JP3943221B2 - Signal processing device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a signal processing apparatus that adjusts so that a video signal obtained from an imaging unit can be expressed based on a predetermined level, and in particular, reads a signal from the imaging unit using a plurality of fields, for example, generates an image by interlace scanning. It is suitable for use in image processing apparatuses, electronic still cameras, and the like.
[0002]
[Prior art]
In general, a video camera captures an image of an object scene as an imaging signal through an image sensor in which light receiving cells are two-dimensionally arranged. Various kinds of signal processing are performed on the captured image signal. In the signal processing, as an example, clamping processing is performed on the input image pickup signal so that the black level becomes a predetermined level. This process is performed in order to represent a color according to a pedestal level that is a reference level of the color of the video signal. The pedestal level represents the black level. Here, for example, the signal charge may be read from the image sensor by the interlace scanning method. That is, the imaging signal is read out in a plurality of fields such as an odd field and an even field. At this time, a time difference occurs in reading the accumulated signal charge. For this reason, in the signal charge to be read, thermal noise is generated in the light receiving cell of the other field while the signal charge is first read from the light receiving cell corresponding to one field and transferred. Therefore, when reading the signal charge of the other field, thermal noise is accumulated in this signal charge according to the stay time (or time difference), so the signal level is higher than the original image pickup signal level obtained by photoelectrically converting the image pickup signal. Will rise slightly. The minute signal level difference between the fields deteriorates the image quality of the screen. In the video camera, for example, an optical black level detection area is provided by shielding a part of the image sensor in this clamping process, and the black level of the imaging signal from this area is detected to bring the imaging signal to a predetermined level. It is processing to become.
[0003]
As a specific example of black level adjustment related to such thermal noise prevention, for example, Japanese Patent Laid-Open No. 9-83836 discloses that the increase in the number of bits is suppressed when controlling the black level, and the slope of the γ curve is not made gentle. Have proposed a signal processing apparatus for a video camera that prevents a change in black level from being visually observed.
[0004]
In addition, as described in Japanese Patent Application Laid-Open No. 5-92537, the present applicant corrects a difference in the reference level of a video signal having a plurality of color components that does not require high-precision manual adjustment. An offset cancel circuit is proposed.
[0005]
[Problems to be solved by the invention]
However, in an electronic still camera which is one of digital cameras, black level correction using an optical black level detection area is not performed as in the video camera described above. Actually, in the case of using an interline type charge coupled device (CCD), even if there is a difference in black level in the field, this difference is not taken into account, and processing for assuming the same black level has been performed so far.
[0006]
Recently, there has been an increasing demand for electronic still cameras to bring the image quality closer to silver halide cameras. From such a situation, it is necessary to correct the black level in consideration of the field difference suitable for the electronic still camera.
[0007]
An object of the present invention is to provide a signal processing apparatus that can eliminate such drawbacks of the prior art and can perform black level correction in consideration of differences between fields when signals are read from different fields. .
[0008]
[Means for Solving the Problems]
In order to solve the above-described problems, the present invention converts a color imaging signal output from an imaging field from an imaging field through an optical system and a color filter into a digital signal by converting it into a digital color imaging signal. In a signal processing apparatus that performs signal processing so that a signal level for an imaging signal can be expressed based on a predetermined level, a predetermined area corresponding to this range is set by a condition specifying signal that specifies a range to be read from a digital color imaging signal And a signal reading means for reading out the signal of the set predetermined area from the digital color image pickup signal, and a color identification indicating the color of the digital color image pickup signal supplied from the image pickup means to the signal output from the signal reading means A first color selecting means for selecting in response to the signal, and for each color from the first color selecting means; A signal storage output means for storing in accordance with a field identification signal for selecting only a digital color imaging signal of a predetermined field from among the supplied digital color imaging signals, and outputting the stored digital color imaging signal for each field; and An adding means for adding the output signal from the signal storage output means and the signal selected by the first color selecting means, and an area different from the area read by the signal reading means among the digital color imaging signals supplied to the apparatus A second color selection means for selecting and outputting a digital color imaging signal according to the color identification signal while adjusting the output timing of the readout, a field identification signal, a condition designation signal, and a color identification signal Between the fields of the digital color imaging signal supplied from the adding means. Control means for calculating a step of the signal level as a field correction signal, and a correction restoration means for adding the field correction signal from the control means and the signal from the second color selection means and restoring the original data in order. It is characterized by having.
