Color correction system and method - Patent Review 4862251

We claim:

1. Apparatus for color correcting video picture signals, said apparatus comprising, in combination:

hue detector means that generates output signals only when the input signals represent a selected band of hues, the amplitude of said output signals representing the saturation of the input signals;

means for varying the location of said band in the spectrum of hues;

means for selectively developing correction signals for the video picture signals corresponding to said selected band of hues; and

correcting means for applying the correction signals to the latter video picture signals.

2. Apparatus as in claim 1, including means for adjusting the width of said band of hues.

3. Apparatus as in claim 1 in which said means for varying the location of said band is adapted to vary said location infinitely throughout said spectrum.

4. Apparatus as in claim 1, wherein the correction signal developing means includes means for discriminating from the video picture signals corresponding to said selected band of hues those video picture signals having a saturation level within a predetermined range of saturation levels, and means for developing correction signals for the signals having a saturation which falls within said predetermined range.

5. Apparatus as in claim 4 in which said predetermined range is selected from the group consisting of; above a first adjustable level; below a second adjustable level; and between two adjustable levels.

6. Apparatus as in claim 1 in which said video picture signals correspond to recorded images forming a program sequence, and including memory means for storing color correction and color correction location signals, and means for reading out of said memory means said color correction and location signals and applying the color correction signals so read out to video picture signals under the control of said location signals for the preparation of a color-corrected recording of said program sequence.

7. Apparatus as in claim 1 including window generator means for generating signals to form a window around a selected area of a video display displaying a video picture composed of video picture signals to be corrected, means for varying the size and location of said window on said display, and means for disabling said correcting means in one of the areas inside or outside of said window.

8. A color correcting device comprising, in combination; means for color correcting selected video picture signals corresponding to a selected band of hues, and hue detector means that generates output signals only when the input signals represent a selected band of hues, the amplitude of said output signals representing the saturation of the input signals; said hue detector means including means for developing a first signal and a second signal, said first and second signals being spaced apart 90.degree. in the hue circle; first modifying means responsive to a sin .theta. signal for modifying the sign and magnitude of said first signal; second modifying means responsive to a cos .theta. signal for modifying the sign and magnitude of said second signal; third modifying means responsive to a D cos .theta. signal for modifying the sign and magnitude of said first signal; fourth modifying means responsive to a D sin .theta. signal for modifying the sign and magnitude of said second signal; combining means responsive to the square of the difference between the third and fourth modified signals for combining the first modified signal and the second modified signal to limit the operation of said color correcting means to signals within said selected band of hues, wherein said combining means forms the product

[A*sin .theta.-B*cos .theta.]*[1-(A*Dcos .theta.-B*D sin .theta.).sup.2 ]

wherein A represents said first signal and B represents said second signal.

9. Apparatus as in claim 8, including means for varying the angle .theta. to select the location of said band of hues in the color spectrum.

10. Apparatus as in claim 8, including means for varying the value of D in order to adjust the width of said band.

11. Apparatus for color correcting selected hues in video picture signals, said apparatus comprising, in combination, hue detector means that generates output signals only when the input signals represent a selected band of hues, the amplitude of said output signals representing the saturation of the input signals, means for delivering said video picture signals to said hue detector means; means for varying the location of said band in the spectrum of hues; width control means for varying the width of said band and adapted for limiting said width to a relatively narrow band; and correction means for developing correction signals to correct the detected signals.

12. A device as in claim 11 in which said video signals include red (R), green (G), and blue (B) component signals, and a luminance (Y) signal, means for forming the signals (R-Y) and (B-Y), and means for modulating said R-Y signal with a signal corresponding to sine .theta. and modulating said (B-Y) signal with a signal corresponding to cos .theta. , where .theta. is a predetermined phase angle, subtracting the latter modulation product from the former modulation product, forming signals proportional to D(R-Y) cos .theta. and D(B-Y) sin .theta. , where D is a width factor, adding the latter signals together and rectifying the result, subtracting the result of the rectifying operation from a reference signal and multiplying that result times the result of subtracting the two modulation products from one another, said width control means comprising means for varying the value of D.

