Function avifSetTileConfiguration

src/write.c:89–119

Set the tile configuration: the number of tiles and the tile size. Tiles improve encoding and decoding speeds when multiple threads are available. However, for image coding, the total tile boundary length affects the compression efficiency because intra prediction can't go across tile boundaries. So the more tiles there are in an image, the worse the compression ratio is. For a given number of ti

// tends to reduce the total tile boundary length inside the image. Use more tiles along the longer
// dimension of the image to make the tile size closer to a square.
void avifSetTileConfiguration(int threads, uint32_t width, uint32_t height, int * tileRowsLog2, int * tileColsLog2)
{
    *tileRowsLog2 = 0;
    *tileColsLog2 = 0;
    if (threads > 1) {
        // Avoid small tiles because they are particularly bad for image coding.
        //
        // Use no more tiles than the number of threads. Aim for one tile per thread. Using more
        // than one thread inside one tile could be less efficient. Using more tiles than the
        // number of threads would result in a compression penalty without much benefit.
        const uint32_t kMinTileArea = 512 * 512;
        const uint32_t kMaxTiles = 32;
        // AV1 requires width <= 65536 and height <= 65536, so their product fits
        // in uint64_t and the resulting tile count fits in uint32_t.
        const uint64_t imageArea = (uint64_t)width * height;
        uint32_t tiles = (uint32_t)((imageArea + kMinTileArea - 1) / kMinTileArea);
        if (tiles > kMaxTiles) {
            tiles = kMaxTiles;
        }
        if (tiles > (uint32_t)threads) {
            tiles = threads;
        }
        int tilesLog2 = floorLog2(tiles);
        // If the image's width is greater than the height, use more tile columns than tile rows.
        if (width >= height) {
            splitTilesLog2(width, height, tilesLog2, tileColsLog2, tileRowsLog2);
        } else {
            splitTilesLog2(height, width, tilesLog2, tileRowsLog2, tileColsLog2);
        }
    }
}

// ---------------------------------------------------------------------------
// avifCodecEncodeOutput