lcms: improve black point handling (especially BT.1886)

First of all, black point compensation is now on by default. This is
really rather harmless and only improves the result (where "improvement"
means "less black clipping").

Second, this adds an option to limit the ICC profile's contrast, which
helps for untagged matrix profiles that are implicitly black scaled even
in colorimetric intent. (Note that this relies on BPC being enabled to
work properly, which is why the two changes are tied together)

Third, this uses the LittleCMS built in black point estimator instead of
relying on the presence of accurate A2B tables. This also checks tags
and does some amounts of noise elimination.

If the option is unspecified and the profile is missing black point
information, print a warning instructing the user to set the option, and
fall back to 1000 otherwise.

1 files changed, 7 insertions, 0 deletions

diff --git a/DOCS/man/vo.rst b/DOCS/man/vo.rst
index bf3fb2e8fd..0e091591e2 100644
--- a/DOCS/man/vo.rst
+++ b/DOCS/man/vo.rst
@@ -951,6 +951,13 @@ Available video output drivers are:
         Default is 128x256x64.
         Sizes must be a power of two, and 512 at most.
 
+    ``icc-contrast=<0-100000>``
+        Specifies an upper limit on the target device's contrast ratio.
+        This is detected automatically from the profile if possible, but for
+        some profiles it might be missing, causing the contrast to be assumed
+        as infinite. As a result, video may appear darker than intended. This
+        only affects BT.1886 content. The default of 0 means no limit.
+
     ``blend-subtitles=<yes|video|no>``
         Blend subtitles directly onto upscaled video frames, before
         interpolation and/or color management (default: no). Enabling this