13. A device as in claim 12 in which said means for varying the locations of said band comprises means for pre-selecting the angle .theta..

14. Apparatus as in claim 13 in which said means for pre-selecting the angle .theta. comprises a single rotary potentiometer.

15. Apparatus as in claim 11, said correction means comprising means for adjusting at least one of the hue, saturation and luminance parameters of the detected signals.

16. A method for color correcting video picture signals corresponding to recorded images, said method comprising the steps of:

providing hue detector means that generates an output signal only when the input signals represent a selected band of hues, the amplitude of said output signal representing the saturation of the input signals, the location of said band in the color spectrum being variable;

setting said location of said band in said color spectrum to correspond to the hue of an image to be corrected,

selectively developing correction signals for the ones of said video picture signals corresponding to the selected band of hues; and

applying the correction signals to the latter video picture signals.

17. A method as in claim 16, wherein the developing step includes discriminating from the video picture signals corresponding to the selected band of hues those video picture signals having a saturation level within a predetermined range of levels and developing correction signals for the signals falling within said range of levels.

18. A method as in claim 16 including providing memory means and control means for controlling the sequential display of pictures corresponding to said picture signals to stop the sequential display, color correcting the picture while it is displayed in still form, storing in said memory means the location of the corrections in said sequence as well as correction information, and replaying said sequence while applying said correction information to the video signals of the pictures being re-played and recording the resulting color-corrected signals on a record medium.

19. A method as in claim 16 including selectively controlling the width of said band in said spectrum to limit or enlarge the portion of a video picture in which signals are detected.

Description Submit all comments and votes

BACKGROUND OF THE INVENTION

The invention relates to systems and methods for color correcting video picture signals. More particularly, the present invention pertains to improved systems and methods for increasing the quality and speed of color correction operations. This patent describes improvements upon the color correction systems and methods disclosed in U.S. Pat. Nos. 4,096,523 (the "Rainbow" patent); 4,223,343 (the "Anamorphic" patent); 4,410,908 (the "Luminance" patent); copending, commonly owned U.S. patent applications Ser. No. 598,468, U.S. Pat. No. 4,679,067, entitled "Color Correction System and Method With Localized Color Sampling" now U.S. Pat. No. 4,679,067; Ser. No. 722,801, U.S. Pat. No. 4,694,329, entitled "Color Correction System and Method With Scene-Change Detection"; now U.S. Pat. No. 4,694,329 allowed and Ser. No. 807,815, entitled "Editing System and Method" now U.S. Pat. No. 4,750,050. The disclosures of these patents and patent applications are hereby incorporated herein by reference.

There is a continuing need to improve the efficiency, speed, and quality of the color correction of video picture signals, especially in film-to-tape and tape-to-tape transfers, and particularly in scene-by-scene color correction. For instance, there is a need to better isolate particular objects for color correction. Furthermore, there is a need to better select a specific color or a specific range of colors for color correction.

OBJECTS OF THE INVENTION

Accordingly, an object of the invention is to satisfy the above needs and provide a system and method for color correcting video picture signals with increased efficiency, speed, and quality.

Another object of the invention is to provide an apparatus and a method for improving the accuracy with which a specific color or a specific range of colors may be color corrected.

An additional object of the invention is to provide an apparatus and a method for more easily identifying and recalling the color corrections associated with particular scenes in an image recording medium that is to be color corrected.

A further object of the invention is to provide an apparatus and a method for better segregating a particular area of the picture produced by the video picture signals and color correcting this particular area.

Yet another object of the invention is to provide an apparatus and a method for improving the ability to color correct color signals having certain levels.

