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WO1992005664A1 - Composition d'images video - Google Patents

Composition d'images video Download PDF

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Publication number
WO1992005664A1
WO1992005664A1 PCT/GB1991/001620 GB9101620W WO9205664A1 WO 1992005664 A1 WO1992005664 A1 WO 1992005664A1 GB 9101620 W GB9101620 W GB 9101620W WO 9205664 A1 WO9205664 A1 WO 9205664A1
Authority
WO
WIPO (PCT)
Prior art keywords
image
store
values
video
control image
Prior art date
Application number
PCT/GB1991/001620
Other languages
English (en)
Inventor
Michael Joseph Kemp
Original Assignee
Spaceward Holdings Limited
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Spaceward Holdings Limited filed Critical Spaceward Holdings Limited
Publication of WO1992005664A1 publication Critical patent/WO1992005664A1/fr

Links

Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N5/00—Details of television systems
    • H04N5/222—Studio circuitry; Studio devices; Studio equipment
    • H04N5/262—Studio circuits, e.g. for mixing, switching-over, change of character of image, other special effects ; Cameras specially adapted for the electronic generation of special effects
    • H04N5/2622—Signal amplitude transition in the zone between image portions, e.g. soft edges
    • G—PHYSICS
    • G06—COMPUTING OR CALCULATING; COUNTING
    • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T15/00—3D [Three Dimensional] image rendering
    • G06T15/50—Lighting effects
    • G06T15/503—Blending, e.g. for anti-aliasing
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N5/00—Details of television systems
    • H04N5/222—Studio circuitry; Studio devices; Studio equipment
    • H04N5/262—Studio circuits, e.g. for mixing, switching-over, change of character of image, other special effects ; Cameras specially adapted for the electronic generation of special effects
    • H04N5/272—Means for inserting a foreground image in a background image, i.e. inlay, outlay
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N9/00—Details of colour television systems
    • H04N9/64—Circuits for processing colour signals
    • H04N9/74—Circuits for processing colour signals for obtaining special effects
    • H04N9/75—Chroma key

