JP2004514338A - High quality color key extraction device - Google Patents

Abstract

The present invention provides a very hardware efficient and versatile way to perform color keying and color component evaluation operations. It also provides a method for significantly limiting the visibility of artifacts caused by filtering images containing key color information. According to the present invention, there is provided a color key extraction device for determining whether an input pixel having a plurality of color components matches a predetermined key color. The apparatus includes a plurality of evaluation circuits, each of which receives one of the color components of the input pixel, evaluates it against a predetermined color component intensity range, and outputs a comparison signal. A matching circuit is operatively connected to each of the evaluation circuits, each of the evaluation circuits determining whether a combination of the comparison signals satisfies a predetermined condition, and the condition is satisfied. Outputs a match signal, whereby the input pixel matches the predetermined key color.

Description

[0001]
(Summary of the Invention)
The present invention relates generally to color key extraction devices, and in particular, to color key extraction devices for high quality applications.
[0002]
Color keying is widely used and implemented in various video and graphics processors for various purposes, for example, to overlay one image on top of another. Color keying is achieved by placing unused colors as key colors in a video or graphics image and displaying replacement colors instead of unused colors. Typically, the key colors are magenta or other rarely used colors. Color keying is generally done at the mixing stage. The input pixel is evaluated to determine if the pixel matches a particular color or color gamut. If there is a match, color replacement is performed for the specific action, for example, color key extraction and key color. Evaluation of input pixels and color replacement with key colors is typically performed on full 24-bit or 32-bit color information, unlike on the color components of the pixels. Therefore, the color keying does not have the versatility that software programmers prefer. Thus, if all conversion or filtering occurs before the key color is extracted and replaced with the replacement color, the key color is filtered into the useful image portion. This makes the artifacts in the final image noticeable.
[0003]
Therefore, there is a need to provide high versatility in the evaluation of input pixels and to significantly reduce the appearance of artifacts in the final image.
[0004]
The present invention provides a very hardware efficient and versatile way to perform color keying and color component evaluation operations. It also provides a method for significantly limiting the visibility of artifacts caused by filtering images containing key color information.
[0005]
According to the present invention, there is provided a color key extraction device for determining whether an input pixel having a plurality of color components matches a predetermined key color. The apparatus includes a plurality of evaluation circuits, each of which is configured to receive and evaluate one of the color components of the input pixel for a predetermined color component intensity range and output a comparison signal; Further, a matching circuit is operatively connected to each of the evaluation circuits, and the matching circuit determines whether a combination of the comparison signals satisfies a predetermined condition, and outputs a match signal if the condition is satisfied. So that the input pixel matches a predetermined key color.
[0006]
According to one aspect of the invention, the match circuit includes a storage element for storing a plurality of bits, the value of each bit indicating whether a particular combination of comparison signals satisfies a predetermined condition. A predetermined condition for a predetermined combination of comparison signals is satisfied when a bit in a storage element corresponding to the predetermined combination is set. The match circuit can be implemented using very low cost, versatile programmable raster operation blocks.
[0007]
According to another aspect of the invention, each of the evaluation circuits receives a predetermined color component of the input pixel, masks the color component with a preselected mask value, and outputs a masked color component value. A first circuit configured as described above, a second circuit configured to mask a preselected upper limit of a predetermined color component intensity range using the mask value, and to output the masked upper limit, A third circuit configured to mask a preselected lower limit of a predetermined color component intensity range using the value and output a masked lower limit; and a masked upper limit of the masked color component value. A first comparator that outputs a first result by comparing with a first comparator, a second comparator that compares a masked color component value with a masked lower limit and outputs a second result, and receives the first and second results. Output the first comparison signal And a road.
[0008]
According to yet another aspect of the invention, there is further provided a color replacement circuit operatively connected to the match circuit, wherein the replacement circuit replaces the input pixel with the replacement pixel when the match circuit outputs a match signal. . By exchanging the key color with a replacement color (eg, a gray color) before filtering, the resulting image will have a change in brightness but not a change in tone.
[0009]
Other objects and attainments, in addition to a full understanding of the invention, will be apparent and understood by referring to the following description and claims, taken in conjunction with the accompanying drawings.
[0010]
The invention will be described in more detail by way of example with reference to the accompanying drawings.
[0011]
In the drawings, the same reference numerals indicate the same or corresponding forms or functions.
[0012]
(Detailed description of preferred embodiments)
FIG. 1 shows a functional block diagram of a representative system suitable for implementing the present invention. As shown in FIG. 1, a digital video / graphics source 10 provides digital video / graphics signals to a memory buffer 16. The digital data is stored in the memory buffer 16 in a standard format. In response to the command, video / graphics data processor 20 receives digital data from memory buffer 16 and processes it. Processor 20 transfers the processed data to video / graphics encoder 26 in a predetermined format. Next, the encoder 26 encodes the data and transfers it to the display device 30 for display.
[0013]