[0009]
Here, the field identification signal is preferably a signal that is selected on the basis of one of the fields when an image formed by imaging is represented by an even number of fields. It is suitable for use when, for example, two or more fields are used for high-speed readout from many high-resolution imaging means.
[0010]
In addition, the condition designation signal has an optical black area to be extracted from the digital color imaging signal, and has a read start position of the optical black area and a width to be extracted in the horizontal and vertical directions from the read start position. A signal to be set or a signal including an instruction to set the reading start position and the reading end position of the optical black area is desirable. As a result, the reading range of the optical black area is accurately set, and the correspondence with the field can be performed without error.
[0011]
It is desirable that the signal storage output means includes a plurality of color storage means for storing each color according to the type of color handled in the color filter.
[0012]
Preferably, the adding means subtracts and inputs the output signal from the signal storage output means and adds and inputs the signal selected by the first color selecting means to output a signal level difference generated between the fields.
[0013]
It is advantageous that the control means supplies a control signal for clearing the storage contents of the signal storage output means one frame after the start of storage.
[0014]
The control means sets the signal level of the field read into the signal storage output means based on the field identification signal as a predetermined reference level, and the signal level of each field supplied from the adding means with respect to the predetermined reference level. If the step is used as a field correction signal for each field and color, complicated calculation is avoided and the difference between the fields is eliminated.
[0015]
The signal level of the field first supplied from the adding means is set as a predetermined reference level, and the step of the signal level of each field with respect to the predetermined reference level is calculated by adding the step of the signal level supplied for each field. Thus, it is possible to correct the black level indicating the color reference so that a level difference between the fields does not occur even when interlace scanning is performed.
[0016]
The correction restoration means includes a correction addition means for adding the field correction signal from the control means and the signal from the second color selection means, and a signal supplied to the second color selection means as an output from the correction addition means. And restoring means for restoring and outputting in the same color order. As a result, the color between fields, particularly the black level, can be set to a predetermined level, so that it is possible to prevent the occurrence of a beat-like striped pattern or the like that has occurred in the image.
[0017]
The signal processing apparatus according to the present invention supplies an output signal obtained by extracting the OB area from the signal reading unit to the first color selection unit, and the first color selection unit outputs a signal of the color selected according to the color identification signal. This is supplied to the adding means and the signal storage output means. The signal storage output means stores only the signal of the field selected by the field identification signal. The adding means adds the signal selected for each color and the signal from the signal storage output means outputted for each field, calculates the level difference of the signal between fields for each color, and supplies it to the control means. Thereby, the signal level difference between the fields is supplied to the control means. The control means performs signal processing using the calculated level step, calculates a field correction signal, and outputs the field correction signal to the correction restoration means. The correction restoration means uses the obtained field correction signal and the second color selection means. By adding the digital color imaging signal whose timing is adjusted in step (2), it is possible to correct the black level based on the optical black area for the read line and eliminate the difference between the fields. Output an image based on level.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Next, an embodiment of a signal processing apparatus according to the present invention will be described in detail with reference to the accompanying drawings.
[0019]
The signal processing apparatus of the present invention is an apparatus that removes a noise signal (offset component) included in a signal generated based on, for example, thermal noise generated during imaging. This signal processing apparatus is applied to an apparatus that performs interlaced scanning that outputs an imaging signal divided into a plurality of fields, for example. At this time, an appropriate black level can be set and the balance of color expression is improved. Can do.
[0020]
First, the configuration and connection relationship of the signal processing device 10 will be briefly described. As shown in FIG. 1, the signal processing apparatus 10 includes an OB area reading unit 11, an RGB selection unit 12, an addition unit 13, a data storage / output unit 14, an RGB selection unit 15, a correction restoration unit 16, and a system control unit 17. Have.
