Grayscale pictures have that je ne sais quoi that usually makes them better than the color ones, at least in my humble opinion, so I usually convert color pictures to grayscale.

We can use convert or mogrify to make this transition from color to grayscale.

Use convert to make a color image a grayscale one

convert -type Grayscale input-picture.png output-picture.png

This will keep your original picture “input-picture.png” in color, and create a new one in grayscale “output-picture.png”

Use mogrify to convert an image to grayscale

mogrify -type Grayscale input-picture.png

I prefer this one, as you can use it to convert bulk pictures to grayscale, with no need to run a bash for loop, or a script.

What I usually do is to copy all files to a new folder, and then run the mogrify command there. Like this:

cp /home/user/my-pics/* /home/user/my-pics-grayscale/

Then run mogrify on the second folder.

mogrify -type Grayscale /home/user/my-pics-grayscale/*

Done, now I have color version of my pictures, and the grayscale images of them.