Set the size of the inter luma quantization deadzone for non-
trellis quantization (default: 21). Lower values help to pre-
serve fine details and film grain (typically useful for high bi-
trate/quality encode), while higher values help filter out these
details to save bits that can be spent again on other mac-
roblocks and frames (typically useful for bitrate-starved en-
codes). It is recommended that you start by tweaking dead-
zone_intra before changing this parameter.