SUMMARY OF THE INVENTION

The invention satisfies the needs identified above and meets the foregoing objects by providing an apparatus in which a predetermined range of colors around an infinitely variable principal color are selected. Color corrections for the video picture signals corresponding to the predetermined range of colors are selectively developed, and then the color corrections are applied to the video picture signals, thereby producing color corrected video picture signals. Accordingly, any object in the video picture may be selected based upon its color. Preferably, the size of the predetermined range of colors is adjustable. Therefore, all of the colors in the object may be selected for color correction, even if the object consists of a wide range of colors. However, the range may be adjusted to be very narrow, if the operator so desires. Thus, the present invention permits particular objects to be selected for color correction based upon their colors. The principal color may be selected from any hue. This advantage results in an improvement in the quality of the color corrected videotape. Moreover, this advantage decreases the time, and therefore the cost, of color correcting motion picture film and videotape.

In accordance with another aspect of the invention, a color corrector includes circuits for discriminating the video picture signals in a specific area from the video picture signals forming the remainder of the picture. Color correction signals are applied to the video picture signals either inside of or outside of the specific area. The size and/or the position of the specific area may be changed at the beginning of each new scene. Consequently, the area may "follow" a particular object as it moves from place to place in various scenes. Hence, greater object selectivity for color corrections is obtained, and better color corrections are developed.

In accordance with a further aspect of the invention, the color corrections for a particular scene are identified or labeled with a video picture from that particular scene. The video picture is displayed for the operator. The operator may use the display to recall the color corrections for that particular scene and apply them to the video picture signals for the present scene. Several video pictures may be shown on the same display, and the operator may utilize an array of pushbuttons arranged like the video pictures on the screen or a light pen in order to choose the color corrections to be recalled. Alternatively, the display may include a touch screen, and the operator may touch the video picture associated with the desired color corrections in order to recall them. The operator does not have to remember the scene number for the particular scene, which may change as the motion picture film or the videotape is edited. This aspect of the invention enables the operator to readily identify, locate, and recall the color corrections he or she desires to work with. Therefore, this aspect of the invention greatly increases the speed with which a motion picture film or a videotape may be color corrected.

In accordance with an additional aspect of the invention, the color corrector may include circuits for discriminating video picture signals based upon their color levels. Specifically, such discrimination circuits may discriminate signals above a predetermined level or signals below a predetermined level or signals between two predetermined levels. Color corrections are selectively developed for the discriminated signals, and the color corrections are applied to the associated video signals to produce color corrected video picture signals. This aspect of the invention further increases object selectivity and speeds the color correction process.

The features of the invention each increase the efficiency of the color correction process. In addition, when two or more features are used together, even greater efficiency results, such efficiency previously being unattainable.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features, and advantages of the present invention will become apparent upon consideration of the following detailed description of illustrative embodiments thereof, especially when taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a diagrammatic illustration of a color correction system according to the invention;

FIG. 2 is a top plan view of the front panel for the color corrector shown in FIG. 1;

FIG. 3 is an enlarged view of a portion of the front panel shown in FIG. 2;

FIG. 4 is an enlarged view of another portion of the front panel shown in FIG. 2;

FIGS. 5A-5D are diagrammatic illustrations of waveforms on a vectorscope and depict the functions of the variable vector controls;

FIGS. 6A-6C are enlarged views of the auxiliary monitor and the main monitor for the color correction system shown in FIG. 1;

FIGS. 7A-7B are a block diagram of the color correction circuits in a color correction system according to the invention;

FIG. 8 is a block diagram of the variable vector control circuits for a color correction system according to the invention;

FIG. 9 is a block diagram of a coefficient processor for the variable vector control circuits illustrated in FIG. 8;

FIG. 10 is a schematic diagram for the level discrimination circuit illustrated in FIG. 8; and

FIGS. 11A-11C are waveform diagrams for the level discrimination circuit illustrated in FIG. 10.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

