Television – Camera – system and detail – Combined image signal generator and general image signal...
Reexamination Certificate
2000-06-22
2004-10-26
Ho, Tuan (Department: 2612)
Television
Camera, system and detail
Combined image signal generator and general image signal...
Reexamination Certificate
active
06809761
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image data forming apparatus, and, more particularly, to an image data forming apparatus such as a digital electronic still camera for recording an image signal produced from a solid-state imaging device such as a charge-coupled device, and also to an image data processing method.
2. Description of the Background Art
In general, a solid-state imaging device, such as a charge-coupled device (CCD), has its dynamic range much narrower than the latitude of a silver-halide photosensitive type of negative film. However, recent advances in the semiconductor manufacturing technology and the wide dynamic range image sensor technology, such as multiple-exposure shooting, have made available a wider dynamic range solid-state imaging device.
Nevertheless, when recorded on an image data recording medium or reproduced on a video monitor, the dynamic range of image data generated by such a wide dynamic range solid-state imaging device must be compressed to a range prescribed by a certain standard. Take the video signal compatible with the NTSC standard television system for example. When the video or image signal is reproduced into visible images for display on a monitor, the dynamic range has to be compressed to the signal characteristics of as narrow as 100IRE. This requires gradation control, for example, by giving a knee curve to the gradation characteristics. In addition, when image data is processed in the form of digital data, each pixel of image data is, in general, dealt with in the form of eight bits per channel. Therefore, the dynamic range of image data generated by a solid-state imaging device has to be compressed to this range through gradation control.
In many cases, the NTSC signal and digital signal data are reproduced basically for the purpose of viewing on a video monitor. This means that, when compressing the dynamic range of image signals obtained from a solid-state imaging device, with a reproduction system in which the brightness and the tint appropriate for a picture are already fixed, gradation control is performed such as to produce a “finished image”, which requires the reproduction system not to make a significant modification but a fine adjustment only. In other words, a conventional image capturing/recording system, which is adapted to record an image signal obtained from a solid-state imaging device, performs most signal processings before recording and records the image signal in the form of a finished or complete image.
From another viewpoint, however, this recording system, adapted to record a finished image, is required to record image data in a form capable of reproducing a picture satisfactory for viewing. This, in turn, requires the image sensor system to perform sophisticated automatic exposure control and automatic white balance control. However, it is not easy to adequately record in a recording dynamic range so restricted as described above a scene, e.g. against the light or in an excess amount of light, which involves a broader dynamic range and in addition a difficulty in calculating an appropriate control value for the automatic exposure control. In addition, because the image data of a finished image is compressed when recorded, the finished image, if unsatisfactory, is difficult to correct.
For example, when a finished image reproduced from digital image data recorded on a recording medium is a little bit over-exposed in its entirety, it is sometimes desired to correct the image toward its under-exposure. It is however not possible to restore highlight data, or part of the image data which has high intensity and was once removed when compressed to a prescribed size, e.g. 8 bits, of recording dynamic range. On such image data, a gradation correction made in the 8-bit dynamic range would give a corrected image whose white part is dimmed or contrast is excessively enhanced.
On the other hand, a large amount of data may be recorded on a silver-halide photosensitive type negative film that has a remarkably wider dynamic range. A print system reproducing a visible image from a silver-halide photosensitive type negative film utilizes this feature of wider dynamic range for printing to correct the image so as to extract only a range of the data appropriate for printing. More specifically, a silver-halide photosensitive type negative film is basically intended to record as much information as possible on a negative film, or a recording medium, so that, when being printed, information only for satisfying the requirements is cut out by correcting the image to form an appropriate finished image. This method is best suited to get an appropriate final image. However, since a silver-halide photosensitive type negative film is so far an intermediate medium, images recorded on a silver-halide negative film cannot be viewed nor therefore used as a finished image.
The ability to record digital image data with a dynamic range as wide as that of a silver-halide photosensitive type negative film and, from this image data, to form and print a finished image, if available, would be very efficient for producing an appropriate final image. However, recording image data with a wide dynamic range and reproducing a finished image from that image data are, in general, incompatible.
For example, assume that there is established an image sensor system with a wide dynamic range capable of covering up to 400% of relative reflectivity (R), or a relative brightness against a gray plate, of a certain part of an objective field. In an imaging system where the imagewise signal from the image sensor system is converted to 8-bit image data for recording onto an image data recording medium, gradation control is performed, when the imagewise signal is converted to eight-bit image data, on the signal which is developed from the imaging sensor system and linear to the amount of light incident to the sensor system. For example, as shown in
FIG. 2
, the image data of a scene taken against light is distributed as plotted by a curve
101
with much image data in a higher relative reflectivity area. More specifically, for a scene including much highlight data as such, effective data may be recorded up to almost the maximum gradation level “
255
” represented by eight bits. The gradation control curve therefor is plotted as indicated by a reference numeral
103
.
On the other hand, the gradation of the image data of a scene taken in the for light or in the shade is plotted as indicated by a reference numeral
105
in
FIG. 3
, with more image data in areas with a lower relative reflectivity. Therefore, performing gradation control for a scene with less highlight data in the eight-bit gradation range makes it difficult to use the entire range efficiently. In addition, because the relative reflectivity of a main object, such as a man or woman, is generally 100% or lower, the application of the same gradation control curve
103
would produce as a whole a dark image that is not practically viewed.
Japanese patent laid-open publication No. 131718/1995 discloses an image composing apparatus that shoots one scene in different exposure amounts in a single shooting operation and then composes the data of the thus obtained plurality of images to form a picture of wider dynamic range. More specifically, this image composing apparatus combines two types of image data: one is standard image data shot with a standard exposure and the other is non-standard image data shot with a non-standard exposure, for example, using a high-speed shuttering. The image composing circuit of the apparatus is adapted to determine from both images the common areas whose intensity level falls in a predetermined range and then shift the intensity levels of the common areas so as to match with each other. The circuit in turn replaces the areas of the non-standard image which have the intensity level falling in the predetermined range for the areas of the standard image which correspond to the former areas of the non-standard image and have
Birch & Stewart Kolasch & Birch, LLP
Fuji Photo Film Co. , Ltd.
Ho Tuan
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