Definitions

  • This invention relates to video image composition systems and in particular to systems in which the images are digital images.
  • Figure 1 illustrates a typical prior art composition system.
  • the system co ⁇ prises a frame store 2 which stores a background image, a frame store 4 which stores a foreground image and a frame store 6 which stores a control image to be used in combining background and foreground images from stores 2 and 4. If we consider a monochrome image in both foreground -and Cackground then the stores 2 and 4 will both be, typically, of 8 bits per pixel.
  • the control image 6 is a single bit per pixel.
  • corresponding pixels are read-out from frame stores 2 and 4 under the control of addressing circuitry 10 and fed to the inputs of a video switch 12. This is controlled by a corresponding bit received from the control image frame store 6 to output either a pixel from the foreground image or a pixel from the background image. If the corresponding pixel in the control image is a 1 nen the foreground image is output to frame store 8 and if it is a 0 then the background image is output.
  • a sample of the pixels stored in the control image frame store 6 is shown at 14 and tvvo samples from the composed image in frame store 8 are shown at 16 and 18. It can be seen that the form of the control image results in a sharp transition from foreground to background with no blending of the two images taking place.
  • This system can be arranged to work with video rate inputs and outputs and therefore without the need for any frame stores.
  • the sharp transitions and jagged edges at 16 and 18 are unattractive in the composed image and do not give a realistic composition.
  • PC is the value of the composite pixel
  • PF and PB are the values of the foreground and background pixels respectively.
  • Alpha is the value stored in the control image.
  • a transition from foreground to background in the control image frame store 6 is shown at 22.
  • the data in the store goes from 0 at the left hand side of the patch 22 to 255 (which corresponds to the value of 1) at the right hand side.
  • the resultant composed image is shown at 24. It can be seen that there are intermediate values of shading between the dark background and the light foreground.
  • control image In many image composition systems the control image is never avail-able as a multi-bit word for each pixel. For example simple chroma-key devices do not have this facility, neither do hard key control images recorded along with a foreground image, for example a "superblack" key. Even when a multi value control image is available the degree of blending which it provides may not be visually acceptable to a user, such as an artist using the image composition facility on a video painting system, and he may wish to vary the degree of blending.
  • a preferred ei ⁇ iodiment of the invention allows for the creation of a composite image with blended transitions whether or not multi valued control image data is available. It also allows the softness of the edge between foreground and background to be controlled by a user.
  • Figure 1 is a circuit diagram of the first prior cart device described
  • FIG. 2 is a circuit diagram of the second prior art device described above
  • FIG. 3 is a circuit diagram of a system embodying the invention.
  • Figure 4 shows a distortion of an image.
  • Figure 5 shows a first modification of figure 3 including a hold-out mask
  • Figure 6 shows a second modification of figure 3 including a hold-out mask.
  • Figure 3 shows a frame store 2 storing a background image, a frame store 4 storing a foreground image, and a frame store 6 storing a control image.
  • the control image conprises a single bit per pixel. Pixels required to produce a composite image of foreground and background are read out from stores 2, 4 and 6 by a pixel address generator 10.
  • the signals from the foreground and background images are fed to a linear interpolator 20 which produces, from them, a composite output which is fed to store 8-
  • the interpolation parameter alpha for the linear interpolator is generated as follows. When a pixel is addressed a patch of pixels surrounding the corresponding pixel in the control irrage 6 is used to generate the value alpha.
  • the connection from the pixel address generator 10 to the store 6 is via an adder 22. This has its other input connected to a local patch addressing circuit 24. For each pixel address the local patch addressing cirucit 24 addresses a patch of pixels in the store 6 by means of this adder. At the same time it addresses a corresponding pixel in a local weighting store 26.
  • the value read out from the weighting store 26 is multiplied by the value read out from the corresponding pixel in the control image 6 in a multiplier 28.
  • the local addressing circuitry 24 is arranged to align the central pixel of the weighting store 26 with the addressed pixel in store 6.
  • the values for the whole of the local patch are summed together in cumulative adder 30. This is clocked by a further signal received from the local patch addressing cirucit 24 until the whole of the patch has been processed.
  • the cumulative adder 30 then makes its output available and this forms one the input to a divider 32.
  • the value is divided by a scaling factor K to produce a valid value for alpha.
  • K The exact value used for K will depend on the size of the weighting store 26 and the values stored therein. It is chosen so that alpha will be in the range 0 to 255 for a linear interpolator which expects an 8 bit alpha value.
  • the alpha output from the divider thus forms the input to the linear interpolator 20.
  • the cumulative adder 30 is zeroed and the process steps onto the next pixel.
  • the weighting store contains the same value in each of its pixels it will be appreciated that when the patch is centered on the the boundary between foreground and background the resultant pixel value will comprise data from both foreground and background. The proportion of foreground or background will increase in dependence on how far the patch overlaps the boundary edge.
  • the weighting store 26 can store different arrangements of values, for example preferably a circular array with a peak at the centre and zeroes at the edges.
  • the shape based on the gausian curve is ideal but in practice any shape with a central peak and declining to the edge gives good results. In practice a square array is unlikely to be used.
  • Tne rate at which a shape stored in the weighting store 26 declines to 0 controls the sharpness of the blend between foreground and background. If the central value is high and all surrounding values are zero then the results will be the same as Figure 1. If the values decline to 0 within two pixels the image is still sharp but the blend should produce very natural looking results without the jagged edges of Figure 1. If the value declines to 0 over 4 pixels then an even softer blend can be achieved.
