avfilter/vf_colordetect: detect fully opaque alpha planes

It can be useful to know if the alpha plane consists of fully opaque
pixels or not, in which case it can e.g. safely be stripped.

This only requires a very minor modification to the AVX2 routines, adding
an extra AND on the read alpha value with the reference alpha value, and a
single extra cheap test per line.

detect_alpha_8_full_c:                                2849.1 ( 1.00x)
detect_alpha_8_full_avx2:                              260.3 (10.95x)
detect_alpha_8_full_avx512icl:                         130.2 (21.87x)
detect_alpha_8_limited_c:                             8349.2 ( 1.00x)
detect_alpha_8_limited_avx2:                           756.6 (11.04x)
detect_alpha_8_limited_avx512icl:                      364.2 (22.93x)
detect_alpha_16_full_c:                               1652.8 ( 1.00x)
detect_alpha_16_full_avx2:                             236.5 ( 6.99x)
detect_alpha_16_full_avx512icl:                        134.6 (12.28x)
detect_alpha_16_limited_c:                            5263.1 ( 1.00x)
detect_alpha_16_limited_avx2:                          797.4 ( 6.60x)
detect_alpha_16_limited_avx512icl:                     400.3 (13.15x)

0 files changed, 0 insertions, 0 deletions