WO1999052275A1 - Video signal processing - Google Patents
Video signal processing Download PDFInfo
- Publication number
- WO1999052275A1 WO1999052275A1 PCT/GB1999/001043 GB9901043W WO9952275A1 WO 1999052275 A1 WO1999052275 A1 WO 1999052275A1 GB 9901043 W GB9901043 W GB 9901043W WO 9952275 A1 WO9952275 A1 WO 9952275A1
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- activity level
- picture
- artefact
- region
- scratch
- Prior art date
Links
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N5/00—Details of television systems
- H04N5/14—Picture signal circuitry for video frequency region
- H04N5/21—Circuitry for suppressing or minimising disturbance, e.g. moiré or halo
- H04N5/213—Circuitry for suppressing or minimising impulsive noise
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N23/00—Cameras or camera modules comprising electronic image sensors; Control thereof
- H04N23/80—Camera processing pipelines; Components thereof
- H04N23/81—Camera processing pipelines; Components thereof for suppressing or minimising disturbance in the image signal generation
Definitions
- This invention relates to the processing of analogue and digital video signals and is especially concerned with the detection of visually disturbing artefacts such as film scratches.
- the present invention provides a method of video processing for detecting the presence of a scratch or other elongate picture artefact in a picture region, wherein the detection threshold depends on a background activity level in the picture region.
- the present invention provides apparatus for processing video signals for detecting the presence of a scratch or other elongate picture artefact in a picture region, comprising means for analysing a background activity level in the picture region and for providing a detection threshold based on the analysis.
- the present invention provides a method of video processing wherein the presence of a scratch or other elongate picture artefact in a picture region is detected through the steps of taking a measure of picture amplitude derivative over the region to provide a background activity level; identifying local derivatives of approximately equal magnitude and opposite polarity to provide a local activity level; subtracting said background activity level from said local activity level and accumulating positive results.
- Figure 1 is a block diagram of scratch detecting video signal processing apparatus according to this invention.
- Figure 2 is a block diagram showing in greater detail certain components of the apparatus shown in Figure 1 .
- Scratches are sharper than normal (background) film video, (ii) Scratches are usually narrow and isolated, (iii) Scratches are highly correlated vertically. (iv) Scratches do not necessarily come close to extreme (black or white) levels, (v) Scratches do not necessarily come to the full picture height, (vi) Scratches, while possibly persisting for several fields, may vary in contrast. (vii) For a particular film scratches may always be light, or always be dark, depending on the film processing and whether a positive or negative film was run in the telecine. As regards point (vii) above, it should be noted that usually either light scratches only or dark scratches only are present in one particular item of film material. However, film material does exist in which both types can be found.
- an input "scratched" video signal 1 which may be of any monochrome or colour standard such as analogue, serial digital, parallel digital, standard or high definition, is passed to both a local picture activity level measurement block 20 and to a background picture activity level measurement block 21 .
- an analogue input signal would need to be digitized prior to processing in the local and background picture activity level measurement blocks 20 and 21 .
- This digitization equipment is not shown in Fig. 1 ) .
- measures are taken of both partial single-sided (i.e. left and right) derivatives. In the presence of a scratch, these are of opposite polarity. For this processing, the magnitude of the smallest of these derivatives is then used as a measure of local activity 2.
- the signs 5 of either the left 1 6 or the right derivatives are also carried forward for use in certain subsequent processes, for example in scratch concealment processes.
- the sign 5 of the left (or right) derivative indicates whether a scratch is dark or light. Note that it does not matter whether the left or right derivative is carried - 4 - forward, as long as this is done consistently. Note also that different delays may be selected between the left and right derivatives. It has been found that for many scratches a 3 pixel delay (as indicated in Fig. 2) provides satisfactory results. Other values are possible. In particular if a certain width of scratches prevails a delay of a particular duration can be selected.
- a measure of the background activity 4 is assessed by processing a number of left and right derivatives at specific horizontal distances (numbers clock intervals) from the central point of a suspect scratch and finding the largest one.
- the background activity value 4 is subtracted from the local activity value 2 to give a difference value as shown in Fig. 2. If this produces a negative value, the output relative activity difference is set to zero. This distinguishes scratches from important periodic picture textures and test signals, e.g. line sweeps.
