MXPA99003539A - Apparatus and method for generating on-screen-display messages using true color mode - Google Patents

Abstract

An apparatus and concomitant method for generating an OSD message by constructing an OSD bitstream defining a plurality of"true color"pixels. The OSD bitstream contains an OSD header and OSD data. An OSD unit retrieves pixel control information from the OSD header which is programmed by a processor of a decoding/displaying system. The OSD header contains information that is used to program a color palette of the OSD unit and to provide instructions as to the treatment of the OSD data. If the"True Color Mode"is enabled in the OSD header, then the OSD unit will bypass the palette and treat the OSD data as true color pixels. Since the same chrominance components are shared between a pair of successive pixels, each successive set of four OSD data bytes represents the actual chrominance and luminance levels for two OSD pixels.

Description

APPARATUS AND METHOD FOR GENERATING SCREEN DEPLOYMENT MESSAGES USING COLOR MODE TRUE Field of the Invention The present invention relates to a method and apparatus for generating Display Display (OSD) messages using a "true color mode". More particularly, this invention relates to a method and apparatus that increases the number of colors available by treating screen display data as true color pixels instead of pointers to the inputs of a screen display palette. BACKGROUND OF THE INVENTION Screen display messages play an important role in consumer electronic products by providing users with interactive information such as menus to guide them through the use and configuration of the product. Other important functions of screen display include the ability to provide subtitling and the display of channel logos. However, the changing standard of digital video technology presents a major problem for generating and displaying display messages on the screen. For example, there are specific requirements for High Definition Television (HDTV) that a high definition television must display up to 216 characters in four (4) "windows" compared to the current requirements of the National Television Systems Committee (NTSC). a maximum of 128 characters in a "window". These new requirements represent severe difficulties in the decoding / display system used to decode and display television signals (eg, high-definition television, National Committee of Television Systems, MPEG, and the like) which must decode the data streams encoded and present the decoded data to a deployment system with minimal delays. Since on-screen display messages must be displayed (overlaid) with the video data, the decoding / deployment system microprocessor must allocate a portion of the memory bandwidth to perform on-screen display functions, thereby increasing the requirement. of the bandwidth of the memory of a decoding / deployment system and the overloading of general physical equipment. Thus, an on-screen display unit of a decoding / deployment system may incorporate a palette of limited size to minimize physical equipment and memory access requirements. Namely, the on-screen display unit employs a palette that uses a plurality of registers (entries) where each entry contains a representation of chrominance and luminance levels for a screen display pixel. When coding address (indexes) to the palette as display data on the screen, a decoding / deployment system is able to minimize physical equipment and memory access requirements.

However, such systems are limited in the number of colors that are available for the deployment of an on-screen display message. Since the palette has a fixed size, it is not very appropriate to change standards that may require support for a greater number of colors in the future. For example, increasing the number of colors from 16 to 256 (standard VGA) would require adding 249 additional records to a palette that currently supports only 16 characters. Increasing the number of registers is certainly possible, but it is not convenient in terms of cost and can cause timing problems (especially for high palette access speed) and other integrated circuit design problems (for example, increasing the area in a Integrated circuit). Additionally, updating an existing decoding / deployment system with a fixed-size pallet is difficult and expensive. Thus, it is necessary to have a method and apparatus to increase the number of colors available for screen display messages without increasing the physical equipment requirements, for example, the size of a screen display palette, a system of decoding / deployment. Brief Description of the Invention The invention relates to a concomitant apparatus and method for generating screen display messages by constructing a valid screen display bit stream having a plurality of "true color" pixels.