FIG. 2 shows the color key extraction and color replacement circuit used in the graphics / video pipeline in processor 20 according to the present invention. In FIG. 2, each input pixel has three color components (RGB or YUV) with 8 bits per color component. These color components are evaluated for color component intensity by the evaluation circuits 37, 137, and 237, respectively. Thus, circuit 37 is used to determine whether the input color component R / Y is within a predetermined color component intensity range of the spectrum between the darkest R / Y and the brightest R / Y. Similarly, the evaluation circuit 137 is used to determine whether the input color component G / U is within a predetermined color component intensity range of the spectrum between the darkest G / U and the brightest G / U. I do. Finally, the evaluation circuit 237 is used to determine whether the input color component B / V is within a predetermined color component intensity range of the spectrum between the darkest B / V and the lightest B / V. I do.
[0014]
In the evaluation circuit 37, the color component R / Y is bit-masked bit by bit using the mask value in the ColorKeyAnd register 38 via the AND gate 40. Again using this mask value, the values stored in ColorKey registers 42 and 48 via AND gates 44 and 50 are masked bit by bit, respectively. The values in registers 42 and 48 are predetermined upper and lower limits, both of which establish a predetermined color component intensity range and evaluate the color component R / Y. As will be appreciated by those skilled in the art, the mask value is determined depending on the application, for example, whether a specific color or color range is defined as a key, and whether images and image contents are pre-processed. Similarly, the upper and lower limits also depend on the application.
[0015]
The masked value at the output of AND gate 40 is evaluated for the masked upper and lower limits via comparators 46 and 52 to determine whether the masked color component is within the masked predetermined color intensity. It is determined.
[0016]
If the masked value is less than or equal to the masked upper limit, the comparator 46 outputs a first indication signal (eg, logic 1) to the AND gate 60. Similarly, if the masked value is greater than or equal to the masked lower limit, comparator 52 outputs a second display signal (eg, logic 1) to AND gate 60. If the masked value is within the masked predetermined color component intensity range, i.e., when both the first and second display signals are provided to AND gate 60, then AND gate 60 will apply a second A positive comparison signal of 1 (eg, logic 1) is output. Otherwise, AND gate 60 outputs a first negative comparison signal (eg, logic 0).
[0017]
The evaluation circuits 137 and 237 operate similarly to the evaluation circuit 37. If each of the color components G / U and B / V is within their masked predetermined color component intensity range, the circuits 137 and 237 generate a second and third positive comparison signal (eg, logic 1). Output each. Otherwise, evaluation circuits 137 and 237 output second and third negative comparison signals (eg, logic 0), respectively.
[0018]
It should be noted that in the default mode, the mask values are all ones, so the mask operation is practically not performed, and the upper and lower limits define the color component intensity range.
[0019]
The comparison signals (K1, K2, K3) from the evaluation circuits 37, 137, 237 are supplied to a programmable raster operation block 64. Depending on the particular combination of comparison signals (positive or negative) and whether a particular bit value in ColorKey ROP register 68 is set, block 64 outputs a match signal (eg, a logic one) to determine the input color and Can be indicated that there is a match between the key colors. The detailed operation of block 64 is described below in connection with FIG.
[0020]
FIG. 3 is a ROP (raster operation) table used for the programming block 64. For a given combination of K1, K2, K3, if the ROP bit (which appears next to the combination) assigned to that combination is set (logic 1), it indicates a match, and a match signal from block 64 is output. Output. If the ROP bit is reset (logic 0), it indicates a mismatch. According to the invention, one or more ROP bits can be set depending on the application. This method realizes versatility in which the sensitivity of one or a plurality of color components can be scanned. For example, only two color components (eg, R / Y and G / U) can be targeted for a particular input color, without having to pay attention to the third component (eg, B / V). In such a case, ROP bits 6 and 7 are set, indicating a match on combinations "110" and "111" for K1, K2, K3 compared to the key color.
[0021]
According to FIG. 2, after the match between the input color and the key color is determined, color replacement can optionally be performed by enabling the AND gate 72 via an enable signal from the ColorKeyReplaceEn register 76. For example, if subsequent filtering is performed, color replacement is performed. To perform color replacement, a logic one is output by AND gate 72 to activate multiplexers 86, 186, 286, and ColorKeyReplace registers 80, 180, 280 for the R / Y, G / U, B / V components. Are selected, and the initial input values are respectively replaced. As an example, a gray color is preferred. Therefore, the pixel value of the color component for the gray color is used as the replacement value. By exchanging a key color with a replacement color (eg, grey) prior to filtering, the resulting image will have a change in brightness but no change in hue. The outputs of the multiplexers 86, 186, 286 are provided to a mixer (not shown) and are combined with the background color.
[0022]
On the other hand, if a match does not occur, as determined by block 64, or if color replacement is not desired, a logic zero is output by AND gate 72 and multiplexers 86, 186, 286 cause the mixer 86, 186, 286 Output directly to. The output of block 64 is also provided to the mixer.
[0023]
After the key colors are extracted, the data goes through a transformation and filtering process to limit the visible artifacts in the final image.
[0024]
The invention can also be used with other types of color components, such as Y, Cr, Cb.
[0025]
Although the present invention has been described with reference to specific embodiments, it will be apparent to those skilled in the art that many alternatives, modifications and variations are possible in light of the foregoing description. It is therefore intended to embrace all such alternatives, modifications and variances that fall within the spirit and scope of the appended claims.
[Brief description of the drawings]
FIG.
FIG. 1 is a functional block diagram of an exemplary system suitable for implementing the present invention.
FIG. 2
FIG. 4 is a circuit diagram of a color key extraction and color replacement circuit according to the present invention.
FIG. 3
FIG. 3 is a diagram illustrating a ROP (raster operation) table used to program the programmable raster operation block of FIG. 2;

