jpegtran optimize without changing filename

I need to optimize some images, but not change their name.

jpegtran -copy none -optimize image.jpg > 开发者_开发问答image.jpg 

However, this seems to create an filesize of 0. When i do it to a different filename, the size is still exactly the same.

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how about:

jpegtran -copy none -optimize -outfile image.jpg image.jpg

I'm not a shell expert by any means, but I think that with your original command, as soon as it is executed, the redirect is set up which overwrites your image.jpg. Then when jpegtran tries to read it in it finds an empty file.

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I use this script. Works flawlessly. I hope this helps.

https://gist.github.com/iimos/7424025

#! /bin/sh

EXTENSIONS="jpe?g"

if [ -z "$1" ]; then
    DIR="`pwd`"
else
    DIR="$1"
fi

# Optimize JPEG images
find "$DIR" -regextype posix-egrep -regex ".*\.($EXTENSIONS)\$" -type f | xargs -I{} jpegtran -optimize -progressive -outfile "{}.optimized" "{}"

# Rename xxx.jpg.optimized -> xxx.jpg
find "$DIR" -name '*.optimized' -print0 | while read -d $'\0' file; do 
    chown $(stat -c "%U:%G" "${file%.optimized}") "$file"
    chmod $(stat -c "%a" "${file%.optimized}") "$file"
    mv -f "$file" "${file%.optimized}"; 
done

Usage 1:

optimize-images.sh /images/dir

Usage 2:

cd /images/dir
optimize-images.sh 

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I did it in three lines:

jpegtran -optimize image.jpg > image.jpg-opt
cp image.jpg-opt image.jpg
rm image.jpg-opt

Works well.

[edit:] This works only for one file at a time.

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jpegtran -copy none -progressive -optimize -outfile filename filename

For comprehensive optimization: -copy none tells jpegtran to suppress all comments and other excess baggage present in the source jpeg, progressive generates a progressive jpeg, -optimize performs the actual optimizations, and -outfile sets the output file name. The last parameter is the input file name: if they are the same, your file is optimized in place.

Edit: you might want to also try mozjpeg, according to this article on lossless jpeg compression tools http://blarg.co.uk/blog/comparison-of-jpeg-lossless-compression-tools

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Without sponge, another alternative with lower HDD or SSD writing access is to use the /dev/shm to save the temporary file and then overwrite it locally right away.

jpegtran -copy none -optimize image.jpg > /dev/shm/tmp.jpg &&  cat /dev/shm/tmp.jpg > ./image.jpg

The concept can be easily adapted into any script, perhaps with caveats about the temporary filename not being the same, in order to avoid collisions if there are multiple instances running at the same time. It's possibly interesting to think about some unique filename pattern generation scheme, perhaps something along the lines of ${originalfilename}-jpgtrantmp-$$.

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Another option if -outfile is not supported:

jpegtran -copy none -optimize image.jpg | sponge image.jpg

sponge is part of moreutils.