odd flickering with show: IM 6.5.6-6 Q16

[fmw42]

IM 6.5.6-6 Q16 Mac OSX Tiger


This works fine with no flickering:

color="rgb(255,255,0)"
convert -size 100x100 xc:"$color" show:


But all 3 of these flicker badly!

color="rgb(255,255,0)"
convert -respect-parenthesis \( -size 100x100 xc:"$color" \) \
-background white -fill black -font Helvetica -pointsize 10 \
label:"$color" -gravity south -append show:

color="rgb(255,255,0)"
convert -respect-parenthesis \( -size 100x100 xc:"$color" \) \
-background white -fill black -font Helvetica -pointsize 10 \
label:"$color" -gravity south -append miff:- | convert - show:

color="rgb(255,255,0)"
convert -respect-parenthesis \( -size 100x100 xc:"$color" \) \
-background white -fill black -font Helvetica -pointsize 10 \
label:"$color" -gravity south -append miff:- | display -

color="rgb(255,255,0)"
convert -respect-parenthesis \( -size 100x100 xc:"$color" \) \
-background white -fill black -font Helvetica -pointsize 10 \
label:"$color" -gravity south -append tmp.png | convert tmp.png show:

and even just

convert tmp.png show:


Is this just a Mac issue with X11 or does it flicker on Linux, too? If so, any explanation or way to avoid the flickering.

P.S. Found that adding -type truecolor eliminated the flickering

color="rgb(255,255,0)"
convert -respect-parenthesis \( -size 100x100 xc:"$color" \) \
-background white -fill black -font Helvetica -pointsize 10 \
label:"$color" -gravity south -append -type truecolor show:

[magick]

The flickering only occurs under Mac's and only with recent releases of Mac OS (older versions used to work fine). We're clueless on what the problem is and how to fix it.

[fmw42]

Note my comment in green, that it appears to be an issue with the type or class of the resulting image. Adding -type truecolor seems to eliminate the issue. So checking the verbose info: we have Type=Palette. The image prior to that with the flickering seems to be Type=PaletteMatte. Thus it appears to be related to the alpha channel.

Testing:

color="rgb(255,255,0)"
convert -respect-parenthesis \( -size 100x100 xc:"$color" \) \
-background white -fill black -font Helvetica -pointsize 10 \
label:"$color" -gravity south -append -alpha off show:

This also cured the flicker. So indeed the flicker occurs when the alpha channel is on even it if the alpha is pure opaque.

Is alpha turned on by default with label: ?