More specifically, in accordance with the invention, a screen display unit retrieves a screen display bit stream from a storage device. The screen display bit stream contains a screen display header and screen display data. The on-screen display header contains control information that is used to program a color palette of the on-screen display unit and to provide instructions on how to process display data on the screen. The control information is programmed by a processor of a decoding / deployment system. If the "Color Mode True "is activated in the on-screen display header, then the on-screen display unit bypasses the palette and treats the on-screen display data as true-color pixels, namely, each successive group of three display data bytes. On-screen display represents the actual chrominance and luminance levels for a screen display pixel.To further reduce the bandwidth requirements of the memory, the same chrominance components are repeated for the next pixel. each screen display pixel is represented by only 16 data bits These and other aspects of the invention will be described with reference to the accompanying drawings Brief Description of the Drawings In the drawings: Figure 1 is a diagram of blocks of a decoding / deployment system that includes a screen display unit in accordance with an aspect of the invention; Figure 2 is a block diagram disclosing the structure of a pixel data stream displayed on a sample screen using a true color mode; and Figure 3 is a flow diagram illustrating the method for constructing a valid screen display data stream with true color mode. Detailed Description of the Drawings Figure 1 illustrates a block diagram of a decoding / display system for television signals 100 (hereinafter the decoding system). The decoding system comprises a processor 130, a random access memory (RAM) 140, a read-only memory (ROM) 142, an on-screen display unit 150, a video decoder 160, and a mixer 170. The output of the mixer 170 is coupled to a display device 190 via the path 180. The present invention is described below in accordance with MPEG standards, International ISO / IEC Standards. 11172 (1991) (generally referred to as MPEG-1 format) and 13818 (1995) (generally referred to as MPEG-2 format). However, those skilled in the art will understand that the present invention can be applied or adapted to other decoding systems by implementing other encoding / decoding formats. In the preferred embodiment, the decoding system 100 performs real-time audio and video decompression of various data streams (bitstreams) 120. The bitstreams 120 may comprise elementary audio and video streams that are encoded in accordance with the MPEG-1 and MPEG-2 standards. The coded bitstreams 120 are generated by an encoder (not shown) and are transmitted to the decoding system through a communication channel. The encoded bitstreams contain a coded representation of a plurality of images and may include the audio information associated with those images, for example, a stream of multimedia data. The multimedia source can be a high definition television station, a video disc, a cable television station and the like. In turn, the decoding system 100 decodes the coded data streams to produce a plurality of decoded images for display on the screen 190 in synchronization with the associated audio information. Nevertheless, for the purpose of this invention, the audio decoding function of the decoding system 100 is irrelevant and therefore, is not described. More specifically, the processor 130 receives bit streams 120 and bit streams 110 as inputs. The bitstreams 110 may comprise several control signals or other data streams that are not included in the bit streams 120. For example, a channel decoder or transport unit (not shown) may be displayed between the transmission channel. and the decoding system 100 for performing the analysis and routing of data packets in data streams or control streams. In the preferred embodiment, the processor 130 performs various control functions, including but not limited to, providing control data to the video decoder 160 and display unit 150, managing access to the memory and controlling the display of the images displayed. Although the present invention describes a single processor, those skilled in the art will understand that the processor 130 may comprise several dedicated devices for managing specific functions, for example, a memory controller, a microprocessor interface unit, and the like. The processor 130 receives bit streams 120 and writes the data packets in the memory 140 via a video decoder 160. Optionally, the bitstreams can pass through a (FIFO) compensator of First into First-Exit (not shown) before transferring them via memory data bus to memory. Additionally, there is generally another memory (not shown) that is used only by the processor 130. The memory 140 is used to store a plurality of data including compressed data, decoded images and the display bitmap. As such, the memory is generally mapped into several compensators, for example a bit compensator for storing compressed data, a screen display compensator for storing the display bitmap on the screen, several frame compensators for storing frames of images and a display compensator to store decoded images. In accordance with the MPEG standards, the video decoder 160 decodes the compressed data in the memory 140 to reconstruct the encoded images in the memory. In some cases, the decoded image is a difference signal that is added to a stored reference image to produce the actual image in accordance with the compression technique used to encode the image (e.g., to facilitate decoding of a compensated image of movement). Once an image is reconstructed, it is stored in the deployment compensator pending deployment via the mixer 170. Similarly, the display unit 150 uses the memory 140 to store the display bitmap on the screen or the Display deployment specification. The on-screen display unit allows a user (manufacturer) to define a bitmap for each field that can be superimposed on the decoded image The on-screen display bitmap can contain information that is stored on a storage device, by example, a read-only memory, on the configuration and options of a particular electronic consumer product.Alternatively, the on-screen display bitmap may contain information regarding subtitling and channel logos that is transmitted from a cable television, a disk video and the like A screen-map bitmap is defined as a set of regions (usually rectangular in shape) of programmable size and position, each of which has a unique palette of available colors. screen display is written to the screen display compensator of the memory 140 which is determined by the user for this purpose. Nevertheless, those skilled in the art will understand that a read-only memory 142 or other equivalent storage devices can also serve this