The object is to make some changes in an image using a single command line entry (or script) rather than a series of preocedures in GIMP. In this image I wanted to cut the haze left by the camera's idea of the scene and return the whole thing to something between what the day was actually like and what a tourist would like to see.
In GIMP Open 'Colors' then Hue and Saturation, and for this example we chose 40%. Next, open Colors and Curves and apply a farly standard Sigmoidal curve. That cuts the haze, boosts the colours and creates some contrast. Finally by opening Colors and Levels I can adjust the left side of the scale to fine tune the dark end and bump the Gamma to in this case, 1.5.
In ImageMagick something similar is achieved with
-convert wh.jpg -modulate 100,140 -sigmoidal-contrast 6,46% -level 5,100%,1.5 IM-enhanced.png
However, looking at the crop you can see the difference in the shadows cast on the creases of the blue top. While the overall colour of the IM result is close to matching the GIMP result, there is a loss of definition in those shadows on the shirt.