General Description

FIG. 1 shows a color correction system 10 constructed according to the invention. The color correction system 10 includes a color corrector 11 having a front panel 12. Portions of the front panel 12 are illustrated in greater detail in FIGS. 2-4. The front panel 12 has a set of variable vector controls 14 and a set of six vector controls 16. The six vector controls 16 function as outlined in the Rainbow, Anamorphic, and Luminance patents. The front panel 12 includes a set of color balance controls 18 and "window" controls 20. The "window" controls 20 are described and depicted in greater detail in application Ser. No. 598,468 U.S. Pat. No. 4,679,067 as well as application Ser. No. 722,801 U.S. Pat. No. 4,694,329. The front panel 12 additionally includes video signal source controls 22. The video signal source controls 22 adjust parameters such as the PEC gain and negative gain for each of the red, green, and blue channels. Moreover, the video signal source controls adjust other parameters, for instance, the horizontal pan, the vertical pan, the zoom, and the contours. Each of the controls in the sets of controls 14, 16, 18, and 22 includes a control knob which is coupled to a shaft-position encoder, as described in the latter patents (U.S. Pat. No. 4,679,067) (U.S. Pat. No. 4,694,329).

The right side of the front panel 12 includes pushbuttons and displays. Specifically, this portion of the front panel includes two rows of pushbuttons 24, which are shown in greater detail in FIG. 4, and three rows of pushbuttons 26, which are shown in greater detail in FIG. 3. The functions of many of these pushbuttons are described in the Rainbow, Anamorphic, and Luminance patents. A display 28 shows the scene number for the color corrections stored in the A buffer and the B buffer. Moreover, the display 28 shows the scene number for the current scene.

A keypad 30 and a display 32 are used to recall the color corrections for a particular scene and apply them to the present scene. For example, if the operator wanted to use the color corrections for scene number 1,234 for the current scene, the operator would press the "call" pushbutton and then the buttons 1, 2, 3, and 4 of the keypad 30 in this sequence in order to recall the desired color corrections. The right portion of the front panel has an array of pushbuttons 34 and a row of pushbuttons 36 for recalling color correction signals for previous scenes in another manner. The operation of the pushbuttons 34 and 36 will be described at length below. The right portion of the front panel 12 has waveform pushbuttons and indicators 38 for selecting various waveforms for viewing on an oscilloscope (not shown) as well as monitor selector pushbuttons and indicators 40 for selecting various signals for monitoring.

The system 10 has a computer 42, which is connected to each of the color corrector 11, a video signal source 44, a videotape recorder 46, and a video memory 48. The video signal source 44 may be a film chain, a telecine, a videotape player, or the like. The video signal source 44 produces video signals from the associated image recording medium. These video signals are delivered to the color corrector 11 so that they may be corrected. The color corrector 11 provides color corrections for the video signals from the video signal source 44 under the direction of the operator and the computer 42, and it produces color corrected video signals. The color corrected video signals are sent to a videotape recorder 46 and to a main monitor 50. The operator may observe the effect of the color corrections on the video signals by looking at the video picture on the main monitor 50. The videotape recorder 46 records the color corrected video signals on a videotape 54, thereby producing a color corrected videotape.

The main monitor is shown with windows W1 and W2. The use of the windows W1 and W2, which are movable in size and/or position, is described further below.

An auxiliary monitor 52 is connected to the computer 42. The auxiliary monitor 52 displays a plurality of video pictures, such as the video pictures 56a-56d. The function of the auxiliary monitor 52 and the video memory 48 is described below during the discussion of the pushbuttons 34 and 36.

Above each of the control knobs in the sets of controls 14, 16, 18, and 22 is a row 35 of four light-emitting diodes ("LEDs"), which are referred to as rangefinder LEDs. The two inner LEDs are green, while the two outer LEDs are red. When the associated control knob is in its center position, the two inner LEDs are energized. If the control knob is turned to the right, the two inner LEDs are deenergized and the rightmost LED is energized. Correspondingly, if the control knob is turned to the left, the two inner LEDs are deenergized, and the leftmost LED is energized. Accordingly, the operator may quickly determine the position of any of the control knobs.