[0021]
Here, in this signal processing device 10, for example, an incident light is an image sensor in which light receiving cells (pixels) including a color filter array (not shown), a charge coupled device (CCD) and the like are two-dimensionally arranged. Data obtained by digitizing a signal obtained through an imaging unit having a digital color, that is, a digital color imaging signal (hereinafter simply referred to as imaging data) is supplied. As shown in FIG. 2A, the incident light is actually applied to all the image sensors 20 of the imaging unit, but is supplied only to a predetermined effective pixel area Ap. This is because the incident light is shielded in a region outside the effective pixel region Ap of the image sensor 20. This region is called an OB region (hereinafter simply referred to as OB: Optical Black) as an optically black region. Also in this OB area, a plurality of pixels are arranged in the horizontal direction (arrow h) and the vertical direction (arrow v).
[0022]
The OB area reading unit 11 has a function of reading imaging data obtained from pixels in the OB area among imaging data obtained from the image sensor 20. The OB area reading unit 11 is supplied with a condition designation signal and a control signal from the system control unit 17. The condition designation signal supplies, for example, instructions such as a vertical readout start line, a horizontal readout start pixel, a horizontal readout width, and a vertical readout width to the OB area readout unit 11. The OB area reading unit 11 takes out a signal from a designated area in the OB area by this condition designation signal. For example, the level “H” region in FIG. 2B is set by the horizontal readout start pixel and the horizontal readout width of the condition designation signal. Usually, the area constituting the image uses the area of the level “H” shown in FIG. 2C as the effective video area. Data read from the designated area is supplied to one end of the RGB selection unit 12. The condition designation signal may be set at the reading start position and the end position in the horizontal and vertical directions.
[0023]
Returning again to FIG. As shown in FIG. 1, the RGB selection unit 12 includes an addition unit 13 and a data storage / output unit according to the color identification signal supplied from the system control unit 17 for the output signal of the OB region supplied from the OB region reading unit 11. Select the output destination to 14.
[0024]
The adding unit 13 includes adders 13a, 13b, and 13c. Data for each color is supplied from the RGB selector 12 to one end of each of the adders 13a, 13b, and 13c, and the data read from the data storage / output unit 14 for each RGB color is subtracted and input to the other end. . The adding unit 13 calculates a signal level difference between fields sequentially output from the OB area reading unit 11 by the addition process. The addition result is supplied to the system control unit 17.
[0025]
The data storage / output unit 14 stores the supplied data based on the repetitive pattern of the color filter array or simply the type of color. In the signal processing apparatus 10 of FIG. 1, it is stored for each of the three primary colors RGB. The data storage / output unit 14 has a function of outputting the memory contents in response to a read request and capable of reliably holding data until a clear signal described later is supplied. Further, a field memory (R field memory 14a, G field memory 14b, and B field memory 14c) is included for each color in accordance with the reading of signal charges from the image sensor 20 by the interlace method.
[0026]
The data storage / output unit 14 uses the field identification signal supplied from the system control unit 17 to write data to each field memory. The field identification signal is a signal for selecting a field having a reference signal level among the screen identification signals. The data storage / output unit 14 reads the read data every time each field is switched. The contents of the read data are erased by a clear signal supplied every frame. Because of this relationship, it is preferable to specify a field to be read at the beginning of reading. The data storage / output unit 14 receives the data of the three primary colors R, G, and B read from the R field memory 14a, the G field memory 14b, and the B field memory 14c, and adds the other ends of the adders 13a, 13b, and 13c of the adder 13 Supply to each side.
[0027]
The RGB selection unit 15 is supplied with data of the entire area read from the image sensor 20. This data is image data before black level correction. The RGB selection unit 15 is supplied with a color identification signal from the system control unit 17, and selects and outputs RGB data of the effective pixel area Ap one by one in accordance with the color identification signal. Incidentally, the RGB selection unit 15 not only simply selects data, but also adjusts the timing so that the signal processing device 10 can reliably correct the black level of the target pixel. The RGB selection unit 15 supplies the RGB data subjected to the timing adjustment to the correction restoration unit 16, respectively.
