The present invention relates to an imaging device to be used in a video camera and the like.
One of the conventional imaging devices is adapted to obtain two image signals by releasing its shutter at high and low speeds, and to produce a synthesized signal from the image signals (see, for example, a patent document 1). When an image of a low brightness object is taken by the imaging device, the imaging device produces a synthesized signal greatly affected by the image taken at low speed. When, on the other hand, an image of a high brightness object is taken by the imaging device, the imaging device produces a synthesized signal greatly affected by the image taken at high speed.
Problems to be Solved by the Invention
The conventional imaging device, however, encounters such a problem that, when the image shows high and low brightness objects in one frame, the image is reduced in quality by reason that the reference level to be used for synthesis of images is a constant in one frame.
It is, therefore, an object of the present invention to provide an imaging device that can enhance an image in comparison with the conventional imaging device, even if the image shows high and low brightness objects in one frame, by improving each of image sections corresponding to the high and low brightness objects.
Means for Solving the Problems
The imaging device according to the present invention comprises: imaging means for producing at least two image signals as long and short exposure signals different in light exposure from each other; knee process means for processing on the long exposure signal; signal synthesizing means for performing the synthesis of the short exposure signal and the long exposure signal processed by the knee process means; and level changing means for changing, on the basis of the signal level of the short exposure signal, a knee level defined at a knee point.
The imaging device thus constructed as previously mentioned according to the present invention can enhance an image in comparison with the conventional imaging device, even if the image shows high and low brightness objects in one frame, by improving each of image sections corresponding to the high and low brightness objects by reason that the knee level is changed on the basis of the signal level of the short exposure signal.
In an imaging device according to the present invention, the signal level changing means is adapted to change, on the basis of the signal level of the short exposure signal, a synthesized level defined as a reference of the synthesis to be performed by the signal synthesizing means.
The imaging device thus constructed as previously mentioned according to the present invention can enhance, in comparison with the conventional imaging device, an image showing high and low brightness objects by reason that the signal level changing means is adapted to change, on the basis of the signal level of the short exposure signal, a synthesized level defined as a reference level for the synthesis to be performed by the signal synthesizing means,
The imaging device according to the present invention, comprises: imaging means for outputting at least two image signals including long and short exposure signals different in light exposure from each other; signal synthesizing means for synthesizing the long and short exposure signals; and level changing means for changing, on the basis of the signal level of the short exposure signal, a synthesized level defined as a reference of the synthesis to be performed by the signal synthesizing means.
The imaging device thus constructed as previously mentioned according to the present invention can enhance an image in comparison with the conventional imaging device, even if the image shows high and low brightness objects in one frame, by improving each of image sections corresponding to the high and low brightness objects by reason that the reference level is changed in each frame on the basis of the signal level of the short exposure signal.
In the imaging device according to the present invention, the knee process means is adapted to perform the knee process at the knee point in each frame.
The imaging device thus constructed as previously mentioned according to the present invention can be reduced in production cost, in comparison with the conventional imaging device in which the knee process is performed in a plurality of knee points, by reason that the knee process means is simple in construction.
When the short exposure signal is being fluctuated in signal level with time, the level changing means is adapted to change continuously the knee level in response to changes of the signal level of the short exposure signal.
The imaging device thus constructed as previously mentioned according to the present invention can enhance an image, in comparison with the conventional imaging device in which the knee level is discontinuously changed, by reason that the knee level is smoothly changed in response to changes of the signal level of the short exposure signal.
When the short exposure signal is being fluctuated in signal level with time, the level changing means is adapted to change continuously the synthesized level in response to changes of the signal level of the short exposure signal.
The imaging device thus constructed as previously mentioned according to the present invention can enhance an image, in comparison with the conventional imaging device in which the synthesized level is discontinuously changed, by reason that the synthesized level is smoothly changed in response to changes of the signal level of the short exposure signal.
The present invention provides an imaging device that can enhance an image in comparison with the conventional imaging device, even if the image shows high and low brightness objects in one frame, by improving each of image sections corresponding to the high and low brightness objects.
The preferred embodiment of the imaging device according to the present invention will be described hereinafter with reference to accompanying drawings.
The following description will be directed to the construction of the imaging device according to the preferred embodiment of the present invention.
As shown in
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Further, the level changing unit 18 is adapted to change the knee level and the synthesized level on the basis of the signal level of the short exposure signal Yshort from the time axis converter 14 as shown in
The following description will be then directed to the operation of the imaging device according to the preferred embodiment of the present invention.
The imaging element 11 produces, at double speed in synchronization with the timing pulse signal produced by the timing pulse generator 22, two imaging signals different in light exposure from each other, and outputs alternatively the image signals as long and short exposure signals Ylong and Yshort in each field.
The preprocessing unit 12 performs the operations such as for example the low frequency signal conversion of the correlation double sampling process, and the automatic gain control of the automatic gain control circuit, and the processed image signal to the A/D converter 13.
