screenshot: don't write PNG colorspace tags by default

Generates too much discussion and confusion.

Fixes #2051.

DOCS/interface-changes.rst

@@ -20,6 +20,7 @@ Interface changes
 ::
 
  --- mpv 0.10.0 will be released ---
+    - change --screenshot-tag-colorspace default value
     - add --stretch-image-subs-to-screen
     - add "playlist/N/title" property
     - add --video-stereo-mode=no to disable auto-conversions

DOCS/man/options.rst

@@ -2620,7 +2620,7 @@ Screenshot
 
     Note that not all formats are supported.
 
-    Default: ``yes``.
+    Default: ``no``.
 
 ``--screenshot-high-bit-depth=<yes|no>``
     If possible, write screenshots with a bit depth similar to the source

video/image_writer.c

@@ -50,7 +50,7 @@ const struct image_writer_opts image_writer_opts_defaults = {
     .jpeg_smooth = 0,
     .jpeg_baseline = 1,
     .jpeg_source_chroma = 1,
-    .tag_csp = 1,
+    .tag_csp = 0,
 };
 
 #define OPT_BASE_STRUCT struct image_writer_opts