sergiomtzlosa/imagemagick repository overview

docker run -ti --rm -v `pwd`:/images sergiomtzlosa/imagemagick magick 

 docker run -ti --rm -v `pwd`:/images sergiomtzlosa/imagemagick magick image.png -set colorspace Gray image.png

FROM alpine:3.6

RUN sed -i -e 's/v[[:digit:]]\..*\//edge\//g' /etc/apk/repositories
RUN sed -e 's;^#http\(.*\)/v3.6/community;http\1/v3.6/community;g' -i /etc/apk/repositories

RUN apk --update add imagemagick=7.0.10.18-r0 && \
    rm -rf /var/cache/apk/*

RUN mkdir -p /images

VOLUME /images

WORKDIR /images