than a threshold value. The image pickup apparatus according to claim 1, wherein the image pickup apparatus is provided. 4. An auto-focusing means having a sensor array is provided, and the selecting means selects a predetermined non-linear conversion means when the outputs of a predetermined number of sensors of the sensor array are smaller than a threshold value. The image pickup apparatus according to claim 1, which is characterized in that.