Help with using imagemagick's montage in a bash script

[Michelle Rothrock]

Hi all—

Hoping for some help with part of a bash script I'm trying to put together!

The script searches for video files recursively in a directory, creates thumbnails using ffmpeg, and then ideally would use those thumbnails to create a simple contact sheet. I'm not an expert at bash, so I've relied heavily on finding and repurposing bits of script from others.

I'm having two problems with imagemagick:

- One, passing it a list of files to compile into a contact sheet has been a little weird; I currently have a workaround which puts the thumbnail filenames into a .txt file (and then later deletes the .txt file). I feel sure there's some more straightforward way to do this

- Two, the -label '%f' option isn't working.

I'm copying the relevant portion of the script below. If anyone has any ideas—or if there's an existing solution to this entire thing I'm trying to do 🙈—I'd really appreciate it.

find "$video_dir" -type f -iname *-thumb.png > $video_dir/thumb_list.txt
read num_imgs <<< $(sed -n '$=' thumb_list.txt)
let num_rows=num_imgs/8
let lefto=num_imgs%8
if [ $lefto -gt 0 ]
then
   let num_rows=num_rows+1
fi
montage @$video_dir/thumb_list.txt -geometry 200x150 -label '%f' -tile 8x$nrow $video_dir/contact_sheet.png
rm $video_dir/thumb_list.txt

[Esmé Cowles]

Michelle-

You should be able to put the output of the find command into a variable with $( ), and the output of math operations with $(( )) which would look like:

thumbs=$( find "$video_dir" -type f -iname *-thumb.png )

num_imgs=$( echo $THUMBS | wc -w ) 

num_rows=$(( $num_imgs / 8 ))

lefto=$(( $num_imgs % 8 ))

if [ $lefto -gt 0 ]; then

   num_rows=$(( $num_rows + 1 ))

fi

montage $thumbs -geometry 200x150 -label '%f' -tile 8x$num_rows $video_dir/contact_sheet.png

That probably depends on not having spaces in the video filenames, though. If you do have spaces in the filenames, then writing to a file and counting the lines like you were doing is probably easier than getting the quoting to work (in my experience).

Hope this helps!

-Esmé

--

Esmé Cowles <esco...@princeton.edu>

Asst. Director, Library Software Engineering

Princeton University Library

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[Kam Woods]

Re the issue with labels not appearing - the label flag must appear before the filenames, so

montage @$video_dir/thumb_list.txt -geometry 200x150 -label '%f' -tile 8x$nrow $video_dir/contact_sheet.png

becomes:

montage -label '%f' @$video_dir/thumb_list.txt -geometry 200x150 -tile 8x$nrow $video_dir/contact_sheet.png

--

[Alex Chan]

On Wednesday 8 May 2024 at 18:51:16 UTC+1 michelle...@gmail.com wrote:

One, passing it a list of files to compile into a contact sheet has been a little weird; I currently have a workaround which puts the thumbnail filenames into a .txt file (and then later deletes the .txt file). I feel sure there's some more straightforward way to do this

IMO putting the thumbnail filenames into a .txt file is fine.

I'd prioritise writing code you understand over something that's more "technically correct" but which you'll find harder to read later.

 

Two, the -label '%f' option isn't working.

Put the `-label` before the filenames:

montage -label '%f' @$video_dir/thumb_list.txt -geometry 200x150 -tile 8x$nrow $video_dir/contact_sheet.png

I'm copying the relevant portion of the script below. If anyone has any ideas—or if there's an existing solution to this entire thing I'm trying to do 🙈—I'd really appreciate it.

find "$video_dir" -type f -iname *-thumb.png > $video_dir/thumb_list.txt
read num_imgs <<< $(sed -n '$=' thumb_list.txt)
let num_rows=num_imgs/8
let lefto=num_imgs%8
if [ $lefto -gt 0 ]
then
   let num_rows=num_rows+1
fi
montage @$video_dir/thumb_list.txt -geometry 200x150 -label '%f' -tile 8x$nrow $video_dir/contact_sheet.png
rm $video_dir/thumb_list.txt

You don't need to work out the row count yourself. If you just pass `tile 8x`, then montage will work out the correct number of rows.

This allows you to simplify your code:

find "$video_dir" -type f -iname *-thumb.png > "$video_dir/thumb_list.txt"

montage -label '%f' "@$video_dir/thumb_list.txt" -geometry 200x150 -tile 8x "$video_dir/contact_sheet.png"
rm "$video_dir/thumb_list.txt"

You can see some more examples here: https://legacy.imagemagick.org/Usage/montage/

~ Alex

[Alex Chan]

(Sorry, I hit "send" on that hastily, and hadn't edited for tone!)

1. The thing about working out the row count is meant as a "hey here's
a thing that might be useful", not something you absolutely have to
do. Sorry if it read a bit curt or strong.
2. The specific section I meant to link in the montage docs is "Tile
Layout Controls", which has examples of the -tile flag:
https://legacy.imagemagick.org/Usage/montage/#tile
3. I didn't know about montage, but now I do and it looks like a fun
tool to add to my toolbox. Thanks Michelle, for letting me know about
it!

~ Alex

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[Michelle Rothrock]

Thanks everyone for your help! Very much improved my code—still tweaking it, but it's close :)

With appreciation—

michelle

To view this discussion on the web visit https://groups.google.com/d/msgid/digital-curation/CAM8-2UrtTGreOpGf1%3D8zziYBM_8asXbksP86C817hQ39MZumog%40mail.gmail.com.

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michelle rothrock

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