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MAGICK Convert (magick)

Table of Contents

Basic

convert <input_file> [<input_file> ...] <output_file>

Geometry

rescale

simple rescale:

convert rose: -resize 50% rose.png

rescale with proper value interpolation (convert sRGB to RGB):

convert rose: -colorspace RGB -resize 50% -colorspace sRGB rose.png

crop

convert rose: -gravity center -crop 10x10+0+0 output_file.png

-gravity center prevent to make tiles.

shave

To specify the amount to be removed, use -shave instead:

convert rose: -shave 10% rose.png

Remove 10% pixels from the image edges.

chop

Remove pixels from the interior of an image.

convert rose: -chop 20x0+10+0 rose.png

remove a vertical band of 20 pixels wide at 10 pixels from the left border.

rotate

convert rose: -rotate 90 out.png

  • clockwise -rotate 90

  • anticlockwise -rotate 270 ( -90 may work )

montage

see full documentation : imagemagick

montage

montage rose: rose: rose: \( pattern:gray50 -set label gray \) -background chartreuse -geometry +0+0 convert_montage.png

another example

montage -label '%f' *.jpg -geometry 300x200+0+0 -background grey mosaic.jpg

  • -background chartreuse set background to Chartreuse color (the only liqueur so good they named a color after it.)

  • -set label associate a label to an image. Must appear before input files.

  • -geometry +0+0 has the extra effect of putting montage in a 'concatenation' mode (no rescale).

Details about geometry descriptor

used by crop, extend, …​.

Format Comment

<scale>%

Height and width both scaled by specified percentage.

<scale_x>%x<scale_y>%

Height and width individually scaled by specified percentages. (Only one % symbol needed.)

<width>

Width given, height automagically selected to preserve aspect ratio.

x<height>

Height given, width automagically selected to preserve aspect ratio.

<width>x<height>

Maximum values of height and width given, aspect ratio preserved.

<width>x<height>^

Minimum values of width and height given, aspect ratio preserved.

<width>x<height>!

Width and height emphatically given, original aspect ratio ignored.

<width>x<height>

Shrinks an image with dimension(s) larger than the corresponding width and/or height argument(s).

<width>x<height><

Enlarges an image with dimension(s) smaller than the corresponding width and/or height argument(s). >

<area>@

Resize image to have specified area in pixels. Aspect ratio is preserved.

{<size>}{<offset>}

Specifying the offset (default is +0+0). Below, {size} refers to any of the forms above.

{<size>}{-}``x``{-}y

Horizontal and vertical offsets x and y, specified in pixels. Signs are required for both. Offsets are affected by ‑gravity setting. Offsets are not affected by % or other size operators.

Alpha channel

extract alpha

convert image.png -alpha extract alpha.png

extract RGB

convert image.png -flatten rgb.png

extract RGB with default RGB value

convert image.png -background black -alpha remove rgb.png

merge RGB and alpha

convert rgb.png alpha.png -alpha off -compose CopyOpacity -composite result.png

Color-spaces

convert gamma_dalai_lama_gray.jpg -set colorspace sRGB -depth 16 -colorspace RGB -resize 50% -colorspace sRGB -depth 8  gamma_dalai_lama_gray.50pc.png

with steps:

  • set colorspace sRGB : Set metadata only, do not touch pixels.

  • depth 16 : Increase image precision.

  • colorspace RGB : Transform pixels from existing colourspace (sRGB) to new colourspace (RGB), and update metadata to be RGB.

  • resize 50% : Now that pixels are in a linear space, resize should be safe.

  • colorspace sRGB : Transform pixels from existing colourspace (RGB) to new colourspace (sRGB), and update colourspace metadata to be sRGB

  • depth 8 : Go back to original precision.

Animate

convert -delay 10 frame1 frame2 out.gif

Patrol cycle (back and forth) just add -----coalesce -duplicate 1,-2-1----

convert -delay 10 frame frame2 -coalesce -duplicate 1,-2-1 -loop 0 out.gif

Syntethise

sample command

rainbow

convert xc:black xc:red xc:yellow xc:green1 xc:cyan xc:blue xc:black +append -filter Cubic -resize 50x30\! rainbow.jpg

grey

convert pattern:gray50 grey.png

rose

convert rose: rose.png

PDF

  1. Allow magick to convert from/to PDF:

# Open the file
sudo nano /etc/ImageMagick-6/policy.xml

# find and edit the line
<policy domain="coder" rights="none" pattern="PDF" />
# to :
<policy domain="coder" rights="read|write" pattern="PDF" />

  1. convert full resolution

convert   -density 250   doc.pdf    -quality 100 -flatten     doc.png  # single page
convert   -density 250   doc.pdf    -quality 100         page%02d.png  # multi pages