JP2000287121A - Image signal processor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image signal processor that can detect a histogram of a required object with a simple circuit configuration. SOLUTION: The image signal processor is provided with an image pickup system 1 that supplies image data, a classification means 3 that sets a range area of values of at least three different picture data divided at least two different threshold values and classifies data of each pixel of the picture data by one image supplied form the image pickup system into at least three areas, a counter means 3 that counts number of pixels of each area to obtain a histogram of the picture data and an adjustment means 3 that adjusts a photographing condition in response to the histogram.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an image sensor.
The present invention relates to a technique for processing image data output from an (imaging element) or the like, and particularly to an image signal processing apparatus that performs digital data processing for setting appropriate imaging conditions.

[0002]

2. Description of the Related Art In photographing a subject, the aperture and exposure time of a camera are adjusted in accordance with subject information such as the brightness of the subject so as to obtain the best reproduced image. If the light intensity distribution of an image signal of one frame obtained from the image sensor can be detected as the subject information, the optimal imaging condition can be determined according to the light intensity distribution.

Therefore, in the prior art, as a simple light intensity distribution, only the data with the maximum light intensity and the data with the minimum light intensity in the image data of one screen are recorded as subject information. Based on the subject information, for example,
The average value of the maximum value and the minimum value is obtained, and it is determined whether the screen to be photographed is bright or dark based on the average value, and the exposure time of the imaging system, the gain of the video signal amplifier, and the like are determined.

[0004] Statistical processing data such as a histogram can be employed as a means for knowing the light intensity distribution of an image. Assuming that the signal obtained by the imaging device is converted into an 8-bit digital signal, the data value of one pixel can be quantized into 2 ⁸ = 256 steps. That is, the data of each pixel can be applied to any of the integer values from 0 to 255. The light intensity of the data of each pixel of the image of one frame is calculated as 0 to 255.
A histogram indicates how many pixels are distributed at each light intensity value in correspondence with any of the values.

[0005] The histogram shown in FIG. 4A shows a case where the light intensity distribution of the image of the subject is in an appropriate state. That is, bright pixels and dark pixels are exactly half each over the entire screen, and their distribution state has a substantially symmetric shape like a Gaussian distribution. Such an ideal subject already satisfies the suitable imaging conditions, so there is no need to change the imaging conditions.

On the other hand, in the histogram of FIG.
Pixels on the screen are unevenly distributed in a dark range as a whole. In the case of such a subject, even if the imaging condition is determined using only the conventional maximum value and minimum value data, the imaging condition is changed to a somewhat appropriate one because the average value AVE corresponds to the data of the maximum number of pixels. can do. That is, for example,
The exposure time can be lengthened and the histogram can be shifted in the overall brighter direction.

[0007]

In the conventional method, for example, a good reproduced image cannot be expected for a subject as shown in FIG. This is because the subject shown in FIG. 5A includes a slightly dark person 10 which is a main subject to be photographed and a streetlight 11 having a small but fairly bright spot in the photographing range. In the condition setting, a photographing result satisfying both the person and the streetlight cannot be obtained.

FIG. 5B shows a light intensity distribution (histogram) of the image.

In the histogram of FIG. 5B, there are two peaks, a peak 20 due to the person 10 as a main subject and a peak 21 due to the high-intensity streetlight 11. When subject information is obtained for such a subject by a conventional method, two values, a minimum value MIN and a maximum value MAX, are obtained. A pixel having light intensity data of an average value AVE of the maximum value and the minimum value is obtained. Is very little on the whole screen. For this, the average value A
When the exposure time is determined based on the VE or the gain of the video signal amplifier is determined, the reproduced image of the person 10 which is the main subject becomes darker, and the reproduced image of the streetlight 11 becomes too bright, and , And neither the person 10 nor the streetlight 11 is in an appropriate imaging condition.

In actual photographing, there are few cases where only a subject having a histogram as shown in FIGS. 4A and 4B is photographed, and a subject having a histogram as shown in FIG. In some cases.

Therefore, in order to be applicable to all conditions of the subject, the aperture and the exposure time of the image pickup system are adjusted based on the data of the histogram, not the data of the minimum value and the maximum value. It is desired to perform some kind of signal processing on the image signal obtained in step (1) to obtain histogram image data having an appropriate light intensity distribution.

On the other hand, the histograms shown in FIGS. 4 and 5 have 256 steps (gradation) of light intensity on the horizontal axis, and in many cases, actually have more steps. Storing the number of pixels for each of such a huge number of stages requires a large memory capacity and processing time, and is difficult to use in a practical photographing apparatus.

An object of the present invention is to provide an image signal processing apparatus capable of detecting a required data distribution (histogram) of a subject with a simple circuit configuration.