function. When the on-screen display function is activated for a particular picture or frame, the processor 130 manipulates the data in the memory 140 to construct a screen display bitstream. The on-screen display bitstream contains an on-screen display header and on-screen display data (data that defines the screen display pixels). More specifically, the processor 130 programs (formats and stores) the on-screen display header in the memory 140. The on-screen display header contains information on the locations of the top and bottom of the field bit maps. On-screen display, palette data, pointing to the next header block and various display modes that include resolution, color and screen display compression. Once the on-screen display header is programmed, the processor 130 may manipulate the on-screen display data in the memory 140 according to a particular implementation. For example, on-screen display data is formatted according to a selected mode, for example, True Color Mode, as described below. Alternatively, the processor can simply program the on-screen display header with pointers to the screen display data in the memory, where the stored screen display data is retrieved without modification to form the screen display bitstream. Then, the processor 130 reports the active state, that is, active screen display, to the screen display unit 150, which responds by requesting the processor 130 to access the on-screen display bitstream stored in the memory 140. The on-screen display bit stream is formed and retrieved as the display unit reads the on-screen display headers, each followed by its associated display screen data. After receiving the screen display bits stream, the screen display unit processes the screen display pixel data in accordance with the instructions or modes selected in the screen display header. Then, the display unit expects a pair of display counters (not shown) to achieve counting values that identify the correct position on the screen to insert the display information on the screen. In the correct position, the display unit sends its output to the mixer 170. The output of the display unit 150 is a stream or sequence of digital words representing respective luminance and chrominance components in the display display. New memory accesses are requested as required to maintain the necessary data flow (screen display bitstream) through the display unit to produce a large screen display image. When the last byte of the screen display pixel data for the current screen display region is read from the memory, the next screen display header is read and the process is repeated and includes the last display region on the screen for the current box. Those skilled in the art will understand that the order of constructing and retrieving the screen display bitstream can be modified as described above. For example, the on-screen display header can be read from the memory when the processor is formatting the on-screen display data, or the on-screen display data can be processed and displayed as on-screen display messages by the display unit on screen without having to recover all the current of display bits on the screen. How the display pixel data is superimposed on the decoded image, the mixer 170 serves to selectively mix or multiplex the decoded image with the display pixel data. Namely, the mixer 170 has the ability to display at each pixel location, a screen display pixel, a pixel of the decoded image or a (mixed) combination of both types of pixels. This capability allows the display of Subtitling (only pixel data to be displayed on the screen) or the display of transparent channel logos (a combination of both on-screen display pixels and decoded image pixels) in a decoded image. The video decoder 160 and a screen display unit 150 form streams or sequences of digital words that represent respective luminance and chrominance components. These sequences of digital words representative of video components are coupled via a mixer 170 to a digital-to-analog converter (DAC) 185. The digital words representing luminance and chrominance are converted to analog luminance and chrominance signals by the respective sections of the digital to analog converter. The screen display unit 150 can be used to display a bitmap defined anywhere on the drop-down screen, regardless of the size and location of the active video area. This bitmap can be defined independently for each field and specified as a collection of on-screen display regions. A region is commonly a rectangular area specified by its boundary and by a bitmap that defines its content. Each region has associated a palette that defines a plurality of colors (for example, 4 or 16 colors) that can be used in that region. If required, one of these colors may be transparent, allowing the background to be seen through as described above. Although the use of a palette provides substantial savings in computing hardware load for low-resolution display deployment implementations, it does not provide the necessary display resolution that is required for high-resolution display deployment implementations. For example, the on-screen display message may need more colors than those available in the palette, where the available colors are limited to the number of entries (or physical records) in the palette. Figure 2 illustrates the structure of a sample screen display bit stream 200 using the true color mode. The screen display bit stream comprises a plurality of screen display headers 210, each followed by screen display data 220. In one embodiment, the header consists of five 64-bit words, followed by any number of 64-bit screen display data words (bitmap). The screen display header 210 contains information regarding the display region coordinates on screen 214, the various inputs of the palette 216 for a particular display region, and various function codes (bits). Those skilled in the art will understand that the screen display header can be of any length. A longer header can provide more information and options, for example, a palette with more inputs, but with the disadvantage of incurring greater computation expense, that is, more read and write cycles are required to implement the deployment functions in screen. In fact, the content of the on-screen display header is illustrative of a particular mode and is not limited to the specific configuration illustrated in Figure 2. The on-screen display region coordinates 214 contain the positions of the left and right edges. right of a display region, that is, the row start and end positions and the column start and end positions. For interlaced display, the region coordinates include the positions (pointers) of the lower and upper field pixel bit maps for the corresponding display region. Finally, the on-screen display region coordinates 214 include a pointer to the next header block in the memory.

