ImageMagick, set relative size in chain of convert operators

user_2936110 0
Viewed 92

I'd need to set the size relative to the size already set. I'd need it because my flow involves defining primitives inside other ones. Eg

convert -size 200x100 xc:black \( -size 30x40% xc:red \) -gravity West -composite out.png

That 30x40% is not working this way, it becomes pixels 30x40. I can achieve this specific goal in the first example by using resize

convert -size 200x100 xc:black \( xc:red -resize 30x40% \) -gravity West -composite out.png

In this second version, xc:red inherits the size 200x100, so -resize works as expected. Though the size of further/inner primitives are not reduced to 60x40, it remains 200x100, so in the third example, the green rectangle has orientation landscape and not portrait

convert -size 200x150 xc:blue \
  \( xc:red -resize 50x100% \
    \( xc:green -resize 40% \) \
    -gravity Center \
    -composite \
  \) \
  -gravity West \
  -composite \
  out.png

So green area is 80x60 pixels, 40% of 200x150. I'd like to somehow reset the size to the size of xc:red after resize by the time I'm introducing xc:green.

imagemagick
1 Answers

I think you are trying to create canvases whereby each one is a percentage of the the size of the previous one. There may be an easier way, but you could save each canvas (and implicitly its size) in a MPR "Magick Persistent Register" (named lump of RAM) as you create it, then recall the latest one and overwrite it each time you want to do something relative to that:

convert -gravity west -size 200x100 xc:black -write MPR:S                      \
   \( MPR:S -resize 30x40% -fill red  -colorize 100 -write MPR:S \) -composite \
   \( MPR:S -resize 50x50% -fill blue -colorize 100 -write MPR:S \) -composite \
   \( MPR:S -resize 50x50% -fill lime -colorize 100 \) -composite  result.png

enter image description here

Alternatively, you could let your bash/POSIX shell do it for you inside an "arithmetic expression":

W=200
H=100
convert -gravity west -size ${W}x${H} xc:black                    \
   \( -size $((W=W*30/100))x$((H=H*40/100)) xc:red  \) -composite \
   \( -size $((W=W*50/100))x$((H=H*50/100)) xc:blue \) -composite \
   result.png

enter image description here

Be aware that the shell only deals with integer maths, so it's not going to end well if you aim for 50% of 25 pixels...

user_28366210
Related