[0028]
The correction restoring unit 16 includes adders 16a, 16b, 16c and a decoding unit 16d corresponding to each color. Each output signal from the RGB selector 15 is input to one end of each of the adders 16a, 16b, and 16c, and offset component data is supplied from the system controller 17 for each color to the other end. The offset component data is signed. The adders 16a, 16b, and 16c remove the offset component from the RGB data by adding the RGB data of the supplied effective pixel area Ap and the offset component data. The adders 16a, 16b, and 16c output the RGB data from which the offset component has been removed to the decoder unit 16d. The decoder unit 16d restores and outputs the RGB data in the order of the arrangement of the color filter array according to the control of the system control unit 17.
[0029]
The system control unit 17 generates and controls various signals such as a field identification signal, a condition designation signal, a color identification signal, a timing control signal, and a memory clear signal. The system control unit 17 generates a control signal using the field selected by the field identification signal as a reference field and supplies the control signal to the data storage / output unit 14. The system control unit 17 generates a setting signal corresponding to the specified condition for the reading area of the OB area, and supplies the generated signal to the OB area reading unit 11. Here, since the arrangement of each color filter is determined when the type of the color filter array to be used is determined, the system control unit 17 considers the relationship between the readout of the signal charge from the light receiving cell and the arranged color filter, and performs color identification. The signal is generated. This color identification signal is supplied to the RGB selectors 12 and 15, respectively. The system control unit 17 supplies a control signal for timing adjustment to the RGB selection unit 15, the decoding unit 16 d, and the like as the timing control signal in order to surely perform the addition processing in the correction restoration unit 16. The system control unit 17 supplies a clear signal to the data storage / output unit 14 for each frame. As a result, the reference is updated for each frame. The system control unit 17 performs a process of calculating a difference between the signal level obtained from the OB area of the reference field and the black level of the television standard, that is, the pedestal level, and includes the field including this difference. When a correction signal is generated and supplied to the correction restoration unit 16 , a better black level correction can be performed.
[0030]
Next, the operation of the signal processing apparatus 10 will be briefly described. Imaging data including the OB area from the image sensor 20 is supplied to the OB area reading unit 11 and the RGB selection unit 15, respectively. The OB area reading unit 11 extracts the imaging data obtained from the pixels in the OB area among the imaging data supplied in response to the condition designation signal supplied from the system control unit 17. The taken image data of the OB area is supplied to the RGB selection unit 12. In addition, the RGB selection unit 12 is supplied with a color identification signal that takes into account the arrangement of the color filter array covering the OB area. The RGB selection unit 12 selects the image data in the OB area according to the color identification signal and outputs the selected data to the one end side of the adders 13a, 13b, and 13c of the addition unit 13 and the data storage / output unit 14.
[0031]
The data storage / output unit 14 stores in the memory only the data in the area designated by the condition designation signal for the vertical readout start pixel that matches the field identification signal supplied from the system control unit 17. The data storage / output unit 14 outputs the read data for each field to the adding unit 13 other than the field taken in as the reference. The data storage / output unit 14 holds the data selected for this reference until a clear signal is supplied from the system control unit 17.
[0032]
The adder 13 is supplied with only the field data based on the control of the system controller 17 in the frame. If the data of the OB area of the field supplied from the RGB selection unit 12 other than the field selected as the reference is added and input, for example, the data of the OB area of the field selected as the reference is subtracted and input, the field between these two fields is input. The accumulated signal level difference can be easily obtained. This addition result is supplied to the system control unit 17 in order to correct the signal level for the current field of the current frame.
[0033]
The RGB selection unit 15 selects the data of the effective pixel area Ap for each color from the imaging data read from the image sensor 20, and outputs the selected data to the correction restoration unit 16. The output destination of the data to be output is selected so that signal processing can be performed for each color in accordance with the color identification signal supplied from the system control unit 17 to the RGB selection unit 15. The color identification signal is supplied so that the color can be selected in the order reflecting the color arrangement of the color filter array. For this output, the RGB selection unit 15 adjusts so that the output is performed with a timing control signal that also takes into account the time required for data reading from the data storage / output unit 14 and the calculation of the system control unit 17. The data of the effective pixel region of the field adjusted in time as described above is output to the correction restoration unit 16.
