Recipies for ImageMagick.

Traces

Before

After

convert $FILE  \
    -resize 800x \
    -unsharp 0.5x0.5+0.75+0.05 \
    -bordercolor White \
    -colorspace Gray \
    -level 50%,50% \
    -negate \
    -morphology EdgeIn Diamond \
    -negate \
    -bordercolor Black \
    -border 1 \
    +level-colors DarkSlateGray,  \
    $FILE
# Don't forget the comma in the option +level-colors

Colorize an image

Not the most straightforward way but...

# Creates a gradient image
convert -size 10x100  gradient:"#67838f"       gradient.png
# Converts ource to black and white
convert source.png -colorspace gray -sigmoidal-contrast 10,40%  bw.png
# Maps the gradient on the black and white image
convert bw.png gradient.png -clut final.png