[FFmpeg-trac] #3317(undetermined:new): Drawtext+Alphamerge results in incorrect alpha value
FFmpeg
trac at avcodec.org
Sat Jan 18 13:24:47 CET 2014
#3317: Drawtext+Alphamerge results in incorrect alpha value
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Reporter: jnvsor | Type: defect
Status: new | Priority: normal
Component: | Version: git-
undetermined | master
Keywords: | Blocked By:
Blocking: | Reproduced by developer: 0
Analyzed by developer: 0 |
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I was trying to create a video of a timer for use in other videos with a
transparent background. There doesn't seem to be a transparent video
source so I used alphamerge to achieve the same effect.
Unfortunately, drawtext with alphamerge results in a max alpha of 235 not
255.
Running the following 3 commands generates the 3 attatched files. Note
that in `alpha.png` the text has 235 alpha, not 255, and that I can't
reproduce without using drawtext directly.
{{{
# Drawtext to alphamerge
ffmpeg -f lavfi -r 30 -t 10 -i "color=c=#FFFFFF" -f lavfi -r 30 -t 10 -i
"color=c=#000000" -filter_complex
"[1]drawtext=text="FFmpeg":fontcolor=white:fontsize=150:fontfile=/usr/share/fonts/truetype/dejavu/DejaVuSansMono.ttf[text];[0][text]alphamerge[out]"
-map "[out]" -vframes 1 -c:v png -pix_fmt rgba alpha.png
# Saving the drawtext mask on it's own
ffmpeg -f lavfi -r 30 -t 10 -i "color=c=#FFFFFF" -f lavfi -r 30 -t 10 -i
"color=c=#000000" -filter_complex
"[1]drawtext=text="FFmpeg":fontcolor=white:fontsize=150:fontfile=/usr/share/fonts/truetype/dejavu/DejaVuSansMono.ttf[out]"
-map "[out]" -vframes 1 -c:v png -pix_fmt rgba noalpha.png
# And applying that mask (No bug here)
ffmpeg -f lavfi -r 30 -t 10 -i "color=c=#FFFFFF" -i noalpha.png
-filter_complex "[0][1]alphamerge[out]" -map "[out]" -vframes 1 -c:v png
-pix_fmt rgba third.png
}}}
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Ticket URL: <https://trac.ffmpeg.org/ticket/3317>
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