- the relative activity difference 6 is compared with a maximum allowed threshold 7, which is derived from a control parameter, defining the maximum expected scratch contrast. Only values less than this threshold 7 pass through. All other values are set to zero.
- the threshold 7 is increased (allowing a wider range of relative activity differences 6 to be passed) when a scratch has been detected in the preceding field .
- the resulting signal 8 will be referred to as y grad, which accordingly equals the relative activity difference 6 if the relative activity difference 6 is less than this threshold 7. If it is larger, then y grad 8 equals zero.
- the use of a maximum threshold 7 prevents the false detection of high contrast vertical lines, such as test signal pulses, and the modification of the threshold 7 in response to previously detected scratches alleviates the detection of medium contrast scratches.
- the y grad value 8 for each pixel from which it was derived is accumulated vertically in a line-store 28.
- the store 28 has one storage location for each pixel on the line (typically 720 locations for standard definition pictures in the case of processing based on luminance only; a - 5 - different number of locations would be provided for other formats, or in the case of processing based on chrominance) and the magnitude of each y grad value 8 is added (i.e. irrespective of the sign 5) to the corresponding stored value and the result returned to the same location in the store.
- the accumulation process is arranged to limit the magnitude of the data to avoid overflow (so that the stored values cannot be greater than a defined maximum value) .
- the sign 5 (derived from the local activity signal) is retained, as mentioned above. Note that the sign 5 would be expected to remain the same over the whole length of the scratch.
- This process exploits the high vertical and temporal correlation of scratches and allows scratches to be tracked reliably.
- the vertically-accumulated values 14 are spread horizontally by comparing each value with its immediate neighbours and, if it is greater than both, assigning the higher value to the two outer pixels.
- a preset number of frames apart, the spread, accumulated data 15 is compared (the comparison has hysteresis as will be explained below), on a pixel-by-pixel basis, with a threshold 1 1 which is derived from a control parameter.
- the results of the comparisons are stored as scratch flags 1 2 along with the accumulated data values.
- the appropriate flag 1 2 is cleared.
- a weak scratch (whose accumulated data value 15 for one isolated field does not exceed the threshold) persists for some fields the associated accumulated data value 15 may, due to accumulation over several fields, exceed the threshold 1 1 eventually. Thus also weak scratches are detected. In other - 6 - words, the level of confidence in a correct assessment as to whether a scratch is present is increased by accumulation over several fields.
- Logic may be provided to set the scratch flag for such a weak scratch only "as of the moment when the threshold is exceeded", or alternatively also retrospectively for a preceding period. The duration of such a preceding period may be determined by the exceeding of a second, lower threshold.
- Hysteresis is provided by lowering the threshold when the relevant flag 1 2 is already set and this prevents the scratch flag from "flickering".
- the sign 1 3 of the accumulated data indicates whether the scratch is light or dark and logic can be provided which prevents scratch flags being set when the sign 5 has the value corresponding to "unexpected" polarity of scratch.
- Every data word (stored in the line store 28) contains the accumulated history 1 5 of a particular column of the picture over several fields.
- the time constant of the recursive filtering improves the noise immunity of the detection process. Further improvement may be obtained by inhibiting the detection of scratches at the edge of the picture.
- window(s) can be applied in which scratch detection is allowed, or alternatively forbidden.
- the resulting scratch flag 1 2 can now be fed downstream to enable a scratch repair (concealment) filter of any known type. This filter is not the subject of the current invention.
- the next described step of the scratch detection process will not be required in many situations. It serves only for optimisation of the control parameters to be used at the other steps.
- this method analyses the picture for the total count of different types of details within different magnitude bands of activity.
- the result is an activity matrix, e.g. 3 x 3 matrix of activity counts for soft, sharp and super-sharp pulses within the contrast ranges of 0%-25%, 25%-50%, and 50%-100%.
- the matrix values are checked against predefined thresholds and the - 7 - picture under test is assigned to one of the predefined groups.
- the result is group identification number. From this analysis, the optimal filter for the particular source of video can be selected. This analysis is also used to modify the threshold values used in the processing which follows.