[0034]
For example, the read line data of the effective pixel area Ap in the second field is sequentially supplied to one end of each of the adders 16a, 16b, and 16c, and the black level correction data corresponding to the read line is supplied to the correction restoration unit 16 for each color. Are supplied to the other ends of the adders 16a, 16b and 16c. As a result, black level correction is performed for each color of the read line.
[0035]
The adders 16a, 16b, and 16c supply the result of the black level correction to the decoding unit 16d. The decoding unit 16d rearranges and outputs the three data supplied in the order of colors appearing in the effective pixel area Ap supplied from the system control unit 17.
[0036]
The black level correction can be accurately performed by the signal processing for performing such a series of controls, and the image can be improved in image quality.
[0037]
A device using the image sensor 20 is desired to have high image quality, and the number of pixels tends to be further increased. In order to complete the operation within the conventional standard corresponding to this further increasing number of pixels, signal charges may be read for, for example, four types of colors. As a modification of the above-described embodiment for the signal processing device 10, FIG. 3 briefly describes the configuration of the color selection unit 12A, the addition unit 13, and the data storage / output unit 14 in this case.
[0038]
For example, the arrangement pattern of the color filter array arranged immediately before the two-dimensional image sensor 20 is “R”, “G ₁ ”, “B”, “G” in the horizontal direction like interline and G stripe RB perfect checkered pattern. _In the case of an arrangement like ₂ ", four field memories are provided to subdivide and process each color. The data storage / output unit 14 of FIG. 3 is provided with an R field memory 14a and a B field memory unit 14c as in FIG. 1, and a G ₁ field memory unit 140 is provided instead of the G field memory unit 14b. A G ₂ field memory unit 141 is newly added. In addition to the color selector 12A and the adder 13 added with the adder 13d shown in FIG. 3, the RGB selector 15 and the correction restoration unit 16 shown in FIG. It is configured to do.
[0039]
In order to control the data storage / output unit 14, a field identification signal is supplied from the system control unit 17, and only the requested field is stored. By this field selection, a desired field can be collected in the memory.
[0040]
The operation of the signal processing apparatus 10 in this case is basically the same as that of the above-described embodiment, and attention is particularly paid to the generation of the color identification signal timing control signal in the system control unit 17 due to an increase in the number of colors to be processed. There must be. Although not shown, in order to accurately perform the adding process in the adding unit 13 including the above-described embodiment, the input timing of the signal supplied from the color selecting unit 12A and the data writing / writing of the data storage / output unit 14 are described. Needless to say, reading is also adjusted. The field identification signal is generated by the system control unit 17 so as to identify an even number of fields such as 2 fields, 4 fields, and the like. As described above, when the field identification signal is selected so as to have an even relationship, the processing can be easily performed. Although not described in detail, the output from the addition unit 13 is supplied to the system control unit 17 and is supplied to the correction restoration unit 16 via the system control unit 17. The correction restoration unit 16 can perform a black level correction process on the currently input image data.
[0041]
With such a configuration, appropriate black level correction can be performed for each pixel of the read line, so that noise that appears in the past due to the time difference between field reads can be suppressed, and image quality can be further improved. . Further, when the function of the apparatus is expanded, it is not necessary to change the basic configuration, and the design can be facilitated.
[0042]
【The invention's effect】
As described above, according to the signal processing apparatus of the present invention, the output signal obtained by extracting the OB area from the signal reading unit is supplied to the first color selection unit and selected according to the color identification signal. The first color selection means supplies outputs to the addition means and the signal storage output means, respectively. The signal storage output means stores only the signal of the field selected by the field identification signal. The adding means adds the signal selected for each color and the signal from the signal storage output means outputted for each field, calculates the level difference of the signal between fields for each color, and supplies it to the control means. The control means performs signal processing using the level difference to calculate a field correction signal and outputs the field correction signal to the correction restoration means. The correction restoration means adjusts the timing using the obtained field correction signal and the second color selection means. Since it is possible to output an image based on a constant black level by correcting the black level based on the optical black area for the line read out by adding the digital color imaging signal thus obtained, Therefore, it is possible to improve the image quality by making noise such as thermal noise appearing due to the time difference read out invisible in the image. Further, when the function of the apparatus is expanded, it is not necessary to change the basic configuration, and the design can be facilitated.