Claims (10)

A color key extraction device that determines whether an input pixel having a plurality of color components matches a predetermined key color,
A plurality of evaluation circuits, each of which is configured to receive one of the color components of the input pixel, evaluate it against a predetermined color component intensity range, and output a comparison signal. Have multiple evaluation circuits,
A matching circuit operatively connected to each of the evaluation circuits, wherein the matching circuit determines whether a combination of comparison signals satisfies a predetermined condition, and outputs a match signal when the condition is matched; A match circuit, whereby the input pixel is configured to match a predetermined key color. Each of the evaluation circuits,
A first circuit configured to receive a predetermined color component of an input pixel, mask the color component with a preselected mask value, and output a masked color component value;
A second circuit configured to mask a preselected upper limit value of a predetermined color component intensity range using the mask value, and to output the masked upper limit value;
A third circuit configured to mask a preselected lower limit of the color component intensity range using the mask value and output the masked lower limit;
A first comparator that compares the masked color component value with the masked upper limit value and outputs a first result;
A second comparator that compares the masked color component value with the masked lower limit and outputs a second result;
2. The apparatus of claim 1, further comprising: an output circuit configured to receive the first and second results and output a first comparison signal. The matching circuit includes a storage element that stores a plurality of bits, and a value of each bit indicates whether a specific combination of the comparison signals satisfies a predetermined condition;
The apparatus of claim 1, wherein a predetermined condition for a predetermined combination of the comparison signals is satisfied when a bit of the storage element corresponding to the predetermined combination is set. The color replacement circuit further comprising: a replacement circuit operatively connected to the matching circuit, wherein the replacement circuit is configured to replace an input pixel with a replacement pixel when the matching circuit outputs a match signal. An apparatus according to claim 1. The color replacement circuit includes a plurality of multiplexers, each of the multiplexers being controlled via the match signal, each of the multiplexers configured to receive one of the input pixel color components and a corresponding replacement color component. 5. The apparatus of claim 4, wherein each multiplexer outputs a corresponding replacement color component upon receiving the match signal. The apparatus of claim 4, further comprising an enable circuit configured to control the color replacement circuit to be enabled or disabled. A method for determining whether an input pixel having a plurality of color components matches a predetermined key color,
(A) evaluating each of the color components of the input pixel against a predetermined color component intensity range;
(B) outputting a comparison signal after evaluating each color component in step (a);
(C) determining whether the combination of the comparison signals satisfies a predetermined condition;
(D) outputting a match signal if the condition is satisfied, whereby the input pixel matches the predetermined key color. Step (a)
Masking a predetermined color component of the input pixel using a preselected mask value to generate a masked component value;
Masking a preselected upper limit of the predetermined color component intensity range using the mask value to generate a masked upper limit;
Masking a preselected lower limit of the color component intensity range using the mask value, generating a masked lower limit;
Comparing the masked color component value with the masked upper limit value to generate a first result;
Comparing the masked color component value with the masked lower limit to generate a second result;
Outputting a first comparison signal based on the first and second results. Step (c) includes providing a plurality of bits, wherein the value of each bit of the plurality of bits indicates whether a particular combination of the comparison signals satisfies the predetermined condition;
The method of claim 7, wherein the predetermined condition for the predetermined combination of comparison signals is satisfied when a bit in the plurality of bits corresponding to the predetermined combination is set. The method of claim 7, further comprising: replacing the input pixel with a replacement pixel when outputting the match signal.

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