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Old 14th June 2018, 18:35   #161  |  Link
Join Date: Jan 2006
Location: Portland, OR
Posts: 2,473
Adaptive quantization (psy-rd, aq-mode, aq-strength). Psychovisual tuning is just as important for still images (albeit a simpler subset).

With aq-mode 3, you’ll get a lower QP in smoother and darker areas, allowing for a higher CRF that will apply to parts of the image that are easier to compress. To get the same visual quality with QP would require a significantly lower QP to make sure the harder parts look good. But that results in that QP being used for the easier parts of frame as well, giving THEM a lower QP than using CRF would, thus increasing total bytes used. For real-world content, QP needs a higher bitrates to achieve the same quality.

This is basically how “JPEG Optimizers” deliver better quality than just using the JPEG quality parameter. HEVC has WAY more awesome tools available for efficient image coding, though.

Hoping for a good —tune stillimage someday.
Ben Waggoner
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