The time axis converter 14 separates one of the image signals from the A/D converter 13 from the other of the image signals from the A/D converter 13, and outputs the long and short exposure signals Ylong and Yshort in parallel at a standard speed.
Here, the level changing unit 18 changes, on the basis of the signal level of the short exposure signal Yshort outputted by the time axis converter 14, the knee level of the knee process unit 15 and the synthesized level of the signal synthesizing unit 17. The level changing unit 18 sets upper and lower limits to ensure that the synthesized level of the signal synthesizing unit 17 is around 100% of the image signal to be outputted by the main signal processing unit 21, and to ensure that the knee level of the knee process unit 15 is slightly smaller than the synthesized level, in other words, the knee level of the knee process unit 15 is around 80% of the image signal to be outputted by the main signal processing unit 21.
The knee process unit 15 performs the knee process on the long exposure signal Ylong received from the time axis converter 14 on the basis of the knee level changed by the level changing unit 18, and outputs as a long exposure signal Ylong2 as shown in
On the other hand, the gamma process unit 16 performs the gamma process on the short exposure signal Yshort from the time axis converter 14, and outputs the short exposure signal Yshort2 shown in
The signal synthesizing unit 17 synthesizes, on the basis of the synthesized level changed by the level changing unit 18, the signal Ymix shown in
The histogram detecting unit 23 divides the synthesized signal Ymix received from the signal synthesizing unit 17 into a plurality sections, and detects histogram information of each section of the synthesized signal Ymix, while the microcomputer 24 calculates correction characteristics of each section of the synthesized signal Ymix on the basis of the histogram information detected by the histogram detecting unit 23, and sets the calculated correction characteristics to the tone correction unit 19. As a method of dividing the synthesized signal Ymix into a plurality of sections, the image represented by the image signal may be simply divided into rectangle sections. As another method, the image is divided into a section larger in brightness than a predetermined threshold level, and a section equal to or smaller in brightness than the threshold level.
In each section, the tone correction of the synthesized signal Ymix from the signal synthesizing unit 17 is then performed by the tone correction unit 19 on the basis of the correction characteristics set by the microcomputer 18. Here, the tone correction unit 19 enhances contrast of the image by performing the tone correction of the synthesized signal Ymix on the basis of the frequency of the histogram of each section.
Then, the area synthesizing unit 20 performs the synthesis of a signal of each section outputted by the signal Ymix, to produce a seamlessly-synthesized signal. Here, the area synthesizing unit 20 synthesizes the signal of each section on the basis of division information used by the histogram detecting unit 23.
Finally, the main signal processing unit 21 performs the luminance signal process, the color signal process, and the like on the synthesized signal from the signal synthesizing unit 20, and outputs the processed signal as an image signal.
When, for example, the imaging device 10 takes an image including, in one frame, high and low brightness sections 31 and 32 corresponding to respective grayscale charts 33 and 34, the imaging element 11 outputs, as an image signal corresponding to a line 35 defined on the image, long and short exposure signals Ylong and Yshort shown in FIGS. 9(a) and 9(b). More specifically, the low brightness section 32 of the long exposure signal Ylong outputted by the imaging element 11 is appropriate in exposure, while the high brightness section 31 of the long exposure signal Ylong is recognized as a saturated signal, inappropriate in exposure. On the other hand, the high brightness section 31 of the short exposure signal Yshort outputted by the imaging element 11 is appropriate in exposure, while the high brightness section 32 of the long exposure signal Ylong is recognized as an extremely small signal, inappropriate in exposure.
Then, the knee process unit 15 produces the long exposure signal Ylong2 from the long exposure signal Ylong by performing the knee process on the long exposure signal Ylong shown in
Then, the signal synthesizing unit 17 synthesizes the signal Ymix shown in
The tone correction unit 19 performs the tone correction on the synthesized signal Ymix shown in
As shown in
From the foregoing description, it will be understood that the imaging device 10 according to the present invention can enhance an image in comparison with the conventional imaging device, even if the image shows high and low brightness objects in one frame, by improving each of image sections corresponding to the high and low brightness objects by reason that the knee level and the synthesized level are changed in one frame on the basis of the signal level of the short exposure signal Yshort.
Further, the imaging device 10 can produce the seamlessly-synthesized signal Ymix by performing, as nonlinear process, the knee process on the long exposure signal Ylong, and performing, as nonlinear process, the gamma process on the short exposure signal Yshort.
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In this embodiment, as shown in
As a method of performing the tone correction of the synthesized signal Ymix, the imaging device 10 may be adapted to perform the tone correction of the synthesized signal Ymix on the basis of a method other than the method mentioned in this embodiment.
As will be seen from the foregoing description, the present invention has an advantageous effect of enhance an image in comparison with the conventional imaging device, even if the image shows high and low brightness objects in one frame, by improving each of image sections corresponding to the high and low brightness objects, and useful as an imaging element to be used in a video camera or the like.
Number | Date | Country | Kind |
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2004-328812 | Nov 2004 | JP | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/JP05/20790 | 11/14/2005 | WO | 5/7/2007 |