Is there and easy way to resize images by right click on image and select resize option without opening any app, if possible all images in folder at once ?
I know that many will lead me to install 3rd party tool to do that. I am already using GIMP and I am very happy with that. I am just curios is there an easy way to do that.
There is for KDE. You can use a dolphin service menu, like e.g. this
There is also nautilus-image-converter that does the same in Nautilus (nowadays stupidly called files), but I have not tried it myself. It is in the repositories (at least in Ubuntu 17.04).
To quickly do this on the CLI
convert image.jpg -resize 50% out.jpg
For this to work, you will need to have imagemagick installed:
sudo apt-get install imagemagick
Not quite an answer to what was asked, but to do all images in a folder at once from the command line.
for f in *.jpg; do convert $f -resize 700 $f; done
This assumes all your images are .jpg and will resize them to 700 pixels wide.
This will overwrite the original file (which is what the question implied was required) but if you want to keep the original, you have a couple of options.
for f in *.jpg; do convert $f -resize 700 ../resized/$f; done
This puts the resized photos into a directory called resized. (You need to create this first)
Or you could change the filename
for f in *.jpg; do convert $f -resize 700 $(basename $f .jpg)-resized.jpg ; done
This adds -resized to the filename of each, e.g. file0001.jpg will be resized and named file0001-resized.jpg