The palette information 216 contains a plurality of entries where each entry contains a representation of chrominance and luminance levels for a screen display pixel. The palette information 216 is used to program the display palette on the screen. Since each on-screen display header contains palette information 216, the available colors can be selectively changed for each on-screen display header and its associated on-screen display data bytes. Each palette entry can contain 16 data bits, that is, six (6) luminance bits, Y, four (4) chrominance bits (color difference signal), Cb and four (4) chrominance bits (signal of color difference), Cr. In a modality, there are 16 entries in the palette that require 4 bits to address each entry. The function codes (bits) 212 contain information relating to various modes, including but not limited to, display options and display current bitstream options. In the preferred embodiment, the function bits contain a single bit to indicate whether the "True Color Mode" is activated. The screen display data 220 contains bitmap data in order from left to right and top to bottom. Screen display data is generally used to define the color index of each pixel in the bitmap formation. In the preferred embodiment, if the "True Color Mode" is activated, then display data 220 contains true-color pixels (true color format) instead of palette indices. In the true color format, the on-screen display data stream consists of one byte of luminance component (Y) 222, followed by two bytes of chrominance components (color difference signals, Cb 224 and Cr 226), followed by another luminance byte 228. This pattern is repeated for the following pixels as shown in Figure 2. The length of each byte is generally set to 8 bits, thus supporting millions of possible color combinations. For this mode of operation, the screen display unit 150 simply bypasses the on-screen display palette and passes the true-color pixels directly to the mixer 170 as described above. Additionally, in order to support "transparent pixels" (wherein the decoded image of the video decoder is displayed in place of the on-screen display pixels in a display region), the Y component is set to all "zeros" . This value causes the mixer 170 to replace the screen display pixel with a corresponding pixel of the decoded image. Additionally, the True Color Mode allows a reduction in memory bandwidth requirements by repeating the same chrominance components for the next pixel in the bitmap. Namely, a pair of successive pixels share the same chrominance components. To illustrate, Figure 2 shows a plurality of data bytes (pixel data) defining pixels, 231-234, where each pixel data structure is 24 bits long (eight bits of Y, eight bits of Cb and eight bits of Cr). However, the pixels 231 and 232 share the same chrominance components 224 and 226. This pattern is repeated for successive pairs of pixels, effectively requiring only 16 bits of data to represent a single pixel (two pixels in 32 bits of data). . This mode of operation allows the processor 130 to gain a 33% saving in the amount of data that must be passed to the display unit of the memory, i.e., a reduction in the size of the display bitstream in screen. Even more importantly, the number of colors available for each display region has increased dramatically without having to increase the size of the on-screen display palette. In fact, the increase of physical equipment, if any, is minimal. Figure 3 illustrates a method 300 for building a screen display bit stream with True Color Mode. The method is generally taken up from a storage device, for example, a memory, and executed by the processor 130. The screen display bitstream is generated by the processor 130 and is processed by the display unit 150. The method 300 constructs a stream of screen display bits by generating an on-screen display header having a true color mode bit, followed by a plurality of bytes of true-color pixel data. With reference to Figure 3, the method 300 starts at step 305 and proceeds to step 310 where a bit in the on-screen display header is designated as a true color mode bit. If the True Color Mode is activated in the on-screen display header, then the on-screen display data bytes are treated in accordance with a normal format, which can be a 4-bit address to a palette (or any other bitstream format, for example, MPEG standards). In step 320, the method 300 determines whether the True Color Mode is activated. If the request is answered negatively, the method 300 proceeds to step 325 where the display data bytes are generated on the screen using a non-true color format. Then method 300 proceeds to step 340. If the request in step 320 is answered affirmatively, method 300 proceeds to step 330 wherein a plurality of true color pixels is disposed in the display data data bytes. Each true color pixel comprises three bytes of on-screen display data, wherein each byte of screen display data is 8 bits long. Since the chrominance components are repeated for successive pixels (or each time another set of chrominance components is discarded), two on-screen display pixels can be placed in four bytes of display data. In step 340, the method 300 determines if there is another display header on the screen after the previously processed on-screen display data. A new on-screen display header may be required if the various modes represented by the function bits 212 are modified. Similarly, a new heading is required for each new display region in a table. If the request is answered negatively, method 300 continues to step 350 where method 300 terminates. If the request is answered affirmatively, method 300 continues to step 320 where steps 320-330 are repeated for each display header in additional screen In this manner, the on-screen display bitstream may comprise true color display data byte and non-true color display data byte. Then a novel method and apparatus for constructing a screen display bit stream defining true-color pixels has been shown and described. However, many changes, modifications, variations, and other uses and applications of the present invention will be apparent to those skilled in the art upon consideration of this specification and the accompanying drawings, which disclose the embodiments thereof. All mentioned changes, modifications, variations and other uses and applications that do not deviate from the spirit and scope of the invention are considered covered by the invention, which will be limited only by the following claims.