  • the softness of the blend can be varied within a wei ⁇ ting store and different results could be acnieved by using different sizes of weighting store.
  • an image composition system will enable a user to load different distributions of weighting values into the weighting store 26. These are selected by standard menu selection techniques.
  • the local patch addressing circuitry 24 can be arranged to adapt to the size of the shape stored in weighting store 26 so that values known to be 0 are not processed. This will result in faster processing of the images.
  • Displacement coordinates (X, Y) can be fed to address generator 10 to effect a displacement of the foreground image with respect to the background. This can lead to the pixels addressed by the local patch addressing circuit 24 being outside the stores 2, 4, and 6. In fact this also occurs in normal processing of pixels adjacent the edges of the background and foreground images. When such illegal addresses are encountered the control image store 6 is arranged to set the output at 0 to simulate total transparency of the foreground image outside its defined area.
  • the system can be adapted to continually reprocess the image from stores 2, 4, and 6 and continually update the store 8 whilst the user moves the position of the foreground image using a tablet and stylus coupled to the pixel address generator 10. Once he has moved the foreground image to a desired position he can permanently store the image in the frame store 8.
  • Store 8 is arranged so that its contents can be viewed on a monitor as the artist moves the foreground image relative to the background image.
  • the speed of movement can be improved by replacing the weighting store values with a single value in the centre until the desired position has been selected (as in the prior art device of figure 1) .
  • the proper weighting array from weighting store 26 can be used to create a softened edged composition and permanently store this in frame store 8.
  • the final image in store 8 in real time.
  • the foreground and background images in stores 2 and 4 can come from real time sources such as video cameras.
  • the control image in store 6 requires temporary storage to allow for the local addressing to take place but otherwise it also can be updated in real time from a source of keying signals.
  • a "double buffered" system is used in accordance with known techniques and stores 4 and 6 are updated together with related foreground and keying signals. In this way a source with a hard key can still give a properly blended final video image.
  • the scaling factor K is fixed at an appropriate power of 2 e.g. 256 as this represents an 8 bit shift rather than a full divide operation.
  • the values stored in weighting store 26 are then carefully selected so that they sum to 256 x 255, thus resulting in a maximum value fed to the linear interpolator of 255.
  • control image store 6 Where values in the control image store 6 are available as ulti bit values for each pixel, good results are obtained by disregarding the additional information and simply using the most significant bit to represent 0 or 1. However, these values could be used as inputs to multiplier 28 with a suitable adjustment to the scaling factor K to give an improved blend over the system shown in Figure 2.
  • Figure 4 shows a typical distortion of the foreground image.
  • a source image 30 is distorted into a smaller rotated image at 32.
  • Figure 4b shows how the old pixel array is mapped onto the new pixel array.
  • Pixel 34 can be seen to c ⁇ prise several whole or part pixels from the source image. It is necessary to calculate the area covered by each of the source pixels to create the new pixel 34 by means of a weighted average of the constitutent pixels. This can be done by known techniques.
  • the image 30 is a foreground image from store 4 a new foreground image is created directly.
  • the values of the control image should be changed from 0 and 1 to 0 and 255 in the case of a simple on/off control image or we can simply use the original values if the control image is already a multi-value image.
  • the weighted average can then be used to produce a new control image in the range 0 to 255.
  • an additional control image or hold out mask is also provided. This represents an area at the background image where the foreground image is not to be applied to the background image. In prior art devices such as that shown in Figure 1 this additional control signal would be used to inhibit switch 12 such that irrespective of the signal received from the control image 6 the pixel from the background would be used in the composed image 8.
  • a hold-out mask when used as shown in figure 5 it is stored in frame store 40 and addressed in parallel with the background image 2 but with the additional displacement from patch addressing circuit 24 via adder 43.
  • the signal is inverted in inverter 42 and fed through an AND gate 44 along with the signal read out from the control image 6.
  • a value 1 from the hold-out mask will force the value 0 into the cumulative adder 30.
  • a value 0 from the hold-out mask enables the control image 6 to pass its values through to the cumulative adder 30.
  • the hold out mask value is an 8 bit value in the range 0 to 255 and it is desired not to provide a variable softening effect then the arrangement of figure 6 can be used.
  • the hold-out mask value is complemented in inverter 42 and ultiplied in multiplier 46 with the final output of divider 32. This then provides a proportionally transparent protection to the pixels of the background image by varying alpha in depedence on the hold-out mask value from store 40 following the variable blending function derived in cumulative adder 30.
  • the hold-out mask store 40 is addressed directly by addressing cicuitry 10. If desired a small change can be made to the value of K or to the overall total of the weighting store 26 so that the output of the this second multiplier will be kept in the range 0 to 255.
  • the control image can be created in a number of known ways such as by the user drawing with a stylus on a graphics tablet whilst viewing an image of the control plane. It may be created as a single bit value or as a multi-bit value signal. Altenatively the control image may be derived directly from a video image itself by means of, for example, selection of a specified range of lu a values (lu a keying) or of chroma values (chroir ⁇ keying) It may also be a separate input to the system.
  • the system has been described herein as a hardware system. However, the invention can be -Lirplemented in software in any general purpose c ⁇ rrputi-ng system.
  • the invention can be applied to any image composition system in which the images an be provided in digital form, for example, film and graphic arts.

