Batch converting PNG to JPG in linux

Question

Does anyone know a good way to batch-convert a bunch of PNGs into JPGs in linux? (I'm using Ubuntu).

A png2jpg binary that I could just drop into a shell script would be ideal.

Answer 1

Your best bet would be to use Imagemagick

I am not an expert in the actual usage, but I know you can pretty much do anything image related with this!

An example is:

convert image.png image.jpg

and it will keep the original as well as creating the converted image. As for batch. I think you need to use the Morgify tool (from the same command line when in imagemagick). Keep in mind that this overwrites the old images.

The command is:

mogrify -format jpg *.png  

Answer 2

There is no reason to install ImageMagick if it won't ever be used again. The linux convert command, as pointed out by Jeffrey, is enough. To avoid that double extension problem this is what the bash code should look like:

for img in *.png; do
    filename=${img%.*}
    convert "$filename.png" "$filename.jpg"
done

Answer 3

The actual "png2jpg" command you are looking for is in reality split into two commands called pngtopnm and cjpeg, and they are part of the netpbm and libjpeg-progs packages, respectively.

png2pnm foo.png | cjpeg > foo.jpeg

Answer 4

For batch processing:

for img in *.png; do
  convert "$img" "$img.jpg"
done

You will end up with file names like image1.png.jpg though.

This will work in bash, and maybe bourne. I don't know about other shells, but the only difference would likely be the loop syntax.

Answer 5

my quick solution for i in $(ls | grep .png); do convert $i $(echo $i.jpg | sed s/.png//g); done

Answer 6

I have a couple more solutions.

The simplest solution is like most already posted. A simple bash for loop.

for i in *.png ; do convert "$i" "${i%.*}.jpg" ; done

For some reason I tend to avoid loops in bash so here is a more unixy xargs approach, using bash for the name-mangling.

ls -1 *.png | xargs -n 1 bash -c 'echo "$0" "${0%.*}.jpg"'

The one I use. It uses GNU Parallel to run multiple jobs at once, giving you a performance boost. It is installed by default on many systems and is almost definitely in your repo (it is a good program to have around).

parallel convert '{}' '{.}.jpg' ::: *.png

The number of jobs defaults to the number of processes you have. I found better CPU usage using 3 jobs on my dual-core system.

parallel -j 3 convert '{}' '{.}.jpg' ::: *.png

And if you want some stats (an ETA, jobs completed, average time per job...)

parallel --eta convert '{}' '{.}.jpg' ::: *.png

The final command that I use looks like this for refrence. I use ls rather than parallel's syntax for who-knows-what reason.

ls -1 *.png | parallel -j 3 --eta convert '{}' '{.}.jpg'