Question

I am trying to place a caption with a semi-transparent background on an image.

This is the example from the docs (http://www.imagemagick.org/Usage/annotating):

width=`identify -format %w dragon.gif`; \
convert -background '#0008' -fill white -gravity center -size ${width}x30 \
      caption:"Faerie Dragons love hot apple pies\!" \
      dragon.gif +swap -gravity south -composite  anno_caption.jpg

This my attempt so far:

convert  -background transparent -colorspace transparent -fill white -gravity center -size 300x300 \
      -font fonts/customfont.ttf caption:'caption text here' \
       'cap.png'

composite -geometry +0+0 'cap_1.png' 'img_1.jpg' 'img_2.jpg'

the caption is created an placed in the top right hand coner of the composite image as expected. The only problem is, the caption background is black, not semi-transparent. I have seen the use of the xc command for transparency (e.g. convert -size 50×50 xc:’#879′ img.png) but I do not see how to apply the command to set the caption bg colour.

EDIT:

I just tested on an ec2 server and the code works as expected. This issue occurs when the code is run on a Mac 10.7x.

Answer 1

Give this a go – it is using rgb with transparency ( rgba ).

convert -size 300x300 -background rgba\(0,255,255,0.25\) -fill white -gravity center caption:'caption text here' cap.png

composite -geometry +0+0 cap.png img_1.jpg img_2.jpg