Fred's ImageMagick Scripts: SKETCH

Fred's ImageMagick Scripts

Licensing:

My scripts are available free of charge for non-commercial (non-profit) use, ONLY.

For use of my scripts in commercial (for-profit) environments or non-free applications, please contact me (Fred Weinhaus) for licensing arrangements. My email address is fmw at alink dot net.

If you: 1) redistribute, 2) incorporate any of these scripts into other free applications or 3) reprogram them in another scripting language, then you must contact me for permission, especially if the result might be used in a commercial or for-profit environment.

Usage, whether stated or not in the script, is restricted to the above licensing arrangements. It is also subject, in a subordinate manner, to the ImageMagick license, which can be found at: http://www.imagemagick.org/script/license.php

Please read the Pointers For Use on my home page to properly install and customize my scripts.

SKETCH

Applies a sketch effect to an image.

Download Script

last modified: December 15, 2018

USAGE: sketch [-k kind] [-e edge] [-c con] [-s sat] [-g] infile outfile
USAGE: sketch [-h or -help]

-k ... kind ... kind of grayscale conversion; options are gray(g) or
............... desat(d); default=desat
-e ... edge ... edge coarseness; integer>0; default=4
-c ... con .... percent contrast change; integer>=0; default=125
-s ... sat .... percent saturation change; integer>=0; default=100
-g ............ output grayscale only

PURPOSE: To apply a sketch effect to an image.

DESCRIPTION: SKETCH applies a sketch like effect to an image. If a color image is provided as input, then the output can be either color or grayscale.

ARGUMENTS:

-k kind ... KIND of grayscale conversion. Choices are gray(g) or desat(d). The default=desat.

-e edge ... EDGE coarseness. Values are integers>0. The default=4.

-c con ... percent CONTRAST change. Values are integers>=0. The default=125. Note that con=125 for kind=desat is similar to con=0 for kind=gray.

-s sat ... percent SATURATION change. Values are integers>=0. The default=100.

-g ... output GRAYSCALE only.

see http://www.photoshopessentials.com/photo-effects/portrait-to-sketch/

REQUIREMENTS: Results for -k gray will be nearly identical to those of -k desat for IM versions prior to 6.7.8.3. Starting at this version, grayscale images became linear and thus the different look for -k gray.

CAVEAT: No guarantee that this script will work on all platforms, nor that trapping of inconsistent parameters is complete and foolproof. Use At Your Own Risk.

EXAMPLES

Example 1 - Kind=desat; Variation in Contrast
Original (http://www.photoshopessentials.com/photo-effects/portrait-to-sketch/)

Arguments: -k desat -c 0	Arguments: -k desat -c 50	Animation -k desat -c 100

Arguments: -k desat -c 125	Arguments: -k desat -c 150	Animation -k desat -c 175

Example 2 - Kind=gray; Variation in Contrast
Original

Arguments: -k gray -c 0	Arguments: -k gray -c 50	Animation -k gray -c 100

Arguments: -k gray -c 125	Arguments: -k gray -c 150	Animation -k gray -c 175

Example 3 - Variation in Edge
Original

Arguments: -k desat -c 125 -s 200 -e 1	Arguments: -k desat -c 125 -s 100 -e 4	Animation -k desat -c 125 -s 100 -e 8

Arguments: -k gray -c 0 -s 200 -e 1	Arguments: -k gray -c 0 -s 100 -e 4	Animation -k gray -c 0 -s 100 -e 8

Example 4 - Output Grayscale
Original

Arguments: -k desat -c 125 -g	Arguments: -k gray -c 0 -g

Example 5 - Desat vs Gray
Original

Arguments: -k desat -c 125	Arguments: -k gray -c 0

Example 6 - Desat vs Gray
Original

Arguments: -k desat -c 125	Arguments: -k gray -c 0

Example 7 - Desat vs Gray
Original

Arguments: -k desat -c 125	Arguments: -k gray -c 0

What the script does is as follows:

Converts the image to grayscale or desaturates it
Negates the gray image and blurs it
Applies a color dodge composition between the gray image and
its negated and blurred version
Optionally applies a level operation to increase contrast
Sets the opacity of the previous image and multiplies the two
so as to adjust the contrast
Increases the saturation of original
Applies a screen composition between the latter two images

This is equivalent to the following IM commands

if [ "$kind" = "gray" ]; then
grayscaling="-colorspace gray"
elif [ "$kind" = "desat" ]; then
grayscaling="-modulate 100,0,100"
fi
if [ $con -le 100 ]; then
con1=$con
con2=0
else
con1=100
con2=`convert xc: -format "%[fx:$con-100]" info:`
fi
convert $infile \ $ -clone 0 $grayscaling $ \
$ -clone 1 -negate -blur 0x${edge} $ \
$ -clone 1 -clone 2 -compose color_dodge -composite -level ${con2}x100% $ \
$ -clone 3 -alpha set -channel a -evaluate set ${con1}% +channel $ \
$ -clone 3 -clone 4 -compose multiply -composite $ \
$ -clone 0 -modulate 100,$sat,100 $ \
-delete 0-4 -compose screen -composite $outfile