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I'm trying to convert(compress) a bunch of JPEG images using imagemagick command mogrify, keeping the original file in the same directory. I'm typing in terminal window : mogrify -quality 25% *.JPEG con-%002d.JPEG then I get the error : mogrify: unable to open image `con-%002d.JPEG': No such file or directory @ error/blob.c/OpenBlob/2712. How can I solve this error? I have run : identify -verbose * | grep Format and the result is for all files : Format: JPEG (Joint Photographic Experts Group JFIF format) exif:thumbnail:JPEGInterchangeFormat: 10718 exif:thumbnail:JPEGInterchangeFormatLength: 8223

My system is Xubuntu 16.04, I appreciate some help, thanks Vladi.

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    mogrify doesn't have an output file option: it always replaces the original files, and con-%002d.JPEG is treated as just another input file (which doesn't exist) after the *.JPEG list.
    – AFH
    Commented Sep 28, 2018 at 21:28
  • What kind of output name are you looking for? Sequential numbering?
    – chew socks
    Commented Sep 28, 2018 at 21:28
  • @chewsocks I read some where(I don't remember where) that I could compress a JPEG file given an output file name which not replace the original file. The output name could be a sequential number or something like con-001.JPEG, con-002.JPEG, con-003.JPEG, ....
    – vladimir pavloski
    Commented Sep 28, 2018 at 22:26
  • You may have been thinking of ffmpeg which does support sequential output naming.
    – chew socks
    Commented Sep 28, 2018 at 22:42
  • @chewsocks No, I'm not wrong, it is on imagemagick mogrify command.
    – vladimir pavloski
    Commented Sep 28, 2018 at 22:49

2 Answers 2

Reset to default
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Per the man page mogrify does not take an output option, it simply overwrites the input file unless the format is changed (the same name is used up to the file extension).

Try this using convert instead.

#!/bin/bash
n=1
for i in *.JPEG; do 
    convert "$i" -format jpg -quality '25%' $(printf con-%03d.JPEG $n)
    n=$((n+1))
done

JPEG vs jpg

I mogrified the same image twice

$ mogrify -format JPEG b.jpg
$ mogrify -format jpg b.jpg

Then

$ diff -u <(identify -verbose b.jpg ) <(identify -verbose b.JPEG)
--- /dev/fd/63  2018-09-29 14:42:27.506462707 -0400
+++ /dev/fd/62  2018-09-29 14:42:27.510462929 -0400
@@ -1 +1 @@
-Image: b.jpg
+Image: b.JPEG
@@ -71,2 +71,2 @@
-    date:create: 2018-09-29T14:37:11-04:00
-    date:modify: 2018-09-29T14:37:11-04:00
+    date:create: 2018-09-29T14:37:03-04:00
+    date:modify: 2018-09-29T14:37:03-04:00
@@ -77 +77 @@
-    filename: b.jpg
+    filename: b.JPEG
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  • OK!! That's done the job. Thanks. Can I ask what's the difference between JPEG format and jpg fomat ? The script above converts to "jpg" then the new file output is saved as ".JPEG" what's the hack? thanks
    – vladimir pavloski
    Commented Sep 29, 2018 at 7:46
  • @vladimirpavloski Good question...habit =P. I avoid capitals in my names so I always think of the format as "jpg". convert doesn't enforce file extensions (you could save JPEG as .txt) and since I was being specific I saw you liked "JPEG".
    – chew socks
    Commented Sep 29, 2018 at 18:47
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Use -write

mogrify -set filename:name '%t_q%Q' -quality 30 -write '%[filename:name].jpg' *.jpg

Above command will write the converted image to a new name: converting name.jpg to name_q30.jpg, name1.jpg to name1_q30.jpg. Keeping your old files safe.

For other percentage escape metadata options, see the docs

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