GNOME Bugzilla – Bug 766060
alpha: doesn't correctly work with black or white in custom mode
Last modified: 2018-11-03 15:09:02 UTC
reference command - replace yellow bar in test pattern 0 with circles from other videotestsrc, works as expected: gst-launch-1.0 videotestsrc ! alpha method=3 target-r=255 target-g=255 target-b=0 ! videomixer sink_0::zorder=1 sink_1::zorder=0 name=mixer ! videoconvert ! gtksink videotestsrc pattern=11 ! mixer. test-commands, white stripe is supposed to be transparent, in fact all others are :) gst-launch-1.0 videotestsrc ! alpha method=3 target-r=255 target-g=255 target-b=255 ! videomixer sink_0::zorder=1 sink_1::zorder=0 name=mixer ! videoconvert ! gtksink videotestsrc pattern=11 ! mixer. same exact symptom with black: gst-launch-1.0 videotestsrc ! alpha method=3 target-r=0 target-g=0 target-b=0 ! videomixer sink_0::zorder=1 sink_1::zorder=0 name=mixer ! videoconvert ! gtksink videotestsrc pattern=11 ! mixer. slomo suggested it may have something to do with alpha's internal HSV conversion. this sounds likely since pure black and white don't have a defined hue value. i'll take a look
*** Bug 773314 has been marked as a duplicate of this bug. ***
Reason for that is that the color keying works by using the hue. And black (and white, and grey) don't have any hue. A different approach would have to be used here.
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