Television – Image signal processing circuitry specific to television – Noise or undesired signal reduction
Patent
1992-10-16
1994-03-22
Kostak, Victor R.
Television
Image signal processing circuitry specific to television
Noise or undesired signal reduction
H04N 964
Patent
active
052969304
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
A. Field of the Invention
This invention relates to a noise reduction processing device for video signals.
B. Description of Related Art
The invention is especially applicable to the use of image intensifiers for increasing the sensitivity of a television camera, which cause a noisy picture. The noise is in the form of a speckle pattern of bright white dots above the background picture, which greatly detracts from the visual quality of the intensified picture. The noise specks are typically very short duration (one frame) single point (about one pixel) events.
Typically to remove this noise, integration techniques are used. Many frames of the output are averaged until the noise peaks are significantly reduced compared to the signal level. However, such integration causes so-called motion smear i.e. blurring, in the case of movement of the camera or of the scene's contents.
SUMMARY OF THE INVENTION
The invention provides a noise reduction processing device for video signals, including a framestore device for receiving successive parts of three video frames in sequence, and a selection device for arbitrating between the outputs of the framestore device for all three video frames for each pixel in the event that the outputs of the framestore device for two video frames for that pixel represent an increase in intensity of at least one eighth of the range of pixel intensity values.
The selection enables localised intensifier noise to be masked without the disadvantages of motion smear by arbitrating between the outputs of the framestore device for all three frames for a pixel which suddenly increases in intensity and hence could represent noise.
The arbitration may be, in the case of a pixel increasing sharply in intensity from one frame to the next, by comparing the output for the third frame for that pixel with that of the other two, and ascertaining whether the output for the third frame is nearer to that for the first frame (of lower intensity), or to that for the second frame (of increased intensity). In the event that, for that pixel, the intensity has fallen back to a level similar to that of the first frame, then it can be assumed that the increased intensity was caused by noise, and the selection device can select the output for the first frame (or the third frame) as the noise reduced output.
The amount by which the intensity of a pixel must increase from one frame to the next in order for the arbitration procedure to be employed is arbitrary. Thus, the arbitration procedure may be employed for an increase in intensity of at least one eighth of the range of pixel intensity values, or at least one quarter, or one half of the range of pixel intensity values, as desired.
The sequence of video frames will usually be immediately succeeding frames, although a sequence omitting every other frame could be employed if desired.
BRIEF DESCRIPTION OF THE DRAWINGS
A noise reduction processing device constructed in accordance with the invention will now be described by way of example with reference to the accompanying drawings, in which:
FIG. 1 is a schematic representation in block diagram form of the noise reduction processing device; and
FIG. 2 is a schematic representation of a suitable implementation for the framestore.
DESCRIPTION OF THE PREFERRED EMBODIMENT
A T.V. monitor 1 receives an image from three framestores A selected by a logical output selection unit 2. Frames from a camera 3 are fed into the three framestores in rotation under the control of a timing and control unit 4.
Each framestore is able to store two interlaced fields. The timing and control unit addresses successive storage locations on a line by line basis so that the lines generated by the camera are stored accordingly. After a frame has been stored in one framestore, the next frame is stored in the next framestore, the next in the other framestore, and the next again in the first framestore, and so on.
The logical output selection unit 2 addresses corresponding storage locations in all three framestor
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patent: 4275418 (1981-06-01), Trump
patent: 4485403 (1984-11-01), Illetschko
patent: 4987481 (1991-01-01), Spears et al.
patent: 4987489 (1991-01-01), Hurley et al.
patent: 5148278 (1992-09-01), Wischermann
GEC Ferranti Defence Systems Limited
Kostak Victor R.
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