[0014]

According to one aspect of the present invention, an imaging system for supplying image data and an area having at least three different image data value ranges divided by at least two different thresholds are set. A classifying unit that classifies data of each pixel of the image data for one screen supplied from the imaging system into the at least three regions; and counts the number of pixels for each region to generate a histogram of the image data. An image signal processing device is provided that includes a counting unit that obtains the image and an adjustment unit that adjusts an imaging condition according to the histogram.

A histogram of the number of pixels classified into at least three data areas is obtained. The adjustment of the imaging conditions is performed based on the histogram.

[0016]

FIG. 1 is a block diagram of an image signal processing apparatus according to an embodiment of the present invention. The imaging system 1 includes an optical system including, for example, a lens, an aperture, and a shutter, and an image sensor (CCD) that converts a light image of a subject into image data of an electric signal. Image data obtained by the imaging system 1 is converted into an 8-bit (or 10-bit) digital signal by an analog-to-digital converter 2. The digital image signal is further input to the signal processing device 3 and subjected to predetermined signal processing. In the signal processing device 3, a histogram of the image data obtained by the imaging system 1 is created, and a control signal to the imaging system 1 is sent according to the histogram. Further, the processing of the image data is also performed inside the signal processing device 3 according to the histogram.

The specific configuration of the signal processing device 3 will be described later with reference to FIG. The image data processed by the signal processing device 3 is written to a recording device (storage device) 4 including a recording medium such as a DRAM. The recording device 4 may be an external recording medium, for example, a magnetic disk or an optical disk. The output of the signal processing device 3 is sent to the display device 5 to display an image. A printer may be provided instead of the display device 5.

For example, when the photographer half-presses the shutter button, the subject is provisionally photographed and a histogram is created. Thereafter, when the photographer fully presses the shutter button, the subject is fully photographed under the imaging conditions (imaging conditions) based on the histogram.

Assume now that a subject as shown in FIG. 5A is photographed. As described above, since such a subject has a histogram as shown in FIG. 5B, an appropriate reproduced image cannot be obtained by the conventional method. Therefore, in the image signal processing device according to the present embodiment, the histogram of the subject is first detected. However, FIG.
In the histogram of 0 to 255 levels shown in (A), a large amount of memory capacity is used, and the adjustment control of the imaging system 1 and the signal processing device 3 by utilizing such detailed histogram data without exception is considerable. To be a complicated process,
Obtain a more practical and simple histogram.

The histogram shown in FIG.
This is the same as that shown in FIG. Here, three different threshold values T ₁ , T ₂ and T ₃ are set for the signal light intensity.
An image signal obtained by the imaging system 1 is converted into a digital signal, and inputs the image data to the signal processing unit 3 in units of pixels, and the pixel values of the input image data is in the range of from 0 to the threshold value T _1, and a pixel falling in the range of up to the threshold T ₂ exceeds the threshold T _1, and the pixel within the scope to threshold T ₃ exceeds the threshold value T _2, the threshold value T ₃
And the number of pixels is counted.

As a result, simplified histograms of four different areas as shown in FIG. 2B are obtained. The horizontal axis indicates the area of four ranges of pixel data values, and the vertical axis indicates the number of pixels. The subject information based on the histogram of FIG. 2B is recorded in the recording device 4, and the gain or tone curve inside the imaging system 1 and the signal processing device 3 is optimally adjusted based on the information.

For example, the histogram of FIG.
This is based on the subject in FIG. The histogram corresponding to the person 10 has a peak 20, and the histogram corresponding to the streetlight 11 corresponds to a peak 21.

Here, a case where the imaging conditions are adjusted so that the person 10 is photographed as the main subject will be described. FIG.
Based on the subject information of the simple histogram in (B), the aperture value and exposure time of the imaging system 1 are adjusted to appropriate values. When the same subject is photographed after the adjustment, the image data becomes histogram image as shown in FIG. In this case, a peak 21 ′ of a high-luminance area corresponding to a bright street light 21 which is not a main subject is shifted to the right end of the histogram,
Resolution goes down. On the other hand, an appropriate exposure condition is obtained for the peak 20 'of the histogram corresponding to the person 10 as the main subject.

The data of the simplified histogram shown in FIG. 2B can be used for signal processing of data after photographing. How the data of the simple histogram is used for controlling the imaging system 1 and the signal processing device 3 is determined by the user in consideration of which main object is to be photographed in the photographing field of view and the image effect at the time of reproduction. It can be determined arbitrarily. Also,
The number of thresholds is not limited to three in the embodiment, and may be any number as long as it is two or more. That is, it is preferable that the area to be classified is three or more and less than the number of gradations. As the number of thresholds increases, the accuracy of the histogram increases. However, the accuracy may be appropriately set in consideration of required accuracy, memory capacity, ease of signal processing, and the like.

Next, an example of a signal processing device 3 for generating a simple histogram and performing signal processing on image data will be described with reference to the block diagram of FIG.

In FIG. 3, reference numeral 30 denotes a digital signal processing device, that is, a DSP, which controls the entire signal processing device 3, writes and reads data between the DRAM 4 and the display device 5, and controls generation of histogram data. .