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  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Computer Graphics (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Theoretical Computer Science (AREA)
  • Image Processing (AREA)

Abstract

Un système de composition d'images vidéo reçoit des premiers et deuxièmes signaux d'images vidéo de source respectives (2, 4). On utilise les signaux dérivés d'une image de commande (6) pour commander la combinaison des première et deuxième images vidéo. On utilise un moyen d'adressage (10) pour extraire des signaux de pixels individuels dans les trois images (2, 4, 6). On calcule un paramètre d'interpolation pour la combinaison des première et deuxième images sur un pixel adressé. La valeur d'interpolation dudit pixel est calculée en fonction des valeurs des images de commande mémorisées dans une connexion située autour de ce pixel. Les première et deuxième images sont combinées dans un interpolateur (20) selon des proportions relatives à la valeur d'interpolation, pour produire une image composite (8).
PCT/GB1991/001620 1990-09-20 1991-09-20 Composition d'images video WO1992005664A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB9020540.2 1990-09-20
GB909020540A GB9020540D0 (en) 1990-09-20 1990-09-20 Video image composition

Publications (1)

Publication Number Publication Date
WO1992005664A1 true WO1992005664A1 (fr) 1992-04-02

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Application Number Title Priority Date Filing Date
PCT/GB1991/001620 WO1992005664A1 (fr) 1990-09-20 1991-09-20 Composition d'images video

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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2260237B (en) * 1991-09-13 1995-07-12 Samsung Electronics Co Ltd Method and apparatus for overlaying images
WO1996029829A1 (fr) * 1995-03-21 1996-09-26 Animal Logic Research Pty. Limited Ameliorations apportees a la composition d'images
EP2472878A1 (fr) * 2010-12-31 2012-07-04 Advanced Digital Broadcast S.A. Procédé et appareil de combinaison d'images d'une interface d'utilisateur graphique avec une vidéo stéréoscopique
EP1800472A4 (fr) * 2004-09-24 2012-11-07 Mtek Vision Co Ltd Procede et appareil de composition d'image

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB886086A (en) * 1958-11-05 1962-01-03 Fernseh Gmbh Apparatus for controlling television signals
US4393394A (en) * 1981-08-17 1983-07-12 Mccoy Reginald F H Television image positioning and combining system
GB2113950A (en) * 1982-01-15 1983-08-10 Quantel Ltd Image composition system

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB886086A (en) * 1958-11-05 1962-01-03 Fernseh Gmbh Apparatus for controlling television signals
US4393394A (en) * 1981-08-17 1983-07-12 Mccoy Reginald F H Television image positioning and combining system
GB2113950A (en) * 1982-01-15 1983-08-10 Quantel Ltd Image composition system

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2260237B (en) * 1991-09-13 1995-07-12 Samsung Electronics Co Ltd Method and apparatus for overlaying images
WO1996029829A1 (fr) * 1995-03-21 1996-09-26 Animal Logic Research Pty. Limited Ameliorations apportees a la composition d'images
EP1800472A4 (fr) * 2004-09-24 2012-11-07 Mtek Vision Co Ltd Procede et appareil de composition d'image
EP2472878A1 (fr) * 2010-12-31 2012-07-04 Advanced Digital Broadcast S.A. Procédé et appareil de combinaison d'images d'une interface d'utilisateur graphique avec une vidéo stéréoscopique
WO2012090059A1 (fr) * 2010-12-31 2012-07-05 Advanced Digital Broadcast S.A. Procédé et appareil de combinaison d'images d'une interface utilisateur graphique avec une vidéo stéréoscopique

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Publication number Publication date
GB9020540D0 (en) 1990-10-31

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