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authorJulius Werner <jwerner@chromium.org>2020-06-24 19:43:36 -0700
committerJulius Werner <jwerner@chromium.org>2020-07-09 00:32:17 +0000
commit7f87812c30ac5e4c3329911aec2ce52050a9abbb (patch)
tree256289352ddd35494ef1ebae7fd4660d8567bbf6 /src/northbridge
parent96b00a50f14e3e41eaf69171945ceeb587b4fe0b (diff)
libpayload: cbgfx: Replace bilinear resampling with Lanczos
This patch improves the image resampling (scaling) code in CBGFX to use the Lanczos algorithm that is widely considered the "best" resampling algorithm (e.g. also the first choice in Python's PIL library). It is of course much more elaborate and therefore slower than bilinear resampling, but a lot of the difference can be made up with optimizations, and the resulting code was found to still produce acceptable speeds for existing Chrome OS UI use cases (on an Arm Cortex-A55 device, time to scale an image to 1101x593 went from ~88ms to ~275ms, a little over 3x slowdown). Nevertheless, if this should be too slow for anyone there's also an option to tune it down a little, but still much better than bilinear (same operation was ~170ms with this). Example images (scaled up by a factor of 7): Old (bilinear): https://i.imgur.com/ytr2n4Z.png New (Lanczos a=3): https://i.imgur.com/f0vKluM.png Signed-off-by: Julius Werner <jwerner@chromium.org> Change-Id: Idde6f61865bfac2801ee4fff40ac64e4ebddff1a Reviewed-on: https://review.coreboot.org/c/coreboot/+/42792 Tested-by: build bot (Jenkins) <no-reply@coreboot.org> Reviewed-by: Yu-Ping Wu <yupingso@google.com> Reviewed-by: Hung-Te Lin <hungte@chromium.org>
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