GoogleCodeExporter
commented
9 years ago The complete list of RGB formats supported at this time is
ARGB, BGRA, ABGR, RGBA - I420/I422 directly convert to these.
RGB24, RAW - 2 step. I420ToARGB, ARGBToRGB24.
RGB565, ARGB1555, ARGB4444 - 2 step. I420ToARGB, ARGBToRGB565 etc.
On Neon it would be easy to do I420ToRGB24. On SSSE3, its not at all easy, and
needs to do 16 pixels - 64 bytes of source, to produce 48 bytes of destination,
to be fully efficient. A compromise might be a single row function that does 2
steps on SSSE3 and 1 step on Neon.
The RGB565 conversion is difficult for both SSSE3 and Neon. The internals of
I420ToARGB use SOA style - 3 registers, R, G, B. While an optimized
ARGBToRGB565 prefers AOS - one register containing 4 pixels of ARGB. On Intel,
the packing converts SOA to AOS, and the RGB565 could be done, except it would
run out of registers in 32 bit. The performance would be roughly the same, but
avoid some calling overhead. Which is not significant on x86, but more so on
Arm.
For NEON the 565 conversion will need AOS conversion and new 565 packing, which
Neon wont do especially well. mask, shift and combine.
A first step is ARGBToRGB565_NEON. second step is I420ToRGB565 row function
that calls both Neon functions. third step is add RGB565 output to I420ToRGB
Neon code.
Original comment by fbarch...@chromium.org on 30 Sep 2012 at 7:10
Original issue reported on code.google.com by
fbarch...@chromium.orgon 29 Sep 2012 at 6:51