[Brief description of the drawings]
FIG. 1 is a schematic block diagram of a signal processing apparatus according to the present invention.
FIG. 2 is a schematic diagram for explaining a relationship between an area read by an OB area reading unit shown in FIG. 1 and an effective pixel area;
FIG. 3 is a block diagram of a specific main configuration of the data storage / output unit shown in FIG. 1 for obtaining a level difference of a signal for each field with respect to four types of colors.
[Explanation of symbols]
10 Signal processor
11 OB area readout section
12, 15 RGB selector
13 Adder
14 Data storage / output section
16 Correction restoration unit
17 System controller
14a R field memory
14b G field memory
14c B field memory
13a, 13b, 13c, 16a, 16b, 16c Adder
16d decoding section

Claims (7)

By converting the color imaging signal output from the imaging means from the imaging field via the optical system and color filter into a digital signal, it is converted into a digital color imaging signal,
In a signal processing apparatus that performs signal processing so that a signal level for the digital color imaging signal can be expressed based on a predetermined level, the apparatus includes:
A signal reading means for setting a predetermined area corresponding to the range by a condition specifying signal for specifying a range to be read from the digital color imaging signal, and reading a signal of the set predetermined area from the digital color imaging signal; ,
First color selection means for selecting a signal output from the signal reading means according to a color identification signal indicating the color of the digital color imaging signal supplied from the imaging means;
According to a field identification signal for selecting only a digital color imaging signal of a predetermined field among the digital color imaging signals supplied for each color from the first color selection means,
Signal storage output means for outputting the stored digital color imaging signal for each field;
Subtracting the output signal from the signal storage output means , adding the signal selected by the first color selection means, and adding the input signal to calculate the signal level difference generated between the fields ;
The digital color imaging signal is selected and output according to the color identification signal while reading an area different from the area read by the signal reading means and adjusting the output timing of the reading. A second color selection means;
The OB area of the field that controls the supply of the field identification signal, the condition designation signal, and the color identification signal, and is based on the signal level difference between the fields of the digital color imaging signal supplied from the adding means Control means for calculating as a field correction signal including the difference between the signal level obtained from the pedestal level ;
Correction correction means for adding the field correction signal from the control means and the signal from the second color selection means and restoring the order of colors appearing in the supplied effective pixel region. Signal processing device.   2. The signal processing apparatus according to claim 1, wherein the field identification signal is a signal that is selected on the basis of one of the fields when the image formed by the imaging is represented by an even number of fields. Signal processing device. The signal processing apparatus according to claim 1, wherein the condition designation signal is:
An area to be extracted from the digital color imaging signal is an optical black area, and a signal for setting a reading start position of the optical black area and a width to be extracted in the horizontal and vertical directions from the reading start position, or A signal processing apparatus comprising: an instruction for setting a reading start position and a reading end position of the optical black area.   2. The signal processing apparatus according to claim 1, wherein the signal storage output means includes a plurality of color storage means for storing each of them according to the type of color handled in the color filter. Processing equipment.   5. The signal processing apparatus according to claim 4, wherein the control means supplies a control signal for clearing the storage contents of the signal storage output means one frame after the start of storage.   2. The signal processing apparatus according to claim 1, wherein the control means sets the signal level of the field read into the signal storage output means based on the field identification signal as the predetermined reference level, A signal processing apparatus characterized in that a step of the signal level of each field supplied from the adding means is used as the field correction signal for each field and color. The signal processing apparatus according to claim 1, wherein the correction restoration unit includes:
Correction addition means for adding the field correction signal from the control means and the signal from the second color selection means;
A signal processing apparatus comprising: restoration means for restoring and outputting the output from the correction addition means in the same color order as the signal supplied to the second color selection means.

Images