Reset buttons 64, 66, and 68, are provided to permit the operator to readily center the control knobs in the sets of controls 16, 18, and 22, respectively. Specifically, the operator presses a reset button, and all of the control knobs in the associated set of controls are electronically centered by zeroing the counter connected to the control knob. The controls 16, 18, and 22 include active-memory pushbutton-indicators 70, 72, and 74, respectively.

The "notch" pushbutton sets the scene boundary between scenes. The "color correct enable" pushbutton makes the "notch" pushbutton effective for color correction events. The "pan enable" pushbutton makes the "notch" pushbutton effective for position related events, such as horizontal pans, vertical pans, and zooms.

The carry forward mode is entered by pressing the "carry forward mode" pushbutton. In this mode, the color corrections from the last scene are carried forward for the next scene. That is, once the operator establishes color corrections for a particular scene and then sets the scene boundary between that scene and the next scene, these color corrections are both stored for the particular scene and applied to the next scene. Thus, the operator may use these color corrections as a basis for color correcting the next scene.

The "picture file" pushbutton is used with the video scene recall feature of the invention, which is described below. The "picture file" pushbutton enables the array of pushbuttons 34 and the row of pushbuttons 36.

The "dissolve" pushbutton is used to produce a linear transition between the color corrections for a given scene and the color corrections for the subsequent scene. For example, the operator may make color corrections for a given scene and then make color corrections for the subsequent scene. If the operator wants a smooth transition between scenes, the operator presses the "dissolve" pushbutton at a frame near the end of the given scene and again presses the "dissolve" pushbutton at a frame near the beginning of the subsequent scene. The computer is programmed to automatically provide a linear transition, for instance, on a frame-by-frame basis, between the color corrections for the given scene and the color corrections for the subsequent scene for all frames between the two dissolve points.

The "source 1," "source 2," "source 3," and "source 4" pushbuttons, which are shown in FIG. 3, enable the operator to select one of a variety of video signal sources. For example, the operator may select a telecine as the video signal source by pressing the "source 1" pushbutton or select a videotape player as the video signal source by pressing the "source 2" pushbutton.

The "load count" pushbutton allows the frame counter to be initialized to any number at the beginning of a new job. The "count mode" pushbutton allows the operator to select among various counting modes for the frame counter, such as, counts by hours, minutes, seconds and film frames or PAL video frames or NTCS video frames.

The "matte ext," "variable vector matte on," "six vector matte on," and "matte store" pushbuttons are described below during the description of the travelling matte feature of the invention.

The "disc load," "disc save," "disc format," "auto save," and "disc test" pushbuttons are utilized to control an external storage device (not shown) for the computer, such as a floppy disc drive or a hard disc drive.

Variable Vector Controls

FIG. 2 illustrates the set of variable vector controls 14. The controls 14 include a variable vector position control 80, a delta control 82, a factor control 84, a saturation control 86, a hue control 88, and a luminance control 90. Furthermore, the variable vector controls 14 include a "set up" pushbutton, the function of which is described below. A plurality of LEDs 94 are located around the circumference of the variable vector position control 80. The LEDs 94 indicate the angular orientation of the variable vector position control 80. The angular orientation of the variable vector position control 80 corresponds to one of the colors on a vectorscope.

The variable vector position control 80 is used to select a particular range of colors for color correction. The principal color within the range of colors is determined by the angular orientation of the variable vector position control 80. The variable vector position control 80 may be used to select any principal color within the precision of the associated counter. For example, if the associated counter is a 12-bit counter, any one of 4,096 different principal colors may be selected with the variable vector position control 80.

The functions of the various controls 80-90 are better explained in conjunction with FIGS. 5A-5D. The circle 96 diagrammatically illustrates a vectorscope. The waveform 98 illustrates the response of the variable vector control circuits when the input signal to the color corrector is from a device which generates a spectrum of color signals. The waveform 98 corresponds to a given angular orientation of the variable vector position control 80. FIG. 5A shows the effect of turning the variable vector position control 80. For example, if the control 80 is turned clockwise to select a different principal color, the response of the vectorscope becomes the waveform 98a. Then, if the control 80 is turned further clockwise to select another principal color, the response of the vectorscope becomes the waveform 98b. Similarly, if the control 80 is turned counterclockwise to select yet another principal color, the response of the vectorscope becomes the waveform 98c. Accordingly, the control 80 may be turned to select the principal color from any hue.