Digital image data for each pixel is supplied from the A / D converter 2 (FIG. 1) to the gate 32 via the bus line 31.
To enter. The gate 32 has a thresholds T _1, if the input image data thresholds T ₁ or less, and outputs the image data to the OB circuit 36, unless thresholds T ₁ or less, another gate 3
3 to output image data. The counter 35 is a gate 3
2 counts the number of pixels thresholds T ₁ following data passing through.

The gate 33 has a threshold T_TwoAnd the input image
Data is threshold T₁Over T_TwoIf below, the OB circuit 36
Output the image data to the threshold T_TwoIf not, another
The image data is output to the gate 34. The counter 35
Threshold T passing through gate 33 ₁Beyond T_TwoThe following data
Is counted.

The gate 34 has a threshold value T _3, and when the input image data is less than or equal to the threshold value T _2, greater T _3, the OB circuit 36 via a separate output line if it exceeds T ₃ Output image data. Counter 35 counts the number of pixel threshold T ₂ to exceed T ₃ following data passing through gate 34, and counts the number of pixels of data exceeding the threshold value T ₃ does not pass through the gate 34.

The count value (count value) of the counter 35 is given to the DSP 30 to create a simple histogram as shown in FIG. 2B and stored in a memory (for example, the DRAM 4).

The OB circuit 36 receives all image data. The OB circuit 36 subtracts an optical black component (dark current component) from the image data to calibrate the image data. The image data output from the OB circuit 36 is
An appropriate gain is given to the variable gain amplifier 37. The image data provided with the predetermined gain is input to the correction circuit 38, where the correction is performed by a tone curve including γ correction and gradation correction. The corrected image data is stored in the DRAM 4 or the display device 5
Is displayed with.

Based on the data of the histogram created by the DSP 30, the aperture or the exposure time of the imaging system 1 is adjusted to a value such that an appropriate cystogram distribution can be obtained, as shown by the dotted line in the figure. Similarly, the gain of the amplifier 37 and the tone curve of the correction circuit 38 are adjusted based on the data of the histogram created by the DSP 30 as shown by the dotted line in the figure. Further, it is also possible to adjust the light emission time and light emission amount of the strobe based on the data of the histogram.

After the imaging conditions are adjusted based on the above-mentioned histogram, the main imaging is performed. In the main imaging, imaging of the subject is performed based on appropriate imaging conditions, and appropriate image data is generated.

Reference numeral 39 denotes a color processing circuit for performing an interpolation operation of color data when, for example, the color filter of the image sensor has a Bayer array or the like.

The embodiments described above are merely examples, and those skilled in the art will be able to make various modifications and applications based on the disclosure of the present specification.

[0036]

As described above, according to the present invention,
At least two thresholds are set for the image data, and it is sequentially detected whether or not the image data of each pixel falls within the threshold range, and a histogram in which data is classified into three or more data areas is obtained. Since the imaging conditions are adjusted based on the histogram, a good reproduced image can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram of an image signal processing device according to an embodiment of the present invention.

FIG. 2 is a diagram for explaining a histogram of the image signal processing device according to the embodiment of the present invention.

FIG. 3 is a block diagram illustrating a configuration of a signal processing unit of the image signal processing device according to the embodiment of the present invention.

FIG. 4 is a diagram illustrating an example of a histogram of image data.

FIG. 5 is a diagram showing an image example of a subject and a histogram thereof.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Imaging system 2 A / D converter 3 Signal processing unit 4 Recording device 5 Display device 30 DSP 31 Bus line 32, 33, 34 Gate circuit 35 Counter 36 OB circuit 37 Amplifier 38 Signal correction circuit 39 Color processing circuit

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H002 CC00 CC01 CC21 DB19 DB24 EB09 FB21 HA04 JA07 JA08 5B047 CA17 CB21 DA01 DA10 DC04 5C022 AB06 AB12 AB20 AC42 AC69

Claims (4)

[Claims] 1. An imaging system for supplying image data, and an area in a range of at least three different image data values divided by at least two different thresholds is set, and an area for one screen supplied from the imaging system is set. Classifying means for classifying the data of each pixel of the image data into the at least three regions; counting means for counting the number of pixels for each region to obtain a histogram of the image data; and imaging conditions according to the histogram. An image signal processing device having an adjusting unit for adjusting. 2. The classification unit includes a comparison unit that compares the threshold value with an input pixel data value and outputs only a value falling within the threshold value for each of the regions. 2. The image signal processing device according to claim 1, further comprising a counter for counting the number of pixel data output from the comparing means. 3. The image data according to claim 1, wherein the image data indicates light intensity.
Or the image signal processing device according to 2. 4. The image processing apparatus according to claim 1, wherein the adjusting unit adjusts an exposure time of the subject, an aperture value, a gain for amplifying image data, or a tone curve according to the histogram.
4. The image signal processing device according to any one of claims 1 to 3.