I have ImageMagick installed on a Linux system I use to host a few websites. From time to time, I need to quickly resize a photo, add a watermark, or do something else to an image on the server. I could easily FTP to the server, grab the files, modify then re-upload. I find it quicker though, if I know exactly what I’m wanting, to just use convert for some of the basic tasks.
To change the Brightness, Contrast or Hue via ‘convert’ in ImageMagick from the Linux command line:
rjk@krenix:~$ convert -modulate 150,100,100 source.jpg newimage.jpg
The 3 values in this 150,100,100
are Brightness, Contrast and Hue.
Value of 100 keeps the current option the same and does not increase/decrease.
That’s brightness, saturation, AND hue — not contrast.