The variable vector controls are nominally effective for a predetermined range of colors around the principal color. For example, colors within plus or minus 5 degrees of the principal color will be color corrected along with the principal color; however, the effectiveness of the color corrections will decrease as the distance from the principal color increases.

The delta or bandwidth control 82 is provided in order to adjust the width of the predetermined range of colors effected by the variable vector control position control 80. FIG. 5B shows the effect of rotating the delta control 82. The delta control 82 may be rotated clockwise in order to increase the width of the range of colors or rotated counterclockwise in order to decrease the width of the range of colors. Hence, the width of the range of colors may be made as large or as small as the operator desires, within the limits of the equipment. For instance, the width of the range of colors may be changed anywhere from plus or minus about 2 degrees around the principal color to plus or minus 90 degrees around the principal color. FIG. 5B shows a waveform 100 with the same principal color as the waveform 98 but with an increased bandwidth. The waveform 100 was obtained by turning the delta control 82 clockwise. FIG. 5B also shows a waveform 102 with the same principal color as the waveform 98 but with a decreased bandwidth. The waveform 102 was obtained by turning the delta control 82 counterclockwise.

Once the desired principal color and the desired range of colors around it have been selected with the variable vector position control 80 and the delta or bandwidth control 82, the saturation control 86, the hue control 88, and the luminance control 90 may be employed to generate color correction signals for the video picture signals corresponding to the selected range of colors. More particularly, the hue control 88 is used to alter the colors in the selected range of colors and shift them in the color spectrum, while the saturation control 90 is used to change the levels of the colors in the selected range of colors. Additionally, the luminance control 92 is utilized to vary the luminance of the colors in the selected range of colors.

FIG. 5C shows the effect of rotating the hue control 88. To shift the colors in the selected range of colors, the hue control 88 is turned clockwise or counterclockwise. FIG. 5C shows a waveform 104 and a waveform 106. The waveform 104 was produced by turning the hue control 88 clockwise after the waveform 98 was selected. Similarly, the waveform 106 was produced by turning the hue control 88 counterclockwise after the waveform 98 was selected. The hue control may shift the color within the selected range of colors by any desirable amount, within the limits of the equipment. For example, the hue control may be designed to shift the principal color by up to 60 degrees in one direction or the other.

FIG. 5D shows the effect of turning the saturation control 86. The saturation control 86 may be rotated clockwise or counterclockwise to increase or decrease, respectively, the saturation levels of the colors in the selected range of colors. As an example, the waveform 108 illustrates what happens when the saturation control 86 is rotated clockwise once the waveform 98 was selected. The waveform 108 has a saturation level above the waveform 98. The waveform 110 illustrates what happens when the saturation control is rotated counterclockwise once the waveform 98 was selected. The waveform 110 has a saturation level below the waveform 98.

The luminance control 92 may be used to increase or decrease the brightness of the colors within the selected range of colors. Of course, the luminance control 92, the hue control 88, and the saturation control 86 may be employed together to alter the associated parameters of the colors within the selected range of colors. The variable vector control knob 80 and the delta control knob 82 are utilized to set the selected range of colors, as noted above. The factor control 84 is used to select those colors within the selected range of colors that have saturation levels either above or below a specified level. The function of the factor control 84 is described in greater detail below during the description of FIGS. 10 and 11.

As an example of the use of the variable vector controls 14, the color correction of a particular scene will be described. Assume the operator desires to color correct a specific object, such as an apple. The operator initially presses the "set up" pushbutton 92, which is part of the variable vector controls 14. This causes all portions of the picture which have colors within the nominal range of colors set by the variable vector position control 80 to become a neutral gray. I