Using IM's CLI, I'm trying to get the average image color for an image, excluding any transparent pixels. The normally used -resize 1x1 info:- is not useful in this case, as obviously transparent pixels will affect the result (and you end up with a totally transparent pixel in some cases)
My fallback right now is extracting them using -define histogram:unique-colors=true -format %c histogram:info:- and manually excluding the transparent ones, but this feels complex for something IM might already provide.
In ImageMagick you can get the average (mean) color excluding transparency by
convert image -scale 1x1! -alpha off -format "%[pixel:u.p]" info:
Example:
convert logo: -transparent white -scale 1x1! -alpha off -format "%[pixel:u.p]\n" info:
srgb(100,81,99)
If using ImageMagick 7, then replace convert with magick.
ADDITION: Here is the long way. Compute the mean of each channel of the image. Compute the mean of the alpha channel. Then divide.
convert logo: -transparent white logot.png
convert logot.png -alpha extract mask.png
declare `convert logot.png -alpha remove -format "IR=%[fx:mean.r]\nIG=%[fx:mean.g]\nIB=%[fx:mean.b]\n" info:`
echo "IR=$IR; IG=$IG; IB=$IB"
IR=0.0651798; IG=0.0529989; IB=0.0641607
MM=`convert mask.png -format "%[fx:mean]\n" info:`
echo "MM=$MM"
MM=0.165872
convert xc: -format "srgb(%[fx:round(255*$IR/$MM)],%[fx:round(255*$IG/$MM)],%[fx:round(255*$IB/$MM)])\n" info:
srgb(100,81,99)