Claims (17)

1. CLAIMS 1.
2. Method for constructing a display bit stream, said method comprises the steps of: forming a stream of bits including a screen display header having a bit to indicate one of a true color mode and a non-true color mode; and generating screen display data that define color values of a screen display pixel, wherein the bit indicates such a true color mode and a palette address for the screen display pixel when the bit indicates the color mode not true The method of claim 1, wherein said on-screen display data defines color values for a plurality of pixels, each such color value comprises a luminance component and a chrominance component.
3. The method of claim 2, wherein a pair of true-color pixels share the same chrominance component.
4. 4. The method of claim 3, wherein said pair of pixels of true color comprises two successive pixels of true color.
5. The method of claim 4, wherein a configuration of such a true-color pixel pair comprises a first luminance component, followed by such a shared chrominance component, followed by a second luminance component. .
6. The method of claim 2, wherein said luminance component of a true color pixel is set to all zeros to implement a transparent mode.
7. The method of claim 1, wherein said on-screen display data generation step is implemented without using a palette.
8. 8. A screen display bit stream stored in a storage medium comprising: a header having a bit to indicate one of a true color mode and a non-true color mode; and a plurality of screen display data bytes, coupled to said header, defining color values of a screen display pixel when the bit indicates such a true color mode and a paddle direction for the screen display pixel when the bit indicates the non-true color mode.
9. The on-screen display bitstream of claim 8, wherein such a color value of each of the plurality of on-screen display data bytes comprises a luminance component and a chrominance component when the bit indicates such true color mode.
10. The on-screen display bitstream of claim 9, wherein a pair of true-color pixels share the same chrominance component.
11. The on-screen display bitstream of claim 10, wherein said pair of pixels of true color comprises two successive true-color pixels.
12. The on-screen display display stream of claim 11, wherein a configuration of said true color pixel pair comprises a first luminance component, followed by such a shared chrominance component, followed by a second luminance component.
13. The method of claim 9, wherein said luminance component of a true color pixel is set to all zeros to implement a transparent mode.
14. 14. Apparatus for generating a screen display bit stream comprising: a storage means for storing an on-screen display header having a bit to indicate one of a true color mode and a non-true color mode and data On screen display coupled to such a header, such screen display data define color values of a screen display pixel when the bit indicates such a true color mode and a palette address for the screen display pixel when the bit indicates non-true color mode; and a processor, coupled to such storage means, to activate said bit in said header to indicate said true color mode and to read said on-screen display header and said on-screen display data when activating such a bit in the mode of true color.
15. 15. The apparatus of claim 14, wherein said storage means is a read-only memory (ROM).
16. 16. The apparatus of claim 14, wherein said storage means is a random access memory (RAM).
17. 17. Apparatus for generating an on-screen display message comprising: a storage means for storing an on-screen display bitstream including an on-screen display header having a bit to indicate one of a true color mode and a non-true color mode and on-screen display data coupled to such a header, such on-screen display data define color values of a plurality of on-screen display pixels when the bit indicates such a true color mode and a pallet address for the plurality of display pixels when the bit indicates the non-true color mode; and a processor, coupled to such storage means, for programming said bit in said header to indicate said true color mode and formatting said display data to define the value of colors of each of said plurality of pixels; and an on-screen display unit, coupled to said processor, for processing such display screen bitstream to form the on-screen display message.