Abstract
Description
Claims
Priority Applications (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
EP99914667A EP1068722A1 (en) | 1998-04-03 | 1999-04-06 | Video signal processing |
AU33396/99A AU3339699A (en) | 1998-04-03 | 1999-04-06 | Video signal processing |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GBGB9807296.0A GB9807296D0 (en) | 1998-04-03 | 1998-04-03 | Video signal processing |
GB9807296.0 | 1998-04-03 |
Publications (1)
Publication Number | Publication Date |
---|---|
WO1999052275A1 true WO1999052275A1 (en) | 1999-10-14 |
Family
ID=10829888
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/GB1999/001043 WO1999052275A1 (en) | 1998-04-03 | 1999-04-06 | Video signal processing |
Country Status (4)
Country | Link |
---|---|
EP (1) | EP1068722A1 (en) |
AU (1) | AU3339699A (en) |
GB (1) | GB9807296D0 (en) |
WO (1) | WO1999052275A1 (en) |
Cited By (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB2370933A (en) * | 2001-01-09 | 2002-07-10 | Sony Uk Ltd | Detecting and reducing visibility of scratches in images. |
WO2002086820A2 (en) * | 2001-03-06 | 2002-10-31 | Hewlett-Packard Company | Automatic background removal method and system |
DE102004005299B4 (en) * | 2004-01-29 | 2006-09-07 | Deutsches Zentrum für Luft- und Raumfahrt e.V. | Method and device for detecting errors in film templates |
US7509115B2 (en) | 2002-12-23 | 2009-03-24 | Arbitron, Inc. | Ensuring EAS performance in audio signal encoding |
Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP0585759A1 (en) * | 1992-08-21 | 1994-03-09 | Eastman Kodak Company | Process for detecting and mapping dirt on the surface of a photographic element |
US5327240A (en) * | 1991-12-24 | 1994-07-05 | Texas Instruments Incorporated | Methods, systems and apparatus for providing improved definition video |
US5589887A (en) * | 1994-09-15 | 1996-12-31 | U.S. Philips Corporation | Method and circuit for detecting and concealing video signal errors |
EP0802669A2 (en) * | 1996-04-17 | 1997-10-22 | Samsung Electronics Co., Ltd. | A method and circuit for reducing noise |
-
1998
- 1998-04-03 GB GBGB9807296.0A patent/GB9807296D0/en not_active Ceased
-
1999
- 1999-04-06 EP EP99914667A patent/EP1068722A1/en not_active Withdrawn
- 1999-04-06 AU AU33396/99A patent/AU3339699A/en not_active Abandoned
- 1999-04-06 WO PCT/GB1999/001043 patent/WO1999052275A1/en not_active Application Discontinuation
Patent Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5327240A (en) * | 1991-12-24 | 1994-07-05 | Texas Instruments Incorporated | Methods, systems and apparatus for providing improved definition video |
EP0585759A1 (en) * | 1992-08-21 | 1994-03-09 | Eastman Kodak Company | Process for detecting and mapping dirt on the surface of a photographic element |
US5589887A (en) * | 1994-09-15 | 1996-12-31 | U.S. Philips Corporation | Method and circuit for detecting and concealing video signal errors |
EP0802669A2 (en) * | 1996-04-17 | 1997-10-22 | Samsung Electronics Co., Ltd. | A method and circuit for reducing noise |
Cited By (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB2370933A (en) * | 2001-01-09 | 2002-07-10 | Sony Uk Ltd | Detecting and reducing visibility of scratches in images. |
WO2002086820A2 (en) * | 2001-03-06 | 2002-10-31 | Hewlett-Packard Company | Automatic background removal method and system |
WO2002086820A3 (en) * | 2001-03-06 | 2004-02-26 | Hewlett Packard Co | Automatic background removal method and system |
US7057767B2 (en) | 2001-03-06 | 2006-06-06 | Hewlett-Packard Development Company, L.P. | Automatic background removal method and system |
US7509115B2 (en) | 2002-12-23 | 2009-03-24 | Arbitron, Inc. | Ensuring EAS performance in audio signal encoding |
DE102004005299B4 (en) * | 2004-01-29 | 2006-09-07 | Deutsches Zentrum für Luft- und Raumfahrt e.V. | Method and device for detecting errors in film templates |
Also Published As
Publication number | Publication date |
---|---|
EP1068722A1 (en) | 2001-01-17 |
AU3339699A (en) | 1999-10-25 |
GB9807296D0 (en) | 1998-06-03 |
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