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The predecimation process consists of downscaling an image by fetching only the necessary pixels in the memory. Vertical and horizontal predecimation are possible:
When 2-D burst mode is used, the access to data in memory is performed through the TILER module of DMM (for more details, see Section 15.1.2, TILER Overview, in Section 15.1, Memory Subsystem), and as a result a maximum of one line can be skipped.
The restriction to horizontal predecimation is that there is at least one useful pixel per 128-bit request. In that case, the DMA engine uses burst mode instead of singles to optimize the requests in terms of latency and SDRAM efficiency.
For RGB and YUV4:2:0 data formats, each pixel data container in memory holds 1 pixel. Thus, when configuring the PIXELINC bit field, the value of n equals the number of pixels to skip:
For YUV4:2:2 format, each 32-bit pixel data container holds the Luma components for 2 pixels, and the Chrominance component of 1 pixel (see Figure 11-45). Therefore, for the valid values of the PIXELINC bit field in the case of the following YUV4:2:2 format, caution must be taken because n equals the number of pixel data containers to skip, not the number of pixels: