Method for processing picture data for expanding the picture format

State of the art

0001The invention is based on a method for processing image data for an extended image format. Conventional transmission standards for the transmission of image data, for example the transmission standard according to ITU-T Recommendation H 261, only provide for the coding of image formats with an aspect ratio of 4: 3. Other picture formats, such as the 16: 9 picture format commonly used in modern TV screens, can not be transferred.

Advantages of the invention

0002With the measures according to the steps of claim 1, extended image formats, eg with a 16: 9 aspect ratio, compatible with existing transmission standards, eg the H. 320 Transmission standard. Videophones, which are not yet able to decode such image formats, can use a modified according to the invention video data stream to only the image information in the conventional image format, eg with an aspect ratio of 4: 3, to evaluate and present. The advantages of an expanded picture format with, for example, an aspect ratio of 16: 9 can also be used for video conferencing. With previous image formats, eg With an aspect ratio of 4: 3, it is fundamentally problematic to position all participants clearly visible. Although all persons can be seen with a wide-angle camera setting, most of the image information is wasted on the background and foreground (walls, table surface, ceiling). With an extended picture format, eg with an aspect ratio of 16: 9 this problem is taken into account.

drawings

0003Reference to the drawings embodiments of the invention are explained in more detail:

Show it

0004<ul id="ul0001" list-style="none"><li>FIG. 1 shows the aspect ratios with expanded and unexpanded image format,</li><li>FIG. 2 shows the arrangement of macroblocks in a picture and in a GOB,</li><li>3 shows the coding of the image data according to the H. 261 standard.</li></ul>

Description of exemplary embodiments

0005The image data supplied in the expanded image format is decomposed into first image data corresponding to an unexpanded image format and to additional image data containing the image information for the image format extension. In particular, the image produced by a camera in the 16: 9 aspect ratio is scaled to a 16: 9 format extended QCIF (common-format) or CIF (common intermediate-format) image with the same vertical resolution. The corresponding 16: 9 picture formats are shown in FIG. 1, where S stands for columns and Z stands for lines. The conventional aspect ratio of 4: 3 is calculated taking into account the pixel format, which is 12:11. For the CIF format follows:<maths id="math0001" num=""><math display="block"><mrow><mtext>(352/288) X (12/11) = 4/3, or (480/288) X (12/11) ≈ 16/9.</mtext></mrow></math><img file="EP0980184A2_D0001.tif" /></maths>

0006From the middle of the 16: 9 image is a 4: 3 QCIF or CIF image extracted, for example, according to the H. 261 Standard coded and transmitted. The remaining image areas, right and left of the extracted standard image (gray area), are used as additional image information with the H. 261 Data reduction algorithms (DCT, motion estimation) encoded and in the GSPARE field according to chapter 4.2.2 of H. 261 Transfer standards. In this, in H. 261 Data stream already existing GSPARE field, information of any size can be transmitted. By default it is envisaged that decoders that can not evaluate this information discard it and, after the end of the GSPARE field, easily decode the data stream relevant to them.

0007An after H. 261 to be encoded image is divided into so-called group of blocks (GOB). A GOB consists of 176 x 48 luminance and 88 x 24 chrominance pixels respectively consisting of 33 macroblocks (MB) of 16 x 16 pixels each (Chapter 4.2.2, 4.2.3 / H. 261). FIG. 2 shows the arrangement of the GOBs and Mbs and the 16: 9 extension on the basis of a CIF image. The gray hatched areas a show the extension of the picture to 16: 9. The names 1ex to 12ex indicate the extensions of the corresponding GOBs 1 to 12 at the edges. The middle white area b has the standard CIF image width.

0008Since the image size is always a multiple of 16 pixels due to the division into macroblocks, the image width shown in FIG. 2 is somewhat too large with 480 pixels. In order to achieve the exact image width to be encoded, 6 pixels each can be set to black on the right and on the left edge of the picture since they would not appear on a 16: 9 display.

0009The standard compliant coding and transmission of additional image data is done with the GSPARE field of each GOB header (chapter 4.2.2 / H 261). This can be transmitted as often as desired and is thus ideal for the transmission of data of variable length. According to chapter 4.2.2.5/H. 261 All decoders must be able to discard the information in these fields if they can not use them. FIG. 3 shows the transmission of the information of the extended image format in H. 261 Bitstream. With 1 is the <img file="EP0980184A2_D0002.tif" />group of blocks start code ", with 2 the <img file="EP0980184A2_D0003.tif" />group number ", with 3 the quantization information, with 4 the <img file="EP0980184A2_D0004.tif" />extra insertion information ", which is set to logical 1 if the following in H. 261 Standard optional data field 5 GSPARE is present. Block 6 designates the MB (macroblock layer) according to Chapter 4.2.3 of H. 261st Blocks 4 and 5 contain the macroblock data of the image format extension. The GSPARE field 5 is inserted only until all the symbols required for coding the macroblocks, such as MBA (macroblock address), MTYPE (information about the data elements provided in the macroblock), MQUANT (type of quantization used), MVD (motion vector data), CBP ( indicates blocks for which transformation coefficients are to be transmitted), TCOEFF (transformation coefficients) and EOB (blocking end identifier) ​​have been transmitted in accordance with sections 4.2.3 and 4.2.4.

0010The invention permits the transmission of overhead image data for extending a transmitted QCIF or CIF image from 4: 3 aspect ratio to a panoramic format with, for example, an aspect ratio of 16: 9 within a H. 320 image stream with full backward compatibility. The use of an extended 16: 9 aspect ratio other than that described herein is to be realized in the same way, so that the invention is not limited to the 16: 9 aspect ratio as an extended picture format.